pgsql: Support index-only scans using the visibility map to avoid heap

2011/10/8 Tom Lane <tgl@sss.pgh.pa.us>:

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.

It looks like it lacks some if(), by reading costsize.c I didn't see
where indexonly is used (so
visibility_fraction is always used....)
Is it ok ?

Robert Haas and Ibrar Ahmed, with some previous work by Heikki Linnakangas.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/a2822fb9337a21f98ac4ce850bb4145acf47ca27

Modified Files
--------------
doc/src/sgml/catalogs.sgml                    |    7 +
doc/src/sgml/config.sgml                      |   19 ++-
doc/src/sgml/indexam.sgml                     |   32 ++++-
doc/src/sgml/ref/postgres-ref.sgml            |    7 +-
src/backend/access/index/genam.c              |    4 +
src/backend/access/index/indexam.c            |  236 ++++++++++++++++---------
src/backend/access/nbtree/nbtree.c            |   92 ++++++++++
src/backend/commands/explain.c                |    5 +-
src/backend/executor/nodeIndexscan.c          |  123 ++++++++++++-
src/backend/nodes/copyfuncs.c                 |    1 +
src/backend/nodes/outfuncs.c                  |    2 +
src/backend/optimizer/path/costsize.c         |   21 +++
src/backend/optimizer/path/indxpath.c         |   89 +++++++++
src/backend/optimizer/plan/createplan.c       |    9 +-
src/backend/optimizer/plan/planner.c          |    2 +-
src/backend/optimizer/util/pathnode.c         |    8 +-
src/backend/optimizer/util/plancat.c          |    1 +
src/backend/optimizer/util/var.c              |   43 +++--
src/backend/tcop/postgres.c                   |    5 +-
src/backend/utils/cache/relcache.c            |    4 +-
src/backend/utils/misc/guc.c                  |    9 +
src/backend/utils/misc/postgresql.conf.sample |    1 +
src/include/access/genam.h                    |    3 +
src/include/access/relscan.h                  |    5 +
src/include/catalog/catversion.h              |    2 +-
src/include/catalog/pg_am.h                   |   52 +++---
src/include/nodes/execnodes.h                 |    2 +
src/include/nodes/plannodes.h                 |    5 +
src/include/nodes/relation.h                  |    6 +
src/include/optimizer/cost.h                  |    4 +-
src/include/optimizer/pathnode.h              |    1 +
src/include/optimizer/var.h                   |    2 +-
src/test/regress/expected/aggregates.out      |   78 ++++----
src/test/regress/expected/rangefuncs.out      |   27 ++--
34 files changed, 704 insertions(+), 203 deletions(-)

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