Re: increasing the default WAL segment size

On Wed, Jan 4, 2017 at 9:47 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On 4 January 2017 at 13:57, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Wed, Jan 4, 2017 at 3:05 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>> Strange response. Nothing has been assumed. I asked for tests and you
>>> provided measurements.
>>
>> Sure, of zero-filling a file with dd. But I also pointed out that in
>> a real PostgreSQL cluster, the change could actually *reduce* latency.
>
> I think we are talking at cross purposes. We agree that the main
> change is useful, but it causes another problem which I can't see how
> you can characterize as reduced latency, based upon your own
> measurements.

Zero-filling files will take longer if the files are bigger. That
will increase latency. But we will also have fewer forced
end-of-segment syncs. That will reduce latency. Which effect is
bigger?

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company