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Subject: Re: Re: BUG #13685: Archiving while idle every archive_timeout with
 wal_level hot_standby
From: Andres Freund <andres@anarazel.de>
Date: Wed, 04 Nov 2015 00:39:18 +0100
To: Michael Paquier <michael.paquier@gmail.com>
CC: Robert Haas <robertmhaas@gmail.com>, Jeff Janes <jeff.janes@gmail.com>,
 "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
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On November 4, 2015 12:37:02 AM GMT+01:00, Michael Paquier <michael.paquier@gmail.com> wrote:
>On Wed, Nov 4, 2015 at 12:43 AM, Andres Freund <andres@anarazel.de>
>wrote:
>> On 2015-11-03 10:23:35 -0500, Robert Haas wrote:
>>> On Mon, Nov 2, 2015 at 12:58 AM, Jeff Janes <jeff.janes@gmail.com>
>wrote:
>>> > If a transaction holding locks aborts on an otherwise idle server,
>perhaps it will take a very long time for a log-shipping standby to
>realize this.  But I have hard time believing that anyone who cares
>about that would be using log-shipping (rather than streaming) anyway.
>>>
>>> I'm sure other people here understand this better than me, but I
>>> wonder if it wouldn't make more sense to somehow log this data only
>if
>>> something material has changed in the data being logged.
>>
>> Phew. That doesn't seem easy to measure. I'm doubtful that it's worth
>> comparing the snapshot and such, especially in the back
>> branches.
>
>Well, I guess that's why I thought it would be more simple to check if
>we are at the beginning of a segment at first sight. This has no
>chance to break if anything else like that is being added in the
>future as it doesn't depend on the record types, though new similar
>records added on a timely manner would need a similar check. Perhaps
>this could be coupled by a check on the last XLOG_SWITCH_XLOG record
>instead of checkpoint activity though.
>
>> We could maybe add something that we only log a snapshot if XXX
>> megabytes have been logged or something. But I don't know which
>number
>> to pick here - and if there's other write activity the price of a
>> snapshot record really isn't high.
>
>On a completely idle system, I don't think we should log any standby
>records. This is what ~9.3 does.

Are you sure? I think it'll around checkpoints, no? I thought Heikki had fixed that, but looking sound that doesn't seem to be the case.

Andres

--- 
Please excuse brevity and formatting - I am writing this on my mobile phone.


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