On 2020/12/16 18:12, Fujii Masao wrote:
On 2020/12/16 16:24, Kyotaro Horiguchi wrote:
At Tue, 15 Dec 2020 23:10:28 +0900, Fujii Masao <masao.fu...@oss.nttdata.com>
wrote in
I pushed the following two patches.
- v1-use-standard-SIGHUP-hanlder-in-syslogger-process.patch
- v1-use-MyLatch-and-standard-SIGHUP-handler-in-startup-process.patch
As I told in other thread [1], I'm thinking to revert this patch
because this change could have bad side-effect on the startup
process waiting for recovery conflict.
Before applying the patch, the latch that the startup process
used to wait for recovery conflict was different from the latch
that SIGHUP signal handler or walreceiver process, etc set to
wake the startup process up. So SIGHUP or walreceiver didn't
wake the startup process waiting for recovery conflict up unnecessary.
But the patch got rid of the dedicated latch for signaling
the startup process. This change forced us to use the same latch
to make the startup process wait or wake up. Which caused SIGHUP
signal handler or walreceiver proces to wake the startup process
waiting on the latch for recovery conflict up unnecessarily
frequently.
While waiting for recovery conflict on buffer pin, deadlock needs
to be checked at least every deadlock_timeout. But that frequent
wakeups could prevent the deadlock timer from being triggered and
could delay that deadlock checks.
I thought that spurious wakeups don't harm. But actually
ResolveRecoveryConflictWithBufferPin doesn't consider spurious
wakeups. Only the timer woke up ResolveRecoveryConflictWithBufferPin
before the patch comes. Currently SIGHUP and XLogFlush() (on
walreceiver) also wake up startup process.
For a moment I thought that ResolveRecoveryConflictWithBufferPin
should wake up at shutdown time by the old recovery latch but it's not
the case since it wakes up after all blockers go away. It seems to me
simpler to revert the patches than making the function properly handle
spurious wakeups.
Therefore, I'm thinking to revert the commit ac22929a26 and
113d3591b8.
[1]
https://www.postgresql.org/message-id/a802f1c0-58d9-bd3f-bc3e-bdad54726...@oss.nttdata.com
As the result, I agree to revert them. But I think we need to add a
comment for the reason we don't use MyLatch for recovery-wakeup after
reverting them.
Agreed. Attached is the patch that reverts those patches and
adds the comments about why both procLatch and recoveryWakeupLatch
are necessary.
Pushed. Thanks!
Regards,
--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION
