pgsql: Track I/O timing for temporary file blocks in EXPLAIN (BUFFERS)

Track I/O timing for temporary file blocks in EXPLAIN (BUFFERS)

Previously, the output of EXPLAIN (BUFFERS) option showed only the I/O
timing spent reading and writing shared and local buffers.  This commit
adds on top of that the I/O timing for temporary buffers in the output
of EXPLAIN (for spilled external sorts, hashes, materialization. etc).
This can be helpful for users in cases where the I/O related to
temporary buffers is the bottleneck.

Like its cousin, this information is available only when track_io_timing
is enabled.  Playing the patch, this is showing an extra overhead of up
to 1% even when using gettimeofday() as implementation for interval
timings, which is slightly within the usual range noise still that's
measurable.

Author: Masahiko Sawada
Reviewed-by: Georgios Kokolatos, Melanie Plageman, Julien Rouhaud,
Ranier Vilela
Discussion: https://postgr.es/m/CAD21AoAJgotTeP83p6HiAGDhs_9Fw9pZ2J=_tYTsiO5Ob-V5GQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/efb0ef909f605817da6b77c1f3fef0a24457ec16

Modified Files
--------------
doc/src/sgml/ref/explain.sgml         |  13 ++--
src/backend/commands/explain.c        |  42 ++++++++++---
src/backend/executor/instrument.c     |   6 ++
src/backend/storage/file/buffile.c    |  29 ++++++++-
src/include/executor/instrument.h     |   6 +-
src/test/regress/expected/explain.out | 112 +++++++++++++++++++---------------
src/test/regress/sql/explain.sql      |   7 ++-
7 files changed, 147 insertions(+), 68 deletions(-)