Re: Remove page-read callback from XLogReaderState.

On 21/01/2020 13:33, Craig Ringer wrote:
> On Tue, 21 Jan 2020 at 18:46, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote:
>> It seems to me that it works perfectly, and everything looks good
>
> I seem to remember some considerable pain in this area when it came to
> timeline switches. Especially with logical decoding and xlog records
> that split across a segment boundary.
>
> My first attempts at logical decoding timeline following appeared fine
> and passed tests until they were put under extended real world
> workloads, at which point they exploded when they tripped corner cases
> like this.
>
> I landed up writing ridiculous regression tests to trigger some of
> these behaviours. I don't recall how many of them made it into the
> final patch to core but it's worth a look in the TAP test suite.

Yeah, the timeline switching stuff is complicated. The small
XLogBeginRead() patch isn't really affected, but it's definitely
something to watch out for in the callback API patch. If you happen to
have any extra ridiculous tests still lying around, would be nice to
look at them.

- Heikki