diff options
Diffstat (limited to 'src/backend/access/nbtree/nbtree.c')
| -rw-r--r-- | src/backend/access/nbtree/nbtree.c | 111 |
1 files changed, 23 insertions, 88 deletions
diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c index c67235ab807..065b5290b0d 100644 --- a/src/backend/access/nbtree/nbtree.c +++ b/src/backend/access/nbtree/nbtree.c @@ -46,8 +46,6 @@ typedef struct IndexBulkDeleteCallback callback; void *callback_state; BTCycleId cycleid; - BlockNumber lastBlockVacuumed; /* highest blkno actually vacuumed */ - BlockNumber lastBlockLocked; /* highest blkno we've cleanup-locked */ BlockNumber totFreePages; /* true total # of free pages */ TransactionId oldestBtpoXact; MemoryContext pagedelcontext; @@ -978,8 +976,6 @@ btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats, vstate.callback = callback; vstate.callback_state = callback_state; vstate.cycleid = cycleid; - vstate.lastBlockVacuumed = BTREE_METAPAGE; /* Initialise at first block */ - vstate.lastBlockLocked = BTREE_METAPAGE; vstate.totFreePages = 0; vstate.oldestBtpoXact = InvalidTransactionId; @@ -1040,39 +1036,6 @@ btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats, } } - /* - * Check to see if we need to issue one final WAL record for this index, - * which may be needed for correctness on a hot standby node when non-MVCC - * index scans could take place. - * - * If the WAL is replayed in hot standby, the replay process needs to get - * cleanup locks on all index leaf pages, just as we've been doing here. - * However, we won't issue any WAL records about pages that have no items - * to be deleted. For pages between pages we've vacuumed, the replay code - * will take locks under the direction of the lastBlockVacuumed fields in - * the XLOG_BTREE_VACUUM WAL records. To cover pages after the last one - * we vacuum, we need to issue a dummy XLOG_BTREE_VACUUM WAL record - * against the last leaf page in the index, if that one wasn't vacuumed. - */ - if (XLogStandbyInfoActive() && - vstate.lastBlockVacuumed < vstate.lastBlockLocked) - { - Buffer buf; - - /* - * The page should be valid, but we can't use _bt_getbuf() because we - * want to use a nondefault buffer access strategy. Since we aren't - * going to delete any items, getting cleanup lock again is probably - * overkill, but for consistency do that anyway. - */ - buf = ReadBufferExtended(rel, MAIN_FORKNUM, vstate.lastBlockLocked, - RBM_NORMAL, info->strategy); - LockBufferForCleanup(buf); - _bt_checkpage(rel, buf); - _bt_delitems_vacuum(rel, buf, NULL, 0, vstate.lastBlockVacuumed); - _bt_relbuf(rel, buf); - } - MemoryContextDelete(vstate.pagedelcontext); /* @@ -1204,13 +1167,6 @@ restart: LockBufferForCleanup(buf); /* - * Remember highest leaf page number we've taken cleanup lock on; see - * notes in btvacuumscan - */ - if (blkno > vstate->lastBlockLocked) - vstate->lastBlockLocked = blkno; - - /* * Check whether we need to recurse back to earlier pages. What we * are concerned about is a page split that happened since we started * the vacuum scan. If the split moved some tuples to a lower page @@ -1225,8 +1181,10 @@ restart: recurse_to = opaque->btpo_next; /* - * Scan over all items to see which ones need deleted according to the - * callback function. + * When each VACUUM begins, it determines an OldestXmin cutoff value. + * Tuples before the cutoff are removed by VACUUM. Scan over all + * items to see which ones need to be deleted according to cutoff + * point using callback. */ ndeletable = 0; minoff = P_FIRSTDATAKEY(opaque); @@ -1245,25 +1203,24 @@ restart: htup = &(itup->t_tid); /* - * During Hot Standby we currently assume that - * XLOG_BTREE_VACUUM records do not produce conflicts. That is - * only true as long as the callback function depends only - * upon whether the index tuple refers to heap tuples removed - * in the initial heap scan. When vacuum starts it derives a - * value of OldestXmin. Backends taking later snapshots could - * have a RecentGlobalXmin with a later xid than the vacuum's - * OldestXmin, so it is possible that row versions deleted - * after OldestXmin could be marked as killed by other - * backends. The callback function *could* look at the index - * tuple state in isolation and decide to delete the index - * tuple, though currently it does not. If it ever did, we - * would need to reconsider whether XLOG_BTREE_VACUUM records - * should cause conflicts. If they did cause conflicts they - * would be fairly harsh conflicts, since we haven't yet - * worked out a way to pass a useful value for - * latestRemovedXid on the XLOG_BTREE_VACUUM records. This - * applies to *any* type of index that marks index tuples as - * killed. + * Hot Standby assumes that it's okay that XLOG_BTREE_VACUUM + * records do not produce their own conflicts. This is safe + * as long as the callback function only considers whether the + * index tuple refers to pre-cutoff heap tuples that were + * certainly already pruned away during VACUUM's initial heap + * scan by the time we get here. (We can rely on conflicts + * produced by heap pruning, rather than producing our own + * now.) + * + * Backends with snapshots acquired after a VACUUM starts but + * before it finishes could have a RecentGlobalXmin with a + * later xid than the VACUUM's OldestXmin cutoff. These + * backends might happen to opportunistically mark some index + * tuples LP_DEAD before we reach them, even though they may + * be after our cutoff. We don't try to kill these "extra" + * index tuples in _bt_delitems_vacuum(). This keep things + * simple, and allows us to always avoid generating our own + * conflicts. */ if (callback(htup, callback_state)) deletable[ndeletable++] = offnum; @@ -1276,29 +1233,7 @@ restart: */ if (ndeletable > 0) { - /* - * Notice that the issued XLOG_BTREE_VACUUM WAL record includes - * all information to the replay code to allow it to get a cleanup - * lock on all pages between the previous lastBlockVacuumed and - * this page. This ensures that WAL replay locks all leaf pages at - * some point, which is important should non-MVCC scans be - * requested. This is currently unused on standby, but we record - * it anyway, so that the WAL contains the required information. - * - * Since we can visit leaf pages out-of-order when recursing, - * replay might end up locking such pages an extra time, but it - * doesn't seem worth the amount of bookkeeping it'd take to avoid - * that. - */ - _bt_delitems_vacuum(rel, buf, deletable, ndeletable, - vstate->lastBlockVacuumed); - - /* - * Remember highest leaf page number we've issued a - * XLOG_BTREE_VACUUM WAL record for. - */ - if (blkno > vstate->lastBlockVacuumed) - vstate->lastBlockVacuumed = blkno; + _bt_delitems_vacuum(rel, buf, deletable, ndeletable); stats->tuples_removed += ndeletable; /* must recompute maxoff */ |