pgsql: Allow HOT updates for some expression indexes

Allow HOT updates for some expression indexes

If the value of an index expression is unchanged after UPDATE,
allow HOT updates where previously we disallowed them, giving
a significant performance boost in those cases.

Particularly useful for indexes such as JSON->>field where the
JSON value changes but the indexed value does not.

Submitted as "surjective indexes" patch, now enabled by use
of new "recheck_on_update" parameter.

Author: Konstantin Knizhnik
Reviewer: Simon Riggs, with much wordsmithing and some cleanup

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/c203d6cf81b4d7e43edb2b75ec1b741ba48e04e0

Modified Files
--------------
doc/src/sgml/ref/create_index.sgml       |  37 +++++++++-
src/backend/access/common/reloptions.c   |  45 ++++++++++++-
src/backend/access/heap/heapam.c         | 105 +++++++++++++++++++++++++++--
src/backend/catalog/index.c              |   3 +-
src/backend/utils/cache/relcache.c       | 112 +++++++++++++++++++++++++++++--
src/bin/psql/tab-complete.c              |   4 +-
src/include/access/reloptions.h          |   2 +
src/include/utils/rel.h                  |  12 +++-
src/include/utils/relcache.h             |   3 +-
src/test/regress/expected/func_index.out |  61 +++++++++++++++++
src/test/regress/parallel_schedule       |   2 +-
src/test/regress/serial_schedule         |   1 +
src/test/regress/sql/func_index.sql      |  30 +++++++++
13 files changed, 395 insertions(+), 22 deletions(-)