Re: adding wait_start column to pg_locks

On 2021-01-25 23:44, Fujii Masao wrote:
> Another comment is; Doesn't the change of MyProc->waitStart need the
> lock table's partition lock? If yes, we can do that by moving
> LWLockRelease(partitionLock) just after the change of
> MyProc->waitStart, but which causes the time that lwlock is being held
> to be long. So maybe we need another way to do that.

Thanks for your comments!

It would be ideal for the consistency of the view to record "waitstart" 
during holding the table partition lock.
However, as you pointed out, it would give non-negligible performance 
impacts.

I may miss something, but as far as I can see, the influence of not 
holding the lock is that "waitstart" can be NULL even though "granted" 
is false.

I think people want to know the start time of the lock when locks are 
held for a long time.
In that case, "waitstart" should have already been recorded.

If this is true, I think the current implementation may be enough on the 
condition that users understand it can happen that "waitStart" is NULL 
and "granted" is false.

Attached a patch describing this in the doc and comments.


Any Thoughts?

Regards,


--
Atsushi Torikoshi