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Support index-only scans using the visibility map to avoid heap fetches.

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When a btree index contains all columns required by the query, and the
visibility map shows that all tuples on a target heap page are
visible-to-all, we don't need to fetch that heap page.  This patch depends
on the previous patches that made the visibility map reliable.

There's a fair amount left to do here, notably trying to figure out a less
chintzy way of estimating the cost of an index-only scan, but the core
functionality seems ready to commit.

Robert Haas and Ibrar Ahmed, with some previous work by Heikki Linnakangas.
This commit is contained in:
Tom Lane
2011-10-07 20:13:02 -04:00
parent caa1054df8
commit a2822fb933
34 changed files with 704 additions and 203 deletions
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4
src/include/optimizer/cost.h
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@@ -52,6 +52,7 @@ extern PGDLLIMPORT int effective_cache_size;
extern Cost disable_cost;
extern bool enable_seqscan;
extern bool enable_indexscan;
extern bool enable_indexonlyscan;
extern bool enable_bitmapscan;
extern bool enable_tidscan;
extern bool enable_sort;
@@ -67,7 +68,8 @@ extern double index_pages_fetched(double tuples_fetched, BlockNumber pages,
double index_pages, PlannerInfo *root);
extern void cost_seqscan(Path *path, PlannerInfo *root, RelOptInfo *baserel);
extern void cost_index(IndexPath *path, PlannerInfo *root, IndexOptInfo *index,
List *indexQuals, List *indexOrderBys, RelOptInfo *outer_rel);
List *indexQuals, List *indexOrderBys,
bool indexonly, RelOptInfo *outer_rel);
extern void cost_bitmap_heap_scan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
Path *bitmapqual, RelOptInfo *outer_rel);
extern void cost_bitmap_and_node(BitmapAndPath *path, PlannerInfo *root);