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

1 files changed, 7 insertions, 6 deletions

diff --git a/doc/src/sgml/ref/explain.sgml b/doc/src/sgml/ref/explain.sgml
index 4d758fb237e..857c4e6e867 100644
--- a/doc/src/sgml/ref/explain.sgml
+++ b/doc/src/sgml/ref/explain.sgml
@@ -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