pg_sleep() doesn't work well with recovery conflict interrupts.

Hi,

Since a64ca63e59c11d8fe6db24eee3d82b61db7c2c83 pg_sleep() uses
WaitLatch() to wait. That's fine in itself. But
procsignal_sigusr1_handler, which is used e.g. when resolving recovery
conflicts, doesn't unconditionally do a SetLatch().
That means that we'll we'll currently not be able to cancel conflicting
backends during recovery for 10min. Now, I don't think that'll happen
too often in practice, but it's still annoying.

As an alternative to doing the PG_TRY/save set_latch_on_sigusr1/set
set_latch_on_sigusr1/PG_CATCH/reset set_latch_on_sigusr1/ dance in
pg_sleep() we could also have RecoveryConflictInterrupt() do an
unconditional SetLatch()?

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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