1 /*-------------------------------------------------------------------------
4 * Support functions to rewrite tables.
6 * These functions provide a facility to completely rewrite a heap, while
7 * preserving visibility information and update chains.
11 * The caller is responsible for creating the new heap, all catalog
12 * changes, supplying the tuples to be written to the new heap, and
13 * rebuilding indexes. The caller must hold AccessExclusiveLock on the
14 * target table, because we assume no one else is writing into it.
16 * To use the facility:
19 * while (fetch next tuple)
22 * rewrite_heap_dead_tuple
25 * // do any transformations here if required
31 * The contents of the new relation shouldn't be relied on until after
32 * end_heap_rewrite is called.
37 * This would be a fairly trivial affair, except that we need to maintain
38 * the ctid chains that link versions of an updated tuple together.
39 * Since the newly stored tuples will have tids different from the original
40 * ones, if we just copied t_ctid fields to the new table the links would
41 * be wrong. When we are required to copy a (presumably recently-dead or
42 * delete-in-progress) tuple whose ctid doesn't point to itself, we have
43 * to substitute the correct ctid instead.
45 * For each ctid reference from A -> B, we might encounter either A first
46 * or B first. (Note that a tuple in the middle of a chain is both A and B
47 * of different pairs.)
49 * If we encounter A first, we'll store the tuple in the unresolved_tups
50 * hash table. When we later encounter B, we remove A from the hash table,
51 * fix the ctid to point to the new location of B, and insert both A and B
54 * If we encounter B first, we can insert B to the new heap right away.
55 * We then add an entry to the old_new_tid_map hash table showing B's
56 * original tid (in the old heap) and new tid (in the new heap).
57 * When we later encounter A, we get the new location of B from the table,
58 * and can write A immediately with the correct ctid.
60 * Entries in the hash tables can be removed as soon as the later tuple
61 * is encountered. That helps to keep the memory usage down. At the end,
62 * both tables are usually empty; we should have encountered both A and B
63 * of each pair. However, it's possible for A to be RECENTLY_DEAD and B
64 * entirely DEAD according to HeapTupleSatisfiesVacuum, because the test
65 * for deadness using OldestXmin is not exact. In such a case we might
66 * encounter B first, and skip it, and find A later. Then A would be added
67 * to unresolved_tups, and stay there until end of the rewrite. Since
68 * this case is very unusual, we don't worry about the memory usage.
70 * Using in-memory hash tables means that we use some memory for each live
71 * update chain in the table, from the time we find one end of the
72 * reference until we find the other end. That shouldn't be a problem in
73 * practice, but if you do something like an UPDATE without a where-clause
74 * on a large table, and then run CLUSTER in the same transaction, you
75 * could run out of memory. It doesn't seem worthwhile to add support for
76 * spill-to-disk, as there shouldn't be that many RECENTLY_DEAD tuples in a
77 * table under normal circumstances. Furthermore, in the typical scenario
78 * of CLUSTERing on an unchanging key column, we'll see all the versions
79 * of a given tuple together anyway, and so the peak memory usage is only
80 * proportional to the number of RECENTLY_DEAD versions of a single row, not
81 * in the whole table. Note that if we do fail halfway through a CLUSTER,
82 * the old table is still valid, so failure is not catastrophic.
84 * We can't use the normal heap_insert function to insert into the new
85 * heap, because heap_insert overwrites the visibility information.
86 * We use a special-purpose raw_heap_insert function instead, which
87 * is optimized for bulk inserting a lot of tuples, knowing that we have
88 * exclusive access to the heap. raw_heap_insert builds new pages in
89 * local storage. When a page is full, or at the end of the process,
90 * we insert it to WAL as a single record and then write it to disk
91 * directly through smgr. Note, however, that any data sent to the new
92 * heap's TOAST table will go through the normal bufmgr.
95 * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
96 * Portions Copyright (c) 1994-5, Regents of the University of California
99 * src/backend/access/heap/rewriteheap.c
101 *-------------------------------------------------------------------------
103 #include "postgres.h"
105 #include <sys/stat.h>
108 #include "miscadmin.h"
110 #include "access/heapam.h"
111 #include "access/heapam_xlog.h"
112 #include "access/rewriteheap.h"
113 #include "access/transam.h"
114 #include "access/tuptoaster.h"
115 #include "access/xact.h"
116 #include "access/xloginsert.h"
118 #include "catalog/catalog.h"
120 #include "lib/ilist.h"
122 #include "replication/logical.h"
123 #include "replication/slot.h"
125 #include "storage/bufmgr.h"
126 #include "storage/fd.h"
127 #include "storage/smgr.h"
129 #include "utils/memutils.h"
130 #include "utils/rel.h"
131 #include "utils/tqual.h"
133 #include "storage/procarray.h"
136 * State associated with a rewrite operation. This is opaque to the user
137 * of the rewrite facility.
139 typedef struct RewriteStateData
141 Relation rs_old_rel; /* source heap */
142 Relation rs_new_rel; /* destination heap */
143 Page rs_buffer; /* page currently being built */
144 BlockNumber rs_blockno; /* block where page will go */
145 bool rs_buffer_valid; /* T if any tuples in buffer */
146 bool rs_use_wal; /* must we WAL-log inserts? */
147 bool rs_logical_rewrite; /* do we need to do logical rewriting */
148 TransactionId rs_oldest_xmin; /* oldest xmin used by caller to
149 * determine tuple visibility */
150 TransactionId rs_freeze_xid;/* Xid that will be used as freeze cutoff
152 TransactionId rs_logical_xmin; /* Xid that will be used as cutoff
153 * point for logical rewrites */
154 MultiXactId rs_cutoff_multi;/* MultiXactId that will be used as cutoff
155 * point for multixacts */
156 MemoryContext rs_cxt; /* for hash tables and entries and tuples in
158 XLogRecPtr rs_begin_lsn; /* XLogInsertLsn when starting the rewrite */
159 HTAB *rs_unresolved_tups; /* unmatched A tuples */
160 HTAB *rs_old_new_tid_map; /* unmatched B tuples */
161 HTAB *rs_logical_mappings; /* logical remapping files */
162 uint32 rs_num_rewrite_mappings; /* # in memory mappings */
166 * The lookup keys for the hash tables are tuple TID and xmin (we must check
167 * both to avoid false matches from dead tuples). Beware that there is
168 * probably some padding space in this struct; it must be zeroed out for
169 * correct hashtable operation.
173 TransactionId xmin; /* tuple xmin */
174 ItemPointerData tid; /* tuple location in old heap */
178 * Entry structures for the hash tables
182 TidHashKey key; /* expected xmin/old location of B tuple */
183 ItemPointerData old_tid; /* A's location in the old heap */
184 HeapTuple tuple; /* A's tuple contents */
187 typedef UnresolvedTupData *UnresolvedTup;
191 TidHashKey key; /* actual xmin/old location of B tuple */
192 ItemPointerData new_tid; /* where we put it in the new heap */
193 } OldToNewMappingData;
195 typedef OldToNewMappingData *OldToNewMapping;
198 * In-Memory data for an xid that might need logical remapping entries
201 typedef struct RewriteMappingFile
203 TransactionId xid; /* xid that might need to see the row */
204 int vfd; /* fd of mappings file */
205 off_t off; /* how far have we written yet */
206 uint32 num_mappings; /* number of in-memory mappings */
207 dlist_head mappings; /* list of in-memory mappings */
208 char path[MAXPGPATH]; /* path, for error messages */
209 } RewriteMappingFile;
212 * A single In-Memeory logical rewrite mapping, hanging of
213 * RewriteMappingFile->mappings.
215 typedef struct RewriteMappingDataEntry
217 LogicalRewriteMappingData map; /* map between old and new location of
220 } RewriteMappingDataEntry;
223 /* prototypes for internal functions */
224 static void raw_heap_insert(RewriteState state, HeapTuple tup);
226 /* internal logical remapping prototypes */
227 static void logical_begin_heap_rewrite(RewriteState state);
228 static void logical_rewrite_heap_tuple(RewriteState state, ItemPointerData old_tid, HeapTuple new_tuple);
229 static void logical_end_heap_rewrite(RewriteState state);
233 * Begin a rewrite of a table
235 * old_heap old, locked heap relation tuples will be read from
236 * new_heap new, locked heap relation to insert tuples to
237 * oldest_xmin xid used by the caller to determine which tuples are dead
238 * freeze_xid xid before which tuples will be frozen
239 * min_multi multixact before which multis will be removed
240 * use_wal should the inserts to the new heap be WAL-logged?
242 * Returns an opaque RewriteState, allocated in current memory context,
243 * to be used in subsequent calls to the other functions.
246 begin_heap_rewrite(Relation old_heap, Relation new_heap, TransactionId oldest_xmin,
247 TransactionId freeze_xid, MultiXactId cutoff_multi,
251 MemoryContext rw_cxt;
252 MemoryContext old_cxt;
256 * To ease cleanup, make a separate context that will contain the
257 * RewriteState struct itself plus all subsidiary data.
259 rw_cxt = AllocSetContextCreate(CurrentMemoryContext,
261 ALLOCSET_DEFAULT_MINSIZE,
262 ALLOCSET_DEFAULT_INITSIZE,
263 ALLOCSET_DEFAULT_MAXSIZE);
264 old_cxt = MemoryContextSwitchTo(rw_cxt);
266 /* Create and fill in the state struct */
267 state = palloc0(sizeof(RewriteStateData));
269 state->rs_old_rel = old_heap;
270 state->rs_new_rel = new_heap;
271 state->rs_buffer = (Page) palloc(BLCKSZ);
272 /* new_heap needn't be empty, just locked */
273 state->rs_blockno = RelationGetNumberOfBlocks(new_heap);
274 state->rs_buffer_valid = false;
275 state->rs_use_wal = use_wal;
276 state->rs_oldest_xmin = oldest_xmin;
277 state->rs_freeze_xid = freeze_xid;
278 state->rs_cutoff_multi = cutoff_multi;
279 state->rs_cxt = rw_cxt;
281 /* Initialize hash tables used to track update chains */
282 memset(&hash_ctl, 0, sizeof(hash_ctl));
283 hash_ctl.keysize = sizeof(TidHashKey);
284 hash_ctl.entrysize = sizeof(UnresolvedTupData);
285 hash_ctl.hcxt = state->rs_cxt;
287 state->rs_unresolved_tups =
288 hash_create("Rewrite / Unresolved ctids",
289 128, /* arbitrary initial size */
291 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
293 hash_ctl.entrysize = sizeof(OldToNewMappingData);
295 state->rs_old_new_tid_map =
296 hash_create("Rewrite / Old to new tid map",
297 128, /* arbitrary initial size */
299 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
301 MemoryContextSwitchTo(old_cxt);
303 logical_begin_heap_rewrite(state);
311 * state and any other resources are freed.
314 end_heap_rewrite(RewriteState state)
316 HASH_SEQ_STATUS seq_status;
317 UnresolvedTup unresolved;
320 * Write any remaining tuples in the UnresolvedTups table. If we have any
321 * left, they should in fact be dead, but let's err on the safe side.
323 hash_seq_init(&seq_status, state->rs_unresolved_tups);
325 while ((unresolved = hash_seq_search(&seq_status)) != NULL)
327 ItemPointerSetInvalid(&unresolved->tuple->t_data->t_ctid);
328 raw_heap_insert(state, unresolved->tuple);
331 /* Write the last page, if any */
332 if (state->rs_buffer_valid)
334 if (state->rs_use_wal)
335 log_newpage(&state->rs_new_rel->rd_node,
340 RelationOpenSmgr(state->rs_new_rel);
342 PageSetChecksumInplace(state->rs_buffer, state->rs_blockno);
344 smgrextend(state->rs_new_rel->rd_smgr, MAIN_FORKNUM, state->rs_blockno,
345 (char *) state->rs_buffer, true);
349 * If the rel is WAL-logged, must fsync before commit. We use heap_sync
350 * to ensure that the toast table gets fsync'd too.
352 * It's obvious that we must do this when not WAL-logging. It's less
353 * obvious that we have to do it even if we did WAL-log the pages. The
354 * reason is the same as in tablecmds.c's copy_relation_data(): we're
355 * writing data that's not in shared buffers, and so a CHECKPOINT
356 * occurring during the rewriteheap operation won't have fsync'd data we
357 * wrote before the checkpoint.
359 if (RelationNeedsWAL(state->rs_new_rel))
360 heap_sync(state->rs_new_rel);
362 logical_end_heap_rewrite(state);
364 /* Deleting the context frees everything */
365 MemoryContextDelete(state->rs_cxt);
369 * Add a tuple to the new heap.
371 * Visibility information is copied from the original tuple, except that
372 * we "freeze" very-old tuples. Note that since we scribble on new_tuple,
373 * it had better be temp storage not a pointer to the original tuple.
375 * state opaque state as returned by begin_heap_rewrite
376 * old_tuple original tuple in the old heap
377 * new_tuple new, rewritten tuple to be inserted to new heap
380 rewrite_heap_tuple(RewriteState state,
381 HeapTuple old_tuple, HeapTuple new_tuple)
383 MemoryContext old_cxt;
384 ItemPointerData old_tid;
389 old_cxt = MemoryContextSwitchTo(state->rs_cxt);
392 * Copy the original tuple's visibility information into new_tuple.
394 * XXX we might later need to copy some t_infomask2 bits, too? Right now,
395 * we intentionally clear the HOT status bits.
397 memcpy(&new_tuple->t_data->t_choice.t_heap,
398 &old_tuple->t_data->t_choice.t_heap,
399 sizeof(HeapTupleFields));
401 new_tuple->t_data->t_infomask &= ~HEAP_XACT_MASK;
402 new_tuple->t_data->t_infomask2 &= ~HEAP2_XACT_MASK;
403 new_tuple->t_data->t_infomask |=
404 old_tuple->t_data->t_infomask & HEAP_XACT_MASK;
407 * While we have our hands on the tuple, we may as well freeze any
408 * eligible xmin or xmax, so that future VACUUM effort can be saved.
410 heap_freeze_tuple(new_tuple->t_data, state->rs_freeze_xid,
411 state->rs_cutoff_multi);
414 * Invalid ctid means that ctid should point to the tuple itself. We'll
415 * override it later if the tuple is part of an update chain.
417 ItemPointerSetInvalid(&new_tuple->t_data->t_ctid);
420 * If the tuple has been updated, check the old-to-new mapping hash table.
422 if (!((old_tuple->t_data->t_infomask & HEAP_XMAX_INVALID) ||
423 HeapTupleHeaderIsOnlyLocked(old_tuple->t_data)) &&
424 !(ItemPointerEquals(&(old_tuple->t_self),
425 &(old_tuple->t_data->t_ctid))))
427 OldToNewMapping mapping;
429 memset(&hashkey, 0, sizeof(hashkey));
430 hashkey.xmin = HeapTupleHeaderGetUpdateXid(old_tuple->t_data);
431 hashkey.tid = old_tuple->t_data->t_ctid;
433 mapping = (OldToNewMapping)
434 hash_search(state->rs_old_new_tid_map, &hashkey,
440 * We've already copied the tuple that t_ctid points to, so we can
441 * set the ctid of this tuple to point to the new location, and
442 * insert it right away.
444 new_tuple->t_data->t_ctid = mapping->new_tid;
446 /* We don't need the mapping entry anymore */
447 hash_search(state->rs_old_new_tid_map, &hashkey,
448 HASH_REMOVE, &found);
454 * We haven't seen the tuple t_ctid points to yet. Stash this
455 * tuple into unresolved_tups to be written later.
457 UnresolvedTup unresolved;
459 unresolved = hash_search(state->rs_unresolved_tups, &hashkey,
463 unresolved->old_tid = old_tuple->t_self;
464 unresolved->tuple = heap_copytuple(new_tuple);
467 * We can't do anything more now, since we don't know where the
468 * tuple will be written.
470 MemoryContextSwitchTo(old_cxt);
476 * Now we will write the tuple, and then check to see if it is the B tuple
477 * in any new or known pair. When we resolve a known pair, we will be
478 * able to write that pair's A tuple, and then we have to check if it
479 * resolves some other pair. Hence, we need a loop here.
481 old_tid = old_tuple->t_self;
486 ItemPointerData new_tid;
488 /* Insert the tuple and find out where it's put in new_heap */
489 raw_heap_insert(state, new_tuple);
490 new_tid = new_tuple->t_self;
492 logical_rewrite_heap_tuple(state, old_tid, new_tuple);
495 * If the tuple is the updated version of a row, and the prior version
496 * wouldn't be DEAD yet, then we need to either resolve the prior
497 * version (if it's waiting in rs_unresolved_tups), or make an entry
498 * in rs_old_new_tid_map (so we can resolve it when we do see it). The
499 * previous tuple's xmax would equal this one's xmin, so it's
500 * RECENTLY_DEAD if and only if the xmin is not before OldestXmin.
502 if ((new_tuple->t_data->t_infomask & HEAP_UPDATED) &&
503 !TransactionIdPrecedes(HeapTupleHeaderGetXmin(new_tuple->t_data),
504 state->rs_oldest_xmin))
507 * Okay, this is B in an update pair. See if we've seen A.
509 UnresolvedTup unresolved;
511 memset(&hashkey, 0, sizeof(hashkey));
512 hashkey.xmin = HeapTupleHeaderGetXmin(new_tuple->t_data);
513 hashkey.tid = old_tid;
515 unresolved = hash_search(state->rs_unresolved_tups, &hashkey,
518 if (unresolved != NULL)
521 * We have seen and memorized the previous tuple already. Now
522 * that we know where we inserted the tuple its t_ctid points
523 * to, fix its t_ctid and insert it to the new heap.
526 heap_freetuple(new_tuple);
527 new_tuple = unresolved->tuple;
529 old_tid = unresolved->old_tid;
530 new_tuple->t_data->t_ctid = new_tid;
533 * We don't need the hash entry anymore, but don't free its
536 hash_search(state->rs_unresolved_tups, &hashkey,
537 HASH_REMOVE, &found);
540 /* loop back to insert the previous tuple in the chain */
546 * Remember the new tid of this tuple. We'll use it to set the
547 * ctid when we find the previous tuple in the chain.
549 OldToNewMapping mapping;
551 mapping = hash_search(state->rs_old_new_tid_map, &hashkey,
555 mapping->new_tid = new_tid;
559 /* Done with this (chain of) tuples, for now */
561 heap_freetuple(new_tuple);
565 MemoryContextSwitchTo(old_cxt);
569 * Register a dead tuple with an ongoing rewrite. Dead tuples are not
570 * copied to the new table, but we still make note of them so that we
571 * can release some resources earlier.
573 * Returns true if a tuple was removed from the unresolved_tups table.
574 * This indicates that that tuple, previously thought to be "recently dead",
575 * is now known really dead and won't be written to the output.
578 rewrite_heap_dead_tuple(RewriteState state, HeapTuple old_tuple)
581 * If we have already seen an earlier tuple in the update chain that
582 * points to this tuple, let's forget about that earlier tuple. It's in
583 * fact dead as well, our simple xmax < OldestXmin test in
584 * HeapTupleSatisfiesVacuum just wasn't enough to detect it. It happens
585 * when xmin of a tuple is greater than xmax, which sounds
586 * counter-intuitive but is perfectly valid.
588 * We don't bother to try to detect the situation the other way round,
589 * when we encounter the dead tuple first and then the recently dead one
590 * that points to it. If that happens, we'll have some unmatched entries
591 * in the UnresolvedTups hash table at the end. That can happen anyway,
592 * because a vacuum might have removed the dead tuple in the chain before
595 UnresolvedTup unresolved;
599 memset(&hashkey, 0, sizeof(hashkey));
600 hashkey.xmin = HeapTupleHeaderGetXmin(old_tuple->t_data);
601 hashkey.tid = old_tuple->t_self;
603 unresolved = hash_search(state->rs_unresolved_tups, &hashkey,
606 if (unresolved != NULL)
608 /* Need to free the contained tuple as well as the hashtable entry */
609 heap_freetuple(unresolved->tuple);
610 hash_search(state->rs_unresolved_tups, &hashkey,
611 HASH_REMOVE, &found);
620 * Insert a tuple to the new relation. This has to track heap_insert
621 * and its subsidiary functions!
623 * t_self of the tuple is set to the new TID of the tuple. If t_ctid of the
624 * tuple is invalid on entry, it's replaced with the new TID as well (in
625 * the inserted data only, not in the caller's copy).
628 raw_heap_insert(RewriteState state, HeapTuple tup)
630 Page page = state->rs_buffer;
638 * If the new tuple is too big for storage or contains already toasted
639 * out-of-line attributes from some other relation, invoke the toaster.
641 * Note: below this point, heaptup is the data we actually intend to store
642 * into the relation; tup is the caller's original untoasted data.
644 if (state->rs_new_rel->rd_rel->relkind == RELKIND_TOASTVALUE)
646 /* toast table entries should never be recursively toasted */
647 Assert(!HeapTupleHasExternal(tup));
650 else if (HeapTupleHasExternal(tup) || tup->t_len > TOAST_TUPLE_THRESHOLD)
651 heaptup = toast_insert_or_update(state->rs_new_rel, tup, NULL,
652 HEAP_INSERT_SKIP_FSM |
654 0 : HEAP_INSERT_SKIP_WAL));
658 len = MAXALIGN(heaptup->t_len); /* be conservative */
661 * If we're gonna fail for oversize tuple, do it right away
663 if (len > MaxHeapTupleSize)
665 (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
666 errmsg("row is too big: size %zu, maximum size %zu",
667 len, MaxHeapTupleSize)));
669 /* Compute desired extra freespace due to fillfactor option */
670 saveFreeSpace = RelationGetTargetPageFreeSpace(state->rs_new_rel,
671 HEAP_DEFAULT_FILLFACTOR);
673 /* Now we can check to see if there's enough free space already. */
674 if (state->rs_buffer_valid)
676 pageFreeSpace = PageGetHeapFreeSpace(page);
678 if (len + saveFreeSpace > pageFreeSpace)
680 /* Doesn't fit, so write out the existing page */
683 if (state->rs_use_wal)
684 log_newpage(&state->rs_new_rel->rd_node,
691 * Now write the page. We say isTemp = true even if it's not a
692 * temp table, because there's no need for smgr to schedule an
693 * fsync for this write; we'll do it ourselves in
696 RelationOpenSmgr(state->rs_new_rel);
698 PageSetChecksumInplace(page, state->rs_blockno);
700 smgrextend(state->rs_new_rel->rd_smgr, MAIN_FORKNUM,
701 state->rs_blockno, (char *) page, true);
704 state->rs_buffer_valid = false;
708 if (!state->rs_buffer_valid)
710 /* Initialize a new empty page */
711 PageInit(page, BLCKSZ, 0);
712 state->rs_buffer_valid = true;
715 /* And now we can insert the tuple into the page */
716 newoff = PageAddItem(page, (Item) heaptup->t_data, heaptup->t_len,
717 InvalidOffsetNumber, false, true);
718 if (newoff == InvalidOffsetNumber)
719 elog(ERROR, "failed to add tuple");
721 /* Update caller's t_self to the actual position where it was stored */
722 ItemPointerSet(&(tup->t_self), state->rs_blockno, newoff);
725 * Insert the correct position into CTID of the stored tuple, too, if the
726 * caller didn't supply a valid CTID.
728 if (!ItemPointerIsValid(&tup->t_data->t_ctid))
731 HeapTupleHeader onpage_tup;
733 newitemid = PageGetItemId(page, newoff);
734 onpage_tup = (HeapTupleHeader) PageGetItem(page, newitemid);
736 onpage_tup->t_ctid = tup->t_self;
739 /* If heaptup is a private copy, release it. */
741 heap_freetuple(heaptup);
744 /* ------------------------------------------------------------------------
745 * Logical rewrite support
747 * When doing logical decoding - which relies on using cmin/cmax of catalog
748 * tuples, via xl_heap_new_cid records - heap rewrites have to log enough
749 * information to allow the decoding backend to updates its internal mapping
750 * of (relfilenode,ctid) => (cmin, cmax) to be correct for the rewritten heap.
752 * For that, every time we find a tuple that's been modified in a catalog
753 * relation within the xmin horizon of any decoding slot, we log a mapping
754 * from the old to the new location.
756 * To deal with rewrites that abort the filename of a mapping file contains
757 * the xid of the transaction performing the rewrite, which then can be
758 * checked before being read in.
760 * For efficiency we don't immediately spill every single map mapping for a
761 * row to disk but only do so in batches when we've collected several of them
762 * in memory or when end_heap_rewrite() has been called.
764 * Crash-Safety: This module diverts from the usual patterns of doing WAL
765 * since it cannot rely on checkpoint flushing out all buffers and thus
766 * waiting for exlusive locks on buffers. Usually the XLogInsert() covering
767 * buffer modifications is performed while the buffer(s) that are being
768 * modified are exlusively locked guaranteeing that both the WAL record and
769 * the modified heap are on either side of the checkpoint. But since the
770 * mapping files we log aren't in shared_buffers that interlock doesn't work.
772 * Instead we simply write the mapping files out to disk, *before* the
773 * XLogInsert() is performed. That guarantees that either the XLogInsert() is
774 * inserted after the checkpoint's redo pointer or that the checkpoint (via
775 * LogicalRewriteHeapCheckpoint()) has flushed the (partial) mapping file to
776 * disk. That leaves the tail end that has not yet been flushed open to
777 * corruption, which is solved by including the current offset in the
778 * xl_heap_rewrite_mapping records and truncating the mapping file to it
779 * during replay. Every time a rewrite is finished all generated mapping files
780 * are synced to disk.
782 * Note that if we were only concerned about crash safety we wouldn't have to
783 * deal with WAL logging at all - an fsync() at the end of a rewrite would be
784 * sufficient for crash safety. Any mapping that hasn't been safely flushed to
785 * disk has to be by an aborted (explicitly or via a crash) transaction and is
786 * ignored by virtue of the xid in its name being subject to a
787 * TransactionDidCommit() check. But we want to support having standbys via
788 * physical replication, both for availability and to do logical decoding
790 * ------------------------------------------------------------------------
794 * Do preparations for logging logical mappings during a rewrite if
795 * necessary. If we detect that we don't need to log anything we'll prevent
796 * any further action by the various logical rewrite functions.
799 logical_begin_heap_rewrite(RewriteState state)
802 TransactionId logical_xmin;
805 * We only need to persist these mappings if the rewritten table can be
806 * accessed during logical decoding, if not, we can skip doing any
809 state->rs_logical_rewrite =
810 RelationIsAccessibleInLogicalDecoding(state->rs_old_rel);
812 if (!state->rs_logical_rewrite)
815 ProcArrayGetReplicationSlotXmin(NULL, &logical_xmin);
818 * If there are no logical slots in progress we don't need to do anything,
819 * there cannot be any remappings for relevant rows yet. The relation's
820 * lock protects us against races.
822 if (logical_xmin == InvalidTransactionId)
824 state->rs_logical_rewrite = false;
828 state->rs_logical_xmin = logical_xmin;
829 state->rs_begin_lsn = GetXLogInsertRecPtr();
830 state->rs_num_rewrite_mappings = 0;
832 memset(&hash_ctl, 0, sizeof(hash_ctl));
833 hash_ctl.keysize = sizeof(TransactionId);
834 hash_ctl.entrysize = sizeof(RewriteMappingFile);
835 hash_ctl.hcxt = state->rs_cxt;
837 state->rs_logical_mappings =
838 hash_create("Logical rewrite mapping",
839 128, /* arbitrary initial size */
841 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
845 * Flush all logical in-memory mappings to disk, but don't fsync them yet.
848 logical_heap_rewrite_flush_mappings(RewriteState state)
850 HASH_SEQ_STATUS seq_status;
851 RewriteMappingFile *src;
852 dlist_mutable_iter iter;
854 Assert(state->rs_logical_rewrite);
856 /* no logical rewrite in progress, no need to iterate over mappings */
857 if (state->rs_num_rewrite_mappings == 0)
860 elog(DEBUG1, "flushing %u logical rewrite mapping entries",
861 state->rs_num_rewrite_mappings);
863 hash_seq_init(&seq_status, state->rs_logical_mappings);
864 while ((src = (RewriteMappingFile *) hash_seq_search(&seq_status)) != NULL)
868 xl_heap_rewrite_mapping xlrec;
873 /* this file hasn't got any new mappings */
874 if (src->num_mappings == 0)
877 if (state->rs_old_rel->rd_rel->relisshared)
880 dboid = MyDatabaseId;
882 xlrec.num_mappings = src->num_mappings;
883 xlrec.mapped_rel = RelationGetRelid(state->rs_old_rel);
884 xlrec.mapped_xid = src->xid;
885 xlrec.mapped_db = dboid;
886 xlrec.offset = src->off;
887 xlrec.start_lsn = state->rs_begin_lsn;
889 /* write all mappings consecutively */
890 len = src->num_mappings * sizeof(LogicalRewriteMappingData);
891 waldata_start = waldata = palloc(len);
894 * collect data we need to write out, but don't modify ondisk data yet
896 dlist_foreach_modify(iter, &src->mappings)
898 RewriteMappingDataEntry *pmap;
900 pmap = dlist_container(RewriteMappingDataEntry, node, iter.cur);
902 memcpy(waldata, &pmap->map, sizeof(pmap->map));
903 waldata += sizeof(pmap->map);
905 /* remove from the list and free */
906 dlist_delete(&pmap->node);
909 /* update bookkeeping */
910 state->rs_num_rewrite_mappings--;
914 Assert(src->num_mappings == 0);
915 Assert(waldata == waldata_start + len);
918 * Note that we deviate from the usual WAL coding practices here,
919 * check the above "Logical rewrite support" comment for reasoning.
921 written = FileWrite(src->vfd, waldata_start, len);
924 (errcode_for_file_access(),
925 errmsg("could not write to file \"%s\", wrote %d of %d: %m", src->path,
930 XLogRegisterData((char *) (&xlrec), sizeof(xlrec));
931 XLogRegisterData(waldata_start, len);
933 /* write xlog record */
934 XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_REWRITE);
936 pfree(waldata_start);
938 Assert(state->rs_num_rewrite_mappings == 0);
942 * Logical remapping part of end_heap_rewrite().
945 logical_end_heap_rewrite(RewriteState state)
947 HASH_SEQ_STATUS seq_status;
948 RewriteMappingFile *src;
950 /* done, no logical rewrite in progress */
951 if (!state->rs_logical_rewrite)
954 /* writeout remaining in-memory entries */
955 if (state->rs_num_rewrite_mappings > 0)
956 logical_heap_rewrite_flush_mappings(state);
958 /* Iterate over all mappings we have written and fsync the files. */
959 hash_seq_init(&seq_status, state->rs_logical_mappings);
960 while ((src = (RewriteMappingFile *) hash_seq_search(&seq_status)) != NULL)
962 if (FileSync(src->vfd) != 0)
964 (errcode_for_file_access(),
965 errmsg("could not fsync file \"%s\": %m", src->path)));
968 /* memory context cleanup will deal with the rest */
972 * Log a single (old->new) mapping for 'xid'.
975 logical_rewrite_log_mapping(RewriteState state, TransactionId xid,
976 LogicalRewriteMappingData *map)
978 RewriteMappingFile *src;
979 RewriteMappingDataEntry *pmap;
983 relid = RelationGetRelid(state->rs_old_rel);
985 /* look for existing mappings for this 'mapped' xid */
986 src = hash_search(state->rs_logical_mappings, &xid,
990 * We haven't yet had the need to map anything for this xid, create
991 * per-xid data structures.
995 char path[MAXPGPATH];
998 if (state->rs_old_rel->rd_rel->relisshared)
1001 dboid = MyDatabaseId;
1003 snprintf(path, MAXPGPATH,
1004 "pg_logical/mappings/" LOGICAL_REWRITE_FORMAT,
1006 (uint32) (state->rs_begin_lsn >> 32),
1007 (uint32) state->rs_begin_lsn,
1008 xid, GetCurrentTransactionId());
1010 dlist_init(&src->mappings);
1011 src->num_mappings = 0;
1013 memcpy(src->path, path, sizeof(path));
1014 src->vfd = PathNameOpenFile(path,
1015 O_CREAT | O_EXCL | O_WRONLY | PG_BINARY,
1019 (errcode_for_file_access(),
1020 errmsg("could not create file \"%s\": %m", path)));
1023 pmap = MemoryContextAlloc(state->rs_cxt,
1024 sizeof(RewriteMappingDataEntry));
1025 memcpy(&pmap->map, map, sizeof(LogicalRewriteMappingData));
1026 dlist_push_tail(&src->mappings, &pmap->node);
1027 src->num_mappings++;
1028 state->rs_num_rewrite_mappings++;
1031 * Write out buffer every time we've too many in-memory entries across all
1034 if (state->rs_num_rewrite_mappings >= 1000 /* arbitrary number */ )
1035 logical_heap_rewrite_flush_mappings(state);
1039 * Perform logical remapping for a tuple that's mapped from old_tid to
1040 * new_tuple->t_self by rewrite_heap_tuple() if necessary for the tuple.
1043 logical_rewrite_heap_tuple(RewriteState state, ItemPointerData old_tid,
1044 HeapTuple new_tuple)
1046 ItemPointerData new_tid = new_tuple->t_self;
1047 TransactionId cutoff = state->rs_logical_xmin;
1050 bool do_log_xmin = false;
1051 bool do_log_xmax = false;
1052 LogicalRewriteMappingData map;
1054 /* no logical rewrite in progress, we don't need to log anything */
1055 if (!state->rs_logical_rewrite)
1058 xmin = HeapTupleHeaderGetXmin(new_tuple->t_data);
1059 /* use *GetUpdateXid to correctly deal with multixacts */
1060 xmax = HeapTupleHeaderGetUpdateXid(new_tuple->t_data);
1063 * Log the mapping iff the tuple has been created recently.
1065 if (TransactionIdIsNormal(xmin) && !TransactionIdPrecedes(xmin, cutoff))
1068 if (!TransactionIdIsNormal(xmax))
1071 * no xmax is set, can't have any permanent ones, so this check is
1075 else if (HEAP_XMAX_IS_LOCKED_ONLY(new_tuple->t_data->t_infomask))
1077 /* only locked, we don't care */
1079 else if (!TransactionIdPrecedes(xmax, cutoff))
1081 /* tuple has been deleted recently, log */
1085 /* if neither needs to be logged, we're done */
1086 if (!do_log_xmin && !do_log_xmax)
1089 /* fill out mapping information */
1090 map.old_node = state->rs_old_rel->rd_node;
1091 map.old_tid = old_tid;
1092 map.new_node = state->rs_new_rel->rd_node;
1093 map.new_tid = new_tid;
1096 * Now persist the mapping for the individual xids that are affected. We
1097 * need to log for both xmin and xmax if they aren't the same transaction
1098 * since the mapping files are per "affected" xid.
1099 * We don't muster all that much effort detecting whether xmin and xmax
1100 * are actually the same transaction, we just check whether the xid is the
1101 * same disregarding subtransactions. Logging too much is relatively
1102 * harmless and we could never do the check fully since subtransaction
1103 * data is thrown away during restarts.
1107 logical_rewrite_log_mapping(state, xmin, &map);
1108 /* separately log mapping for xmax unless it'd be redundant */
1109 if (do_log_xmax && !TransactionIdEquals(xmin, xmax))
1110 logical_rewrite_log_mapping(state, xmax, &map);
1114 * Replay XLOG_HEAP2_REWRITE records
1117 heap_xlog_logical_rewrite(XLogReaderState *r)
1119 char path[MAXPGPATH];
1121 xl_heap_rewrite_mapping *xlrec;
1125 xlrec = (xl_heap_rewrite_mapping *) XLogRecGetData(r);
1127 snprintf(path, MAXPGPATH,
1128 "pg_logical/mappings/" LOGICAL_REWRITE_FORMAT,
1129 xlrec->mapped_db, xlrec->mapped_rel,
1130 (uint32) (xlrec->start_lsn >> 32),
1131 (uint32) xlrec->start_lsn,
1132 xlrec->mapped_xid, XLogRecGetXid(r));
1134 fd = OpenTransientFile(path,
1135 O_CREAT | O_WRONLY | PG_BINARY,
1139 (errcode_for_file_access(),
1140 errmsg("could not create file \"%s\": %m", path)));
1143 * Truncate all data that's not guaranteed to have been safely fsynced (by
1144 * previous record or by the last checkpoint).
1146 if (ftruncate(fd, xlrec->offset) != 0)
1148 (errcode_for_file_access(),
1149 errmsg("could not truncate file \"%s\" to %u: %m",
1150 path, (uint32) xlrec->offset)));
1152 /* now seek to the position we want to write our data to */
1153 if (lseek(fd, xlrec->offset, SEEK_SET) != xlrec->offset)
1155 (errcode_for_file_access(),
1156 errmsg("could not seek to end of file \"%s\": %m",
1159 data = XLogRecGetData(r) + sizeof(*xlrec);
1161 len = xlrec->num_mappings * sizeof(LogicalRewriteMappingData);
1163 /* write out tail end of mapping file (again) */
1164 if (write(fd, data, len) != len)
1166 (errcode_for_file_access(),
1167 errmsg("could not write to file \"%s\": %m", path)));
1170 * Now fsync all previously written data. We could improve things and only
1171 * do this for the last write to a file, but the required bookkeeping
1172 * doesn't seem worth the trouble.
1174 if (pg_fsync(fd) != 0)
1176 (errcode_for_file_access(),
1177 errmsg("could not fsync file \"%s\": %m", path)));
1179 CloseTransientFile(fd);
1183 * Perform a checkpoint for logical rewrite mappings
1185 * This serves two tasks:
1186 * 1) Remove all mappings not needed anymore based on the logical restart LSN
1187 * 2) Flush all remaining mappings to disk, so that replay after a checkpoint
1188 * only has to deal with the parts of a mapping that have been written out
1189 * after the checkpoint started.
1193 CheckPointLogicalRewriteHeap(void)
1198 struct dirent *mapping_de;
1199 char path[MAXPGPATH];
1202 * We start of with a minimum of the last redo pointer. No new decoding
1203 * slot will start before that, so that's a safe upper bound for removal.
1205 redo = GetRedoRecPtr();
1207 /* now check for the restart ptrs from existing slots */
1208 cutoff = ReplicationSlotsComputeLogicalRestartLSN();
1210 /* don't start earlier than the restart lsn */
1211 if (cutoff != InvalidXLogRecPtr && redo < cutoff)
1214 mappings_dir = AllocateDir("pg_logical/mappings");
1215 while ((mapping_de = ReadDir(mappings_dir, "pg_logical/mappings")) != NULL)
1217 struct stat statbuf;
1221 TransactionId rewrite_xid;
1222 TransactionId create_xid;
1226 if (strcmp(mapping_de->d_name, ".") == 0 ||
1227 strcmp(mapping_de->d_name, "..") == 0)
1230 snprintf(path, MAXPGPATH, "pg_logical/mappings/%s", mapping_de->d_name);
1231 if (lstat(path, &statbuf) == 0 && !S_ISREG(statbuf.st_mode))
1234 /* Skip over files that cannot be ours. */
1235 if (strncmp(mapping_de->d_name, "map-", 4) != 0)
1238 if (sscanf(mapping_de->d_name, LOGICAL_REWRITE_FORMAT,
1239 &dboid, &relid, &hi, &lo, &rewrite_xid, &create_xid) != 6)
1240 elog(ERROR, "could not parse filename \"%s\"", mapping_de->d_name);
1242 lsn = ((uint64) hi) << 32 | lo;
1244 if (lsn < cutoff || cutoff == InvalidXLogRecPtr)
1246 elog(DEBUG1, "removing logical rewrite file \"%s\"", path);
1247 if (unlink(path) < 0)
1249 (errcode_for_file_access(),
1250 errmsg("could not remove file \"%s\": %m", path)));
1254 int fd = OpenTransientFile(path, O_RDONLY | PG_BINARY, 0);
1257 * The file cannot vanish due to concurrency since this function
1258 * is the only one removing logical mappings and it's run while
1259 * CheckpointLock is held exclusively.
1263 (errcode_for_file_access(),
1264 errmsg("could not open file \"%s\": %m", path)));
1267 * We could try to avoid fsyncing files that either haven't
1268 * changed or have only been created since the checkpoint's start,
1269 * but it's currently not deemed worth the effort.
1271 else if (pg_fsync(fd) != 0)
1273 (errcode_for_file_access(),
1274 errmsg("could not fsync file \"%s\": %m", path)));
1275 CloseTransientFile(fd);
1278 FreeDir(mappings_dir);