From: David Steele <david@pgmasters.net>
To: Noah Misch <noah@leadboat.com>
To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: robertmhaas@gmail.com
Cc: masao.fujii@oss.nttdata.com
Cc: pgsql-hackers@postgresql.org
Subject: Re: remove more archiving overhead
Date: Mon, 19 Sep 2022 07:56:35 -0700
Message-ID: <02051aee-2ba1-3dd0-e162-8b2e8db79022@pgmasters.net> (raw)
In-Reply-To: <20220919143923.GA1706070@rfd.leadboat.com>
References: <20220708.105652.1551158050191356887.horikyota.ntt@gmail.com>
<44dbf5e4-8eec-da56-daba-755128b3723e@pgmasters.net>
<20220708165450.GA2356733@nathanxps13>
<20220731065156.GA3694276@rfd.leadboat.com>
<20220802050219.GA475090@nathanxps13>
<20220803071617.GA3817792@rfd.leadboat.com>
<ebb0f19f-5452-678c-0d19-1b8b260fd331@enterprisedb.com>
<20220917215427.GB3189289@nathanxps13>
<20220918071312.GB1658466@rfd.leadboat.com>
<7476bc05-3b8d-dab4-64e9-b569c54631d6@enterprisedb.com>
<20220919143923.GA1706070@rfd.leadboat.com>
On 9/19/22 07:39, Noah Misch wrote:
> On Mon, Sep 19, 2022 at 06:08:29AM -0400, Peter Eisentraut wrote:
>> On 18.09.22 09:13, Noah Misch wrote:
>>>>> This documentation change only covers archive_library. How are users of
>>>>> archive_command supposed to handle this?
>>>>
>>>> I believe users of archive_command need to do something similar to what is
>>>> described here. However, it might be more reasonable to expect
>>>> archive_command users to simply return false when there is a pre-existing
>>>> file, as the deleted text notes. IIRC that is why I added that sentence
>>>> originally.
>>>
>>> What makes the answer for archive_command diverge from the answer for
>>> archive_library?
>>
>> I suspect what we are really trying to say here is
>>
>> ===
>> Archiving setups (using either archive_command or archive_library) should be
>> prepared for the rare case that an identical archive file is being archived
>> a second time. In such a case, they should compare that the source and the
>> target file are identical and proceed without error if so.
>>
>> In some cases, it is difficult or impossible to configure archive_command or
>> archive_library to do this. In such cases, the archiving command or library
>> should error like in the case for any pre-existing target file, and
>> operators need to be prepared to resolve such cases manually.
>> ===
>>
>> Is that correct?
>
> I wanted it to stop saying anything like the second paragraph, hence commit
> d263ced. Implementing a proper archiving setup is not especially difficult,
> and inviting the operator to work around a wrong implementation invites
> damaging mistakes under time pressure.
I would also not want to state that duplicate WAL is rare. In practice
it is pretty common when things are going wrong. Also, implying it is
rare might lead a user to decide they don't need to worry about it.
Regards,
-David
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To: pgsql-hackers@postgresql.org
Cc: david@pgmasters.net, noah@leadboat.com, peter.eisentraut@enterprisedb.com, nathandbossart@gmail.com, horikyota.ntt@gmail.com, robertmhaas@gmail.com, masao.fujii@oss.nttdata.com
Subject: Re: remove more archiving overhead
In-Reply-To: <02051aee-2ba1-3dd0-e162-8b2e8db79022@pgmasters.net>
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