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

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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
This commit is contained in:
Michael Paquier
2022-04-08 11:27:21 +09:00
parent dafae9707a
commit efb0ef909f
7 changed files with 147 additions and 68 deletions
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13
doc/src/sgml/ref/explain.sgml
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@@ -174,14 +174,15 @@ ROLLBACK;
Include information on buffer usage. Specifically, include the number of
shared blocks hit, read, dirtied, and written, the number of local blocks
hit, read, dirtied, and written, the number of temp blocks read and
written, and the time spent reading and writing data file blocks
(in milliseconds) if <xref linkend="guc-track-io-timing"/> is enabled.
A <emphasis>hit</emphasis> means that a read was avoided because the block was
found already in cache when needed.
written, and the time spent reading and writing data file blocks and
temporary file blocks (in milliseconds) if
<xref linkend="guc-track-io-timing"/> is enabled. A
<emphasis>hit</emphasis> means that a read was avoided because the block
was found already in cache when needed.
Shared blocks contain data from regular tables and indexes;
local blocks contain data from temporary tables and indexes;
while temp blocks contain short-term working data used in sorts, hashes,
Materialize plan nodes, and similar cases.
while temporary blocks contain short-term working data used in sorts,
hashes, Materialize plan nodes, and similar cases.
The number of blocks <emphasis>dirtied</emphasis> indicates the number of
previously unmodified blocks that were changed by this query; while the
number of blocks <emphasis>written</emphasis> indicates the number of