Re: increasing the default WAL segment size

On 2016-08-26 13:07:09 +0900, Michael Paquier wrote:
> On Fri, Aug 26, 2016 at 12:54 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > On Fri, Aug 26, 2016 at 9:04 AM, Michael Paquier
> > <michael(dot)paquier(at)gmail(dot)com> wrote:
> >> On Fri, Aug 26, 2016 at 12:25 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >>> If we change the default to 64MB, then I think it won't allow to use
> >>> old databases as-is because we store it in pg_control (I think one
> >>> will get below error [1] for old databases, if we just change default
> >>> and don't do anything else). Do you have way to address it or you
> >>> think it is okay?
> >>
> >> Those would still be able to work with ./configure
> >> --with-wal-segsize=16, so that's not really an issue.
> >>
> >
> > Right, but do we need suggest users to do so? The question/point was
> > if we deliver server with default value as 64MB, then it won't allow
> > to start old database.
>
> Right, pg_upgrade could be made smarter by enforcing a conversion with
> a dedicated option: we could get away by filling the existing segments
> with zeros and add an XLOG switch record at the end of each segments
> formerly at 16MB converted to 64MB. That would still be better than
> converting each page LSN :(

Maybe I'm missing something here - but why would we need to do any of
that? The WAL already isn't compatible between versions, and we don't
reuse the old server's WAL anyway? Isn't all that's needed relaxing some
error check?