pgsql: Expose track_iotiming data via the statistics collector.

Expose track_iotiming data via the statistics collector.

Ants Aasma's original patch to add timing information for buffer I/O
requests exposed this data at the relation level, which was judged too
costly.  I've here exposed it at the database level instead.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/644828908fb132ee1f1da5b8b7975c0d73d6158a

Modified Files
--------------
doc/src/sgml/config.sgml             |    7 +++++--
doc/src/sgml/monitoring.sgml         |   19 +++++++++++++++++++
src/backend/catalog/system_views.sql |    2 ++
src/backend/postmaster/pgstat.c      |   16 ++++++++++++++--
src/backend/storage/buffer/bufmgr.c  |   10 +++++++---
src/backend/utils/adt/pgstatfuncs.c  |   32 ++++++++++++++++++++++++++++++++
src/include/catalog/catversion.h     |    2 +-
src/include/catalog/pg_proc.h        |    4 ++++
src/include/pgstat.h                 |   14 ++++++++++++++
src/test/regress/expected/rules.out  |    2 +-
10 files changed, 99 insertions(+), 9 deletions(-)