Re: pgsql: Avoid improbable PANIC during heap_update.
От | Jaime Casanova |
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Тема | Re: pgsql: Avoid improbable PANIC during heap_update. |
Дата | |
Msg-id | YzVPfCKNrmi0aLEh@ahch-to обсуждение исходный текст |
Ответ на | pgsql: Avoid improbable PANIC during heap_update. (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: pgsql: Avoid improbable PANIC during heap_update.
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Список | pgsql-committers |
On Tue, Apr 13, 2021 at 04:17:39PM +0000, Tom Lane wrote: > Avoid improbable PANIC during heap_update. > > heap_update needs to clear any existing "all visible" flag on > the old tuple's page (and on the new page too, if different). > Per coding rules, to do this it must acquire pin on the appropriate > visibility-map page while not holding exclusive buffer lock; > which creates a race condition since someone else could set the > flag whenever we're not holding the buffer lock. The code is > supposed to handle that by re-checking the flag after acquiring > buffer lock and retrying if it became set. However, one code > path through heap_update itself, as well as one in its subroutine > RelationGetBufferForTuple, failed to do this. The end result, > in the unlikely event that a concurrent VACUUM did set the flag > while we're transiently not holding lock, is a non-recurring > "PANIC: wrong buffer passed to visibilitymap_clear" failure. > Hi, This doesn't look as improbable because I saw it at least 3 times with v15beta4. The first time I thought it was my fault, then I tried with a commit on september 25 (didn't remember which exactly but that doesn't seems too relevant). Finally I saw it again in a build with TRACE_VISIBILITYMAP defined (the same commit). But I haven't see it anymore on rc1. Anyway I'm attaching the backtrace (this is from the build with TRACE_VISIBILITYMAP), the query that was running at the time was (no changes were made to quad_poly_tbl table nor any indexes were added to this table): """ update public.quad_poly_tbl set id = public.quad_poly_tbl.id returning public.quad_poly_tbl.id as c0 """ -- Jaime Casanova Director de Servicios Profesionales SystemGuards - Consultores de PostgreSQL
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