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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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8
src/backend/optimizer/util/pathnode.c
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@ -25,8 +25,8 @@
#include "optimizer/paths.h"
#include "optimizer/tlist.h"
#include "parser/parsetree.h"
#include "utils/selfuncs.h"
#include "utils/lsyscache.h"
#include "utils/selfuncs.h"
static List *translate_sub_tlist(List *tlist, int relid);
@ -418,6 +418,7 @@ create_seqscan_path(PlannerInfo *root, RelOptInfo *rel)
* 'indexscandir' is ForwardScanDirection or BackwardScanDirection
* for an ordered index, or NoMovementScanDirection for
* an unordered index.
* 'indexonly' is true if an index-only scan is wanted.
* 'outer_rel' is the outer relation if this is a join inner indexscan path.
* (pathkeys and indexscandir are ignored if so.) NULL if not.
*
@ -430,6 +431,7 @@ create_index_path(PlannerInfo *root,
List *indexorderbys,
List *pathkeys,
ScanDirection indexscandir,
bool indexonly,
RelOptInfo *outer_rel)
{
IndexPath *pathnode = makeNode(IndexPath);
@ -468,6 +470,7 @@ create_index_path(PlannerInfo *root,
pathnode->isjoininner = (outer_rel != NULL);
pathnode->indexscandir = indexscandir;
pathnode->indexonly = indexonly;
if (outer_rel != NULL)
{
@ -506,7 +509,8 @@ create_index_path(PlannerInfo *root,
pathnode->rows = rel->rows;
}
cost_index(pathnode, root, index, indexquals, indexorderbys, outer_rel);
cost_index(pathnode, root, index, indexquals, indexorderbys,
indexonly, outer_rel);
return pathnode;
}