Re: User concurrency thresholding: where do I look?

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



The count is only for a 10-second snapshot.. Plus remember there are about 1000 users running so the connection being profiled only gets 0.01 of the period on CPU.. And the count is for that CONNECTION only.

Anyway using the lock wait script it shows the real picture as you requested. Here the combined time means time "spent waiting" for the lock.

bash-3.00# echo 500 users
500 users
bash-3.00# ./4_lwlock_waits.d 20764

            Lock Id            Mode           Count
         OidGenLock       Exclusive               1
CheckpointStartLock          Shared               3
         OidGenLock          Shared               4
      WALInsertLock       Exclusive               7
      FreeSpaceLock       Exclusive               8
         XidGenLock       Exclusive              15
CheckpointStartLock       Exclusive              16

            Lock Id   Combined Time (ns)
         XidGenLock              3825000
         OidGenLock              5307100
      WALInsertLock              6317800
      FreeSpaceLock              7244100
CheckpointStartLock             22199200

bash-3.00# echo 600 users
600 users
bash-3.00# ./4_lwlock_waits.d 20764

            Lock Id            Mode           Count
         OidGenLock       Exclusive               1
      WALInsertLock       Exclusive               1
CheckpointStartLock          Shared               4
CheckpointStartLock       Exclusive              11
         XidGenLock       Exclusive              21

            Lock Id   Combined Time (ns)
         OidGenLock              1728200
      WALInsertLock              2040700
         XidGenLock             19878500
CheckpointStartLock             24156500

bash-3.00# echo 700 users
700 users
bash-3.00# ./4_lwlock_waits.d 20764

            Lock Id            Mode           Count
         OidGenLock          Shared               1
         XidGenLock          Shared               1
CheckpointStartLock          Shared               2
      WALInsertLock       Exclusive               4
CheckpointStartLock       Exclusive               6
      FreeSpaceLock       Exclusive               6
         XidGenLock       Exclusive              13

            Lock Id   Combined Time (ns)
         OidGenLock              1730000
      WALInsertLock              7253400
      FreeSpaceLock             10977700
CheckpointStartLock             13356800
         XidGenLock             38220500

bash-3.00# echo 800 users
800 users
bash-3.00# ./4_lwlock_waits.d 20764

            Lock Id            Mode           Count
CheckpointStartLock          Shared               1
      WALInsertLock       Exclusive               2
         XidGenLock          Shared               2
CheckpointStartLock       Exclusive               5
      FreeSpaceLock       Exclusive               8
         XidGenLock       Exclusive              12

            Lock Id   Combined Time (ns)
      WALInsertLock              3746800
      FreeSpaceLock              7628900
CheckpointStartLock             11297500
         XidGenLock             16649000

bash-3.00# echo 900 users  - BIG DROP IN THROUGHPUT OCCURS...
900 users
bash-3.00# ./4_lwlock_waits.d 20764

            Lock Id            Mode           Count
         OidGenLock       Exclusive               1
         OidGenLock          Shared               1
         XidGenLock          Shared               1
      FreeSpaceLock       Exclusive               2
      WALInsertLock       Exclusive               2
CheckpointStartLock          Shared               6
         XidGenLock       Exclusive              12
CheckpointStartLock       Exclusive             121

            Lock Id   Combined Time (ns)
         OidGenLock              1968100
      FreeSpaceLock              2076300
      WALInsertLock              2190400
         XidGenLock             20259400
CheckpointStartLock           1407294300

bash-3.00# echo 950 users
950 users
bash-3.00# ./4_lwlock_waits.d 20764

            Lock Id            Mode           Count
         OidGenLock       Exclusive               1
         OidGenLock          Shared               2
CheckpointStartLock          Shared               3
      WALInsertLock       Exclusive               4
      FreeSpaceLock       Exclusive               5
         XidGenLock       Exclusive              11
CheckpointStartLock       Exclusive              50

            Lock Id   Combined Time (ns)
      WALInsertLock              5577100
      FreeSpaceLock              9115900
         XidGenLock             13765800
         OidGenLock             50155500
CheckpointStartLock            759872200

bash-3.00# echo 1000 users
1000 users
bash-3.00# ./4_lwlock_waits.d 20764

            Lock Id            Mode           Count
         OidGenLock          Shared               1
      WALInsertLock       Exclusive               1
         XidGenLock       Exclusive               5
CheckpointStartLock          Shared               6
CheckpointStartLock       Exclusive             102

            Lock Id   Combined Time (ns)
         OidGenLock                21900
      WALInsertLock                82500
         XidGenLock              3313400
CheckpointStartLock           1448289900

bash-3.00# echo 1050 users
1050 users
bash-3.00# ./4_lwlock_waits.d 20764

            Lock Id            Mode           Count
      FreeSpaceLock       Exclusive               1
CheckpointStartLock          Shared               3
         XidGenLock       Exclusive               3
CheckpointStartLock       Exclusive             146

            Lock Id   Combined Time (ns)
      FreeSpaceLock                18400
         XidGenLock              1900900
CheckpointStartLock           2392893700

bash-3.00#






-Jignesh




Tom Lane wrote:
"Jignesh K. Shah" <J.K.Shah@xxxxxxx> writes:
Here is how I got the numbers..
I had about 1600 users login into postgresql. Then started the run with 500 users and using DTrace I started tracking Postgresql Locking "as viewed from one user/connection". Echo statements indicate how many users were active at that point and how was throughput performing. All IO is done on /tmp which means on a RAM disk.

bash-3.00# echo 500 users - baseline number
500 users
bash-3.00# ./3_lwlock_acquires.d 19178
I don't think I believe these numbers.  For one thing, CheckpointLock
is simply not ever taken in shared mode.  The ratios of counts for
different locks seems pretty improbable too, eg there is no way on
earth that the LockMgrLocks are taken more often shared than
exclusive (I would expect no shared acquires at all in the sort of
test you are running).  Not to mention that the absolute number of
counts seems way too low.  So I think the counting tool is broken.

Combined time of what exactly? It looks like this must be the total
duration the lock is held, at least assuming that the time for
CheckpointLock is correctly reported.  It'd be much more useful to see
the total time spent waiting to acquire the lock.

			regards, tom lane

---------------------------(end of broadcast)---------------------------
TIP 3: Have you checked our extensive FAQ?

               http://www.postgresql.org/docs/faq

---------------------------(end of broadcast)---------------------------
TIP 1: if posting/reading through Usenet, please send an appropriate
      subscribe-nomail command to majordomo@xxxxxxxxxxxxxx so that your
      message can get through to the mailing list cleanly

[Postgresql General]     [Postgresql PHP]     [PHP Users]     [PHP Home]     [PHP on Windows]     [Kernel Newbies]     [PHP Classes]     [PHP Books]     [PHP Databases]     [Yosemite]

  Powered by Linux