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e221c0befb
As implemented in 5891c7a8ed, setting "force" to true in
pgstat_report_wal() causes the routine to not wait for the pgstat
shmem lock if it cannot be acquired, in which case the WAL and I/O
statistics finish by not being flushed. The origin of the confusion
comes from pgstat_flush_wal() and pgstat_flush_io(), that use "nowait"
as sole argument. The I/O stats are new in v16.
This is the opposite behavior of what has been used in
pgstat_report_stat(), where "force" is the opposite of "nowait". In
this case, when "force" is true, the routine sets "nowait" to false,
which would cause the routine to wait for the pgstat shmem lock,
ensuring that the stats are always flushed. When "force" is false,
"nowait" is set to true, and the stats would only not be flushed if the
pgstat shmem lock can be acquired, returning immediately without
flushing the stats if the lock cannot be acquired.
This commit changes pgstat_report_wal() so as "force" has the same
behavior as in pgstat_report_stat(). There are currently three callers
of pgstat_report_wal():
- Two in the checkpointer where force=true during a shutdown and the
main checkpointer loop. Now the code behaves so as the stats are always
flushed.
- One in the main loop of the bgwriter, where force=false. Now the code
behaves so as the stats would not be flushed if the pgstat shmem lock
could not be acquired.
Before this commit, some stats on WAL and I/O could have been lost after
a shutdown, for example.
Reported-by: Ryoga Yoshida
Author: Ryoga Yoshida, Michael Paquier
Discussion: https://postgr.es/m/f87a4d7be70530606b864fd1df91718c@oss.nttdata.com
Backpatch-through: 15
# Generating dummy probes If Postgres isn't configured with dtrace enabled, we need to generate dummy probes for the entries in probes.d, that do nothing. This is accomplished in Unix via the sed script `Gen_dummy_probes.sed`. We used to use this in MSVC builds using the perl utility `psed`, which mimicked sed. However, that utility disappeared from Windows perl distributions and so we converted the sed script to a perl script to be used in MSVC builds. We still keep the sed script as the authoritative source for generating these dummy probes because except on Windows perl is not a hard requirement when building from a tarball. So, if you need to change the way dummy probes are generated, first change the sed script, and when it's working generate the perl script. This can be accomplished by using the perl utility s2p. s2p is no longer part of the perl core, so it might not be on your system, but it is available on CPAN and also in many package systems. e.g. on Fedora it can be installed using `cpan App::s2p` or `dnf install perl-App-s2p`. The Makefile contains a recipe for regenerating Gen_dummy_probes.pl, so all you need to do is once you have s2p installed is `make Gen_dummy_probes.pl` Note that in a VPATH build this will generate the file in the vpath tree, not the source tree.