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Measure the number of all-visible pages for use in index-only scan costing.

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Add a column pg_class.relallvisible to remember the number of pages that
were all-visible according to the visibility map as of the last VACUUM
(or ANALYZE, or some other operations that update pg_class.relpages).
Use relallvisible/relpages, instead of an arbitrary constant, to estimate
how many heap page fetches can be avoided during an index-only scan.

This is pretty primitive and will no doubt see refinements once we've
acquired more field experience with the index-only scan mechanism, but
it's way better than using a constant.

Note: I had to adjust an underspecified query in the window.sql regression
test, because it was changing answers when the plan changed to use an
index-only scan.  Some of the adjacent tests perhaps should be adjusted
as well, but I didn't do that here.
This commit is contained in:
Tom Lane
2011-10-14 17:23:01 -04:00
parent dea95c7a7b
commit e6858e6657
22 changed files with 246 additions and 72 deletions
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2
src/backend/optimizer/util/relnode.c
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@ -109,6 +109,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
rel->indexlist = NIL;
rel->pages = 0;
rel->tuples = 0;
rel->allvisfrac = 0;
rel->subplan = NULL;
rel->subroot = NULL;
rel->baserestrictinfo = NIL;
@ -362,6 +363,7 @@ build_join_rel(PlannerInfo *root,
joinrel->indexlist = NIL;
joinrel->pages = 0;
joinrel->tuples = 0;
joinrel->allvisfrac = 0;
joinrel->subplan = NULL;
joinrel->subroot = NULL;
joinrel->baserestrictinfo = NIL;