diff options
Diffstat (limited to 'src/backend/access/hash/hash.c')
| -rw-r--r-- | src/backend/access/hash/hash.c | 20 |
1 files changed, 17 insertions, 3 deletions
diff --git a/src/backend/access/hash/hash.c b/src/backend/access/hash/hash.c index 19695ee1022..30c82e191c6 100644 --- a/src/backend/access/hash/hash.c +++ b/src/backend/access/hash/hash.c @@ -22,6 +22,7 @@ #include "access/relscan.h" #include "catalog/index.h" #include "commands/vacuum.h" +#include "miscadmin.h" #include "optimizer/plancat.h" #include "utils/index_selfuncs.h" #include "utils/rel.h" @@ -97,6 +98,7 @@ hashbuild(Relation heap, Relation index, IndexInfo *indexInfo) double reltuples; double allvisfrac; uint32 num_buckets; + long sort_threshold; HashBuildState buildstate; /* @@ -120,12 +122,24 @@ hashbuild(Relation heap, Relation index, IndexInfo *indexInfo) * then we'll thrash horribly. To prevent that scenario, we can sort the * tuples by (expected) bucket number. However, such a sort is useless * overhead when the index does fit in RAM. We choose to sort if the - * initial index size exceeds NBuffers. + * initial index size exceeds maintenance_work_mem, or the number of + * buffers usable for the index, whichever is less. (Limiting by the + * number of buffers should reduce thrashing between PG buffers and kernel + * buffers, which seems useful even if no physical I/O results. Limiting + * by maintenance_work_mem is useful to allow easy testing of the sort + * code path, and may be useful to DBAs as an additional control knob.) * * NOTE: this test will need adjustment if a bucket is ever different from - * one page. + * one page. Also, "initial index size" accounting does not include the + * metapage, nor the first bitmap page. */ - if (num_buckets >= (uint32) NBuffers) + sort_threshold = (maintenance_work_mem * 1024L) / BLCKSZ; + if (index->rd_rel->relpersistence != RELPERSISTENCE_TEMP) + sort_threshold = Min(sort_threshold, NBuffers); + else + sort_threshold = Min(sort_threshold, NLocBuffer); + + if (num_buckets >= (uint32) sort_threshold) buildstate.spool = _h_spoolinit(heap, index, num_buckets); else buildstate.spool = NULL; |