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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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5
src/backend/tcop/postgres.c
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@ -3065,7 +3065,7 @@ set_debug_options(int debug_flag, GucContext context, GucSource source)
bool
set_plan_disabling_options(const char *arg, GucContext context, GucSource source)
{
char *tmp = NULL;
const char *tmp = NULL;
switch (arg[0])
{
@ -3075,6 +3075,9 @@ set_plan_disabling_options(const char *arg, GucContext context, GucSource source
case 'i': /* indexscan */
tmp = "enable_indexscan";
break;
case 'o': /* indexonlyscan */
tmp = "enable_indexonlyscan";
break;
case 'b': /* bitmapscan */
tmp = "enable_bitmapscan";
break;