1 /*-------------------------------------------------------------------------
4 * POSTGRES heap tuple header definitions.
7 * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
8 * Portions Copyright (c) 1994, Regents of the University of California
10 * src/include/access/htup_details.h
12 *-------------------------------------------------------------------------
14 #ifndef HTUP_DETAILS_H
15 #define HTUP_DETAILS_H
17 #include "access/htup.h"
18 #include "access/tupdesc.h"
19 #include "access/tupmacs.h"
20 #include "access/transam.h"
21 #include "storage/bufpage.h"
24 * MaxTupleAttributeNumber limits the number of (user) columns in a tuple.
25 * The key limit on this value is that the size of the fixed overhead for
26 * a tuple, plus the size of the null-values bitmap (at 1 bit per column),
27 * plus MAXALIGN alignment, must fit into t_hoff which is uint8. On most
28 * machines the upper limit without making t_hoff wider would be a little
29 * over 1700. We use round numbers here and for MaxHeapAttributeNumber
30 * so that alterations in HeapTupleHeaderData layout won't change the
31 * supported max number of columns.
33 #define MaxTupleAttributeNumber 1664 /* 8 * 208 */
36 * MaxHeapAttributeNumber limits the number of (user) columns in a table.
37 * This should be somewhat less than MaxTupleAttributeNumber. It must be
38 * at least one less, else we will fail to do UPDATEs on a maximal-width
39 * table (because UPDATE has to form working tuples that include CTID).
40 * In practice we want some additional daylight so that we can gracefully
41 * support operations that add hidden "resjunk" columns, for example
42 * SELECT * FROM wide_table ORDER BY foo, bar, baz.
43 * In any case, depending on column data types you will likely be running
44 * into the disk-block-based limit on overall tuple size if you have more
45 * than a thousand or so columns. TOAST won't help.
47 #define MaxHeapAttributeNumber 1600 /* 8 * 200 */
50 * Heap tuple header. To avoid wasting space, the fields should be
51 * laid out in such a way as to avoid structure padding.
53 * Datums of composite types (row types) share the same general structure
54 * as on-disk tuples, so that the same routines can be used to build and
55 * examine them. However the requirements are slightly different: a Datum
56 * does not need any transaction visibility information, and it does need
57 * a length word and some embedded type information. We can achieve this
58 * by overlaying the xmin/cmin/xmax/cmax/xvac fields of a heap tuple
59 * with the fields needed in the Datum case. Typically, all tuples built
60 * in-memory will be initialized with the Datum fields; but when a tuple is
61 * about to be inserted in a table, the transaction fields will be filled,
62 * overwriting the datum fields.
64 * The overall structure of a heap tuple looks like:
65 * fixed fields (HeapTupleHeaderData struct)
66 * nulls bitmap (if HEAP_HASNULL is set in t_infomask)
67 * alignment padding (as needed to make user data MAXALIGN'd)
68 * object ID (if HEAP_HASOID is set in t_infomask)
71 * We store five "virtual" fields Xmin, Cmin, Xmax, Cmax, and Xvac in three
72 * physical fields. Xmin and Xmax are always really stored, but Cmin, Cmax
73 * and Xvac share a field. This works because we know that Cmin and Cmax
74 * are only interesting for the lifetime of the inserting and deleting
75 * transaction respectively. If a tuple is inserted and deleted in the same
76 * transaction, we store a "combo" command id that can be mapped to the real
77 * cmin and cmax, but only by use of local state within the originating
78 * backend. See combocid.c for more details. Meanwhile, Xvac is only set by
79 * old-style VACUUM FULL, which does not have any command sub-structure and so
80 * does not need either Cmin or Cmax. (This requires that old-style VACUUM
81 * FULL never try to move a tuple whose Cmin or Cmax is still interesting,
82 * ie, an insert-in-progress or delete-in-progress tuple.)
84 * A word about t_ctid: whenever a new tuple is stored on disk, its t_ctid
85 * is initialized with its own TID (location). If the tuple is ever updated,
86 * its t_ctid is changed to point to the replacement version of the tuple.
87 * Thus, a tuple is the latest version of its row iff XMAX is invalid or
88 * t_ctid points to itself (in which case, if XMAX is valid, the tuple is
89 * either locked or deleted). One can follow the chain of t_ctid links
90 * to find the newest version of the row. Beware however that VACUUM might
91 * erase the pointed-to (newer) tuple before erasing the pointing (older)
92 * tuple. Hence, when following a t_ctid link, it is necessary to check
93 * to see if the referenced slot is empty or contains an unrelated tuple.
94 * Check that the referenced tuple has XMIN equal to the referencing tuple's
95 * XMAX to verify that it is actually the descendant version and not an
96 * unrelated tuple stored into a slot recently freed by VACUUM. If either
97 * check fails, one may assume that there is no live descendant version.
99 * t_ctid is sometimes used to store a speculative insertion token, instead
100 * of a real TID. A speculative token is set on a tuple that's being
101 * inserted, until the inserter is sure that it wants to go ahead with the
102 * insertion. Hence a token should only be seen on a tuple with an XMAX
103 * that's still in-progress, or invalid/aborted. The token is replaced with
104 * the tuple's real TID when the insertion is confirmed. One should never
105 * see a speculative insertion token while following a chain of t_ctid links,
106 * because they are not used on updates, only insertions.
108 * Following the fixed header fields, the nulls bitmap is stored (beginning
109 * at t_bits). The bitmap is *not* stored if t_infomask shows that there
110 * are no nulls in the tuple. If an OID field is present (as indicated by
111 * t_infomask), then it is stored just before the user data, which begins at
112 * the offset shown by t_hoff. Note that t_hoff must be a multiple of
116 typedef struct HeapTupleFields
118 TransactionId t_xmin; /* inserting xact ID */
119 TransactionId t_xmax; /* deleting or locking xact ID */
123 CommandId t_cid; /* inserting or deleting command ID, or both */
124 TransactionId t_xvac; /* old-style VACUUM FULL xact ID */
128 typedef struct DatumTupleFields
130 int32 datum_len_; /* varlena header (do not touch directly!) */
132 int32 datum_typmod; /* -1, or identifier of a record type */
134 Oid datum_typeid; /* composite type OID, or RECORDOID */
137 * Note: field ordering is chosen with thought that Oid might someday
142 struct HeapTupleHeaderData
146 HeapTupleFields t_heap;
147 DatumTupleFields t_datum;
150 ItemPointerData t_ctid; /* current TID of this or newer tuple (or a
151 * speculative insertion token) */
153 /* Fields below here must match MinimalTupleData! */
155 uint16 t_infomask2; /* number of attributes + various flags */
157 uint16 t_infomask; /* various flag bits, see below */
159 uint8 t_hoff; /* sizeof header incl. bitmap, padding */
161 /* ^ - 23 bytes - ^ */
163 bits8 t_bits[FLEXIBLE_ARRAY_MEMBER]; /* bitmap of NULLs */
165 /* MORE DATA FOLLOWS AT END OF STRUCT */
168 /* typedef appears in tupbasics.h */
170 #define SizeofHeapTupleHeader offsetof(HeapTupleHeaderData, t_bits)
173 * information stored in t_infomask:
175 #define HEAP_HASNULL 0x0001 /* has null attribute(s) */
176 #define HEAP_HASVARWIDTH 0x0002 /* has variable-width attribute(s) */
177 #define HEAP_HASEXTERNAL 0x0004 /* has external stored attribute(s) */
178 #define HEAP_HASOID 0x0008 /* has an object-id field */
179 #define HEAP_XMAX_KEYSHR_LOCK 0x0010 /* xmax is a key-shared locker */
180 #define HEAP_COMBOCID 0x0020 /* t_cid is a combo cid */
181 #define HEAP_XMAX_EXCL_LOCK 0x0040 /* xmax is exclusive locker */
182 #define HEAP_XMAX_LOCK_ONLY 0x0080 /* xmax, if valid, is only a locker */
184 /* xmax is a shared locker */
185 #define HEAP_XMAX_SHR_LOCK (HEAP_XMAX_EXCL_LOCK | HEAP_XMAX_KEYSHR_LOCK)
187 #define HEAP_LOCK_MASK (HEAP_XMAX_SHR_LOCK | HEAP_XMAX_EXCL_LOCK | \
188 HEAP_XMAX_KEYSHR_LOCK)
189 #define HEAP_XMIN_COMMITTED 0x0100 /* t_xmin committed */
190 #define HEAP_XMIN_INVALID 0x0200 /* t_xmin invalid/aborted */
191 #define HEAP_XMIN_FROZEN (HEAP_XMIN_COMMITTED|HEAP_XMIN_INVALID)
192 #define HEAP_XMAX_COMMITTED 0x0400 /* t_xmax committed */
193 #define HEAP_XMAX_INVALID 0x0800 /* t_xmax invalid/aborted */
194 #define HEAP_XMAX_IS_MULTI 0x1000 /* t_xmax is a MultiXactId */
195 #define HEAP_UPDATED 0x2000 /* this is UPDATEd version of row */
196 #define HEAP_MOVED_OFF 0x4000 /* moved to another place by pre-9.0
197 * VACUUM FULL; kept for binary
199 #define HEAP_MOVED_IN 0x8000 /* moved from another place by pre-9.0
200 * VACUUM FULL; kept for binary
202 #define HEAP_MOVED (HEAP_MOVED_OFF | HEAP_MOVED_IN)
204 #define HEAP_XACT_MASK 0xFFF0 /* visibility-related bits */
207 * A tuple is only locked (i.e. not updated by its Xmax) if the
208 * HEAP_XMAX_LOCK_ONLY bit is set; or, for pg_upgrade's sake, if the Xmax is
209 * not a multi and the EXCL_LOCK bit is set.
211 * See also HeapTupleHeaderIsOnlyLocked, which also checks for a possible
212 * aborted updater transaction.
214 * Beware of multiple evaluations of the argument.
216 #define HEAP_XMAX_IS_LOCKED_ONLY(infomask) \
217 (((infomask) & HEAP_XMAX_LOCK_ONLY) || \
218 (((infomask) & (HEAP_XMAX_IS_MULTI | HEAP_LOCK_MASK)) == HEAP_XMAX_EXCL_LOCK))
221 * A tuple that has HEAP_XMAX_IS_MULTI and HEAP_XMAX_LOCK_ONLY but neither of
222 * XMAX_EXCL_LOCK and XMAX_KEYSHR_LOCK must come from a tuple that was
223 * share-locked in 9.2 or earlier and then pg_upgrade'd.
225 * In 9.2 and prior, HEAP_XMAX_IS_MULTI was only set when there were multiple
226 * FOR SHARE lockers of that tuple. That set HEAP_XMAX_LOCK_ONLY (with a
227 * different name back then) but neither of HEAP_XMAX_EXCL_LOCK and
228 * HEAP_XMAX_KEYSHR_LOCK. That combination is no longer possible in 9.3 and
229 * up, so if we see that combination we know for certain that the tuple was
230 * locked in an earlier release; since all such lockers are gone (they cannot
231 * survive through pg_upgrade), such tuples can safely be considered not
234 * We must not resolve such multixacts locally, because the result would be
235 * bogus, regardless of where they stand with respect to the current valid
238 #define HEAP_LOCKED_UPGRADED(infomask) \
240 ((infomask) & HEAP_XMAX_IS_MULTI) && \
241 ((infomask) & HEAP_XMAX_LOCK_ONLY) && \
242 (((infomask) & (HEAP_XMAX_EXCL_LOCK | HEAP_XMAX_KEYSHR_LOCK)) == 0) \
246 * Use these to test whether a particular lock is applied to a tuple
248 #define HEAP_XMAX_IS_SHR_LOCKED(infomask) \
249 (((infomask) & HEAP_LOCK_MASK) == HEAP_XMAX_SHR_LOCK)
250 #define HEAP_XMAX_IS_EXCL_LOCKED(infomask) \
251 (((infomask) & HEAP_LOCK_MASK) == HEAP_XMAX_EXCL_LOCK)
252 #define HEAP_XMAX_IS_KEYSHR_LOCKED(infomask) \
253 (((infomask) & HEAP_LOCK_MASK) == HEAP_XMAX_KEYSHR_LOCK)
255 /* turn these all off when Xmax is to change */
256 #define HEAP_XMAX_BITS (HEAP_XMAX_COMMITTED | HEAP_XMAX_INVALID | \
257 HEAP_XMAX_IS_MULTI | HEAP_LOCK_MASK | HEAP_XMAX_LOCK_ONLY)
260 * information stored in t_infomask2:
262 #define HEAP_NATTS_MASK 0x07FF /* 11 bits for number of attributes */
263 /* bits 0x1800 are available */
264 #define HEAP_KEYS_UPDATED 0x2000 /* tuple was updated and key cols
265 * modified, or tuple deleted */
266 #define HEAP_HOT_UPDATED 0x4000 /* tuple was HOT-updated */
267 #define HEAP_ONLY_TUPLE 0x8000 /* this is heap-only tuple */
269 #define HEAP2_XACT_MASK 0xE000 /* visibility-related bits */
272 * HEAP_TUPLE_HAS_MATCH is a temporary flag used during hash joins. It is
273 * only used in tuples that are in the hash table, and those don't need
274 * any visibility information, so we can overlay it on a visibility flag
275 * instead of using up a dedicated bit.
277 #define HEAP_TUPLE_HAS_MATCH HEAP_ONLY_TUPLE /* tuple has a join match */
280 * Special value used in t_ctid.ip_posid, to indicate that it holds a
281 * speculative insertion token rather than a real TID. This must be higher
282 * than MaxOffsetNumber, so that it can be distinguished from a valid
283 * offset number in a regular item pointer.
285 #define SpecTokenOffsetNumber 0xfffe
288 * HeapTupleHeader accessor macros
290 * Note: beware of multiple evaluations of "tup" argument. But the Set
291 * macros evaluate their other argument only once.
295 * HeapTupleHeaderGetRawXmin returns the "raw" xmin field, which is the xid
296 * originally used to insert the tuple. However, the tuple might actually
297 * be frozen (via HeapTupleHeaderSetXminFrozen) in which case the tuple's xmin
298 * is visible to every snapshot. Prior to PostgreSQL 9.4, we actually changed
299 * the xmin to FrozenTransactionId, and that value may still be encountered
302 #define HeapTupleHeaderGetRawXmin(tup) \
304 (tup)->t_choice.t_heap.t_xmin \
307 #define HeapTupleHeaderGetXmin(tup) \
309 HeapTupleHeaderXminFrozen(tup) ? \
310 FrozenTransactionId : HeapTupleHeaderGetRawXmin(tup) \
313 #define HeapTupleHeaderSetXmin(tup, xid) \
315 (tup)->t_choice.t_heap.t_xmin = (xid) \
318 #define HeapTupleHeaderXminCommitted(tup) \
320 (tup)->t_infomask & HEAP_XMIN_COMMITTED \
323 #define HeapTupleHeaderXminInvalid(tup) \
325 ((tup)->t_infomask & (HEAP_XMIN_COMMITTED|HEAP_XMIN_INVALID)) == \
329 #define HeapTupleHeaderXminFrozen(tup) \
331 ((tup)->t_infomask & (HEAP_XMIN_FROZEN)) == HEAP_XMIN_FROZEN \
334 #define HeapTupleHeaderSetXminCommitted(tup) \
336 AssertMacro(!HeapTupleHeaderXminInvalid(tup)), \
337 ((tup)->t_infomask |= HEAP_XMIN_COMMITTED) \
340 #define HeapTupleHeaderSetXminInvalid(tup) \
342 AssertMacro(!HeapTupleHeaderXminCommitted(tup)), \
343 ((tup)->t_infomask |= HEAP_XMIN_INVALID) \
346 #define HeapTupleHeaderSetXminFrozen(tup) \
348 AssertMacro(!HeapTupleHeaderXminInvalid(tup)), \
349 ((tup)->t_infomask |= HEAP_XMIN_FROZEN) \
353 * HeapTupleHeaderGetRawXmax gets you the raw Xmax field. To find out the Xid
354 * that updated a tuple, you might need to resolve the MultiXactId if certain
355 * bits are set. HeapTupleHeaderGetUpdateXid checks those bits and takes care
356 * to resolve the MultiXactId if necessary. This might involve multixact I/O,
357 * so it should only be used if absolutely necessary.
359 #define HeapTupleHeaderGetUpdateXid(tup) \
361 (!((tup)->t_infomask & HEAP_XMAX_INVALID) && \
362 ((tup)->t_infomask & HEAP_XMAX_IS_MULTI) && \
363 !((tup)->t_infomask & HEAP_XMAX_LOCK_ONLY)) ? \
364 HeapTupleGetUpdateXid(tup) \
366 HeapTupleHeaderGetRawXmax(tup) \
369 #define HeapTupleHeaderGetRawXmax(tup) \
371 (tup)->t_choice.t_heap.t_xmax \
374 #define HeapTupleHeaderSetXmax(tup, xid) \
376 (tup)->t_choice.t_heap.t_xmax = (xid) \
380 * HeapTupleHeaderGetRawCommandId will give you what's in the header whether
381 * it is useful or not. Most code should use HeapTupleHeaderGetCmin or
382 * HeapTupleHeaderGetCmax instead, but note that those Assert that you can
383 * get a legitimate result, ie you are in the originating transaction!
385 #define HeapTupleHeaderGetRawCommandId(tup) \
387 (tup)->t_choice.t_heap.t_field3.t_cid \
390 /* SetCmin is reasonably simple since we never need a combo CID */
391 #define HeapTupleHeaderSetCmin(tup, cid) \
393 Assert(!((tup)->t_infomask & HEAP_MOVED)); \
394 (tup)->t_choice.t_heap.t_field3.t_cid = (cid); \
395 (tup)->t_infomask &= ~HEAP_COMBOCID; \
398 /* SetCmax must be used after HeapTupleHeaderAdjustCmax; see combocid.c */
399 #define HeapTupleHeaderSetCmax(tup, cid, iscombo) \
401 Assert(!((tup)->t_infomask & HEAP_MOVED)); \
402 (tup)->t_choice.t_heap.t_field3.t_cid = (cid); \
404 (tup)->t_infomask |= HEAP_COMBOCID; \
406 (tup)->t_infomask &= ~HEAP_COMBOCID; \
409 #define HeapTupleHeaderGetXvac(tup) \
411 ((tup)->t_infomask & HEAP_MOVED) ? \
412 (tup)->t_choice.t_heap.t_field3.t_xvac \
414 InvalidTransactionId \
417 #define HeapTupleHeaderSetXvac(tup, xid) \
419 Assert((tup)->t_infomask & HEAP_MOVED); \
420 (tup)->t_choice.t_heap.t_field3.t_xvac = (xid); \
423 #define HeapTupleHeaderIsSpeculative(tup) \
425 (tup)->t_ctid.ip_posid == SpecTokenOffsetNumber \
428 #define HeapTupleHeaderGetSpeculativeToken(tup) \
430 AssertMacro(HeapTupleHeaderIsSpeculative(tup)), \
431 ItemPointerGetBlockNumber(&(tup)->t_ctid) \
434 #define HeapTupleHeaderSetSpeculativeToken(tup, token) \
436 ItemPointerSet(&(tup)->t_ctid, token, SpecTokenOffsetNumber) \
439 #define HeapTupleHeaderGetDatumLength(tup) \
442 #define HeapTupleHeaderSetDatumLength(tup, len) \
443 SET_VARSIZE(tup, len)
445 #define HeapTupleHeaderGetTypeId(tup) \
447 (tup)->t_choice.t_datum.datum_typeid \
450 #define HeapTupleHeaderSetTypeId(tup, typeid) \
452 (tup)->t_choice.t_datum.datum_typeid = (typeid) \
455 #define HeapTupleHeaderGetTypMod(tup) \
457 (tup)->t_choice.t_datum.datum_typmod \
460 #define HeapTupleHeaderSetTypMod(tup, typmod) \
462 (tup)->t_choice.t_datum.datum_typmod = (typmod) \
465 #define HeapTupleHeaderGetOid(tup) \
467 ((tup)->t_infomask & HEAP_HASOID) ? \
468 *((Oid *) ((char *)(tup) + (tup)->t_hoff - sizeof(Oid))) \
473 #define HeapTupleHeaderSetOid(tup, oid) \
475 Assert((tup)->t_infomask & HEAP_HASOID); \
476 *((Oid *) ((char *)(tup) + (tup)->t_hoff - sizeof(Oid))) = (oid); \
480 * Note that we stop considering a tuple HOT-updated as soon as it is known
481 * aborted or the would-be updating transaction is known aborted. For best
482 * efficiency, check tuple visibility before using this macro, so that the
483 * INVALID bits will be as up to date as possible.
485 #define HeapTupleHeaderIsHotUpdated(tup) \
487 ((tup)->t_infomask2 & HEAP_HOT_UPDATED) != 0 && \
488 ((tup)->t_infomask & HEAP_XMAX_INVALID) == 0 && \
489 !HeapTupleHeaderXminInvalid(tup) \
492 #define HeapTupleHeaderSetHotUpdated(tup) \
494 (tup)->t_infomask2 |= HEAP_HOT_UPDATED \
497 #define HeapTupleHeaderClearHotUpdated(tup) \
499 (tup)->t_infomask2 &= ~HEAP_HOT_UPDATED \
502 #define HeapTupleHeaderIsHeapOnly(tup) \
504 (tup)->t_infomask2 & HEAP_ONLY_TUPLE \
507 #define HeapTupleHeaderSetHeapOnly(tup) \
509 (tup)->t_infomask2 |= HEAP_ONLY_TUPLE \
512 #define HeapTupleHeaderClearHeapOnly(tup) \
514 (tup)->t_infomask2 &= ~HEAP_ONLY_TUPLE \
517 #define HeapTupleHeaderHasMatch(tup) \
519 (tup)->t_infomask2 & HEAP_TUPLE_HAS_MATCH \
522 #define HeapTupleHeaderSetMatch(tup) \
524 (tup)->t_infomask2 |= HEAP_TUPLE_HAS_MATCH \
527 #define HeapTupleHeaderClearMatch(tup) \
529 (tup)->t_infomask2 &= ~HEAP_TUPLE_HAS_MATCH \
532 #define HeapTupleHeaderGetNatts(tup) \
533 ((tup)->t_infomask2 & HEAP_NATTS_MASK)
535 #define HeapTupleHeaderSetNatts(tup, natts) \
537 (tup)->t_infomask2 = ((tup)->t_infomask2 & ~HEAP_NATTS_MASK) | (natts) \
540 #define HeapTupleHeaderHasExternal(tup) \
541 (((tup)->t_infomask & HEAP_HASEXTERNAL) != 0)
546 * Computes size of null bitmap given number of data columns.
548 #define BITMAPLEN(NATTS) (((int)(NATTS) + 7) / 8)
551 * MaxHeapTupleSize is the maximum allowed size of a heap tuple, including
552 * header and MAXALIGN alignment padding. Basically it's BLCKSZ minus the
553 * other stuff that has to be on a disk page. Since heap pages use no
554 * "special space", there's no deduction for that.
556 * NOTE: we allow for the ItemId that must point to the tuple, ensuring that
557 * an otherwise-empty page can indeed hold a tuple of this size. Because
558 * ItemIds and tuples have different alignment requirements, don't assume that
559 * you can, say, fit 2 tuples of size MaxHeapTupleSize/2 on the same page.
561 #define MaxHeapTupleSize (BLCKSZ - MAXALIGN(SizeOfPageHeaderData + sizeof(ItemIdData)))
562 #define MinHeapTupleSize MAXALIGN(SizeofHeapTupleHeader)
565 * MaxHeapTuplesPerPage is an upper bound on the number of tuples that can
566 * fit on one heap page. (Note that indexes could have more, because they
567 * use a smaller tuple header.) We arrive at the divisor because each tuple
568 * must be maxaligned, and it must have an associated item pointer.
570 * Note: with HOT, there could theoretically be more line pointers (not actual
571 * tuples) than this on a heap page. However we constrain the number of line
572 * pointers to this anyway, to avoid excessive line-pointer bloat and not
573 * require increases in the size of work arrays.
575 #define MaxHeapTuplesPerPage \
576 ((int) ((BLCKSZ - SizeOfPageHeaderData) / \
577 (MAXALIGN(SizeofHeapTupleHeader) + sizeof(ItemIdData))))
580 * MaxAttrSize is a somewhat arbitrary upper limit on the declared size of
581 * data fields of char(n) and similar types. It need not have anything
582 * directly to do with the *actual* upper limit of varlena values, which
583 * is currently 1Gb (see TOAST structures in postgres.h). I've set it
584 * at 10Mb which seems like a reasonable number --- tgl 8/6/00.
586 #define MaxAttrSize (10 * 1024 * 1024)
590 * MinimalTuple is an alternative representation that is used for transient
591 * tuples inside the executor, in places where transaction status information
592 * is not required, the tuple rowtype is known, and shaving off a few bytes
593 * is worthwhile because we need to store many tuples. The representation
594 * is chosen so that tuple access routines can work with either full or
595 * minimal tuples via a HeapTupleData pointer structure. The access routines
596 * see no difference, except that they must not access the transaction status
597 * or t_ctid fields because those aren't there.
599 * For the most part, MinimalTuples should be accessed via TupleTableSlot
600 * routines. These routines will prevent access to the "system columns"
601 * and thereby prevent accidental use of the nonexistent fields.
603 * MinimalTupleData contains a length word, some padding, and fields matching
604 * HeapTupleHeaderData beginning with t_infomask2. The padding is chosen so
605 * that offsetof(t_infomask2) is the same modulo MAXIMUM_ALIGNOF in both
606 * structs. This makes data alignment rules equivalent in both cases.
608 * When a minimal tuple is accessed via a HeapTupleData pointer, t_data is
609 * set to point MINIMAL_TUPLE_OFFSET bytes before the actual start of the
610 * minimal tuple --- that is, where a full tuple matching the minimal tuple's
611 * data would start. This trick is what makes the structs seem equivalent.
613 * Note that t_hoff is computed the same as in a full tuple, hence it includes
614 * the MINIMAL_TUPLE_OFFSET distance. t_len does not include that, however.
616 * MINIMAL_TUPLE_DATA_OFFSET is the offset to the first useful (non-pad) data
617 * other than the length word. tuplesort.c and tuplestore.c use this to avoid
618 * writing the padding to disk.
620 #define MINIMAL_TUPLE_OFFSET \
621 ((offsetof(HeapTupleHeaderData, t_infomask2) - sizeof(uint32)) / MAXIMUM_ALIGNOF * MAXIMUM_ALIGNOF)
622 #define MINIMAL_TUPLE_PADDING \
623 ((offsetof(HeapTupleHeaderData, t_infomask2) - sizeof(uint32)) % MAXIMUM_ALIGNOF)
624 #define MINIMAL_TUPLE_DATA_OFFSET \
625 offsetof(MinimalTupleData, t_infomask2)
627 struct MinimalTupleData
629 uint32 t_len; /* actual length of minimal tuple */
631 char mt_padding[MINIMAL_TUPLE_PADDING];
633 /* Fields below here must match HeapTupleHeaderData! */
635 uint16 t_infomask2; /* number of attributes + various flags */
637 uint16 t_infomask; /* various flag bits, see below */
639 uint8 t_hoff; /* sizeof header incl. bitmap, padding */
641 /* ^ - 23 bytes - ^ */
643 bits8 t_bits[FLEXIBLE_ARRAY_MEMBER]; /* bitmap of NULLs */
645 /* MORE DATA FOLLOWS AT END OF STRUCT */
648 /* typedef appears in htup.h */
650 #define SizeofMinimalTupleHeader offsetof(MinimalTupleData, t_bits)
654 * GETSTRUCT - given a HeapTuple pointer, return address of the user data
656 #define GETSTRUCT(TUP) ((char *) ((TUP)->t_data) + (TUP)->t_data->t_hoff)
659 * Accessor macros to be used with HeapTuple pointers.
662 #define HeapTupleHasNulls(tuple) \
663 (((tuple)->t_data->t_infomask & HEAP_HASNULL) != 0)
665 #define HeapTupleNoNulls(tuple) \
666 (!((tuple)->t_data->t_infomask & HEAP_HASNULL))
668 #define HeapTupleHasVarWidth(tuple) \
669 (((tuple)->t_data->t_infomask & HEAP_HASVARWIDTH) != 0)
671 #define HeapTupleAllFixed(tuple) \
672 (!((tuple)->t_data->t_infomask & HEAP_HASVARWIDTH))
674 #define HeapTupleHasExternal(tuple) \
675 (((tuple)->t_data->t_infomask & HEAP_HASEXTERNAL) != 0)
677 #define HeapTupleIsHotUpdated(tuple) \
678 HeapTupleHeaderIsHotUpdated((tuple)->t_data)
680 #define HeapTupleSetHotUpdated(tuple) \
681 HeapTupleHeaderSetHotUpdated((tuple)->t_data)
683 #define HeapTupleClearHotUpdated(tuple) \
684 HeapTupleHeaderClearHotUpdated((tuple)->t_data)
686 #define HeapTupleIsHeapOnly(tuple) \
687 HeapTupleHeaderIsHeapOnly((tuple)->t_data)
689 #define HeapTupleSetHeapOnly(tuple) \
690 HeapTupleHeaderSetHeapOnly((tuple)->t_data)
692 #define HeapTupleClearHeapOnly(tuple) \
693 HeapTupleHeaderClearHeapOnly((tuple)->t_data)
695 #define HeapTupleGetOid(tuple) \
696 HeapTupleHeaderGetOid((tuple)->t_data)
698 #define HeapTupleSetOid(tuple, oid) \
699 HeapTupleHeaderSetOid((tuple)->t_data, (oid))
705 * Fetch a user attribute's value as a Datum (might be either a
706 * value, or a pointer into the data area of the tuple).
708 * This must not be used when a system attribute might be requested.
709 * Furthermore, the passed attnum MUST be valid. Use heap_getattr()
710 * instead, if in doubt.
712 * This gets called many times, so we macro the cacheable and NULL
713 * lookups, and call nocachegetattr() for the rest.
717 #if !defined(DISABLE_COMPLEX_MACRO)
719 #define fastgetattr(tup, attnum, tupleDesc, isnull) \
721 AssertMacro((attnum) > 0), \
722 (*(isnull) = false), \
723 HeapTupleNoNulls(tup) ? \
725 (tupleDesc)->attrs[(attnum)-1]->attcacheoff >= 0 ? \
727 fetchatt((tupleDesc)->attrs[(attnum)-1], \
728 (char *) (tup)->t_data + (tup)->t_data->t_hoff + \
729 (tupleDesc)->attrs[(attnum)-1]->attcacheoff) \
732 nocachegetattr((tup), (attnum), (tupleDesc)) \
736 att_isnull((attnum)-1, (tup)->t_data->t_bits) ? \
738 (*(isnull) = true), \
743 nocachegetattr((tup), (attnum), (tupleDesc)) \
747 #else /* defined(DISABLE_COMPLEX_MACRO) */
749 extern Datum fastgetattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
751 #endif /* defined(DISABLE_COMPLEX_MACRO) */
757 * Extract an attribute of a heap tuple and return it as a Datum.
758 * This works for either system or user attributes. The given attnum
759 * is properly range-checked.
761 * If the field in question has a NULL value, we return a zero Datum
762 * and set *isnull == true. Otherwise, we set *isnull == false.
764 * <tup> is the pointer to the heap tuple. <attnum> is the attribute
765 * number of the column (field) caller wants. <tupleDesc> is a
766 * pointer to the structure describing the row and all its fields.
769 #define heap_getattr(tup, attnum, tupleDesc, isnull) \
773 ((attnum) > (int) HeapTupleHeaderGetNatts((tup)->t_data)) ? \
775 (*(isnull) = true), \
779 fastgetattr((tup), (attnum), (tupleDesc), (isnull)) \
782 heap_getsysattr((tup), (attnum), (tupleDesc), (isnull)) \
786 /* prototypes for functions in common/heaptuple.c */
787 extern Size heap_compute_data_size(TupleDesc tupleDesc,
788 Datum *values, bool *isnull);
789 extern void heap_fill_tuple(TupleDesc tupleDesc,
790 Datum *values, bool *isnull,
791 char *data, Size data_size,
792 uint16 *infomask, bits8 *bit);
793 extern bool heap_attisnull(HeapTuple tup, int attnum);
794 extern Datum nocachegetattr(HeapTuple tup, int attnum,
796 extern Datum heap_getsysattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
798 extern HeapTuple heap_copytuple(HeapTuple tuple);
799 extern void heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest);
800 extern Datum heap_copy_tuple_as_datum(HeapTuple tuple, TupleDesc tupleDesc);
801 extern HeapTuple heap_form_tuple(TupleDesc tupleDescriptor,
802 Datum *values, bool *isnull);
803 extern HeapTuple heap_modify_tuple(HeapTuple tuple,
808 extern void heap_deform_tuple(HeapTuple tuple, TupleDesc tupleDesc,
809 Datum *values, bool *isnull);
810 extern void heap_freetuple(HeapTuple htup);
811 extern MinimalTuple heap_form_minimal_tuple(TupleDesc tupleDescriptor,
812 Datum *values, bool *isnull);
813 extern void heap_free_minimal_tuple(MinimalTuple mtup);
814 extern MinimalTuple heap_copy_minimal_tuple(MinimalTuple mtup);
815 extern HeapTuple heap_tuple_from_minimal_tuple(MinimalTuple mtup);
816 extern MinimalTuple minimal_tuple_from_heap_tuple(HeapTuple htup);
818 #endif /* HTUP_DETAILS_H */