Re: increasing the default WAL segment size

On Tue, Jan 3, 2017 at 3:38 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On 3 January 2017 at 16:24, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Jan 3, 2017 at 11:16 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>> On 3 January 2017 at 15:44, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>>>> Yeah. I don't think there's any way to get around the fact that there
>>>> will be bigger latency spikes in some cases with larger WAL files.
>>>
>>> One way would be for the WALwriter to zerofill new files ahead of
>>> time, thus avoiding the latency spike.
>>
>> Sure, we could do that. I think it's an independent improvement,
>> though: it is beneficial with or without this patch.
>
> The latency spike problem is exacerbated by increasing file size, so I
> think if we are allowing people to increase file size in this release
> then we should fix the knock-on problem it causes in this release
> also. If we don't fix it as part of this patch I would consider it an
> open item.

I think I'd like to see some benchmark results before forming an
opinion on whether that's a must-fix issue. I'm not sure I believe
that allowing a larger WAL segment size is going to make things worse
more than it makes them better. I think that should be tested, not
assumed true.

--
Robert Haas
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