granicus.if.org Git - postgresql/blob - src/backend/access/heap/tuptoaster.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * tuptoaster.c
   4  *        Support routines for external and compressed storage of
   5  *        variable size attributes.
   6  *
   7  * Copyright (c) 2000-2013, PostgreSQL Global Development Group
   8  *
   9  *
  10  * IDENTIFICATION
  11  *        src/backend/access/heap/tuptoaster.c
  12  *
  13  *
  14  * INTERFACE ROUTINES
  15  *              toast_insert_or_update -
  16  *                      Try to make a given tuple fit into one page by compressing
  17  *                      or moving off attributes
  18  *
  19  *              toast_delete -
  20  *                      Reclaim toast storage when a tuple is deleted
  21  *
  22  *              heap_tuple_untoast_attr -
  23  *                      Fetch back a given value from the "secondary" relation
  24  *
  25  *-------------------------------------------------------------------------
  26  */
  27
  28 #include "postgres.h"
  29
  30 #include <unistd.h>
  31 #include <fcntl.h>
  32
  33 #include "access/genam.h"
  34 #include "access/heapam.h"
  35 #include "access/tuptoaster.h"
  36 #include "access/xact.h"
  37 #include "catalog/catalog.h"
  38 #include "utils/fmgroids.h"
  39 #include "utils/pg_lzcompress.h"
  40 #include "utils/rel.h"
  41 #include "utils/typcache.h"
  42 #include "utils/tqual.h"
  43
  44
  45 #undef TOAST_DEBUG
  46
  47 /*
  48  * Testing whether an externally-stored value is compressed now requires
  49  * comparing extsize (the actual length of the external data) to rawsize
  50  * (the original uncompressed datum's size).  The latter includes VARHDRSZ
  51  * overhead, the former doesn't.  We never use compression unless it actually
  52  * saves space, so we expect either equality or less-than.
  53  */
  54 #define VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer) \
  55         ((toast_pointer).va_extsize < (toast_pointer).va_rawsize - VARHDRSZ)
  56
  57 /*
  58  * Macro to fetch the possibly-unaligned contents of an EXTERNAL datum
  59  * into a local "struct varatt_external" toast pointer.  This should be
  60  * just a memcpy, but some versions of gcc seem to produce broken code
  61  * that assumes the datum contents are aligned.  Introducing an explicit
  62  * intermediate "varattrib_1b_e *" variable seems to fix it.
  63  */
  64 #define VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr) \
  65 do { \
  66         varattrib_1b_e *attre = (varattrib_1b_e *) (attr); \
  67         Assert(VARATT_IS_EXTERNAL(attre)); \
  68         Assert(VARSIZE_EXTERNAL(attre) == sizeof(toast_pointer) + VARHDRSZ_EXTERNAL); \
  69         memcpy(&(toast_pointer), VARDATA_EXTERNAL(attre), sizeof(toast_pointer)); \
  70 } while (0)
  71
  72
  73 static void toast_delete_datum(Relation rel, Datum value);
  74 static Datum toast_save_datum(Relation rel, Datum value,
  75                                  struct varlena * oldexternal, int options);
  76 static bool toastrel_valueid_exists(Relation toastrel, Oid valueid);
  77 static bool toastid_valueid_exists(Oid toastrelid, Oid valueid);
  78 static struct varlena *toast_fetch_datum(struct varlena * attr);
  79 static struct varlena *toast_fetch_datum_slice(struct varlena * attr,
  80                                                 int32 sliceoffset, int32 length);
  81
  82
  83 /* ----------
  84  * heap_tuple_fetch_attr -
  85  *
  86  *      Public entry point to get back a toasted value from
  87  *      external source (possibly still in compressed format).
  88  *
  89  * This will return a datum that contains all the data internally, ie, not
  90  * relying on external storage or memory, but it can still be compressed or
  91  * have a short header.
  92  ----------
  93  */
  94 struct varlena *
  95 heap_tuple_fetch_attr(struct varlena * attr)
  96 {
  97         struct varlena *result;
  98
  99         if (VARATT_IS_EXTERNAL_ONDISK(attr))
 100         {
 101                 /*
 102                  * This is an external stored plain value
 103                  */
 104                 result = toast_fetch_datum(attr);
 105         }
 106         else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
 107         {
 108                 /*
 109                  * copy into the caller's memory context. That's not required in all
 110                  * cases but sufficient for now since this is mainly used when we need
 111                  * to persist a Datum for unusually long time, like in a HOLD cursor.
 112                  */
 113                 struct varatt_indirect redirect;
 114                 VARATT_EXTERNAL_GET_POINTER(redirect, attr);
 115                 attr = (struct varlena *)redirect.pointer;
 116
 117                 /* nested indirect Datums aren't allowed */
 118                 Assert(!VARATT_IS_EXTERNAL_INDIRECT(attr));
 119
 120                 /* doesn't make much sense, but better handle it */
 121                 if (VARATT_IS_EXTERNAL_ONDISK(attr))
 122                         return heap_tuple_fetch_attr(attr);
 123
 124                 /* copy datum verbatim */
 125                 result = (struct varlena *) palloc(VARSIZE_ANY(attr));
 126                 memcpy(result, attr, VARSIZE_ANY(attr));
 127         }
 128         else
 129         {
 130                 /*
 131                  * This is a plain value inside of the main tuple - why am I called?
 132                  */
 133                 result = attr;
 134         }
 135
 136         return result;
 137 }
 138
 139
 140 /* ----------
 141  * heap_tuple_untoast_attr -
 142  *
 143  *      Public entry point to get back a toasted value from compression
 144  *      or external storage.
 145  * ----------
 146  */
 147 struct varlena *
 148 heap_tuple_untoast_attr(struct varlena * attr)
 149 {
 150         if (VARATT_IS_EXTERNAL_ONDISK(attr))
 151         {
 152                 /*
 153                  * This is an externally stored datum --- fetch it back from there
 154                  */
 155                 attr = toast_fetch_datum(attr);
 156                 /* If it's compressed, decompress it */
 157                 if (VARATT_IS_COMPRESSED(attr))
 158                 {
 159                         PGLZ_Header *tmp = (PGLZ_Header *) attr;
 160
 161                         attr = (struct varlena *) palloc(PGLZ_RAW_SIZE(tmp) + VARHDRSZ);
 162                         SET_VARSIZE(attr, PGLZ_RAW_SIZE(tmp) + VARHDRSZ);
 163                         pglz_decompress(tmp, VARDATA(attr));
 164                         pfree(tmp);
 165                 }
 166         }
 167         else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
 168         {
 169                 struct varatt_indirect redirect;
 170                 VARATT_EXTERNAL_GET_POINTER(redirect, attr);
 171                 attr = (struct varlena *)redirect.pointer;
 172
 173                 /* nested indirect Datums aren't allowed */
 174                 Assert(!VARATT_IS_EXTERNAL_INDIRECT(attr));
 175
 176                 attr = heap_tuple_untoast_attr(attr);
 177         }
 178         else if (VARATT_IS_COMPRESSED(attr))
 179         {
 180                 /*
 181                  * This is a compressed value inside of the main tuple
 182                  */
 183                 PGLZ_Header *tmp = (PGLZ_Header *) attr;
 184
 185                 attr = (struct varlena *) palloc(PGLZ_RAW_SIZE(tmp) + VARHDRSZ);
 186                 SET_VARSIZE(attr, PGLZ_RAW_SIZE(tmp) + VARHDRSZ);
 187                 pglz_decompress(tmp, VARDATA(attr));
 188         }
 189         else if (VARATT_IS_SHORT(attr))
 190         {
 191                 /*
 192                  * This is a short-header varlena --- convert to 4-byte header format
 193                  */
 194                 Size            data_size = VARSIZE_SHORT(attr) - VARHDRSZ_SHORT;
 195                 Size            new_size = data_size + VARHDRSZ;
 196                 struct varlena *new_attr;
 197
 198                 new_attr = (struct varlena *) palloc(new_size);
 199                 SET_VARSIZE(new_attr, new_size);
 200                 memcpy(VARDATA(new_attr), VARDATA_SHORT(attr), data_size);
 201                 attr = new_attr;
 202         }
 203
 204         return attr;
 205 }
 206
 207
 208 /* ----------
 209  * heap_tuple_untoast_attr_slice -
 210  *
 211  *              Public entry point to get back part of a toasted value
 212  *              from compression or external storage.
 213  * ----------
 214  */
 215 struct varlena *
 216 heap_tuple_untoast_attr_slice(struct varlena * attr,
 217                                                           int32 sliceoffset, int32 slicelength)
 218 {
 219         struct varlena *preslice;
 220         struct varlena *result;
 221         char       *attrdata;
 222         int32           attrsize;
 223
 224         if (VARATT_IS_EXTERNAL_ONDISK(attr))
 225         {
 226                 struct varatt_external toast_pointer;
 227
 228                 VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 229
 230                 /* fast path for non-compressed external datums */
 231                 if (!VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
 232                         return toast_fetch_datum_slice(attr, sliceoffset, slicelength);
 233
 234                 /* fetch it back (compressed marker will get set automatically) */
 235                 preslice = toast_fetch_datum(attr);
 236         }
 237         else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
 238         {
 239                 struct varatt_indirect redirect;
 240                 VARATT_EXTERNAL_GET_POINTER(redirect, attr);
 241
 242                 /* nested indirect Datums aren't allowed */
 243                 Assert(!VARATT_IS_EXTERNAL_INDIRECT(redirect.pointer));
 244
 245                 return heap_tuple_untoast_attr_slice(redirect.pointer,
 246                                                                                          sliceoffset, slicelength);
 247         }
 248         else
 249                 preslice = attr;
 250
 251         if (VARATT_IS_COMPRESSED(preslice))
 252         {
 253                 PGLZ_Header *tmp = (PGLZ_Header *) preslice;
 254                 Size            size = PGLZ_RAW_SIZE(tmp) + VARHDRSZ;
 255
 256                 preslice = (struct varlena *) palloc(size);
 257                 SET_VARSIZE(preslice, size);
 258                 pglz_decompress(tmp, VARDATA(preslice));
 259
 260                 if (tmp != (PGLZ_Header *) attr)
 261                         pfree(tmp);
 262         }
 263
 264         if (VARATT_IS_SHORT(preslice))
 265         {
 266                 attrdata = VARDATA_SHORT(preslice);
 267                 attrsize = VARSIZE_SHORT(preslice) - VARHDRSZ_SHORT;
 268         }
 269         else
 270         {
 271                 attrdata = VARDATA(preslice);
 272                 attrsize = VARSIZE(preslice) - VARHDRSZ;
 273         }
 274
 275         /* slicing of datum for compressed cases and plain value */
 276
 277         if (sliceoffset >= attrsize)
 278         {
 279                 sliceoffset = 0;
 280                 slicelength = 0;
 281         }
 282
 283         if (((sliceoffset + slicelength) > attrsize) || slicelength < 0)
 284                 slicelength = attrsize - sliceoffset;
 285
 286         result = (struct varlena *) palloc(slicelength + VARHDRSZ);
 287         SET_VARSIZE(result, slicelength + VARHDRSZ);
 288
 289         memcpy(VARDATA(result), attrdata + sliceoffset, slicelength);
 290
 291         if (preslice != attr)
 292                 pfree(preslice);
 293
 294         return result;
 295 }
 296
 297
 298 /* ----------
 299  * toast_raw_datum_size -
 300  *
 301  *      Return the raw (detoasted) size of a varlena datum
 302  *      (including the VARHDRSZ header)
 303  * ----------
 304  */
 305 Size
 306 toast_raw_datum_size(Datum value)
 307 {
 308         struct varlena *attr = (struct varlena *) DatumGetPointer(value);
 309         Size            result;
 310
 311         if (VARATT_IS_EXTERNAL_ONDISK(attr))
 312         {
 313                 /* va_rawsize is the size of the original datum -- including header */
 314                 struct varatt_external toast_pointer;
 315
 316                 VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 317                 result = toast_pointer.va_rawsize;
 318         }
 319         else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
 320         {
 321                 struct varatt_indirect toast_pointer;
 322                 VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 323
 324                 /* nested indirect Datums aren't allowed */
 325                 Assert(!VARATT_IS_EXTERNAL_INDIRECT(toast_pointer.pointer));
 326
 327                 return toast_raw_datum_size(PointerGetDatum(toast_pointer.pointer));
 328         }
 329         else if (VARATT_IS_COMPRESSED(attr))
 330         {
 331                 /* here, va_rawsize is just the payload size */
 332                 result = VARRAWSIZE_4B_C(attr) + VARHDRSZ;
 333         }
 334         else if (VARATT_IS_SHORT(attr))
 335         {
 336                 /*
 337                  * we have to normalize the header length to VARHDRSZ or else the
 338                  * callers of this function will be confused.
 339                  */
 340                 result = VARSIZE_SHORT(attr) - VARHDRSZ_SHORT + VARHDRSZ;
 341         }
 342         else
 343         {
 344                 /* plain untoasted datum */
 345                 result = VARSIZE(attr);
 346         }
 347         return result;
 348 }
 349
 350 /* ----------
 351  * toast_datum_size
 352  *
 353  *      Return the physical storage size (possibly compressed) of a varlena datum
 354  * ----------
 355  */
 356 Size
 357 toast_datum_size(Datum value)
 358 {
 359         struct varlena *attr = (struct varlena *) DatumGetPointer(value);
 360         Size            result;
 361
 362         if (VARATT_IS_EXTERNAL_ONDISK(attr))
 363         {
 364                 /*
 365                  * Attribute is stored externally - return the extsize whether
 366                  * compressed or not.  We do not count the size of the toast pointer
 367                  * ... should we?
 368                  */
 369                 struct varatt_external toast_pointer;
 370
 371                 VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 372                 result = toast_pointer.va_extsize;
 373         }
 374         else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
 375         {
 376                 struct varatt_indirect toast_pointer;
 377                 VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 378
 379                 /* nested indirect Datums aren't allowed */
 380                 Assert(!VARATT_IS_EXTERNAL_INDIRECT(attr));
 381
 382                 return toast_datum_size(PointerGetDatum(toast_pointer.pointer));
 383         }
 384         else if (VARATT_IS_SHORT(attr))
 385         {
 386                 result = VARSIZE_SHORT(attr);
 387         }
 388         else
 389         {
 390                 /*
 391                  * Attribute is stored inline either compressed or not, just calculate
 392                  * the size of the datum in either case.
 393                  */
 394                 result = VARSIZE(attr);
 395         }
 396         return result;
 397 }
 398
 399
 400 /* ----------
 401  * toast_delete -
 402  *
 403  *      Cascaded delete toast-entries on DELETE
 404  * ----------
 405  */
 406 void
 407 toast_delete(Relation rel, HeapTuple oldtup)
 408 {
 409         TupleDesc       tupleDesc;
 410         Form_pg_attribute *att;
 411         int                     numAttrs;
 412         int                     i;
 413         Datum           toast_values[MaxHeapAttributeNumber];
 414         bool            toast_isnull[MaxHeapAttributeNumber];
 415
 416         /*
 417          * We should only ever be called for tuples of plain relations or
 418          * materialized views --- recursing on a toast rel is bad news.
 419          */
 420         Assert(rel->rd_rel->relkind == RELKIND_RELATION ||
 421                    rel->rd_rel->relkind == RELKIND_MATVIEW);
 422
 423         /*
 424          * Get the tuple descriptor and break down the tuple into fields.
 425          *
 426          * NOTE: it's debatable whether to use heap_deform_tuple() here or just
 427          * heap_getattr() only the varlena columns.  The latter could win if there
 428          * are few varlena columns and many non-varlena ones. However,
 429          * heap_deform_tuple costs only O(N) while the heap_getattr way would cost
 430          * O(N^2) if there are many varlena columns, so it seems better to err on
 431          * the side of linear cost.  (We won't even be here unless there's at
 432          * least one varlena column, by the way.)
 433          */
 434         tupleDesc = rel->rd_att;
 435         att = tupleDesc->attrs;
 436         numAttrs = tupleDesc->natts;
 437
 438         Assert(numAttrs <= MaxHeapAttributeNumber);
 439         heap_deform_tuple(oldtup, tupleDesc, toast_values, toast_isnull);
 440
 441         /*
 442          * Check for external stored attributes and delete them from the secondary
 443          * relation.
 444          */
 445         for (i = 0; i < numAttrs; i++)
 446         {
 447                 if (att[i]->attlen == -1)
 448                 {
 449                         Datum           value = toast_values[i];
 450
 451                         if (toast_isnull[i])
 452                                 continue;
 453                         else if (VARATT_IS_EXTERNAL_ONDISK(PointerGetDatum(value)))
 454                                 toast_delete_datum(rel, value);
 455                         else if (VARATT_IS_EXTERNAL_INDIRECT(PointerGetDatum(value)))
 456                                 elog(ERROR, "attempt to delete tuple containing indirect datums");
 457                 }
 458         }
 459 }
 460
 461
 462 /* ----------
 463  * toast_insert_or_update -
 464  *
 465  *      Delete no-longer-used toast-entries and create new ones to
 466  *      make the new tuple fit on INSERT or UPDATE
 467  *
 468  * Inputs:
 469  *      newtup: the candidate new tuple to be inserted
 470  *      oldtup: the old row version for UPDATE, or NULL for INSERT
 471  *      options: options to be passed to heap_insert() for toast rows
 472  * Result:
 473  *      either newtup if no toasting is needed, or a palloc'd modified tuple
 474  *      that is what should actually get stored
 475  *
 476  * NOTE: neither newtup nor oldtup will be modified.  This is a change
 477  * from the pre-8.1 API of this routine.
 478  * ----------
 479  */
 480 HeapTuple
 481 toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup,
 482                                            int options)
 483 {
 484         HeapTuple       result_tuple;
 485         TupleDesc       tupleDesc;
 486         Form_pg_attribute *att;
 487         int                     numAttrs;
 488         int                     i;
 489
 490         bool            need_change = false;
 491         bool            need_free = false;
 492         bool            need_delold = false;
 493         bool            has_nulls = false;
 494
 495         Size            maxDataLen;
 496         Size            hoff;
 497
 498         char            toast_action[MaxHeapAttributeNumber];
 499         bool            toast_isnull[MaxHeapAttributeNumber];
 500         bool            toast_oldisnull[MaxHeapAttributeNumber];
 501         Datum           toast_values[MaxHeapAttributeNumber];
 502         Datum           toast_oldvalues[MaxHeapAttributeNumber];
 503         struct varlena *toast_oldexternal[MaxHeapAttributeNumber];
 504         int32           toast_sizes[MaxHeapAttributeNumber];
 505         bool            toast_free[MaxHeapAttributeNumber];
 506         bool            toast_delold[MaxHeapAttributeNumber];
 507
 508         /*
 509          * We should only ever be called for tuples of plain relations ---
 510          * recursing on a toast rel is bad news.
 511          */
 512         Assert(rel->rd_rel->relkind == RELKIND_RELATION ||
 513                    rel->rd_rel->relkind == RELKIND_MATVIEW);
 514
 515         /*
 516          * Get the tuple descriptor and break down the tuple(s) into fields.
 517          */
 518         tupleDesc = rel->rd_att;
 519         att = tupleDesc->attrs;
 520         numAttrs = tupleDesc->natts;
 521
 522         Assert(numAttrs <= MaxHeapAttributeNumber);
 523         heap_deform_tuple(newtup, tupleDesc, toast_values, toast_isnull);
 524         if (oldtup != NULL)
 525                 heap_deform_tuple(oldtup, tupleDesc, toast_oldvalues, toast_oldisnull);
 526
 527         /* ----------
 528          * Then collect information about the values given
 529          *
 530          * NOTE: toast_action[i] can have these values:
 531          *              ' '             default handling
 532          *              'p'             already processed --- don't touch it
 533          *              'x'             incompressible, but OK to move off
 534          *
 535          * NOTE: toast_sizes[i] is only made valid for varlena attributes with
 536          *              toast_action[i] different from 'p'.
 537          * ----------
 538          */
 539         memset(toast_action, ' ', numAttrs * sizeof(char));
 540         memset(toast_oldexternal, 0, numAttrs * sizeof(struct varlena *));
 541         memset(toast_free, 0, numAttrs * sizeof(bool));
 542         memset(toast_delold, 0, numAttrs * sizeof(bool));
 543
 544         for (i = 0; i < numAttrs; i++)
 545         {
 546                 struct varlena *old_value;
 547                 struct varlena *new_value;
 548
 549                 if (oldtup != NULL)
 550                 {
 551                         /*
 552                          * For UPDATE get the old and new values of this attribute
 553                          */
 554                         old_value = (struct varlena *) DatumGetPointer(toast_oldvalues[i]);
 555                         new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
 556
 557                         /*
 558                          * If the old value is stored on disk, check if it has changed so
 559                          * we have to delete it later.
 560                          */
 561                         if (att[i]->attlen == -1 && !toast_oldisnull[i] &&
 562                                 VARATT_IS_EXTERNAL_ONDISK(old_value))
 563                         {
 564                                 if (toast_isnull[i] || !VARATT_IS_EXTERNAL_ONDISK(new_value) ||
 565                                         memcmp((char *) old_value, (char *) new_value,
 566                                                    VARSIZE_EXTERNAL(old_value)) != 0)
 567                                 {
 568                                         /*
 569                                          * The old external stored value isn't needed any more
 570                                          * after the update
 571                                          */
 572                                         toast_delold[i] = true;
 573                                         need_delold = true;
 574                                 }
 575                                 else
 576                                 {
 577                                         /*
 578                                          * This attribute isn't changed by this update so we reuse
 579                                          * the original reference to the old value in the new
 580                                          * tuple.
 581                                          */
 582                                         toast_action[i] = 'p';
 583                                         continue;
 584                                 }
 585                         }
 586                 }
 587                 else
 588                 {
 589                         /*
 590                          * For INSERT simply get the new value
 591                          */
 592                         new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
 593                 }
 594
 595                 /*
 596                  * Handle NULL attributes
 597                  */
 598                 if (toast_isnull[i])
 599                 {
 600                         toast_action[i] = 'p';
 601                         has_nulls = true;
 602                         continue;
 603                 }
 604
 605                 /*
 606                  * Now look at varlena attributes
 607                  */
 608                 if (att[i]->attlen == -1)
 609                 {
 610                         /*
 611                          * If the table's attribute says PLAIN always, force it so.
 612                          */
 613                         if (att[i]->attstorage == 'p')
 614                                 toast_action[i] = 'p';
 615
 616                         /*
 617                          * We took care of UPDATE above, so any external value we find
 618                          * still in the tuple must be someone else's we cannot reuse.
 619                          * Fetch it back (without decompression, unless we are forcing
 620                          * PLAIN storage).      If necessary, we'll push it out as a new
 621                          * external value below.
 622                          */
 623                         if (VARATT_IS_EXTERNAL(new_value))
 624                         {
 625                                 toast_oldexternal[i] = new_value;
 626                                 if (att[i]->attstorage == 'p')
 627                                         new_value = heap_tuple_untoast_attr(new_value);
 628                                 else
 629                                         new_value = heap_tuple_fetch_attr(new_value);
 630                                 toast_values[i] = PointerGetDatum(new_value);
 631                                 toast_free[i] = true;
 632                                 need_change = true;
 633                                 need_free = true;
 634                         }
 635
 636                         /*
 637                          * Remember the size of this attribute
 638                          */
 639                         toast_sizes[i] = VARSIZE_ANY(new_value);
 640                 }
 641                 else
 642                 {
 643                         /*
 644                          * Not a varlena attribute, plain storage always
 645                          */
 646                         toast_action[i] = 'p';
 647                 }
 648         }
 649
 650         /* ----------
 651          * Compress and/or save external until data fits into target length
 652          *
 653          *      1: Inline compress attributes with attstorage 'x', and store very
 654          *         large attributes with attstorage 'x' or 'e' external immediately
 655          *      2: Store attributes with attstorage 'x' or 'e' external
 656          *      3: Inline compress attributes with attstorage 'm'
 657          *      4: Store attributes with attstorage 'm' external
 658          * ----------
 659          */
 660
 661         /* compute header overhead --- this should match heap_form_tuple() */
 662         hoff = offsetof(HeapTupleHeaderData, t_bits);
 663         if (has_nulls)
 664                 hoff += BITMAPLEN(numAttrs);
 665         if (newtup->t_data->t_infomask & HEAP_HASOID)
 666                 hoff += sizeof(Oid);
 667         hoff = MAXALIGN(hoff);
 668         /* now convert to a limit on the tuple data size */
 669         maxDataLen = TOAST_TUPLE_TARGET - hoff;
 670
 671         /*
 672          * Look for attributes with attstorage 'x' to compress.  Also find large
 673          * attributes with attstorage 'x' or 'e', and store them external.
 674          */
 675         while (heap_compute_data_size(tupleDesc,
 676                                                                   toast_values, toast_isnull) > maxDataLen)
 677         {
 678                 int                     biggest_attno = -1;
 679                 int32           biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
 680                 Datum           old_value;
 681                 Datum           new_value;
 682
 683                 /*
 684                  * Search for the biggest yet unprocessed internal attribute
 685                  */
 686                 for (i = 0; i < numAttrs; i++)
 687                 {
 688                         if (toast_action[i] != ' ')
 689                                 continue;
 690                         if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
 691                                 continue;               /* can't happen, toast_action would be 'p' */
 692                         if (VARATT_IS_COMPRESSED(DatumGetPointer(toast_values[i])))
 693                                 continue;
 694                         if (att[i]->attstorage != 'x' && att[i]->attstorage != 'e')
 695                                 continue;
 696                         if (toast_sizes[i] > biggest_size)
 697                         {
 698                                 biggest_attno = i;
 699                                 biggest_size = toast_sizes[i];
 700                         }
 701                 }
 702
 703                 if (biggest_attno < 0)
 704                         break;
 705
 706                 /*
 707                  * Attempt to compress it inline, if it has attstorage 'x'
 708                  */
 709                 i = biggest_attno;
 710                 if (att[i]->attstorage == 'x')
 711                 {
 712                         old_value = toast_values[i];
 713                         new_value = toast_compress_datum(old_value);
 714
 715                         if (DatumGetPointer(new_value) != NULL)
 716                         {
 717                                 /* successful compression */
 718                                 if (toast_free[i])
 719                                         pfree(DatumGetPointer(old_value));
 720                                 toast_values[i] = new_value;
 721                                 toast_free[i] = true;
 722                                 toast_sizes[i] = VARSIZE(DatumGetPointer(toast_values[i]));
 723                                 need_change = true;
 724                                 need_free = true;
 725                         }
 726                         else
 727                         {
 728                                 /* incompressible, ignore on subsequent compression passes */
 729                                 toast_action[i] = 'x';
 730                         }
 731                 }
 732                 else
 733                 {
 734                         /* has attstorage 'e', ignore on subsequent compression passes */
 735                         toast_action[i] = 'x';
 736                 }
 737
 738                 /*
 739                  * If this value is by itself more than maxDataLen (after compression
 740                  * if any), push it out to the toast table immediately, if possible.
 741                  * This avoids uselessly compressing other fields in the common case
 742                  * where we have one long field and several short ones.
 743                  *
 744                  * XXX maybe the threshold should be less than maxDataLen?
 745                  */
 746                 if (toast_sizes[i] > maxDataLen &&
 747                         rel->rd_rel->reltoastrelid != InvalidOid)
 748                 {
 749                         old_value = toast_values[i];
 750                         toast_action[i] = 'p';
 751                         toast_values[i] = toast_save_datum(rel, toast_values[i],
 752                                                                                            toast_oldexternal[i], options);
 753                         if (toast_free[i])
 754                                 pfree(DatumGetPointer(old_value));
 755                         toast_free[i] = true;
 756                         need_change = true;
 757                         need_free = true;
 758                 }
 759         }
 760
 761         /*
 762          * Second we look for attributes of attstorage 'x' or 'e' that are still
 763          * inline.      But skip this if there's no toast table to push them to.
 764          */
 765         while (heap_compute_data_size(tupleDesc,
 766                                                                   toast_values, toast_isnull) > maxDataLen &&
 767                    rel->rd_rel->reltoastrelid != InvalidOid)
 768         {
 769                 int                     biggest_attno = -1;
 770                 int32           biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
 771                 Datum           old_value;
 772
 773                 /*------
 774                  * Search for the biggest yet inlined attribute with
 775                  * attstorage equals 'x' or 'e'
 776                  *------
 777                  */
 778                 for (i = 0; i < numAttrs; i++)
 779                 {
 780                         if (toast_action[i] == 'p')
 781                                 continue;
 782                         if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
 783                                 continue;               /* can't happen, toast_action would be 'p' */
 784                         if (att[i]->attstorage != 'x' && att[i]->attstorage != 'e')
 785                                 continue;
 786                         if (toast_sizes[i] > biggest_size)
 787                         {
 788                                 biggest_attno = i;
 789                                 biggest_size = toast_sizes[i];
 790                         }
 791                 }
 792
 793                 if (biggest_attno < 0)
 794                         break;
 795
 796                 /*
 797                  * Store this external
 798                  */
 799                 i = biggest_attno;
 800                 old_value = toast_values[i];
 801                 toast_action[i] = 'p';
 802                 toast_values[i] = toast_save_datum(rel, toast_values[i],
 803                                                                                    toast_oldexternal[i], options);
 804                 if (toast_free[i])
 805                         pfree(DatumGetPointer(old_value));
 806                 toast_free[i] = true;
 807
 808                 need_change = true;
 809                 need_free = true;
 810         }
 811
 812         /*
 813          * Round 3 - this time we take attributes with storage 'm' into
 814          * compression
 815          */
 816         while (heap_compute_data_size(tupleDesc,
 817                                                                   toast_values, toast_isnull) > maxDataLen)
 818         {
 819                 int                     biggest_attno = -1;
 820                 int32           biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
 821                 Datum           old_value;
 822                 Datum           new_value;
 823
 824                 /*
 825                  * Search for the biggest yet uncompressed internal attribute
 826                  */
 827                 for (i = 0; i < numAttrs; i++)
 828                 {
 829                         if (toast_action[i] != ' ')
 830                                 continue;
 831                         if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
 832                                 continue;               /* can't happen, toast_action would be 'p' */
 833                         if (VARATT_IS_COMPRESSED(DatumGetPointer(toast_values[i])))
 834                                 continue;
 835                         if (att[i]->attstorage != 'm')
 836                                 continue;
 837                         if (toast_sizes[i] > biggest_size)
 838                         {
 839                                 biggest_attno = i;
 840                                 biggest_size = toast_sizes[i];
 841                         }
 842                 }
 843
 844                 if (biggest_attno < 0)
 845                         break;
 846
 847                 /*
 848                  * Attempt to compress it inline
 849                  */
 850                 i = biggest_attno;
 851                 old_value = toast_values[i];
 852                 new_value = toast_compress_datum(old_value);
 853
 854                 if (DatumGetPointer(new_value) != NULL)
 855                 {
 856                         /* successful compression */
 857                         if (toast_free[i])
 858                                 pfree(DatumGetPointer(old_value));
 859                         toast_values[i] = new_value;
 860                         toast_free[i] = true;
 861                         toast_sizes[i] = VARSIZE(DatumGetPointer(toast_values[i]));
 862                         need_change = true;
 863                         need_free = true;
 864                 }
 865                 else
 866                 {
 867                         /* incompressible, ignore on subsequent compression passes */
 868                         toast_action[i] = 'x';
 869                 }
 870         }
 871
 872         /*
 873          * Finally we store attributes of type 'm' externally.  At this point we
 874          * increase the target tuple size, so that 'm' attributes aren't stored
 875          * externally unless really necessary.
 876          */
 877         maxDataLen = TOAST_TUPLE_TARGET_MAIN - hoff;
 878
 879         while (heap_compute_data_size(tupleDesc,
 880                                                                   toast_values, toast_isnull) > maxDataLen &&
 881                    rel->rd_rel->reltoastrelid != InvalidOid)
 882         {
 883                 int                     biggest_attno = -1;
 884                 int32           biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
 885                 Datum           old_value;
 886
 887                 /*--------
 888                  * Search for the biggest yet inlined attribute with
 889                  * attstorage = 'm'
 890                  *--------
 891                  */
 892                 for (i = 0; i < numAttrs; i++)
 893                 {
 894                         if (toast_action[i] == 'p')
 895                                 continue;
 896                         if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
 897                                 continue;               /* can't happen, toast_action would be 'p' */
 898                         if (att[i]->attstorage != 'm')
 899                                 continue;
 900                         if (toast_sizes[i] > biggest_size)
 901                         {
 902                                 biggest_attno = i;
 903                                 biggest_size = toast_sizes[i];
 904                         }
 905                 }
 906
 907                 if (biggest_attno < 0)
 908                         break;
 909
 910                 /*
 911                  * Store this external
 912                  */
 913                 i = biggest_attno;
 914                 old_value = toast_values[i];
 915                 toast_action[i] = 'p';
 916                 toast_values[i] = toast_save_datum(rel, toast_values[i],
 917                                                                                    toast_oldexternal[i], options);
 918                 if (toast_free[i])
 919                         pfree(DatumGetPointer(old_value));
 920                 toast_free[i] = true;
 921
 922                 need_change = true;
 923                 need_free = true;
 924         }
 925
 926         /*
 927          * In the case we toasted any values, we need to build a new heap tuple
 928          * with the changed values.
 929          */
 930         if (need_change)
 931         {
 932                 HeapTupleHeader olddata = newtup->t_data;
 933                 HeapTupleHeader new_data;
 934                 int32           new_header_len;
 935                 int32           new_data_len;
 936                 int32           new_tuple_len;
 937
 938                 /*
 939                  * Calculate the new size of the tuple.
 940                  *
 941                  * Note: we used to assume here that the old tuple's t_hoff must equal
 942                  * the new_header_len value, but that was incorrect.  The old tuple
 943                  * might have a smaller-than-current natts, if there's been an ALTER
 944                  * TABLE ADD COLUMN since it was stored; and that would lead to a
 945                  * different conclusion about the size of the null bitmap, or even
 946                  * whether there needs to be one at all.
 947                  */
 948                 new_header_len = offsetof(HeapTupleHeaderData, t_bits);
 949                 if (has_nulls)
 950                         new_header_len += BITMAPLEN(numAttrs);
 951                 if (olddata->t_infomask & HEAP_HASOID)
 952                         new_header_len += sizeof(Oid);
 953                 new_header_len = MAXALIGN(new_header_len);
 954                 new_data_len = heap_compute_data_size(tupleDesc,
 955                                                                                           toast_values, toast_isnull);
 956                 new_tuple_len = new_header_len + new_data_len;
 957
 958                 /*
 959                  * Allocate and zero the space needed, and fill HeapTupleData fields.
 960                  */
 961                 result_tuple = (HeapTuple) palloc0(HEAPTUPLESIZE + new_tuple_len);
 962                 result_tuple->t_len = new_tuple_len;
 963                 result_tuple->t_self = newtup->t_self;
 964                 result_tuple->t_tableOid = newtup->t_tableOid;
 965                 new_data = (HeapTupleHeader) ((char *) result_tuple + HEAPTUPLESIZE);
 966                 result_tuple->t_data = new_data;
 967
 968                 /*
 969                  * Copy the existing tuple header, but adjust natts and t_hoff.
 970                  */
 971                 memcpy(new_data, olddata, offsetof(HeapTupleHeaderData, t_bits));
 972                 HeapTupleHeaderSetNatts(new_data, numAttrs);
 973                 new_data->t_hoff = new_header_len;
 974                 if (olddata->t_infomask & HEAP_HASOID)
 975                         HeapTupleHeaderSetOid(new_data, HeapTupleHeaderGetOid(olddata));
 976
 977                 /* Copy over the data, and fill the null bitmap if needed */
 978                 heap_fill_tuple(tupleDesc,
 979                                                 toast_values,
 980                                                 toast_isnull,
 981                                                 (char *) new_data + new_header_len,
 982                                                 new_data_len,
 983                                                 &(new_data->t_infomask),
 984                                                 has_nulls ? new_data->t_bits : NULL);
 985         }
 986         else
 987                 result_tuple = newtup;
 988
 989         /*
 990          * Free allocated temp values
 991          */
 992         if (need_free)
 993                 for (i = 0; i < numAttrs; i++)
 994                         if (toast_free[i])
 995                                 pfree(DatumGetPointer(toast_values[i]));
 996
 997         /*
 998          * Delete external values from the old tuple
 999          */
1000         if (need_delold)
1001                 for (i = 0; i < numAttrs; i++)
1002                         if (toast_delold[i])
1003                                 toast_delete_datum(rel, toast_oldvalues[i]);
1004
1005         return result_tuple;
1006 }
1007
1008
1009 /* ----------
1010  * toast_flatten_tuple -
1011  *
1012  *      "Flatten" a tuple to contain no out-of-line toasted fields.
1013  *      (This does not eliminate compressed or short-header datums.)
1014  * ----------
1015  */
1016 HeapTuple
1017 toast_flatten_tuple(HeapTuple tup, TupleDesc tupleDesc)
1018 {
1019         HeapTuple       new_tuple;
1020         Form_pg_attribute *att = tupleDesc->attrs;
1021         int                     numAttrs = tupleDesc->natts;
1022         int                     i;
1023         Datum           toast_values[MaxTupleAttributeNumber];
1024         bool            toast_isnull[MaxTupleAttributeNumber];
1025         bool            toast_free[MaxTupleAttributeNumber];
1026
1027         /*
1028          * Break down the tuple into fields.
1029          */
1030         Assert(numAttrs <= MaxTupleAttributeNumber);
1031         heap_deform_tuple(tup, tupleDesc, toast_values, toast_isnull);
1032
1033         memset(toast_free, 0, numAttrs * sizeof(bool));
1034
1035         for (i = 0; i < numAttrs; i++)
1036         {
1037                 /*
1038                  * Look at non-null varlena attributes
1039                  */
1040                 if (!toast_isnull[i] && att[i]->attlen == -1)
1041                 {
1042                         struct varlena *new_value;
1043
1044                         new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
1045                         if (VARATT_IS_EXTERNAL(new_value))
1046                         {
1047                                 new_value = toast_fetch_datum(new_value);
1048                                 toast_values[i] = PointerGetDatum(new_value);
1049                                 toast_free[i] = true;
1050                         }
1051                 }
1052         }
1053
1054         /*
1055          * Form the reconfigured tuple.
1056          */
1057         new_tuple = heap_form_tuple(tupleDesc, toast_values, toast_isnull);
1058
1059         /*
1060          * Be sure to copy the tuple's OID and identity fields.  We also make a
1061          * point of copying visibility info, just in case anybody looks at those
1062          * fields in a syscache entry.
1063          */
1064         if (tupleDesc->tdhasoid)
1065                 HeapTupleSetOid(new_tuple, HeapTupleGetOid(tup));
1066
1067         new_tuple->t_self = tup->t_self;
1068         new_tuple->t_tableOid = tup->t_tableOid;
1069
1070         new_tuple->t_data->t_choice = tup->t_data->t_choice;
1071         new_tuple->t_data->t_ctid = tup->t_data->t_ctid;
1072         new_tuple->t_data->t_infomask &= ~HEAP_XACT_MASK;
1073         new_tuple->t_data->t_infomask |=
1074                 tup->t_data->t_infomask & HEAP_XACT_MASK;
1075         new_tuple->t_data->t_infomask2 &= ~HEAP2_XACT_MASK;
1076         new_tuple->t_data->t_infomask2 |=
1077                 tup->t_data->t_infomask2 & HEAP2_XACT_MASK;
1078
1079         /*
1080          * Free allocated temp values
1081          */
1082         for (i = 0; i < numAttrs; i++)
1083                 if (toast_free[i])
1084                         pfree(DatumGetPointer(toast_values[i]));
1085
1086         return new_tuple;
1087 }
1088
1089
1090 /* ----------
1091  * toast_flatten_tuple_attribute -
1092  *
1093  *      If a Datum is of composite type, "flatten" it to contain no toasted fields.
1094  *      This must be invoked on any potentially-composite field that is to be
1095  *      inserted into a tuple.  Doing this preserves the invariant that toasting
1096  *      goes only one level deep in a tuple.
1097  *
1098  *      Note that flattening does not mean expansion of short-header varlenas,
1099  *      so in one sense toasting is allowed within composite datums.
1100  * ----------
1101  */
1102 Datum
1103 toast_flatten_tuple_attribute(Datum value,
1104                                                           Oid typeId, int32 typeMod)
1105 {
1106         TupleDesc       tupleDesc;
1107         HeapTupleHeader olddata;
1108         HeapTupleHeader new_data;
1109         int32           new_header_len;
1110         int32           new_data_len;
1111         int32           new_tuple_len;
1112         HeapTupleData tmptup;
1113         Form_pg_attribute *att;
1114         int                     numAttrs;
1115         int                     i;
1116         bool            need_change = false;
1117         bool            has_nulls = false;
1118         Datum           toast_values[MaxTupleAttributeNumber];
1119         bool            toast_isnull[MaxTupleAttributeNumber];
1120         bool            toast_free[MaxTupleAttributeNumber];
1121
1122         /*
1123          * See if it's a composite type, and get the tupdesc if so.
1124          */
1125         tupleDesc = lookup_rowtype_tupdesc_noerror(typeId, typeMod, true);
1126         if (tupleDesc == NULL)
1127                 return value;                   /* not a composite type */
1128
1129         att = tupleDesc->attrs;
1130         numAttrs = tupleDesc->natts;
1131
1132         /*
1133          * Break down the tuple into fields.
1134          */
1135         olddata = DatumGetHeapTupleHeader(value);
1136         Assert(typeId == HeapTupleHeaderGetTypeId(olddata));
1137         Assert(typeMod == HeapTupleHeaderGetTypMod(olddata));
1138         /* Build a temporary HeapTuple control structure */
1139         tmptup.t_len = HeapTupleHeaderGetDatumLength(olddata);
1140         ItemPointerSetInvalid(&(tmptup.t_self));
1141         tmptup.t_tableOid = InvalidOid;
1142         tmptup.t_data = olddata;
1143
1144         Assert(numAttrs <= MaxTupleAttributeNumber);
1145         heap_deform_tuple(&tmptup, tupleDesc, toast_values, toast_isnull);
1146
1147         memset(toast_free, 0, numAttrs * sizeof(bool));
1148
1149         for (i = 0; i < numAttrs; i++)
1150         {
1151                 /*
1152                  * Look at non-null varlena attributes
1153                  */
1154                 if (toast_isnull[i])
1155                         has_nulls = true;
1156                 else if (att[i]->attlen == -1)
1157                 {
1158                         struct varlena *new_value;
1159
1160                         new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
1161                         if (VARATT_IS_EXTERNAL(new_value) ||
1162                                 VARATT_IS_COMPRESSED(new_value))
1163                         {
1164                                 new_value = heap_tuple_untoast_attr(new_value);
1165                                 toast_values[i] = PointerGetDatum(new_value);
1166                                 toast_free[i] = true;
1167                                 need_change = true;
1168                         }
1169                 }
1170         }
1171
1172         /*
1173          * If nothing to untoast, just return the original tuple.
1174          */
1175         if (!need_change)
1176         {
1177                 ReleaseTupleDesc(tupleDesc);
1178                 return value;
1179         }
1180
1181         /*
1182          * Calculate the new size of the tuple.
1183          *
1184          * This should match the reconstruction code in toast_insert_or_update.
1185          */
1186         new_header_len = offsetof(HeapTupleHeaderData, t_bits);
1187         if (has_nulls)
1188                 new_header_len += BITMAPLEN(numAttrs);
1189         if (olddata->t_infomask & HEAP_HASOID)
1190                 new_header_len += sizeof(Oid);
1191         new_header_len = MAXALIGN(new_header_len);
1192         new_data_len = heap_compute_data_size(tupleDesc,
1193                                                                                   toast_values, toast_isnull);
1194         new_tuple_len = new_header_len + new_data_len;
1195
1196         new_data = (HeapTupleHeader) palloc0(new_tuple_len);
1197
1198         /*
1199          * Copy the existing tuple header, but adjust natts and t_hoff.
1200          */
1201         memcpy(new_data, olddata, offsetof(HeapTupleHeaderData, t_bits));
1202         HeapTupleHeaderSetNatts(new_data, numAttrs);
1203         new_data->t_hoff = new_header_len;
1204         if (olddata->t_infomask & HEAP_HASOID)
1205                 HeapTupleHeaderSetOid(new_data, HeapTupleHeaderGetOid(olddata));
1206
1207         /* Reset the datum length field, too */
1208         HeapTupleHeaderSetDatumLength(new_data, new_tuple_len);
1209
1210         /* Copy over the data, and fill the null bitmap if needed */
1211         heap_fill_tuple(tupleDesc,
1212                                         toast_values,
1213                                         toast_isnull,
1214                                         (char *) new_data + new_header_len,
1215                                         new_data_len,
1216                                         &(new_data->t_infomask),
1217                                         has_nulls ? new_data->t_bits : NULL);
1218
1219         /*
1220          * Free allocated temp values
1221          */
1222         for (i = 0; i < numAttrs; i++)
1223                 if (toast_free[i])
1224                         pfree(DatumGetPointer(toast_values[i]));
1225         ReleaseTupleDesc(tupleDesc);
1226
1227         return PointerGetDatum(new_data);
1228 }
1229
1230
1231 /* ----------
1232  * toast_compress_datum -
1233  *
1234  *      Create a compressed version of a varlena datum
1235  *
1236  *      If we fail (ie, compressed result is actually bigger than original)
1237  *      then return NULL.  We must not use compressed data if it'd expand
1238  *      the tuple!
1239  *
1240  *      We use VAR{SIZE,DATA}_ANY so we can handle short varlenas here without
1241  *      copying them.  But we can't handle external or compressed datums.
1242  * ----------
1243  */
1244 Datum
1245 toast_compress_datum(Datum value)
1246 {
1247         struct varlena *tmp;
1248         int32           valsize = VARSIZE_ANY_EXHDR(DatumGetPointer(value));
1249
1250         Assert(!VARATT_IS_EXTERNAL(DatumGetPointer(value)));
1251         Assert(!VARATT_IS_COMPRESSED(DatumGetPointer(value)));
1252
1253         /*
1254          * No point in wasting a palloc cycle if value size is out of the allowed
1255          * range for compression
1256          */
1257         if (valsize < PGLZ_strategy_default->min_input_size ||
1258                 valsize > PGLZ_strategy_default->max_input_size)
1259                 return PointerGetDatum(NULL);
1260
1261         tmp = (struct varlena *) palloc(PGLZ_MAX_OUTPUT(valsize));
1262
1263         /*
1264          * We recheck the actual size even if pglz_compress() reports success,
1265          * because it might be satisfied with having saved as little as one byte
1266          * in the compressed data --- which could turn into a net loss once you
1267          * consider header and alignment padding.  Worst case, the compressed
1268          * format might require three padding bytes (plus header, which is
1269          * included in VARSIZE(tmp)), whereas the uncompressed format would take
1270          * only one header byte and no padding if the value is short enough.  So
1271          * we insist on a savings of more than 2 bytes to ensure we have a gain.
1272          */
1273         if (pglz_compress(VARDATA_ANY(DatumGetPointer(value)), valsize,
1274                                           (PGLZ_Header *) tmp, PGLZ_strategy_default) &&
1275                 VARSIZE(tmp) < valsize - 2)
1276         {
1277                 /* successful compression */
1278                 return PointerGetDatum(tmp);
1279         }
1280         else
1281         {
1282                 /* incompressible data */
1283                 pfree(tmp);
1284                 return PointerGetDatum(NULL);
1285         }
1286 }
1287
1288
1289 /* ----------
1290  * toast_save_datum -
1291  *
1292  *      Save one single datum into the secondary relation and return
1293  *      a Datum reference for it.
1294  *
1295  * rel: the main relation we're working with (not the toast rel!)
1296  * value: datum to be pushed to toast storage
1297  * oldexternal: if not NULL, toast pointer previously representing the datum
1298  * options: options to be passed to heap_insert() for toast rows
1299  * ----------
1300  */
1301 static Datum
1302 toast_save_datum(Relation rel, Datum value,
1303                                  struct varlena * oldexternal, int options)
1304 {
1305         Relation        toastrel;
1306         Relation        toastidx;
1307         HeapTuple       toasttup;
1308         TupleDesc       toasttupDesc;
1309         Datum           t_values[3];
1310         bool            t_isnull[3];
1311         CommandId       mycid = GetCurrentCommandId(true);
1312         struct varlena *result;
1313         struct varatt_external toast_pointer;
1314         struct
1315         {
1316                 struct varlena hdr;
1317                 char            data[TOAST_MAX_CHUNK_SIZE]; /* make struct big enough */
1318                 int32           align_it;       /* ensure struct is aligned well enough */
1319         }                       chunk_data;
1320         int32           chunk_size;
1321         int32           chunk_seq = 0;
1322         char       *data_p;
1323         int32           data_todo;
1324         Pointer         dval = DatumGetPointer(value);
1325
1326         Assert(!VARATT_IS_EXTERNAL(value));
1327
1328         /*
1329          * Open the toast relation and its index.  We can use the index to check
1330          * uniqueness of the OID we assign to the toasted item, even though it has
1331          * additional columns besides OID.
1332          */
1333         toastrel = heap_open(rel->rd_rel->reltoastrelid, RowExclusiveLock);
1334         toasttupDesc = toastrel->rd_att;
1335         toastidx = index_open(toastrel->rd_rel->reltoastidxid, RowExclusiveLock);
1336
1337         /*
1338          * Get the data pointer and length, and compute va_rawsize and va_extsize.
1339          *
1340          * va_rawsize is the size of the equivalent fully uncompressed datum, so
1341          * we have to adjust for short headers.
1342          *
1343          * va_extsize is the actual size of the data payload in the toast records.
1344          */
1345         if (VARATT_IS_SHORT(dval))
1346         {
1347                 data_p = VARDATA_SHORT(dval);
1348                 data_todo = VARSIZE_SHORT(dval) - VARHDRSZ_SHORT;
1349                 toast_pointer.va_rawsize = data_todo + VARHDRSZ;                /* as if not short */
1350                 toast_pointer.va_extsize = data_todo;
1351         }
1352         else if (VARATT_IS_COMPRESSED(dval))
1353         {
1354                 data_p = VARDATA(dval);
1355                 data_todo = VARSIZE(dval) - VARHDRSZ;
1356                 /* rawsize in a compressed datum is just the size of the payload */
1357                 toast_pointer.va_rawsize = VARRAWSIZE_4B_C(dval) + VARHDRSZ;
1358                 toast_pointer.va_extsize = data_todo;
1359                 /* Assert that the numbers look like it's compressed */
1360                 Assert(VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer));
1361         }
1362         else
1363         {
1364                 data_p = VARDATA(dval);
1365                 data_todo = VARSIZE(dval) - VARHDRSZ;
1366                 toast_pointer.va_rawsize = VARSIZE(dval);
1367                 toast_pointer.va_extsize = data_todo;
1368         }
1369
1370         /*
1371          * Insert the correct table OID into the result TOAST pointer.
1372          *
1373          * Normally this is the actual OID of the target toast table, but during
1374          * table-rewriting operations such as CLUSTER, we have to insert the OID
1375          * of the table's real permanent toast table instead.  rd_toastoid is set
1376          * if we have to substitute such an OID.
1377          */
1378         if (OidIsValid(rel->rd_toastoid))
1379                 toast_pointer.va_toastrelid = rel->rd_toastoid;
1380         else
1381                 toast_pointer.va_toastrelid = RelationGetRelid(toastrel);
1382
1383         /*
1384          * Choose an OID to use as the value ID for this toast value.
1385          *
1386          * Normally we just choose an unused OID within the toast table.  But
1387          * during table-rewriting operations where we are preserving an existing
1388          * toast table OID, we want to preserve toast value OIDs too.  So, if
1389          * rd_toastoid is set and we had a prior external value from that same
1390          * toast table, re-use its value ID.  If we didn't have a prior external
1391          * value (which is a corner case, but possible if the table's attstorage
1392          * options have been changed), we have to pick a value ID that doesn't
1393          * conflict with either new or existing toast value OIDs.
1394          */
1395         if (!OidIsValid(rel->rd_toastoid))
1396         {
1397                 /* normal case: just choose an unused OID */
1398                 toast_pointer.va_valueid =
1399                         GetNewOidWithIndex(toastrel,
1400                                                            RelationGetRelid(toastidx),
1401                                                            (AttrNumber) 1);
1402         }
1403         else
1404         {
1405                 /* rewrite case: check to see if value was in old toast table */
1406                 toast_pointer.va_valueid = InvalidOid;
1407                 if (oldexternal != NULL)
1408                 {
1409                         struct varatt_external old_toast_pointer;
1410
1411                         Assert(VARATT_IS_EXTERNAL_ONDISK(oldexternal));
1412                         /* Must copy to access aligned fields */
1413                         VARATT_EXTERNAL_GET_POINTER(old_toast_pointer, oldexternal);
1414                         if (old_toast_pointer.va_toastrelid == rel->rd_toastoid)
1415                         {
1416                                 /* This value came from the old toast table; reuse its OID */
1417                                 toast_pointer.va_valueid = old_toast_pointer.va_valueid;
1418
1419                                 /*
1420                                  * There is a corner case here: the table rewrite might have
1421                                  * to copy both live and recently-dead versions of a row, and
1422                                  * those versions could easily reference the same toast value.
1423                                  * When we copy the second or later version of such a row,
1424                                  * reusing the OID will mean we select an OID that's already
1425                                  * in the new toast table.      Check for that, and if so, just
1426                                  * fall through without writing the data again.
1427                                  *
1428                                  * While annoying and ugly-looking, this is a good thing
1429                                  * because it ensures that we wind up with only one copy of
1430                                  * the toast value when there is only one copy in the old
1431                                  * toast table.  Before we detected this case, we'd have made
1432                                  * multiple copies, wasting space; and what's worse, the
1433                                  * copies belonging to already-deleted heap tuples would not
1434                                  * be reclaimed by VACUUM.
1435                                  */
1436                                 if (toastrel_valueid_exists(toastrel,
1437                                                                                         toast_pointer.va_valueid))
1438                                 {
1439                                         /* Match, so short-circuit the data storage loop below */
1440                                         data_todo = 0;
1441                                 }
1442                         }
1443                 }
1444                 if (toast_pointer.va_valueid == InvalidOid)
1445                 {
1446                         /*
1447                          * new value; must choose an OID that doesn't conflict in either
1448                          * old or new toast table
1449                          */
1450                         do
1451                         {
1452                                 toast_pointer.va_valueid =
1453                                         GetNewOidWithIndex(toastrel,
1454                                                                            RelationGetRelid(toastidx),
1455                                                                            (AttrNumber) 1);
1456                         } while (toastid_valueid_exists(rel->rd_toastoid,
1457                                                                                         toast_pointer.va_valueid));
1458                 }
1459         }
1460
1461         /*
1462          * Initialize constant parts of the tuple data
1463          */
1464         t_values[0] = ObjectIdGetDatum(toast_pointer.va_valueid);
1465         t_values[2] = PointerGetDatum(&chunk_data);
1466         t_isnull[0] = false;
1467         t_isnull[1] = false;
1468         t_isnull[2] = false;
1469
1470         /*
1471          * Split up the item into chunks
1472          */
1473         while (data_todo > 0)
1474         {
1475                 /*
1476                  * Calculate the size of this chunk
1477                  */
1478                 chunk_size = Min(TOAST_MAX_CHUNK_SIZE, data_todo);
1479
1480                 /*
1481                  * Build a tuple and store it
1482                  */
1483                 t_values[1] = Int32GetDatum(chunk_seq++);
1484                 SET_VARSIZE(&chunk_data, chunk_size + VARHDRSZ);
1485                 memcpy(VARDATA(&chunk_data), data_p, chunk_size);
1486                 toasttup = heap_form_tuple(toasttupDesc, t_values, t_isnull);
1487
1488                 heap_insert(toastrel, toasttup, mycid, options, NULL);
1489
1490                 /*
1491                  * Create the index entry.      We cheat a little here by not using
1492                  * FormIndexDatum: this relies on the knowledge that the index columns
1493                  * are the same as the initial columns of the table.
1494                  *
1495                  * Note also that there had better not be any user-created index on
1496                  * the TOAST table, since we don't bother to update anything else.
1497                  */
1498                 index_insert(toastidx, t_values, t_isnull,
1499                                          &(toasttup->t_self),
1500                                          toastrel,
1501                                          toastidx->rd_index->indisunique ?
1502                                          UNIQUE_CHECK_YES : UNIQUE_CHECK_NO);
1503
1504                 /*
1505                  * Free memory
1506                  */
1507                 heap_freetuple(toasttup);
1508
1509                 /*
1510                  * Move on to next chunk
1511                  */
1512                 data_todo -= chunk_size;
1513                 data_p += chunk_size;
1514         }
1515
1516         /*
1517          * Done - close toast relation
1518          */
1519         index_close(toastidx, RowExclusiveLock);
1520         heap_close(toastrel, RowExclusiveLock);
1521
1522         /*
1523          * Create the TOAST pointer value that we'll return
1524          */
1525         result = (struct varlena *) palloc(TOAST_POINTER_SIZE);
1526         SET_VARTAG_EXTERNAL(result, VARTAG_ONDISK);
1527         memcpy(VARDATA_EXTERNAL(result), &toast_pointer, sizeof(toast_pointer));
1528
1529         return PointerGetDatum(result);
1530 }
1531
1532
1533 /* ----------
1534  * toast_delete_datum -
1535  *
1536  *      Delete a single external stored value.
1537  * ----------
1538  */
1539 static void
1540 toast_delete_datum(Relation rel, Datum value)
1541 {
1542         struct varlena *attr = (struct varlena *) DatumGetPointer(value);
1543         struct varatt_external toast_pointer;
1544         Relation        toastrel;
1545         Relation        toastidx;
1546         ScanKeyData toastkey;
1547         SysScanDesc toastscan;
1548         HeapTuple       toasttup;
1549
1550         if (!VARATT_IS_EXTERNAL_ONDISK(attr))
1551                 return;
1552
1553         /* Must copy to access aligned fields */
1554         VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
1555
1556         /*
1557          * Open the toast relation and its index
1558          */
1559         toastrel = heap_open(toast_pointer.va_toastrelid, RowExclusiveLock);
1560         toastidx = index_open(toastrel->rd_rel->reltoastidxid, RowExclusiveLock);
1561
1562         /*
1563          * Setup a scan key to find chunks with matching va_valueid
1564          */
1565         ScanKeyInit(&toastkey,
1566                                 (AttrNumber) 1,
1567                                 BTEqualStrategyNumber, F_OIDEQ,
1568                                 ObjectIdGetDatum(toast_pointer.va_valueid));
1569
1570         /*
1571          * Find all the chunks.  (We don't actually care whether we see them in
1572          * sequence or not, but since we've already locked the index we might as
1573          * well use systable_beginscan_ordered.)
1574          */
1575         toastscan = systable_beginscan_ordered(toastrel, toastidx,
1576                                                                                    SnapshotToast, 1, &toastkey);
1577         while ((toasttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
1578         {
1579                 /*
1580                  * Have a chunk, delete it
1581                  */
1582                 simple_heap_delete(toastrel, &toasttup->t_self);
1583         }
1584
1585         /*
1586          * End scan and close relations
1587          */
1588         systable_endscan_ordered(toastscan);
1589         index_close(toastidx, RowExclusiveLock);
1590         heap_close(toastrel, RowExclusiveLock);
1591 }
1592
1593
1594 /* ----------
1595  * toastrel_valueid_exists -
1596  *
1597  *      Test whether a toast value with the given ID exists in the toast relation
1598  * ----------
1599  */
1600 static bool
1601 toastrel_valueid_exists(Relation toastrel, Oid valueid)
1602 {
1603         bool            result = false;
1604         ScanKeyData toastkey;
1605         SysScanDesc toastscan;
1606
1607         /*
1608          * Setup a scan key to find chunks with matching va_valueid
1609          */
1610         ScanKeyInit(&toastkey,
1611                                 (AttrNumber) 1,
1612                                 BTEqualStrategyNumber, F_OIDEQ,
1613                                 ObjectIdGetDatum(valueid));
1614
1615         /*
1616          * Is there any such chunk?
1617          */
1618         toastscan = systable_beginscan(toastrel, toastrel->rd_rel->reltoastidxid,
1619                                                                    true, SnapshotToast, 1, &toastkey);
1620
1621         if (systable_getnext(toastscan) != NULL)
1622                 result = true;
1623
1624         systable_endscan(toastscan);
1625
1626         return result;
1627 }
1628
1629 /* ----------
1630  * toastid_valueid_exists -
1631  *
1632  *      As above, but work from toast rel's OID not an open relation
1633  * ----------
1634  */
1635 static bool
1636 toastid_valueid_exists(Oid toastrelid, Oid valueid)
1637 {
1638         bool            result;
1639         Relation        toastrel;
1640
1641         toastrel = heap_open(toastrelid, AccessShareLock);
1642
1643         result = toastrel_valueid_exists(toastrel, valueid);
1644
1645         heap_close(toastrel, AccessShareLock);
1646
1647         return result;
1648 }
1649
1650
1651 /* ----------
1652  * toast_fetch_datum -
1653  *
1654  *      Reconstruct an in memory Datum from the chunks saved
1655  *      in the toast relation
1656  * ----------
1657  */
1658 static struct varlena *
1659 toast_fetch_datum(struct varlena * attr)
1660 {
1661         Relation        toastrel;
1662         Relation        toastidx;
1663         ScanKeyData toastkey;
1664         SysScanDesc toastscan;
1665         HeapTuple       ttup;
1666         TupleDesc       toasttupDesc;
1667         struct varlena *result;
1668         struct varatt_external toast_pointer;
1669         int32           ressize;
1670         int32           residx,
1671                                 nextidx;
1672         int32           numchunks;
1673         Pointer         chunk;
1674         bool            isnull;
1675         char       *chunkdata;
1676         int32           chunksize;
1677
1678         if (VARATT_IS_EXTERNAL_INDIRECT(attr))
1679                 elog(ERROR, "shouldn't be called for indirect tuples");
1680
1681         /* Must copy to access aligned fields */
1682         VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
1683
1684         ressize = toast_pointer.va_extsize;
1685         numchunks = ((ressize - 1) / TOAST_MAX_CHUNK_SIZE) + 1;
1686
1687         result = (struct varlena *) palloc(ressize + VARHDRSZ);
1688
1689         if (VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
1690                 SET_VARSIZE_COMPRESSED(result, ressize + VARHDRSZ);
1691         else
1692                 SET_VARSIZE(result, ressize + VARHDRSZ);
1693
1694         /*
1695          * Open the toast relation and its index
1696          */
1697         toastrel = heap_open(toast_pointer.va_toastrelid, AccessShareLock);
1698         toasttupDesc = toastrel->rd_att;
1699         toastidx = index_open(toastrel->rd_rel->reltoastidxid, AccessShareLock);
1700
1701         /*
1702          * Setup a scan key to fetch from the index by va_valueid
1703          */
1704         ScanKeyInit(&toastkey,
1705                                 (AttrNumber) 1,
1706                                 BTEqualStrategyNumber, F_OIDEQ,
1707                                 ObjectIdGetDatum(toast_pointer.va_valueid));
1708
1709         /*
1710          * Read the chunks by index
1711          *
1712          * Note that because the index is actually on (valueid, chunkidx) we will
1713          * see the chunks in chunkidx order, even though we didn't explicitly ask
1714          * for it.
1715          */
1716         nextidx = 0;
1717
1718         toastscan = systable_beginscan_ordered(toastrel, toastidx,
1719                                                                                    SnapshotToast, 1, &toastkey);
1720         while ((ttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
1721         {
1722                 /*
1723                  * Have a chunk, extract the sequence number and the data
1724                  */
1725                 residx = DatumGetInt32(fastgetattr(ttup, 2, toasttupDesc, &isnull));
1726                 Assert(!isnull);
1727                 chunk = DatumGetPointer(fastgetattr(ttup, 3, toasttupDesc, &isnull));
1728                 Assert(!isnull);
1729                 if (!VARATT_IS_EXTENDED(chunk))
1730                 {
1731                         chunksize = VARSIZE(chunk) - VARHDRSZ;
1732                         chunkdata = VARDATA(chunk);
1733                 }
1734                 else if (VARATT_IS_SHORT(chunk))
1735                 {
1736                         /* could happen due to heap_form_tuple doing its thing */
1737                         chunksize = VARSIZE_SHORT(chunk) - VARHDRSZ_SHORT;
1738                         chunkdata = VARDATA_SHORT(chunk);
1739                 }
1740                 else
1741                 {
1742                         /* should never happen */
1743                         elog(ERROR, "found toasted toast chunk for toast value %u in %s",
1744                                  toast_pointer.va_valueid,
1745                                  RelationGetRelationName(toastrel));
1746                         chunksize = 0;          /* keep compiler quiet */
1747                         chunkdata = NULL;
1748                 }
1749
1750                 /*
1751                  * Some checks on the data we've found
1752                  */
1753                 if (residx != nextidx)
1754                         elog(ERROR, "unexpected chunk number %d (expected %d) for toast value %u in %s",
1755                                  residx, nextidx,
1756                                  toast_pointer.va_valueid,
1757                                  RelationGetRelationName(toastrel));
1758                 if (residx < numchunks - 1)
1759                 {
1760                         if (chunksize != TOAST_MAX_CHUNK_SIZE)
1761                                 elog(ERROR, "unexpected chunk size %d (expected %d) in chunk %d of %d for toast value %u in %s",
1762                                          chunksize, (int) TOAST_MAX_CHUNK_SIZE,
1763                                          residx, numchunks,
1764                                          toast_pointer.va_valueid,
1765                                          RelationGetRelationName(toastrel));
1766                 }
1767                 else if (residx == numchunks - 1)
1768                 {
1769                         if ((residx * TOAST_MAX_CHUNK_SIZE + chunksize) != ressize)
1770                                 elog(ERROR, "unexpected chunk size %d (expected %d) in final chunk %d for toast value %u in %s",
1771                                          chunksize,
1772                                          (int) (ressize - residx * TOAST_MAX_CHUNK_SIZE),
1773                                          residx,
1774                                          toast_pointer.va_valueid,
1775                                          RelationGetRelationName(toastrel));
1776                 }
1777                 else
1778                         elog(ERROR, "unexpected chunk number %d (out of range %d..%d) for toast value %u in %s",
1779                                  residx,
1780                                  0, numchunks - 1,
1781                                  toast_pointer.va_valueid,
1782                                  RelationGetRelationName(toastrel));
1783
1784                 /*
1785                  * Copy the data into proper place in our result
1786                  */
1787                 memcpy(VARDATA(result) + residx * TOAST_MAX_CHUNK_SIZE,
1788                            chunkdata,
1789                            chunksize);
1790
1791                 nextidx++;
1792         }
1793
1794         /*
1795          * Final checks that we successfully fetched the datum
1796          */
1797         if (nextidx != numchunks)
1798                 elog(ERROR, "missing chunk number %d for toast value %u in %s",
1799                          nextidx,
1800                          toast_pointer.va_valueid,
1801                          RelationGetRelationName(toastrel));
1802
1803         /*
1804          * End scan and close relations
1805          */
1806         systable_endscan_ordered(toastscan);
1807         index_close(toastidx, AccessShareLock);
1808         heap_close(toastrel, AccessShareLock);
1809
1810         return result;
1811 }
1812
1813 /* ----------
1814  * toast_fetch_datum_slice -
1815  *
1816  *      Reconstruct a segment of a Datum from the chunks saved
1817  *      in the toast relation
1818  * ----------
1819  */
1820 static struct varlena *
1821 toast_fetch_datum_slice(struct varlena * attr, int32 sliceoffset, int32 length)
1822 {
1823         Relation        toastrel;
1824         Relation        toastidx;
1825         ScanKeyData toastkey[3];
1826         int                     nscankeys;
1827         SysScanDesc toastscan;
1828         HeapTuple       ttup;
1829         TupleDesc       toasttupDesc;
1830         struct varlena *result;
1831         struct varatt_external toast_pointer;
1832         int32           attrsize;
1833         int32           residx;
1834         int32           nextidx;
1835         int                     numchunks;
1836         int                     startchunk;
1837         int                     endchunk;
1838         int32           startoffset;
1839         int32           endoffset;
1840         int                     totalchunks;
1841         Pointer         chunk;
1842         bool            isnull;
1843         char       *chunkdata;
1844         int32           chunksize;
1845         int32           chcpystrt;
1846         int32           chcpyend;
1847
1848         Assert(VARATT_IS_EXTERNAL_ONDISK(attr));
1849
1850         /* Must copy to access aligned fields */
1851         VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
1852
1853         /*
1854          * It's nonsense to fetch slices of a compressed datum -- this isn't lo_*
1855          * we can't return a compressed datum which is meaningful to toast later
1856          */
1857         Assert(!VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer));
1858
1859         attrsize = toast_pointer.va_extsize;
1860         totalchunks = ((attrsize - 1) / TOAST_MAX_CHUNK_SIZE) + 1;
1861
1862         if (sliceoffset >= attrsize)
1863         {
1864                 sliceoffset = 0;
1865                 length = 0;
1866         }
1867
1868         if (((sliceoffset + length) > attrsize) || length < 0)
1869                 length = attrsize - sliceoffset;
1870
1871         result = (struct varlena *) palloc(length + VARHDRSZ);
1872
1873         if (VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
1874                 SET_VARSIZE_COMPRESSED(result, length + VARHDRSZ);
1875         else
1876                 SET_VARSIZE(result, length + VARHDRSZ);
1877
1878         if (length == 0)
1879                 return result;                  /* Can save a lot of work at this point! */
1880
1881         startchunk = sliceoffset / TOAST_MAX_CHUNK_SIZE;
1882         endchunk = (sliceoffset + length - 1) / TOAST_MAX_CHUNK_SIZE;
1883         numchunks = (endchunk - startchunk) + 1;
1884
1885         startoffset = sliceoffset % TOAST_MAX_CHUNK_SIZE;
1886         endoffset = (sliceoffset + length - 1) % TOAST_MAX_CHUNK_SIZE;
1887
1888         /*
1889          * Open the toast relation and its index
1890          */
1891         toastrel = heap_open(toast_pointer.va_toastrelid, AccessShareLock);
1892         toasttupDesc = toastrel->rd_att;
1893         toastidx = index_open(toastrel->rd_rel->reltoastidxid, AccessShareLock);
1894
1895         /*
1896          * Setup a scan key to fetch from the index. This is either two keys or
1897          * three depending on the number of chunks.
1898          */
1899         ScanKeyInit(&toastkey[0],
1900                                 (AttrNumber) 1,
1901                                 BTEqualStrategyNumber, F_OIDEQ,
1902                                 ObjectIdGetDatum(toast_pointer.va_valueid));
1903
1904         /*
1905          * Use equality condition for one chunk, a range condition otherwise:
1906          */
1907         if (numchunks == 1)
1908         {
1909                 ScanKeyInit(&toastkey[1],
1910                                         (AttrNumber) 2,
1911                                         BTEqualStrategyNumber, F_INT4EQ,
1912                                         Int32GetDatum(startchunk));
1913                 nscankeys = 2;
1914         }
1915         else
1916         {
1917                 ScanKeyInit(&toastkey[1],
1918                                         (AttrNumber) 2,
1919                                         BTGreaterEqualStrategyNumber, F_INT4GE,
1920                                         Int32GetDatum(startchunk));
1921                 ScanKeyInit(&toastkey[2],
1922                                         (AttrNumber) 2,
1923                                         BTLessEqualStrategyNumber, F_INT4LE,
1924                                         Int32GetDatum(endchunk));
1925                 nscankeys = 3;
1926         }
1927
1928         /*
1929          * Read the chunks by index
1930          *
1931          * The index is on (valueid, chunkidx) so they will come in order
1932          */
1933         nextidx = startchunk;
1934         toastscan = systable_beginscan_ordered(toastrel, toastidx,
1935                                                                                  SnapshotToast, nscankeys, toastkey);
1936         while ((ttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
1937         {
1938                 /*
1939                  * Have a chunk, extract the sequence number and the data
1940                  */
1941                 residx = DatumGetInt32(fastgetattr(ttup, 2, toasttupDesc, &isnull));
1942                 Assert(!isnull);
1943                 chunk = DatumGetPointer(fastgetattr(ttup, 3, toasttupDesc, &isnull));
1944                 Assert(!isnull);
1945                 if (!VARATT_IS_EXTENDED(chunk))
1946                 {
1947                         chunksize = VARSIZE(chunk) - VARHDRSZ;
1948                         chunkdata = VARDATA(chunk);
1949                 }
1950                 else if (VARATT_IS_SHORT(chunk))
1951                 {
1952                         /* could happen due to heap_form_tuple doing its thing */
1953                         chunksize = VARSIZE_SHORT(chunk) - VARHDRSZ_SHORT;
1954                         chunkdata = VARDATA_SHORT(chunk);
1955                 }
1956                 else
1957                 {
1958                         /* should never happen */
1959                         elog(ERROR, "found toasted toast chunk for toast value %u in %s",
1960                                  toast_pointer.va_valueid,
1961                                  RelationGetRelationName(toastrel));
1962                         chunksize = 0;          /* keep compiler quiet */
1963                         chunkdata = NULL;
1964                 }
1965
1966                 /*
1967                  * Some checks on the data we've found
1968                  */
1969                 if ((residx != nextidx) || (residx > endchunk) || (residx < startchunk))
1970                         elog(ERROR, "unexpected chunk number %d (expected %d) for toast value %u in %s",
1971                                  residx, nextidx,
1972                                  toast_pointer.va_valueid,
1973                                  RelationGetRelationName(toastrel));
1974                 if (residx < totalchunks - 1)
1975                 {
1976                         if (chunksize != TOAST_MAX_CHUNK_SIZE)
1977                                 elog(ERROR, "unexpected chunk size %d (expected %d) in chunk %d of %d for toast value %u in %s when fetching slice",
1978                                          chunksize, (int) TOAST_MAX_CHUNK_SIZE,
1979                                          residx, totalchunks,
1980                                          toast_pointer.va_valueid,
1981                                          RelationGetRelationName(toastrel));
1982                 }
1983                 else if (residx == totalchunks - 1)
1984                 {
1985                         if ((residx * TOAST_MAX_CHUNK_SIZE + chunksize) != attrsize)
1986                                 elog(ERROR, "unexpected chunk size %d (expected %d) in final chunk %d for toast value %u in %s when fetching slice",
1987                                          chunksize,
1988                                          (int) (attrsize - residx * TOAST_MAX_CHUNK_SIZE),
1989                                          residx,
1990                                          toast_pointer.va_valueid,
1991                                          RelationGetRelationName(toastrel));
1992                 }
1993                 else
1994                         elog(ERROR, "unexpected chunk number %d (out of range %d..%d) for toast value %u in %s",
1995                                  residx,
1996                                  0, totalchunks - 1,
1997                                  toast_pointer.va_valueid,
1998                                  RelationGetRelationName(toastrel));
1999
2000                 /*
2001                  * Copy the data into proper place in our result
2002                  */
2003                 chcpystrt = 0;
2004                 chcpyend = chunksize - 1;
2005                 if (residx == startchunk)
2006                         chcpystrt = startoffset;
2007                 if (residx == endchunk)
2008                         chcpyend = endoffset;
2009
2010                 memcpy(VARDATA(result) +
2011                            (residx * TOAST_MAX_CHUNK_SIZE - sliceoffset) + chcpystrt,
2012                            chunkdata + chcpystrt,
2013                            (chcpyend - chcpystrt) + 1);
2014
2015                 nextidx++;
2016         }
2017
2018         /*
2019          * Final checks that we successfully fetched the datum
2020          */
2021         if (nextidx != (endchunk + 1))
2022                 elog(ERROR, "missing chunk number %d for toast value %u in %s",
2023                          nextidx,
2024                          toast_pointer.va_valueid,
2025                          RelationGetRelationName(toastrel));
2026
2027         /*
2028          * End scan and close relations
2029          */
2030         systable_endscan_ordered(toastscan);
2031         index_close(toastidx, AccessShareLock);
2032         heap_close(toastrel, AccessShareLock);
2033
2034         return result;
2035 }