On Fri, Mar 10, 2023 at 6:58 PM Thomas Munro <thomas.mu...@gmail.com> wrote: > ... Perhaps something like 0004, which also shows the sort > of thing that we might consider back-patching to 14 and 15 (next > revision I'll move that up the front and put it in back-patchable > form).
I think this is the minimal back-patchable change. I propose to go ahead and do that, and then to kick the ideas about latch API changes into a new thread for the next commitfest.
From 1758cf16d22af7c9bae56bc6a40c394ba0107207 Mon Sep 17 00:00:00 2001 From: Thomas Munro <thomas.mu...@gmail.com> Date: Sat, 11 Mar 2023 10:42:20 +1300 Subject: [PATCH] Fix fractional vacuum_cost_delay. Commit 4753ef37 changed vacuum_delay_point() to use the WaitLatch() API, to fix the problem that vacuum could keep running for a very long time after the postmaster died. Unfortunately, that broke commit caf626b2's support for fractional vacuum_cost_delay, which shipped in PostgreSQL 12. WaitLatch() works in whole milliseconds. For now, revert the chance from commit 4753ef37, but add an explicit check for postmaster death. That's an extra system call on systems other than Linux and FreeBSD, but that overhead doesn't matter much considering that we willingly went to sleep and woke up again. (In later work, we might add higher resolution timeouts to the latch API so that we could do this in the standard programming pattern.) Back-patch to 14, where commit 4753ef37 arrived. Reported-by: Melanie Plageman <melanieplage...@gmail.com> Discussion: https://postgr.es/m/CAAKRu_b-q0hXCBUCAATh0Z4Zi6UkiC0k2DFgoD3nC-r3SkR3tg%40mail.gmail.com --- src/backend/commands/vacuum.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c index 2e12baf8eb..c54360a6a0 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -50,6 +50,7 @@ #include "postmaster/bgworker_internals.h" #include "storage/bufmgr.h" #include "storage/lmgr.h" +#include "storage/pmsignal.h" #include "storage/proc.h" #include "storage/procarray.h" #include "utils/acl.h" @@ -2232,11 +2233,18 @@ vacuum_delay_point(void) if (msec > VacuumCostDelay * 4) msec = VacuumCostDelay * 4; - (void) WaitLatch(MyLatch, - WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH, - msec, - WAIT_EVENT_VACUUM_DELAY); - ResetLatch(MyLatch); + pgstat_report_wait_start(WAIT_EVENT_VACUUM_DELAY); + pg_usleep(msec * 1000); + pgstat_report_wait_end(); + + /* + * We don't want to ignore postmaster death during very long vacuums + * with vacuum_cost_delay configured. We can't use the usual + * WaitLatch() approach here because we want microsecond-based sleep + * durations above. + */ + if (IsUnderPostmaster && !PostmasterIsAlive()) + exit(1); VacuumCostBalance = 0; -- 2.39.2
