Re: Maximum number of WAL files in the pg_xlog directory

2014-12-30 18:45 GMT+01:00 Jeff Janes <jeff(dot)janes(at)gmail(dot)com>:

> On Tue, Dec 30, 2014 at 12:35 AM, Guillaume Lelarge <
> guillaume(at)lelarge(dot)info> wrote:
>
>> Sorry for my very late answer. It's been a tough month.
>>
>> 2014-11-27 0:00 GMT+01:00 Bruce Momjian <bruce(at)momjian(dot)us>:
>>
>>> On Mon, Nov 3, 2014 at 12:39:26PM -0800, Jeff Janes wrote:
>>> > It looked to me that the formula, when descending from a previously
>>> stressed
>>> > state, would be:
>>> >
>>> > greatest(1 + checkpoint_completion_target) * checkpoint_segments,
>>> > wal_keep_segments) + 1 +
>>> > 2 * checkpoint_segments + 1
>>>
>>> I don't think we can assume checkpoint_completion_target is at all
>>> reliable enough to base a maximum calculation on, assuming anything
>>> above the maximum is cause of concern and something to inform the admins
>>> about.
>>>
>>> Assuming checkpoint_completion_target is 1 for maximum purposes, how
>>> about:
>>>
>>> max(2 * checkpoint_segments, wal_keep_segments) + 2 *
>>> checkpoint_segments + 2
>>>
>>>
>> Seems something I could agree on. At least, it makes sense, and it works
>> for my customers. Although I'm wondering why "+ 2", and not "+ 1". It seems
>> Jeff and you agree on this, so I may have misunderstood something.
>>
>
> From hazy memory, one +1 comes from the currently active WAL file, which
> exists but is not counted towards either wal_keep_segments nor towards
> recycled files. And the other +1 comes from the formula for how many
> recycled files to retain, which explicitly has a +1 in it.
>
>

OK, that seems much better. Thanks, Jeff.

>

--
Guillaume.
http://blog.guillaume.lelarge.info
http://www.dalibo.com