On Wed, 2008-12-17 at 21:26 +0000, Simon Riggs wrote: > Hot Standby won't work with hash indexes because they are > non-recoverable. > > We have a number of ways of dealing with this:
> 2. Specific Solution: make hashcostestimate() massively increase cost of > scans during recovery so that they will very seldom be picked and make > hashbeginscan() refuse scans during recovery in case they do happen > (2) seems most appropriate, since it will last only until (1) is > complete in a later release. Code *fragment* enclosed here for discussion. (Not an independent patch) -- Simon Riggs www.2ndQuadrant.com PostgreSQL Training, Services and Support
Index: src/backend/access/hash/hash.c =================================================================== RCS file: /home/sriggs/pg/REPOSITORY/pgsql/src/backend/access/hash/hash.c,v retrieving revision 1.107 diff -c -r1.107 hash.c *** src/backend/access/hash/hash.c 13 Nov 2008 17:42:10 -0000 1.107 --- src/backend/access/hash/hash.c 17 Dec 2008 22:46:43 -0000 *************** *** 341,346 **** --- 341,357 ---- IndexScanDesc scan; HashScanOpaque so; + /* + * Hash indexes are not recoverable, so should not be used + * during recovery mode. We try to avoid this by tweaking the + * cost of hash index scans during recovery (see selfuncs.c), + * but we may still get called, so specifically prevent scans here. + * This is a reasonably ugly hack that we expect to remove again + * as soon as hash indexes write WAL records. + */ + if (IsRecoveryProcessingMode()) + elog(ERROR, "Cannot use hash index while recovery is in progress"); + scan = RelationGetIndexScan(rel, keysz, scankey); so = (HashScanOpaque) palloc(sizeof(HashScanOpaqueData)); so->hashso_bucket_valid = false; Index: src/backend/utils/adt/selfuncs.c =================================================================== RCS file: /home/sriggs/pg/REPOSITORY/pgsql/src/backend/utils/adt/selfuncs.c,v retrieving revision 1.257 diff -c -r1.257 selfuncs.c *** src/backend/utils/adt/selfuncs.c 23 Oct 2008 00:24:50 -0000 1.257 --- src/backend/utils/adt/selfuncs.c 17 Dec 2008 22:41:17 -0000 *************** *** 5911,5919 **** Selectivity *indexSelectivity = (Selectivity *) PG_GETARG_POINTER(6); double *indexCorrelation = (double *) PG_GETARG_POINTER(7); genericcostestimate(root, index, indexQuals, outer_rel, 0.0, indexStartupCost, indexTotalCost, ! indexSelectivity, indexCorrelation); PG_RETURN_VOID(); } --- 5911,5929 ---- Selectivity *indexSelectivity = (Selectivity *) PG_GETARG_POINTER(6); double *indexCorrelation = (double *) PG_GETARG_POINTER(7); + /* + * Hash indexes are not recoverable, so should not be used + * during recovery mode. Dissuade attempts to use them by adding + * the same disableCost as if enable_indexscan = off was selected. + * This is a reasonably ugly hack that we expect to remove again + * as soon as hash indexes write WAL records. + */ + if (IsRecoveryProcessingMode()) + *indexStartupCost += 100000000.0; + genericcostestimate(root, index, indexQuals, outer_rel, 0.0, indexStartupCost, indexTotalCost, ! indexSelectivity, indexCorrelation); PG_RETURN_VOID(); }
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