Re: [BUG] non archived WAL removed during production crash recovery
От | Fujii Masao |
---|---|
Тема | Re: [BUG] non archived WAL removed during production crash recovery |
Дата | |
Msg-id | 3d543ef2-ae02-5e59-3bfe-b79d00dab360@oss.nttdata.com обсуждение исходный текст |
Ответ на | Re: [BUG] non archived WAL removed during production crash recovery (Jehan-Guillaume de Rorthais <jgdr@dalibo.com>) |
Ответы |
Re: [BUG] non archived WAL removed during production crash recovery
(Jehan-Guillaume de Rorthais <jgdr@dalibo.com>)
Re: [BUG] non archived WAL removed during production crash recovery (Jehan-Guillaume de Rorthais <jgdr@dalibo.com>) |
Список | pgsql-bugs |
On 2020/04/02 22:49, Jehan-Guillaume de Rorthais wrote: > On Thu, 2 Apr 2020 19:38:59 +0900 > Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > >> On 2020/04/02 16:23, Kyotaro Horiguchi wrote: >>> At Thu, 2 Apr 2020 14:19:15 +0900, Fujii Masao >>> <masao.fujii@oss.nttdata.com> wrote in > [...] >>>> is whether to remove such WAL files in archive recovery case with >>>> archive_mode=on. Those WAL files would be required when recovering >>>> from the backup taken before that archive recovery happens. >>>> So it seems unsafe to remove them in that case. >>> >>> I'm not sure I'm getting the intention correctly, but I think it >>> responsibility of the operator to provide a complete set of archived >>> WAL files for a backup. Could you elaborate what operation steps are >>> you assuming of? >> >> Please imagine the case where you need to do archive recovery >> from the database snapshot taken while there are many WAL files >> with .ready files. Those WAL files have not been archived yet. >> In this case, ISTM those WAL files should not be removed until >> they are archived, when archive_mode = on. > > If you rely on snapshot without pg_start/stop_backup, I agree. Theses WAL > should be archived if: > > * archive_mode >= on for primary > * archive_mode = always for standby > >>>> Therefore, IMO that the patch should change the code so that >>>> no unarchived WAL files are removed not only in crash recovery >>>> but also archive recovery. Thought? >>> >>> Agreed if "an unarchived WAL" means "a WAL file that is marked .ready" >>> and it should be archived immediately. My previous mail is written >>> based on the same thought. >> >> Ok, so our *current* consensus seems the followings. Right? >> >> - If archive_mode=off, any WAL files with .ready files are removed in >> crash recovery, archive recoery and standby mode. > > yes > >> - If archive_mode=on, WAL files with .ready files are removed only in >> standby mode. In crash recovery and archive recovery cases, they keep >> remaining and would be archived after recovery finishes (i.e., during >> normal processing). > > yes > >> - If archive_mode=always, in crash recovery, archive recovery and >> standby mode, WAL files with .ready files are archived if WAL archiver >> is running. > > yes > >> That is, WAL files with .ready files are removed when either >> archive_mode!=always in standby mode or archive_mode=off. > > sounds fine to me. > > [...] >>>>>>>> Another is to make the startup process remove .ready file if >>>>>>>> necessary. >>>>>>> >>>>>>> I'm not sure to understand this one. >>>> >>>> I was thinking to make the startup process remove such unarchived WAL >>>> files >>>> if archive_mode=on and StandbyModeRequested/ArchiveRecoveryRequested >>>> is true. > > Ok, understood. > >>> As mentioned above, I don't understand the point of preserving WAL >>> files that are either marked as .ready or not marked at all on a >>> standby with archive_mode=on. >> >> Maybe yes. But I'm not confident about that there is no such case. > > Well, it seems to me that this is what you suggested few paragraph away: > > «.ready files are removed when either archive_mode!=always in standby mode» Yes, so I'm fine with that as the first consensus because the behavior is obviously better than the current one. *If* the case where no WAL files should be removed is found, I'd just like to propose the additional patch. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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