Re: autovacuum truncate exclusive lock round two

Attached is a new patch that addresses most of the points raised in
discussion before.

1) Most of the configuration variables are derived from deadlock_timeout
now. The "check for conflicting lock request" interval is
deadlock_timeout/10, clamped to 10ms. The "try to acquire exclusive
lock" interval is deadlock_timeout/20, also clamped to 10ms. The only
GUC variable remaining is autovacuum_truncate_lock_try=2000ms with a
range from 0 (just try once) to 20000ms.

I'd like to point out that this is a significant change in functionality
as without the config option for the check interval, there is no longer
any possibility to disable the call to LockHasWaiters() and return to
the original (deadlock code kills autovacuum) behavior.

2) The partition lock in LockHasWaiters() was lowered to LW_SHARED. The
LW_EXCLUSIVE was indeed a copy/paste result.

3) The instr_time handling was simplified as suggested.

4) Lower case TRUE/FALSE.

I did not touch the part about suppressing the stats and the ANALYZE
step of "auto vacuum+analyze". The situation is no different today. When
the deadlock code kills autovacuum, stats aren't updated either. And
this patch is meant to cause autovacuum to finish the truncate in a few
minutes or hours, so that the situation fixes itself.

Jan

--
Anyone who trades liberty for security deserves neither
liberty nor security. -- Benjamin Franklin