LWLock statistics collector - Mailing list pgsql-patches

Hi,

Here is a patch to collect statistics of LWLocks.
The following information are available on pg_stat_lwlocks view:
  - sh_call : number of locked for share mode
  - sh_wait : number of blocked for share mode
  - ex_call : number of locked for exclusive mode
  - ex_wait : number of blocked for exclusive mode

This feature is for developers, so available only if LWLOCK_STAT is defined
(default off). Otherwise, stab functions are installed.

There is room for discussion.
  - Should not collect information for shared buffers?
        If not, we can reduce consumption of memory for stats.
  - Information for LWLockConditionalAcquire()
        It is not gathered now because of the size limitation of LWLockStat
        struct. I intended the total size of LWLock to be less than 64bytes.
  - Information for spinlocks
        Number of sleeps in s_lock() might be useful for analyzing
        spinlock-level lock contentions.
  - Documentation
        Where to document such a feature for only developers?
  ...

Comments welcome.


# SELECT * FROM pg_stat_lwlocks;
 kind |           lwlock           | sh_call | sh_wait | ex_call | ex_wait
------+----------------------------+---------+---------+---------+---------
    0 | BufFreelistLock            |       0 |       0 |    1237 |       0
    1 | ShmemIndexLock             |       0 |       0 |     437 |       0
    2 | OidGenLock                 |       0 |       0 |       0 |       0
    3 | XidGenLock                 |   80086 |       9 |    8174 |       0
    4 | ProcArrayLock              |  162491 |      59 |   16231 |      38
    5 | SInvalLock                 |  163423 |       0 |     180 |       0
    6 | FreeSpaceLock              |       0 |       0 |     399 |       0
    7 | WALInsertLock              |       0 |       0 |   67214 |     247
    8 | WALWriteLock               |       0 |       0 |    8028 |      12
    9 | ControlFileLock            |       0 |       0 |      16 |       0
   10 | CheckpointLock             |       0 |       0 |       0 |       0
   11 | CheckpointStartLock        |    8028 |       0 |       0 |       0
   12 | CLogControlLock            |   22449 |       9 |    8028 |       4
   13 | SubtransControlLock        |   32731 |       0 |       4 |       0
   14 | MultiXactGenLock           |       0 |       0 |       0 |       0
   15 | MultiXactOffsetControlLock |       0 |       0 |       0 |       0
   16 | MultiXactMemberControlLock |       0 |       0 |       0 |       0
   17 | RelCacheInitLock           |       0 |       0 |       0 |       0
   18 | BgWriterCommLock           |       0 |       0 |    1185 |       0
   19 | TwoPhaseStateLock          |       0 |       0 |       0 |       0
   20 | TablespaceCreateLock       |       0 |       0 |       0 |       0
   21 | BtreeVacuumLock            |       0 |       0 |      12 |       0
   22 | BufMappingLock             |  322414 |       1 |     315 |       0
   23 | LockMgrLock                |       0 |       0 |  207585 |    6927
   24 | BufferIO                   |       0 |       0 |    2295 |       0
   25 | BufferContent              |  522714 |     362 |   83375 |     324
   26 | CLogBuffer                 |       0 |       0 |       0 |       0
   27 | SubTransBuffer             |       0 |       0 |       0 |       0
   28 | MultiXactOffsetBuffer      |       0 |       0 |       0 |       0
   29 | MultiXactMemberBuffer      |       0 |       0 |       0 |       0
(30 rows)

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center