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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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2
src/backend/nodes/outfuncs.c
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@ -447,6 +447,7 @@ _outIndexScan(StringInfo str, IndexScan *node)
WRITE_NODE_FIELD(indexorderby);
WRITE_NODE_FIELD(indexorderbyorig);
WRITE_ENUM_FIELD(indexorderdir, ScanDirection);
WRITE_BOOL_FIELD(indexonly);
}
static void
@ -1500,6 +1501,7 @@ _outIndexPath(StringInfo str, IndexPath *node)
WRITE_NODE_FIELD(indexorderbys);
WRITE_BOOL_FIELD(isjoininner);
WRITE_ENUM_FIELD(indexscandir, ScanDirection);
WRITE_BOOL_FIELD(indexonly);
WRITE_FLOAT_FIELD(indextotalcost, "%.2f");
WRITE_FLOAT_FIELD(indexselectivity, "%.4f");
WRITE_FLOAT_FIELD(rows, "%.0f");