From: | Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> |
---|---|
To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Decouple last important WAL record LSN from WAL insert locks |
Date: | 2022-11-29 07:30:16 |
Message-ID: | CALj2ACXtQdrGXtb=rbUOXddm1wU1vD9z6q_39FQyX0166dq==A@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Mon, Nov 28, 2022 at 11:55 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> > Is tracking lastImportantPos as pg_atomic_uint64 in XLogCtlInsert any
> > better than an explicit spinlock? I think it's better on platforms
> > where atomics are supported, however, it boils down to using a spin
> > lock on the platforms where atomics aren't supported.
>
> A central atomic in XLogCtlInsert would be better than a spinlock protected
> variable, but still bad. We do *not* want to have more central state that
> needs to be manipulated, we want *less*.
Agreed.
> If we wanted to optimize this - and I haven't seen any evidence it's worth
> doing so - we should just optimize the lock acquisitions in
> GetLastImportantRecPtr() away. *Without* centralizing the state.
Hm. I can think of converting lastImportantAt from XLogRecPtr to
pg_atomic_uint64 and letting it stay within the WALInsertLock
structure. This prevents torn-reads and also avoids WAL insertion lock
acquire-release cycles in GetLastImportantRecPtr(). Please see the
attached patch herewith.
If this idea is worth it, I would like to bring this and the other
thread [1] that converts insertingAt to atomic and modifies other WAL
insert locks related code under one roof and start a new thread. BTW,
the patch at [1] seems to be showing a good benefit for
high-concurrent inserts with small records.
Thoughts?
--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
Attachment | Content-Type | Size |
---|---|---|
v2-0001-Convert-lastImportantAt-to-64-bit-atomic-for-torn.patch | application/x-patch | 2.4 KB |
From | Date | Subject | |
---|---|---|---|
Next Message | walther | 2022-11-29 07:32:19 | Re: fixing CREATEROLE |
Previous Message | Peter Smith | 2022-11-29 07:29:48 | Re: [DOCS] Stats views and functions not in order? |