diff options
Diffstat (limited to 'src/backend/optimizer/util/plancat.c')
| -rw-r--r-- | src/backend/optimizer/util/plancat.c | 29 |
1 files changed, 27 insertions, 2 deletions
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c index 48d7493351d..c9679a19e28 100644 --- a/src/backend/optimizer/util/plancat.c +++ b/src/backend/optimizer/util/plancat.c @@ -9,7 +9,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.100 2004/12/31 22:00:23 pgsql Exp $ + * $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.101 2005/03/24 19:14:49 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -234,7 +234,32 @@ estimate_rel_size(Relation rel, int32 *attr_widths, case RELKIND_INDEX: case RELKIND_TOASTVALUE: /* it has storage, ok to call the smgr */ - *pages = curpages = RelationGetNumberOfBlocks(rel); + curpages = RelationGetNumberOfBlocks(rel); + + /* + * HACK: if the relation has never yet been vacuumed, use a + * minimum estimate of 10 pages. This emulates a desirable + * aspect of pre-8.0 behavior, which is that we wouldn't assume + * a newly created relation is really small, which saves us from + * making really bad plans during initial data loading. (The + * plans are not wrong when they are made, but if they are cached + * and used again after the table has grown a lot, they are bad.) + * It would be better to force replanning if the table size has + * changed a lot since the plan was made ... but we don't + * currently have any infrastructure for redoing cached plans at + * all, so we have to kluge things here instead. + * + * We approximate "never vacuumed" by "has relpages = 0", which + * means this will also fire on genuinely empty relations. Not + * great, but fortunately that's a seldom-seen case in the real + * world, and it shouldn't degrade the quality of the plan too + * much anyway to err in this direction. + */ + if (curpages < 10 && rel->rd_rel->relpages == 0) + curpages = 10; + + /* report estimated # pages */ + *pages = curpages; /* quick exit if rel is clearly empty */ if (curpages == 0) { |