[ADMIN] cancelled queries on standby

[MirrorX]

hello to all,

i am facing an issue concerning cancelled queries made on a hot standby
server. if we suppose that there are some tables that are never changed (no
inserts/updates/deletes) and that autovacuum is set to false for these
tables, what else could there be affecting these tables and consequently
cancelling my queries? thx in advance for any suggestions

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[Greg Smith]

Post by MirrorX
i am facing an issue concerning cancelled queries made on a hot standby
server. if we suppose that there are some tables that are never changed (no
inserts/updates/deletes) and that autovacuum is set to false for these
tables, what else could there be affecting these tables and consequently
cancelling my queries? thx in advance for any suggestions

Query cancellation isn't targeted this way. Whether or not a query
needs to be canceled by vacuum cleanup depends on whether any open
transaction can see the rows that are being cleaned up. I think you
have the understandable belief what rows are actually being viewed by
the query running on the standby matter; they don't.

Let's say you have a long-running query Q accessing a table A on the
standby. Then some vacuum cleanup of table B happens on the master. Q
can then be canceled when those cleanup records are replicated. The
fact that A is never changed and doesn't have autovacuum enabled doesn't
matter. Because it's possible for Q to see B, it's canceled regardless
of whether it's looked at it yet.

[MirrorX]

thanks a lot. the way it works is crystal clear to me now

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