Re: LogwrtResult contended spinlock

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Anastasia Lubennikova <a(dot)lubennikova(at)postgrespro(dot)ru>
Cc: Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers(at)lists(dot)postgresql(dot)org, Jaime Casanova <jaime(dot)casanova(at)2ndquadrant(dot)com>
Subject: Re: LogwrtResult contended spinlock
Date: 2020-11-24 15:01:53
Message-ID: 20201124150153.GA10181@alvherre.pgsql
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On 2020-Nov-24, Anastasia Lubennikova wrote:

> On 04.09.2020 20:13, Andres Freund wrote:

> > Re general routine: On second thought, it might actually be worth having
> > it. Even just for LSNs - there's plenty places where it's useful to
> > ensure a variable is at least a certain size. I think I would be in
> > favor of a general helper function.
> Do you mean by general helper function something like this?
> void
> swap_lsn(XLogRecPtr old_value, XLogRecPtr new_value, bool to_largest)

Something like that, yeah, though maybe name it "pg_atomic_increase_lsn"
or some similar name that makes it clear that

1. it is supposed to use atomics
2. it can only be used to *advance* a value rather than a generic swap.

(I'm not 100% clear that that's the exact API we need.)

> This CF entry was inactive for a while. Alvaro, are you going to continue
> working on it?

Yes, please move it forward. I'll post an update sometime before the
next CF.

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