Re: Remove Deprecated Exclusive Backup Mode

From: David Steele <david(at)pgmasters(dot)net>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, Stephen Frost <sfrost(at)snowman(dot)net>, Adrien NAYRAT <adrien(dot)nayrat(at)anayrat(dot)info>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Remove Deprecated Exclusive Backup Mode
Date: 2019-03-07 09:34:55
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On 3/5/19 12:36 AM, Bruce Momjian wrote:
> On Thu, Feb 28, 2019 at 05:08:24PM +0200, David Steele wrote:
>> On 2/28/19 4:44 PM, Fujii Masao wrote:
>>> On Wed, Feb 27, 2019 at 4:35 PM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> wrote:
>>>> Fujii Masao wrote:
>>>>> So, let me clarify the situations;
>>>>> (3) If backup_label.pending exists but recovery.signal doesn't, the server
>>>>> ignores (or removes) backup_label.pending and do the recovery
>>>>> starting the pg_control's REDO location. This case can happen if
>>>>> the server crashes while an exclusive backup is in progress.
>>>>> So crash-in-the-middle-of-backup doesn't prevent the recovery from
>>>>> starting in this idea
>>>> That's where I see the problem with your idea.
>>>> It is fairly easy for someone to restore a backup and then just start
>>>> the server without first creating "recovery.signal", and that would
>>>> lead to data corruption.
>>> Isn't this case problematic even when a backup was taken by pg_basebackup?
>>> Because of lack of recovery.signal, no archived WAL files are replayed and
>>> the database may not reach to the latest point.
>> It is problematic because we have a message encouraging users to delete
>> backup_label when in fact they should be creating recovery.signal.
> Should we issue a client NOTICE/WARNING message as part of
> pg_start_backup to indicate what to do if the server crashes before
> pg_stop_backup()?

I'm not in favor of this since it will just encourage users to change
their log level and possibly miss important notices/warnings.


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