Re: increasing the default WAL segment size

On Wed, Aug 24, 2016 at 11:02 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
>> On 2016-08-24 22:33:49 -0400, Tom Lane wrote:
>>> ... but I think this is just folly. You'd have to do major amounts
>>> of work to keep, eg, slave servers on the same page as the master
>>> about what the segment size is.
>
>> Don't think it'd actually be all that complicated, we already verify
>> the compatibility of some things. But I'm doubtful it's worth it, and
>> I'm also rather doubtful that it's actually without overhead.
>
> My point is basically that it'll introduce failure modes that we don't
> currently concern ourselves with. Yes, you can do configure
> --with-wal-segsize, but it's on your own head whether the resulting build
> will interoperate with anything else --- and I'm quite sure nobody tests,
> eg, walsender or walreceiver to see if they fail sanely in such cases.
> I don't think we'd get to take such a laissez-faire position with respect
> to an initdb option.

I am really confused by this. If you connect a slave to a master
other than the one that you cloned to create the salve, of course
that's going to fail. But if the slave is cloned from the master,
then the segment size is going to match. It seems like the only thing
we need to do to make this work is make sure to get the segment size
from the control file rather than anywhere else, which doesn't seem
very difficult. What am I missing?

--
Robert Haas
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