How about a option to disable autovacuum cancellation on lock conflict?

Hi,

I've more than once seen that autovacuums on certain tables never
succeed because regular exclusive (or similar) lockers cause it to give
way/up before finishing. Usually if some part of the application uses
explicit exclusive locks.

In general I think it's quite imortant that autovacuum bheaves that
way. But I think it might be worhtwile to offer an option to disable
that behaviour. If some piece of application logic requires exclusive
locks and that leads to complete starvation of autovacuum, there's
really nothing that can be done but to manually schedule vacuums right
now.

I can see two possible solutions:

1) Add a reloption that allows to configure whether autovacuum gives way
to locks acquired by user backends.
2) Add a second set of autovacuum_*_scale_factor variables that governs
a threshhold after which autovacuum doesn't get cancelled anymore.

Opinions?

Greetings,

Andres Freund

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Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services