| From: | Michail Nikolaev <michail(dot)nikolaev(at)gmail(dot)com> |
|---|---|
| To: | Andrey Borodin <x4mmm(at)yandex-team(dot)ru> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Kirill Reshke <reshkekirill(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Slow standby snapshot |
| Date: | 2021-11-09 21:15:42 |
| Message-ID: | CANtu0ohnft26vSQ-Nnd9DuVgFOyNzxG7MRQVSeXhreMH0fh7iw@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Hello, Andrey.
Thanks for your feedback.
> Current patch addresses another problem. In presence of old enough transaction enumeration of KnownAssignedXids with shared lock prevents adding new transactions with exclusive lock. And recovery effectively pauses.
Actually, I see two problems here (caused by the presence of old long
transactions). The first one is lock contention which causes recovery
pauses. The second one - just high CPU usage on standby by
KnownAssignedXidsGetAndSetXmin.
> All in all, I think using proposed "KnownAssignedXidsNext" patch solves real problem and the problem of binary searches should be addressed by compressing KnownAssignedXids more often.
I updated the patch a little. KnownAssignedXidsGetAndSetXmin now
causes fewer cache misses because some values are stored in variables
(registers). I think it is better to not lean on the compiler here
because of `volatile` args.
Also, I have added some comments.
Best regards,
Michail.
| Attachment | Content-Type | Size |
|---|---|---|
| v2-0001-known-assignment-xid-next.patch | text/x-patch | 7.2 KB |
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Joshua Brindle | 2021-11-09 21:22:59 | Re: Support for NSS as a libpq TLS backend |
| Previous Message | Jonathan S. Katz | 2021-11-09 20:45:34 | Re: 2021-11-11 release announcement draft |