[check_postgres] "locks" check - checking age of lock, not max number of locks

[Aleksey Tsalolikhin]

First of all, check_postgres is incredibly useful, thank you!

Summary:

I would like to request a feature of monitoring lock age (not quantity),
please.  check_postgres would return WARNING if there is any lock
extant for longer than X seconds, and CRITICAL if there is any lock
extant for Y seconds.

This would be useful because I have a powerful database server
and I don't know at what point (how many) locks would be problematic;
but I do know that if I have a lock that is around for longer than X seconds,
it is problematic.  So I'd like to monitor for this abnormal state.

Slightly more verbose version follows.
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Why check lock age instead of number of locks?

Situation:  I've upgraded our database server (it was I/O bound) and
it's doing great now; but Nagios is firing off too many alerts due to
lock count going over threshold.  I've tried bumping up the thresholds
but I still get alerts -- what happens is we go over threshold briefly
and then recover (go under threshold).

I've realized I don't care how many locks I have; I do care if the locks
I have are "old" locks, as it can lead to work stacking up and not
flowing through the system; and the system "jams".

I have a new beefy server and I don't know how many locks it can
handle in the course of normal operation (and our work volume is
growing, so I can't just take a baseline).  I can't say that having X
MANY locks is bad; but I can say with certainty that having any
lock that is over a minute old is abnormal and BAD.   I'd like to
be alerted of locks that persist for more than a minute, not
of lots of locks that come and go quickly (which is OK).

What do you think, would this be generally useful?

Yours very truly,
Aleksey