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Diffstat (limited to 'src/backend/access/heap/rewriteheap.c')
| -rw-r--r-- | src/backend/access/heap/rewriteheap.c | 1295 |
1 files changed, 1295 insertions, 0 deletions
diff --git a/src/backend/access/heap/rewriteheap.c b/src/backend/access/heap/rewriteheap.c new file mode 100644 index 0000000..15bef9f --- /dev/null +++ b/src/backend/access/heap/rewriteheap.c @@ -0,0 +1,1295 @@ +/*------------------------------------------------------------------------- + * + * rewriteheap.c + * Support functions to rewrite tables. + * + * These functions provide a facility to completely rewrite a heap, while + * preserving visibility information and update chains. + * + * INTERFACE + * + * The caller is responsible for creating the new heap, all catalog + * changes, supplying the tuples to be written to the new heap, and + * rebuilding indexes. The caller must hold AccessExclusiveLock on the + * target table, because we assume no one else is writing into it. + * + * To use the facility: + * + * begin_heap_rewrite + * while (fetch next tuple) + * { + * if (tuple is dead) + * rewrite_heap_dead_tuple + * else + * { + * // do any transformations here if required + * rewrite_heap_tuple + * } + * } + * end_heap_rewrite + * + * The contents of the new relation shouldn't be relied on until after + * end_heap_rewrite is called. + * + * + * IMPLEMENTATION + * + * This would be a fairly trivial affair, except that we need to maintain + * the ctid chains that link versions of an updated tuple together. + * Since the newly stored tuples will have tids different from the original + * ones, if we just copied t_ctid fields to the new table the links would + * be wrong. When we are required to copy a (presumably recently-dead or + * delete-in-progress) tuple whose ctid doesn't point to itself, we have + * to substitute the correct ctid instead. + * + * For each ctid reference from A -> B, we might encounter either A first + * or B first. (Note that a tuple in the middle of a chain is both A and B + * of different pairs.) + * + * If we encounter A first, we'll store the tuple in the unresolved_tups + * hash table. When we later encounter B, we remove A from the hash table, + * fix the ctid to point to the new location of B, and insert both A and B + * to the new heap. + * + * If we encounter B first, we can insert B to the new heap right away. + * We then add an entry to the old_new_tid_map hash table showing B's + * original tid (in the old heap) and new tid (in the new heap). + * When we later encounter A, we get the new location of B from the table, + * and can write A immediately with the correct ctid. + * + * Entries in the hash tables can be removed as soon as the later tuple + * is encountered. That helps to keep the memory usage down. At the end, + * both tables are usually empty; we should have encountered both A and B + * of each pair. However, it's possible for A to be RECENTLY_DEAD and B + * entirely DEAD according to HeapTupleSatisfiesVacuum, because the test + * for deadness using OldestXmin is not exact. In such a case we might + * encounter B first, and skip it, and find A later. Then A would be added + * to unresolved_tups, and stay there until end of the rewrite. Since + * this case is very unusual, we don't worry about the memory usage. + * + * Using in-memory hash tables means that we use some memory for each live + * update chain in the table, from the time we find one end of the + * reference until we find the other end. That shouldn't be a problem in + * practice, but if you do something like an UPDATE without a where-clause + * on a large table, and then run CLUSTER in the same transaction, you + * could run out of memory. It doesn't seem worthwhile to add support for + * spill-to-disk, as there shouldn't be that many RECENTLY_DEAD tuples in a + * table under normal circumstances. Furthermore, in the typical scenario + * of CLUSTERing on an unchanging key column, we'll see all the versions + * of a given tuple together anyway, and so the peak memory usage is only + * proportional to the number of RECENTLY_DEAD versions of a single row, not + * in the whole table. Note that if we do fail halfway through a CLUSTER, + * the old table is still valid, so failure is not catastrophic. + * + * We can't use the normal heap_insert function to insert into the new + * heap, because heap_insert overwrites the visibility information. + * We use a special-purpose raw_heap_insert function instead, which + * is optimized for bulk inserting a lot of tuples, knowing that we have + * exclusive access to the heap. raw_heap_insert builds new pages in + * local storage. When a page is full, or at the end of the process, + * we insert it to WAL as a single record and then write it to disk + * directly through smgr. Note, however, that any data sent to the new + * heap's TOAST table will go through the normal bufmgr. + * + * + * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group + * Portions Copyright (c) 1994-5, Regents of the University of California + * + * IDENTIFICATION + * src/backend/access/heap/rewriteheap.c + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include <sys/stat.h> +#include <unistd.h> + +#include "access/heapam.h" +#include "access/heapam_xlog.h" +#include "access/heaptoast.h" +#include "access/rewriteheap.h" +#include "access/transam.h" +#include "access/xact.h" +#include "access/xloginsert.h" +#include "catalog/catalog.h" +#include "lib/ilist.h" +#include "miscadmin.h" +#include "pgstat.h" +#include "replication/logical.h" +#include "replication/slot.h" +#include "storage/bufmgr.h" +#include "storage/fd.h" +#include "storage/procarray.h" +#include "storage/smgr.h" +#include "utils/memutils.h" +#include "utils/rel.h" + +/* + * State associated with a rewrite operation. This is opaque to the user + * of the rewrite facility. + */ +typedef struct RewriteStateData +{ + Relation rs_old_rel; /* source heap */ + Relation rs_new_rel; /* destination heap */ + Page rs_buffer; /* page currently being built */ + BlockNumber rs_blockno; /* block where page will go */ + bool rs_buffer_valid; /* T if any tuples in buffer */ + bool rs_logical_rewrite; /* do we need to do logical rewriting */ + TransactionId rs_oldest_xmin; /* oldest xmin used by caller to determine + * tuple visibility */ + TransactionId rs_freeze_xid; /* Xid that will be used as freeze cutoff + * point */ + TransactionId rs_logical_xmin; /* Xid that will be used as cutoff point + * for logical rewrites */ + MultiXactId rs_cutoff_multi; /* MultiXactId that will be used as cutoff + * point for multixacts */ + MemoryContext rs_cxt; /* for hash tables and entries and tuples in + * them */ + XLogRecPtr rs_begin_lsn; /* XLogInsertLsn when starting the rewrite */ + HTAB *rs_unresolved_tups; /* unmatched A tuples */ + HTAB *rs_old_new_tid_map; /* unmatched B tuples */ + HTAB *rs_logical_mappings; /* logical remapping files */ + uint32 rs_num_rewrite_mappings; /* # in memory mappings */ +} RewriteStateData; + +/* + * The lookup keys for the hash tables are tuple TID and xmin (we must check + * both to avoid false matches from dead tuples). Beware that there is + * probably some padding space in this struct; it must be zeroed out for + * correct hashtable operation. + */ +typedef struct +{ + TransactionId xmin; /* tuple xmin */ + ItemPointerData tid; /* tuple location in old heap */ +} TidHashKey; + +/* + * Entry structures for the hash tables + */ +typedef struct +{ + TidHashKey key; /* expected xmin/old location of B tuple */ + ItemPointerData old_tid; /* A's location in the old heap */ + HeapTuple tuple; /* A's tuple contents */ +} UnresolvedTupData; + +typedef UnresolvedTupData *UnresolvedTup; + +typedef struct +{ + TidHashKey key; /* actual xmin/old location of B tuple */ + ItemPointerData new_tid; /* where we put it in the new heap */ +} OldToNewMappingData; + +typedef OldToNewMappingData *OldToNewMapping; + +/* + * In-Memory data for an xid that might need logical remapping entries + * to be logged. + */ +typedef struct RewriteMappingFile +{ + TransactionId xid; /* xid that might need to see the row */ + int vfd; /* fd of mappings file */ + off_t off; /* how far have we written yet */ + uint32 num_mappings; /* number of in-memory mappings */ + dlist_head mappings; /* list of in-memory mappings */ + char path[MAXPGPATH]; /* path, for error messages */ +} RewriteMappingFile; + +/* + * A single In-Memory logical rewrite mapping, hanging off + * RewriteMappingFile->mappings. + */ +typedef struct RewriteMappingDataEntry +{ + LogicalRewriteMappingData map; /* map between old and new location of the + * tuple */ + dlist_node node; +} RewriteMappingDataEntry; + + +/* prototypes for internal functions */ +static void raw_heap_insert(RewriteState state, HeapTuple tup); + +/* internal logical remapping prototypes */ +static void logical_begin_heap_rewrite(RewriteState state); +static void logical_rewrite_heap_tuple(RewriteState state, ItemPointerData old_tid, HeapTuple new_tuple); +static void logical_end_heap_rewrite(RewriteState state); + + +/* + * Begin a rewrite of a table + * + * old_heap old, locked heap relation tuples will be read from + * new_heap new, locked heap relation to insert tuples to + * oldest_xmin xid used by the caller to determine which tuples are dead + * freeze_xid xid before which tuples will be frozen + * cutoff_multi multixact before which multis will be removed + * + * Returns an opaque RewriteState, allocated in current memory context, + * to be used in subsequent calls to the other functions. + */ +RewriteState +begin_heap_rewrite(Relation old_heap, Relation new_heap, TransactionId oldest_xmin, + TransactionId freeze_xid, MultiXactId cutoff_multi) +{ + RewriteState state; + MemoryContext rw_cxt; + MemoryContext old_cxt; + HASHCTL hash_ctl; + + /* + * To ease cleanup, make a separate context that will contain the + * RewriteState struct itself plus all subsidiary data. + */ + rw_cxt = AllocSetContextCreate(CurrentMemoryContext, + "Table rewrite", + ALLOCSET_DEFAULT_SIZES); + old_cxt = MemoryContextSwitchTo(rw_cxt); + + /* Create and fill in the state struct */ + state = palloc0(sizeof(RewriteStateData)); + + state->rs_old_rel = old_heap; + state->rs_new_rel = new_heap; + state->rs_buffer = (Page) palloc(BLCKSZ); + /* new_heap needn't be empty, just locked */ + state->rs_blockno = RelationGetNumberOfBlocks(new_heap); + state->rs_buffer_valid = false; + state->rs_oldest_xmin = oldest_xmin; + state->rs_freeze_xid = freeze_xid; + state->rs_cutoff_multi = cutoff_multi; + state->rs_cxt = rw_cxt; + + /* Initialize hash tables used to track update chains */ + hash_ctl.keysize = sizeof(TidHashKey); + hash_ctl.entrysize = sizeof(UnresolvedTupData); + hash_ctl.hcxt = state->rs_cxt; + + state->rs_unresolved_tups = + hash_create("Rewrite / Unresolved ctids", + 128, /* arbitrary initial size */ + &hash_ctl, + HASH_ELEM | HASH_BLOBS | HASH_CONTEXT); + + hash_ctl.entrysize = sizeof(OldToNewMappingData); + + state->rs_old_new_tid_map = + hash_create("Rewrite / Old to new tid map", + 128, /* arbitrary initial size */ + &hash_ctl, + HASH_ELEM | HASH_BLOBS | HASH_CONTEXT); + + MemoryContextSwitchTo(old_cxt); + + logical_begin_heap_rewrite(state); + + return state; +} + +/* + * End a rewrite. + * + * state and any other resources are freed. + */ +void +end_heap_rewrite(RewriteState state) +{ + HASH_SEQ_STATUS seq_status; + UnresolvedTup unresolved; + + /* + * Write any remaining tuples in the UnresolvedTups table. If we have any + * left, they should in fact be dead, but let's err on the safe side. + */ + hash_seq_init(&seq_status, state->rs_unresolved_tups); + + while ((unresolved = hash_seq_search(&seq_status)) != NULL) + { + ItemPointerSetInvalid(&unresolved->tuple->t_data->t_ctid); + raw_heap_insert(state, unresolved->tuple); + } + + /* Write the last page, if any */ + if (state->rs_buffer_valid) + { + if (RelationNeedsWAL(state->rs_new_rel)) + log_newpage(&state->rs_new_rel->rd_node, + MAIN_FORKNUM, + state->rs_blockno, + state->rs_buffer, + true); + + PageSetChecksumInplace(state->rs_buffer, state->rs_blockno); + + RelationOpenSmgr(state->rs_new_rel); + smgrextend(state->rs_new_rel->rd_smgr, MAIN_FORKNUM, state->rs_blockno, + (char *) state->rs_buffer, true); + } + + /* + * When we WAL-logged rel pages, we must nonetheless fsync them. The + * reason is the same as in storage.c's RelationCopyStorage(): we're + * writing data that's not in shared buffers, and so a CHECKPOINT + * occurring during the rewriteheap operation won't have fsync'd data we + * wrote before the checkpoint. + */ + if (RelationNeedsWAL(state->rs_new_rel)) + { + /* for an empty table, this could be first smgr access */ + RelationOpenSmgr(state->rs_new_rel); + smgrimmedsync(state->rs_new_rel->rd_smgr, MAIN_FORKNUM); + } + + logical_end_heap_rewrite(state); + + /* Deleting the context frees everything */ + MemoryContextDelete(state->rs_cxt); +} + +/* + * Add a tuple to the new heap. + * + * Visibility information is copied from the original tuple, except that + * we "freeze" very-old tuples. Note that since we scribble on new_tuple, + * it had better be temp storage not a pointer to the original tuple. + * + * state opaque state as returned by begin_heap_rewrite + * old_tuple original tuple in the old heap + * new_tuple new, rewritten tuple to be inserted to new heap + */ +void +rewrite_heap_tuple(RewriteState state, + HeapTuple old_tuple, HeapTuple new_tuple) +{ + MemoryContext old_cxt; + ItemPointerData old_tid; + TidHashKey hashkey; + bool found; + bool free_new; + + old_cxt = MemoryContextSwitchTo(state->rs_cxt); + + /* + * Copy the original tuple's visibility information into new_tuple. + * + * XXX we might later need to copy some t_infomask2 bits, too? Right now, + * we intentionally clear the HOT status bits. + */ + memcpy(&new_tuple->t_data->t_choice.t_heap, + &old_tuple->t_data->t_choice.t_heap, + sizeof(HeapTupleFields)); + + new_tuple->t_data->t_infomask &= ~HEAP_XACT_MASK; + new_tuple->t_data->t_infomask2 &= ~HEAP2_XACT_MASK; + new_tuple->t_data->t_infomask |= + old_tuple->t_data->t_infomask & HEAP_XACT_MASK; + + /* + * While we have our hands on the tuple, we may as well freeze any + * eligible xmin or xmax, so that future VACUUM effort can be saved. + */ + heap_freeze_tuple(new_tuple->t_data, + state->rs_old_rel->rd_rel->relfrozenxid, + state->rs_old_rel->rd_rel->relminmxid, + state->rs_freeze_xid, + state->rs_cutoff_multi); + + /* + * Invalid ctid means that ctid should point to the tuple itself. We'll + * override it later if the tuple is part of an update chain. + */ + ItemPointerSetInvalid(&new_tuple->t_data->t_ctid); + + /* + * If the tuple has been updated, check the old-to-new mapping hash table. + */ + if (!((old_tuple->t_data->t_infomask & HEAP_XMAX_INVALID) || + HeapTupleHeaderIsOnlyLocked(old_tuple->t_data)) && + !HeapTupleHeaderIndicatesMovedPartitions(old_tuple->t_data) && + !(ItemPointerEquals(&(old_tuple->t_self), + &(old_tuple->t_data->t_ctid)))) + { + OldToNewMapping mapping; + + memset(&hashkey, 0, sizeof(hashkey)); + hashkey.xmin = HeapTupleHeaderGetUpdateXid(old_tuple->t_data); + hashkey.tid = old_tuple->t_data->t_ctid; + + mapping = (OldToNewMapping) + hash_search(state->rs_old_new_tid_map, &hashkey, + HASH_FIND, NULL); + + if (mapping != NULL) + { + /* + * We've already copied the tuple that t_ctid points to, so we can + * set the ctid of this tuple to point to the new location, and + * insert it right away. + */ + new_tuple->t_data->t_ctid = mapping->new_tid; + + /* We don't need the mapping entry anymore */ + hash_search(state->rs_old_new_tid_map, &hashkey, + HASH_REMOVE, &found); + Assert(found); + } + else + { + /* + * We haven't seen the tuple t_ctid points to yet. Stash this + * tuple into unresolved_tups to be written later. + */ + UnresolvedTup unresolved; + + unresolved = hash_search(state->rs_unresolved_tups, &hashkey, + HASH_ENTER, &found); + Assert(!found); + + unresolved->old_tid = old_tuple->t_self; + unresolved->tuple = heap_copytuple(new_tuple); + + /* + * We can't do anything more now, since we don't know where the + * tuple will be written. + */ + MemoryContextSwitchTo(old_cxt); + return; + } + } + + /* + * Now we will write the tuple, and then check to see if it is the B tuple + * in any new or known pair. When we resolve a known pair, we will be + * able to write that pair's A tuple, and then we have to check if it + * resolves some other pair. Hence, we need a loop here. + */ + old_tid = old_tuple->t_self; + free_new = false; + + for (;;) + { + ItemPointerData new_tid; + + /* Insert the tuple and find out where it's put in new_heap */ + raw_heap_insert(state, new_tuple); + new_tid = new_tuple->t_self; + + logical_rewrite_heap_tuple(state, old_tid, new_tuple); + + /* + * If the tuple is the updated version of a row, and the prior version + * wouldn't be DEAD yet, then we need to either resolve the prior + * version (if it's waiting in rs_unresolved_tups), or make an entry + * in rs_old_new_tid_map (so we can resolve it when we do see it). The + * previous tuple's xmax would equal this one's xmin, so it's + * RECENTLY_DEAD if and only if the xmin is not before OldestXmin. + */ + if ((new_tuple->t_data->t_infomask & HEAP_UPDATED) && + !TransactionIdPrecedes(HeapTupleHeaderGetXmin(new_tuple->t_data), + state->rs_oldest_xmin)) + { + /* + * Okay, this is B in an update pair. See if we've seen A. + */ + UnresolvedTup unresolved; + + memset(&hashkey, 0, sizeof(hashkey)); + hashkey.xmin = HeapTupleHeaderGetXmin(new_tuple->t_data); + hashkey.tid = old_tid; + + unresolved = hash_search(state->rs_unresolved_tups, &hashkey, + HASH_FIND, NULL); + + if (unresolved != NULL) + { + /* + * We have seen and memorized the previous tuple already. Now + * that we know where we inserted the tuple its t_ctid points + * to, fix its t_ctid and insert it to the new heap. + */ + if (free_new) + heap_freetuple(new_tuple); + new_tuple = unresolved->tuple; + free_new = true; + old_tid = unresolved->old_tid; + new_tuple->t_data->t_ctid = new_tid; + + /* + * We don't need the hash entry anymore, but don't free its + * tuple just yet. + */ + hash_search(state->rs_unresolved_tups, &hashkey, + HASH_REMOVE, &found); + Assert(found); + + /* loop back to insert the previous tuple in the chain */ + continue; + } + else + { + /* + * Remember the new tid of this tuple. We'll use it to set the + * ctid when we find the previous tuple in the chain. + */ + OldToNewMapping mapping; + + mapping = hash_search(state->rs_old_new_tid_map, &hashkey, + HASH_ENTER, &found); + Assert(!found); + + mapping->new_tid = new_tid; + } + } + + /* Done with this (chain of) tuples, for now */ + if (free_new) + heap_freetuple(new_tuple); + break; + } + + MemoryContextSwitchTo(old_cxt); +} + +/* + * Register a dead tuple with an ongoing rewrite. Dead tuples are not + * copied to the new table, but we still make note of them so that we + * can release some resources earlier. + * + * Returns true if a tuple was removed from the unresolved_tups table. + * This indicates that that tuple, previously thought to be "recently dead", + * is now known really dead and won't be written to the output. + */ +bool +rewrite_heap_dead_tuple(RewriteState state, HeapTuple old_tuple) +{ + /* + * If we have already seen an earlier tuple in the update chain that + * points to this tuple, let's forget about that earlier tuple. It's in + * fact dead as well, our simple xmax < OldestXmin test in + * HeapTupleSatisfiesVacuum just wasn't enough to detect it. It happens + * when xmin of a tuple is greater than xmax, which sounds + * counter-intuitive but is perfectly valid. + * + * We don't bother to try to detect the situation the other way round, + * when we encounter the dead tuple first and then the recently dead one + * that points to it. If that happens, we'll have some unmatched entries + * in the UnresolvedTups hash table at the end. That can happen anyway, + * because a vacuum might have removed the dead tuple in the chain before + * us. + */ + UnresolvedTup unresolved; + TidHashKey hashkey; + bool found; + + memset(&hashkey, 0, sizeof(hashkey)); + hashkey.xmin = HeapTupleHeaderGetXmin(old_tuple->t_data); + hashkey.tid = old_tuple->t_self; + + unresolved = hash_search(state->rs_unresolved_tups, &hashkey, + HASH_FIND, NULL); + + if (unresolved != NULL) + { + /* Need to free the contained tuple as well as the hashtable entry */ + heap_freetuple(unresolved->tuple); + hash_search(state->rs_unresolved_tups, &hashkey, + HASH_REMOVE, &found); + Assert(found); + return true; + } + + return false; +} + +/* + * Insert a tuple to the new relation. This has to track heap_insert + * and its subsidiary functions! + * + * t_self of the tuple is set to the new TID of the tuple. If t_ctid of the + * tuple is invalid on entry, it's replaced with the new TID as well (in + * the inserted data only, not in the caller's copy). + */ +static void +raw_heap_insert(RewriteState state, HeapTuple tup) +{ + Page page = state->rs_buffer; + Size pageFreeSpace, + saveFreeSpace; + Size len; + OffsetNumber newoff; + HeapTuple heaptup; + + /* + * If the new tuple is too big for storage or contains already toasted + * out-of-line attributes from some other relation, invoke the toaster. + * + * Note: below this point, heaptup is the data we actually intend to store + * into the relation; tup is the caller's original untoasted data. + */ + if (state->rs_new_rel->rd_rel->relkind == RELKIND_TOASTVALUE) + { + /* toast table entries should never be recursively toasted */ + Assert(!HeapTupleHasExternal(tup)); + heaptup = tup; + } + else if (HeapTupleHasExternal(tup) || tup->t_len > TOAST_TUPLE_THRESHOLD) + { + int options = HEAP_INSERT_SKIP_FSM; + + /* + * While rewriting the heap for VACUUM FULL / CLUSTER, make sure data + * for the TOAST table are not logically decoded. The main heap is + * WAL-logged as XLOG FPI records, which are not logically decoded. + */ + options |= HEAP_INSERT_NO_LOGICAL; + + heaptup = heap_toast_insert_or_update(state->rs_new_rel, tup, NULL, + options); + } + else + heaptup = tup; + + len = MAXALIGN(heaptup->t_len); /* be conservative */ + + /* + * If we're gonna fail for oversize tuple, do it right away + */ + if (len > MaxHeapTupleSize) + ereport(ERROR, + (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), + errmsg("row is too big: size %zu, maximum size %zu", + len, MaxHeapTupleSize))); + + /* Compute desired extra freespace due to fillfactor option */ + saveFreeSpace = RelationGetTargetPageFreeSpace(state->rs_new_rel, + HEAP_DEFAULT_FILLFACTOR); + + /* Now we can check to see if there's enough free space already. */ + if (state->rs_buffer_valid) + { + pageFreeSpace = PageGetHeapFreeSpace(page); + + if (len + saveFreeSpace > pageFreeSpace) + { + /* + * Doesn't fit, so write out the existing page. It always + * contains a tuple. Hence, unlike RelationGetBufferForTuple(), + * enforce saveFreeSpace unconditionally. + */ + + /* XLOG stuff */ + if (RelationNeedsWAL(state->rs_new_rel)) + log_newpage(&state->rs_new_rel->rd_node, + MAIN_FORKNUM, + state->rs_blockno, + page, + true); + + /* + * Now write the page. We say skipFsync = true because there's no + * need for smgr to schedule an fsync for this write; we'll do it + * ourselves in end_heap_rewrite. + */ + RelationOpenSmgr(state->rs_new_rel); + + PageSetChecksumInplace(page, state->rs_blockno); + + smgrextend(state->rs_new_rel->rd_smgr, MAIN_FORKNUM, + state->rs_blockno, (char *) page, true); + + state->rs_blockno++; + state->rs_buffer_valid = false; + } + } + + if (!state->rs_buffer_valid) + { + /* Initialize a new empty page */ + PageInit(page, BLCKSZ, 0); + state->rs_buffer_valid = true; + } + + /* And now we can insert the tuple into the page */ + newoff = PageAddItem(page, (Item) heaptup->t_data, heaptup->t_len, + InvalidOffsetNumber, false, true); + if (newoff == InvalidOffsetNumber) + elog(ERROR, "failed to add tuple"); + + /* Update caller's t_self to the actual position where it was stored */ + ItemPointerSet(&(tup->t_self), state->rs_blockno, newoff); + + /* + * Insert the correct position into CTID of the stored tuple, too, if the + * caller didn't supply a valid CTID. + */ + if (!ItemPointerIsValid(&tup->t_data->t_ctid)) + { + ItemId newitemid; + HeapTupleHeader onpage_tup; + + newitemid = PageGetItemId(page, newoff); + onpage_tup = (HeapTupleHeader) PageGetItem(page, newitemid); + + onpage_tup->t_ctid = tup->t_self; + } + + /* If heaptup is a private copy, release it. */ + if (heaptup != tup) + heap_freetuple(heaptup); +} + +/* ------------------------------------------------------------------------ + * Logical rewrite support + * + * When doing logical decoding - which relies on using cmin/cmax of catalog + * tuples, via xl_heap_new_cid records - heap rewrites have to log enough + * information to allow the decoding backend to updates its internal mapping + * of (relfilenode,ctid) => (cmin, cmax) to be correct for the rewritten heap. + * + * For that, every time we find a tuple that's been modified in a catalog + * relation within the xmin horizon of any decoding slot, we log a mapping + * from the old to the new location. + * + * To deal with rewrites that abort the filename of a mapping file contains + * the xid of the transaction performing the rewrite, which then can be + * checked before being read in. + * + * For efficiency we don't immediately spill every single map mapping for a + * row to disk but only do so in batches when we've collected several of them + * in memory or when end_heap_rewrite() has been called. + * + * Crash-Safety: This module diverts from the usual patterns of doing WAL + * since it cannot rely on checkpoint flushing out all buffers and thus + * waiting for exclusive locks on buffers. Usually the XLogInsert() covering + * buffer modifications is performed while the buffer(s) that are being + * modified are exclusively locked guaranteeing that both the WAL record and + * the modified heap are on either side of the checkpoint. But since the + * mapping files we log aren't in shared_buffers that interlock doesn't work. + * + * Instead we simply write the mapping files out to disk, *before* the + * XLogInsert() is performed. That guarantees that either the XLogInsert() is + * inserted after the checkpoint's redo pointer or that the checkpoint (via + * CheckPointLogicalRewriteHeap()) has flushed the (partial) mapping file to + * disk. That leaves the tail end that has not yet been flushed open to + * corruption, which is solved by including the current offset in the + * xl_heap_rewrite_mapping records and truncating the mapping file to it + * during replay. Every time a rewrite is finished all generated mapping files + * are synced to disk. + * + * Note that if we were only concerned about crash safety we wouldn't have to + * deal with WAL logging at all - an fsync() at the end of a rewrite would be + * sufficient for crash safety. Any mapping that hasn't been safely flushed to + * disk has to be by an aborted (explicitly or via a crash) transaction and is + * ignored by virtue of the xid in its name being subject to a + * TransactionDidCommit() check. But we want to support having standbys via + * physical replication, both for availability and to do logical decoding + * there. + * ------------------------------------------------------------------------ + */ + +/* + * Do preparations for logging logical mappings during a rewrite if + * necessary. If we detect that we don't need to log anything we'll prevent + * any further action by the various logical rewrite functions. + */ +static void +logical_begin_heap_rewrite(RewriteState state) +{ + HASHCTL hash_ctl; + TransactionId logical_xmin; + + /* + * We only need to persist these mappings if the rewritten table can be + * accessed during logical decoding, if not, we can skip doing any + * additional work. + */ + state->rs_logical_rewrite = + RelationIsAccessibleInLogicalDecoding(state->rs_old_rel); + + if (!state->rs_logical_rewrite) + return; + + ProcArrayGetReplicationSlotXmin(NULL, &logical_xmin); + + /* + * If there are no logical slots in progress we don't need to do anything, + * there cannot be any remappings for relevant rows yet. The relation's + * lock protects us against races. + */ + if (logical_xmin == InvalidTransactionId) + { + state->rs_logical_rewrite = false; + return; + } + + state->rs_logical_xmin = logical_xmin; + state->rs_begin_lsn = GetXLogInsertRecPtr(); + state->rs_num_rewrite_mappings = 0; + + hash_ctl.keysize = sizeof(TransactionId); + hash_ctl.entrysize = sizeof(RewriteMappingFile); + hash_ctl.hcxt = state->rs_cxt; + + state->rs_logical_mappings = + hash_create("Logical rewrite mapping", + 128, /* arbitrary initial size */ + &hash_ctl, + HASH_ELEM | HASH_BLOBS | HASH_CONTEXT); +} + +/* + * Flush all logical in-memory mappings to disk, but don't fsync them yet. + */ +static void +logical_heap_rewrite_flush_mappings(RewriteState state) +{ + HASH_SEQ_STATUS seq_status; + RewriteMappingFile *src; + dlist_mutable_iter iter; + + Assert(state->rs_logical_rewrite); + + /* no logical rewrite in progress, no need to iterate over mappings */ + if (state->rs_num_rewrite_mappings == 0) + return; + + elog(DEBUG1, "flushing %u logical rewrite mapping entries", + state->rs_num_rewrite_mappings); + + hash_seq_init(&seq_status, state->rs_logical_mappings); + while ((src = (RewriteMappingFile *) hash_seq_search(&seq_status)) != NULL) + { + char *waldata; + char *waldata_start; + xl_heap_rewrite_mapping xlrec; + Oid dboid; + uint32 len; + int written; + + /* this file hasn't got any new mappings */ + if (src->num_mappings == 0) + continue; + + if (state->rs_old_rel->rd_rel->relisshared) + dboid = InvalidOid; + else + dboid = MyDatabaseId; + + xlrec.num_mappings = src->num_mappings; + xlrec.mapped_rel = RelationGetRelid(state->rs_old_rel); + xlrec.mapped_xid = src->xid; + xlrec.mapped_db = dboid; + xlrec.offset = src->off; + xlrec.start_lsn = state->rs_begin_lsn; + + /* write all mappings consecutively */ + len = src->num_mappings * sizeof(LogicalRewriteMappingData); + waldata_start = waldata = palloc(len); + + /* + * collect data we need to write out, but don't modify ondisk data yet + */ + dlist_foreach_modify(iter, &src->mappings) + { + RewriteMappingDataEntry *pmap; + + pmap = dlist_container(RewriteMappingDataEntry, node, iter.cur); + + memcpy(waldata, &pmap->map, sizeof(pmap->map)); + waldata += sizeof(pmap->map); + + /* remove from the list and free */ + dlist_delete(&pmap->node); + pfree(pmap); + + /* update bookkeeping */ + state->rs_num_rewrite_mappings--; + src->num_mappings--; + } + + Assert(src->num_mappings == 0); + Assert(waldata == waldata_start + len); + + /* + * Note that we deviate from the usual WAL coding practices here, + * check the above "Logical rewrite support" comment for reasoning. + */ + written = FileWrite(src->vfd, waldata_start, len, src->off, + WAIT_EVENT_LOGICAL_REWRITE_WRITE); + if (written != len) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not write to file \"%s\", wrote %d of %d: %m", src->path, + written, len))); + src->off += len; + + XLogBeginInsert(); + XLogRegisterData((char *) (&xlrec), sizeof(xlrec)); + XLogRegisterData(waldata_start, len); + + /* write xlog record */ + XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_REWRITE); + + pfree(waldata_start); + } + Assert(state->rs_num_rewrite_mappings == 0); +} + +/* + * Logical remapping part of end_heap_rewrite(). + */ +static void +logical_end_heap_rewrite(RewriteState state) +{ + HASH_SEQ_STATUS seq_status; + RewriteMappingFile *src; + + /* done, no logical rewrite in progress */ + if (!state->rs_logical_rewrite) + return; + + /* writeout remaining in-memory entries */ + if (state->rs_num_rewrite_mappings > 0) + logical_heap_rewrite_flush_mappings(state); + + /* Iterate over all mappings we have written and fsync the files. */ + hash_seq_init(&seq_status, state->rs_logical_mappings); + while ((src = (RewriteMappingFile *) hash_seq_search(&seq_status)) != NULL) + { + if (FileSync(src->vfd, WAIT_EVENT_LOGICAL_REWRITE_SYNC) != 0) + ereport(data_sync_elevel(ERROR), + (errcode_for_file_access(), + errmsg("could not fsync file \"%s\": %m", src->path))); + FileClose(src->vfd); + } + /* memory context cleanup will deal with the rest */ +} + +/* + * Log a single (old->new) mapping for 'xid'. + */ +static void +logical_rewrite_log_mapping(RewriteState state, TransactionId xid, + LogicalRewriteMappingData *map) +{ + RewriteMappingFile *src; + RewriteMappingDataEntry *pmap; + Oid relid; + bool found; + + relid = RelationGetRelid(state->rs_old_rel); + + /* look for existing mappings for this 'mapped' xid */ + src = hash_search(state->rs_logical_mappings, &xid, + HASH_ENTER, &found); + + /* + * We haven't yet had the need to map anything for this xid, create + * per-xid data structures. + */ + if (!found) + { + char path[MAXPGPATH]; + Oid dboid; + + if (state->rs_old_rel->rd_rel->relisshared) + dboid = InvalidOid; + else + dboid = MyDatabaseId; + + snprintf(path, MAXPGPATH, + "pg_logical/mappings/" LOGICAL_REWRITE_FORMAT, + dboid, relid, + LSN_FORMAT_ARGS(state->rs_begin_lsn), + xid, GetCurrentTransactionId()); + + dlist_init(&src->mappings); + src->num_mappings = 0; + src->off = 0; + memcpy(src->path, path, sizeof(path)); + src->vfd = PathNameOpenFile(path, + O_CREAT | O_EXCL | O_WRONLY | PG_BINARY); + if (src->vfd < 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not create file \"%s\": %m", path))); + } + + pmap = MemoryContextAlloc(state->rs_cxt, + sizeof(RewriteMappingDataEntry)); + memcpy(&pmap->map, map, sizeof(LogicalRewriteMappingData)); + dlist_push_tail(&src->mappings, &pmap->node); + src->num_mappings++; + state->rs_num_rewrite_mappings++; + + /* + * Write out buffer every time we've too many in-memory entries across all + * mapping files. + */ + if (state->rs_num_rewrite_mappings >= 1000 /* arbitrary number */ ) + logical_heap_rewrite_flush_mappings(state); +} + +/* + * Perform logical remapping for a tuple that's mapped from old_tid to + * new_tuple->t_self by rewrite_heap_tuple() if necessary for the tuple. + */ +static void +logical_rewrite_heap_tuple(RewriteState state, ItemPointerData old_tid, + HeapTuple new_tuple) +{ + ItemPointerData new_tid = new_tuple->t_self; + TransactionId cutoff = state->rs_logical_xmin; + TransactionId xmin; + TransactionId xmax; + bool do_log_xmin = false; + bool do_log_xmax = false; + LogicalRewriteMappingData map; + + /* no logical rewrite in progress, we don't need to log anything */ + if (!state->rs_logical_rewrite) + return; + + xmin = HeapTupleHeaderGetXmin(new_tuple->t_data); + /* use *GetUpdateXid to correctly deal with multixacts */ + xmax = HeapTupleHeaderGetUpdateXid(new_tuple->t_data); + + /* + * Log the mapping iff the tuple has been created recently. + */ + if (TransactionIdIsNormal(xmin) && !TransactionIdPrecedes(xmin, cutoff)) + do_log_xmin = true; + + if (!TransactionIdIsNormal(xmax)) + { + /* + * no xmax is set, can't have any permanent ones, so this check is + * sufficient + */ + } + else if (HEAP_XMAX_IS_LOCKED_ONLY(new_tuple->t_data->t_infomask)) + { + /* only locked, we don't care */ + } + else if (!TransactionIdPrecedes(xmax, cutoff)) + { + /* tuple has been deleted recently, log */ + do_log_xmax = true; + } + + /* if neither needs to be logged, we're done */ + if (!do_log_xmin && !do_log_xmax) + return; + + /* fill out mapping information */ + map.old_node = state->rs_old_rel->rd_node; + map.old_tid = old_tid; + map.new_node = state->rs_new_rel->rd_node; + map.new_tid = new_tid; + + /* --- + * Now persist the mapping for the individual xids that are affected. We + * need to log for both xmin and xmax if they aren't the same transaction + * since the mapping files are per "affected" xid. + * We don't muster all that much effort detecting whether xmin and xmax + * are actually the same transaction, we just check whether the xid is the + * same disregarding subtransactions. Logging too much is relatively + * harmless and we could never do the check fully since subtransaction + * data is thrown away during restarts. + * --- + */ + if (do_log_xmin) + logical_rewrite_log_mapping(state, xmin, &map); + /* separately log mapping for xmax unless it'd be redundant */ + if (do_log_xmax && !TransactionIdEquals(xmin, xmax)) + logical_rewrite_log_mapping(state, xmax, &map); +} + +/* + * Replay XLOG_HEAP2_REWRITE records + */ +void +heap_xlog_logical_rewrite(XLogReaderState *r) +{ + char path[MAXPGPATH]; + int fd; + xl_heap_rewrite_mapping *xlrec; + uint32 len; + char *data; + + xlrec = (xl_heap_rewrite_mapping *) XLogRecGetData(r); + + snprintf(path, MAXPGPATH, + "pg_logical/mappings/" LOGICAL_REWRITE_FORMAT, + xlrec->mapped_db, xlrec->mapped_rel, + LSN_FORMAT_ARGS(xlrec->start_lsn), + xlrec->mapped_xid, XLogRecGetXid(r)); + + fd = OpenTransientFile(path, + O_CREAT | O_WRONLY | PG_BINARY); + if (fd < 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not create file \"%s\": %m", path))); + + /* + * Truncate all data that's not guaranteed to have been safely fsynced (by + * previous record or by the last checkpoint). + */ + pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_TRUNCATE); + if (ftruncate(fd, xlrec->offset) != 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not truncate file \"%s\" to %u: %m", + path, (uint32) xlrec->offset))); + pgstat_report_wait_end(); + + data = XLogRecGetData(r) + sizeof(*xlrec); + + len = xlrec->num_mappings * sizeof(LogicalRewriteMappingData); + + /* write out tail end of mapping file (again) */ + errno = 0; + pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_MAPPING_WRITE); + if (pg_pwrite(fd, data, len, xlrec->offset) != len) + { + /* if write didn't set errno, assume problem is no disk space */ + if (errno == 0) + errno = ENOSPC; + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not write to file \"%s\": %m", path))); + } + pgstat_report_wait_end(); + + /* + * Now fsync all previously written data. We could improve things and only + * do this for the last write to a file, but the required bookkeeping + * doesn't seem worth the trouble. + */ + pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_MAPPING_SYNC); + if (pg_fsync(fd) != 0) + ereport(data_sync_elevel(ERROR), + (errcode_for_file_access(), + errmsg("could not fsync file \"%s\": %m", path))); + pgstat_report_wait_end(); + + if (CloseTransientFile(fd) != 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not close file \"%s\": %m", path))); +} + +/* --- + * Perform a checkpoint for logical rewrite mappings + * + * This serves two tasks: + * 1) Remove all mappings not needed anymore based on the logical restart LSN + * 2) Flush all remaining mappings to disk, so that replay after a checkpoint + * only has to deal with the parts of a mapping that have been written out + * after the checkpoint started. + * --- + */ +void +CheckPointLogicalRewriteHeap(void) +{ + XLogRecPtr cutoff; + XLogRecPtr redo; + DIR *mappings_dir; + struct dirent *mapping_de; + char path[MAXPGPATH + 20]; + + /* + * We start of with a minimum of the last redo pointer. No new decoding + * slot will start before that, so that's a safe upper bound for removal. + */ + redo = GetRedoRecPtr(); + + /* now check for the restart ptrs from existing slots */ + cutoff = ReplicationSlotsComputeLogicalRestartLSN(); + + /* don't start earlier than the restart lsn */ + if (cutoff != InvalidXLogRecPtr && redo < cutoff) + cutoff = redo; + + mappings_dir = AllocateDir("pg_logical/mappings"); + while ((mapping_de = ReadDir(mappings_dir, "pg_logical/mappings")) != NULL) + { + struct stat statbuf; + Oid dboid; + Oid relid; + XLogRecPtr lsn; + TransactionId rewrite_xid; + TransactionId create_xid; + uint32 hi, + lo; + + if (strcmp(mapping_de->d_name, ".") == 0 || + strcmp(mapping_de->d_name, "..") == 0) + continue; + + snprintf(path, sizeof(path), "pg_logical/mappings/%s", mapping_de->d_name); + if (lstat(path, &statbuf) == 0 && !S_ISREG(statbuf.st_mode)) + continue; + + /* Skip over files that cannot be ours. */ + if (strncmp(mapping_de->d_name, "map-", 4) != 0) + continue; + + if (sscanf(mapping_de->d_name, LOGICAL_REWRITE_FORMAT, + &dboid, &relid, &hi, &lo, &rewrite_xid, &create_xid) != 6) + elog(ERROR, "could not parse filename \"%s\"", mapping_de->d_name); + + lsn = ((uint64) hi) << 32 | lo; + + if (lsn < cutoff || cutoff == InvalidXLogRecPtr) + { + elog(DEBUG1, "removing logical rewrite file \"%s\"", path); + if (unlink(path) < 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not remove file \"%s\": %m", path))); + } + else + { + /* on some operating systems fsyncing a file requires O_RDWR */ + int fd = OpenTransientFile(path, O_RDWR | PG_BINARY); + + /* + * The file cannot vanish due to concurrency since this function + * is the only one removing logical mappings and only one + * checkpoint can be in progress at a time. + */ + if (fd < 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not open file \"%s\": %m", path))); + + /* + * We could try to avoid fsyncing files that either haven't + * changed or have only been created since the checkpoint's start, + * but it's currently not deemed worth the effort. + */ + pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_CHECKPOINT_SYNC); + if (pg_fsync(fd) != 0) + ereport(data_sync_elevel(ERROR), + (errcode_for_file_access(), + errmsg("could not fsync file \"%s\": %m", path))); + pgstat_report_wait_end(); + + if (CloseTransientFile(fd) != 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not close file \"%s\": %m", path))); + } + } + FreeDir(mappings_dir); + + /* persist directory entries to disk */ + fsync_fname("pg_logical/mappings", true); +} |