Re: Don't try fetching future segment of a TLI.

Hi,

I've tested patch provided by Kyotaro and do confirm it fixes the issue.
Any chance it will be merged to one of the next minor releases?

Thank you very much!

сб, 1 февр. 2020 г. в 08:31, David Steele <david(at)pgmasters(dot)net>:

> On 1/28/20 8:02 PM, Kyotaro Horiguchi wrote:
> > At Tue, 28 Jan 2020 19:13:32 +0300, Pavel Suderevsky
> >> Regading influence: issue is not about the large amount of WALs to
> apply
> >> but in searching for the non-existing WALs on the remote storage,
> each such
> >> search can take 5-10 seconds while obtaining existing WAL takes
> >> milliseconds.
> >
> > Wow. I didn't know of a file system that takes that much seconds to
> > trying non-existent files. Although I still think this is not a bug,
> > but avoiding that actually leads to a big win on such systems.
>
> I have not tested this case but I can imagine it would be slow in
> practice. It's axiomatic that is hard to prove a negative. With
> multi-region replication it might well take some time to be sure that
> the file *really* doesn't exist and hasn't just been lost in a single
> region.
>
> > After a thought, I think it's safe and effectively doable to let
> > XLogFileReadAnyTLI() refrain from trying WAL segments of too-high
> > TLIs. Some garbage archive files out of the range of a timeline might
> > be seen, for example, after reusing archive directory without clearing
> > files. However, fetching such garbages just to fail doesn't
> > contribute durability or reliablity at all, I think.
>
> The patch seems sane, the trick will be testing it.
>
> Pavel, do you have an environment where you can ensure this is a
> performance benefit?
>
> Regards,
> --
> -David
> david(at)pgmasters(dot)net
>