Date: Wed, 8 Apr 2020 15:26:03 +0200
From: Jehan-Guillaume de Rorthais <jgdr@dalibo.com>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: masao.fujii@oss.nttdata.com, pgsql-bugs@lists.postgresql.org,
 michael@paquier.xyz
Subject: Re: [BUG] non archived WAL removed during production crash recovery
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On Wed, 08 Apr 2020 17:39:09 +0900 (JST)
Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote:

> At Tue, 7 Apr 2020 17:17:36 +0200, Jehan-Guillaume de Rorthais
> <jgdr@dalibo.com> wrote in 
> > > +/* Recovery state */
> > > +typedef enum RecoveryState
> > > +{
> > > +	NOT_IN_RECOVERY = 0,
> > > +	IN_CRASH_RECOVERY,
> > > +	IN_ARCHIVE_RECOVERY
> > > +} RecoveryState;  
> 
> I'm not sure the complexity is required here. Are we asuume that
> archive_mode can be changed before restarting?

I assume it can yes. Eg., one can restore a PITR backup as a standby and change
the value of archive_mode to either off, on or always.

> At Thu, 2 Apr 2020 15:49:15 +0200, Jehan-Guillaume de Rorthais
> <jgdr@dalibo.com> wrote in 
> > > 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 = off no WAL files are marked as ".ready".

Sure, on the primary side.

What if you build a standby from a backup with archive_mode=on with
some .ready files in there? 

> > > - 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  
> 
> So if we assume archive_mode won't be changed after a crash before
> restarting, if archive_mode = on on a standy, WAL files are not marked
> as ".ready".

.ready files can be inherited from the old primary when building the standby,
depending on the method. See previous explanations from Fujii-san:
https://www.postgresql.org/message-id/flat/ca964b3a-61a0-902e-c7b3-3abbc01a921f%40oss.nttdata.com#ddd6cbad6c5e576e2e1ae53868ca3eea

> If it is "always", WAL files that are to be archived are
> marked as ".ready".  Finally, the condition reduces to:
> 
> If archiver is running, archive ".ready" files. Otherwise ignore
> ".ready" and just remove WAL files after use.
> >   
> > > 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.  
> 
> That situation implies that archive_mode has been changed.

Why? archive_mode may have been "always" on the primary when eg. a snapshot has
been created.

Regards,