Re: walsender waiting_for_ping spuriously set - Mailing list pgsql-hackers

From Ashutosh Bapat
Subject Re: walsender waiting_for_ping spuriously set
Date
Msg-id CAG-ACPX_ouARUnzOL2tM2OWM5q62rDzRrFfs_BqUOc4Hf9zpOQ@mail.gmail.com
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In response to walsender waiting_for_ping spuriously set  (Alvaro Herrera <alvherre@2ndquadrant.com>)
List pgsql-hackers
The patch looks good to me. Thanks for improving comments around that code. I like the change to set waiting_for_ping_response in WalSndKeepalive. Thanks.

On Fri, 7 Aug 2020 at 04:26, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
Ashutosh Bapat noticed that WalSndWaitForWal() is setting
waiting_for_ping_response after sending a keepalive that does *not*
request a reply.  The bad consequence is that other callers that do
require a reply end up in not sending a keepalive, because they think it
was already sent previously.  So the whole thing gets stuck.

He found that commit 41d5f8ad734 failed to remove the setting of
waiting_for_ping_response after changing the "request" parameter
WalSndKeepalive from true to false; that seems to have been an omission
and it breaks the algorithm.  Thread at [1].

The simplest fix is just to remove the line that sets
waiting_for_ping_response, but I think it is less error-prone to have
WalSndKeepalive set the flag itself, instead of expecting its callers to
do it (and know when to).  Patch attached.  Also rewords some related
commentary.

[1] https://postgr.es/m/flat/BLU436-SMTP25712B7EF9FC2ADEB87C522DC040@phx.gbl

--
Álvaro Herrera       Valdivia, Chile


--
Best Wishes,
Ashutosh

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