From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)lists(dot)postgresql(dot)org, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com> |
Subject: | Re: Questionable ping logic in LogicalRepApplyLoop |
Date: | 2020-09-04 20:41:47 |
Message-ID: | 20200904204147.GA18660@alvherre.pgsql |
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On 2020-Sep-04, Tom Lane wrote:
> While playing around with clang's scan-build I noticed this warning:
>
> worker.c:2281:7: warning: Value stored to 'ping_sent' is never read
> ping_sent = true;
> ^ ~~~~
>
> At first I thought it was a harmless unnecessary update, but looking
> closer I wonder whether it isn't telling us there is a logic bug here.
> Specifically, I wonder why the "ping_sent" variable is local to the
> loop starting at line 2084, rather than having the same lifespan as
> "last_recv_timestamp". Do we really want to forget that we sent a
> ping anytime we have to wait for more data?
Ah ... maybe this bug is the reason why the bug fixed by 470687b4a5bb
did not affect logical replication.
> In short, we could remove the ping_sent variable entirely without
> changing this code's behavior. I'm not 100% sure what semantics
> it's trying to achieve, but I don't think it's achieving them.
I imagine that moving the variable one block-scope outwards (together
with last_recv_timestamp) is what was intended.
... oh look! commit 3f60f690fac1 moved last_recv_timestamp without
realizing that ping_sent had to get the same treatment.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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