Re: increasing the default WAL segment size

On 5 April 2017 at 06:04, Beena Emerson <memissemerson(at)gmail(dot)com> wrote:

>> >> No commitment yet to increasing wal-segsize in the way this patch has
>> >> it.
>> >>
>> >
>> > What part of patch you don't like and do you have any suggestions to
>> > improve the same?
>>
>> I think there are still some questions and disagreements about how it
>> should behave.
>
>
> The WALfilename - LSN mapping disruption for higher values you mean? Is
> there anything else I have missed?

I see various issues raised but not properly addressed

1. we would need to drop support for segment sizes < 16MB unless we
adopt a new incompatible filename format.
I think at 16MB the naming should be the same as now and that
WALfilename -> LSN is very important.
For this release, I think we should just allow >= 16MB and avoid the
issue thru lack of time.

2. It's not clear to me the advantage of being able to pick varying
filesizes. I see great disadvantage in having too many options, which
greatly increases the chance of incompatibility, annoyance and
breakage. I favour a small number of values that have been shown by
testing to be sweet spots in performance and usability. (1GB has been
suggested)

3. New file allocation has been a problem raised with this patch for
some months now.

Lack of clarity and/or movement on these issues is very, very close to
getting the patch rejected now. Let's not approach this with the
viewpoint that I or others want it to be rejected, lets work forwards
and get some solid changes that will improve the world without causing
problems.

--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services