pgsql: Microvacuum for GIST

Microvacuum for GIST

Mark index tuple as dead if it's pointed by kill_prior_tuple during
ordinary (search) scan and remove it during insert process if there is no
enough space for new tuple to insert. This improves select performance
because index will not return tuple marked as dead and improves insert
performance because it reduces number of page split.

Anastasia Lubennikova <a(dot)lubennikova(at)postgrespro(dot)ru> with
minor editorialization by me

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/013ebc0a7b7ea9c1b1ab7a3d4dd75ea121ea8ba7

Modified Files
--------------
src/backend/access/gist/gist.c | 82 +++++++++++++++++++++
src/backend/access/gist/gistget.c | 137 +++++++++++++++++++++++++++++++++++-
src/backend/access/gist/gistscan.c | 5 ++
src/include/access/gist.h | 9 ++-
src/include/access/gist_private.h | 11 ++-
5 files changed, 241 insertions(+), 3 deletions(-)