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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2011-10-07 20:13:02 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2011-10-07 20:14:13 -0400 |
| commit | a2822fb9337a21f98ac4ce850bb4145acf47ca27 (patch) | |
| tree | c239fe9a32ff0225e906711a76348cee1567f0d8 /src/include/nodes/relation.h | |
| parent | caa1054df8408b165e5f66ff25c87b6dd0a0a1e7 (diff) | |
| download | postgresql-a2822fb9337a21f98ac4ce850bb4145acf47ca27.tar.gz postgresql-a2822fb9337a21f98ac4ce850bb4145acf47ca27.zip | |
Support index-only scans using the visibility map to avoid heap fetches.
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.
Diffstat (limited to 'src/include/nodes/relation.h')
| -rw-r--r-- | src/include/nodes/relation.h | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h index ecbbc1cd39a..cf48ba433c8 100644 --- a/src/include/nodes/relation.h +++ b/src/include/nodes/relation.h @@ -482,6 +482,7 @@ typedef struct IndexOptInfo bool unique; /* true if a unique index */ bool hypothetical; /* true if index doesn't really exist */ bool amcanorderbyop; /* does AM support order by operator result? */ + bool amcanreturn; /* does AM know how to return tuples? */ bool amoptionalkey; /* can query omit key for the first column? */ bool amsearchnulls; /* can AM search for NULL/NOT NULL entries? */ bool amhasgettuple; /* does AM have amgettuple interface? */ @@ -672,6 +673,10 @@ typedef struct Path * NoMovementScanDirection for an indexscan, but the planner wants to * distinguish ordered from unordered indexes for building pathkeys.) * + * 'indexonly' is TRUE for an index-only scan, that is, the index's access + * method has amcanreturn = TRUE and we only need columns available from the + * index. + * * 'indextotalcost' and 'indexselectivity' are saved in the IndexPath so that * we need not recompute them when considering using the same index in a * bitmap index/heap scan (see BitmapHeapPath). The costs of the IndexPath @@ -693,6 +698,7 @@ typedef struct IndexPath List *indexorderbys; bool isjoininner; ScanDirection indexscandir; + bool indexonly; Cost indextotalcost; Selectivity indexselectivity; double rows; /* estimated number of result tuples */ |