On 12 January 2012 01:48, Robert Haas <robertmhaas@gmail.com> wrote:
> I've had cause, a few times this development cycle, to want to measure
> the amount of spinning on each lwlock in the system. To that end,
> I've found the attached patch useful. Note that if you don't define
> LWLOCK_STATS, this changes nothing except that the return value from
> s_lock becomes int rather than void. If you do define LWLOCK_STATS,
> then LWLockAcquire() counts the number of pg_usleep() calls that are
> required to acquire each LWLock, in addition to the other statistics.
> Since this has come up for me a few times now, I'd like to proposing
> including it in core.
>
> Just to whet your appetite, here are the top spinners on a 32-client
> SELECT-only test on a 32-core Itanium server. All the locks not shown
> below have two orders of magnitude less of a problem than these do.
>
> lwlock 48: shacq 6042357 exacq 34590 blk 53 spin 1288
> lwlock 42: shacq 5014729 exacq 34942 blk 58 spin 1321
> lwlock 43: shacq 5448771 exacq 34725 blk 44 spin 1608
> lwlock 44: shacq 6420992 exacq 34980 blk 67 spin 1713
> lwlock 35: shacq 6353111 exacq 34256 blk 59 spin 1784
> lwlock 38: shacq 6052801 exacq 34913 blk 70 spin 1801
> lwlock 46: shacq 6401413 exacq 34698 blk 58 spin 1879
> lwlock 36: shacq 6051887 exacq 35309 blk 73 spin 1915
> lwlock 45: shacq 6812817 exacq 35170 blk 59 spin 1924
> lwlock 33: shacq 6793666 exacq 35009 blk 59 spin 1955
> lwlock 34: shacq 6395994 exacq 34941 blk 58 spin 2019
> lwlock 40: shacq 6388136 exacq 34579 blk 51 spin 2054
> lwlock 37: shacq 7250574 exacq 35242 blk 73 spin 2409
> lwlock 39: shacq 7109729 exacq 34892 blk 65 spin 2632
> lwlock 47: shacq 8243963 exacq 35256 blk 88 spin 3018
> lwlock 328936: shacq 33992167 exacq 0 blk 0 spin 59816
> lwlock 4: shacq 33994583 exacq 168 blk 40 spin 74018
> lwlock 41: shacq 40098590 exacq 35001 blk 440 spin 81324
> grant total: shacq 361775238 exacq 172965995 blk 2315 spin 245342
>
> This is a 5-minute test run. If I had to take a shot in the dark, the
> buffer mapping lock in the #1 spot is the one protecting the root page
> of pgbench_acocunts_pkey, and the high numbered lock in position #3 is
> the content lock on the buffer itself.
Patch missing.
--
Thom
