Horton

walsender waiting_for_ping spuriously set

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Pg Hackers <pgsql-hackers@lists.postgresql.org>
Cc: ashutosh.bapat@2ndquadrant.com
Date: 2020-08-06T22:55:58Z
Lists: pgsql-hackers

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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

Commits

  1. walsnd: Don't set waiting_for_ping_response spuriously

  2. Be less aggressive in asking for feedback of logical walsender clients.