From 2cc41acd8fa3ebb8f0501c6102a253fb7053cf46 Mon Sep 17 00:00:00 2001 From: Kevin Grittner Date: Fri, 6 May 2016 07:47:12 -0500 Subject: Fix hash index vs "snapshot too old" problemms Hash indexes are not WAL-logged, and so do not maintain the LSN of index pages. Since the "snapshot too old" feature counts on detecting error conditions using the LSN of a table and all indexes on it, this makes it impossible to safely do early vacuuming on any table with a hash index, so add this to the tests for whether the xid used to vacuum a table can be adjusted based on old_snapshot_threshold. While at it, add a paragraph to the docs for old_snapshot_threshold which specifically mentions this and other aspects of the feature which may otherwise surprise users. Problem reported and patch reviewed by Amit Kapila --- src/backend/utils/cache/relcache.c | 46 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 46 insertions(+) (limited to 'src/backend/utils/cache/relcache.c') diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c index 432feefa609..79cc3df590a 100644 --- a/src/backend/utils/cache/relcache.c +++ b/src/backend/utils/cache/relcache.c @@ -5312,6 +5312,52 @@ RelationIdIsInInitFile(Oid relationId) return RelationSupportsSysCache(relationId); } +/* + * Tells whether any index for the relation is unlogged. + * + * Any index using the hash AM is implicitly unlogged. + * + * Note: There doesn't seem to be any way to have an unlogged index attached + * to a permanent table except to create a hash index, but it seems best to + * keep this general so that it returns sensible results even when they seem + * obvious (like for an unlogged table) and to handle possible future unlogged + * indexes on permanent tables. + */ +bool +RelationHasUnloggedIndex(Relation rel) +{ + List *indexoidlist; + ListCell *indexoidscan; + bool result = false; + + indexoidlist = RelationGetIndexList(rel); + + foreach(indexoidscan, indexoidlist) + { + Oid indexoid = lfirst_oid(indexoidscan); + HeapTuple tp; + Form_pg_class reltup; + + tp = SearchSysCache1(RELOID, ObjectIdGetDatum(indexoid)); + if (!HeapTupleIsValid(tp)) + elog(ERROR, "cache lookup failed for relation %u", indexoid); + reltup = (Form_pg_class) GETSTRUCT(tp); + + if (reltup->relpersistence == RELPERSISTENCE_UNLOGGED + || reltup->relam == HASH_AM_OID) + result = true; + + ReleaseSysCache(tp); + + if (result == true) + break; + } + + list_free(indexoidlist); + + return result; +} + /* * Invalidate (remove) the init file during commit of a transaction that * changed one or more of the relation cache entries that are kept in the -- cgit v1.2.3