I tried CLOG Buffers 32 and the performance is as good as 64 bit.. (I
havent tried 16 yet though.. ) I am going to try your second patch now..
Also here is the breakup by Mode. The combined time is the total time it
waits for all counts.
Lock Id Mode Count
ProcArrayLock Shared 1
CLogControlLock Exclusive 4
CLogControlLock Shared 4
XidGenLock Shared 4
XidGenLock Exclusive 7
WALInsertLock Exclusive 21
WALWriteLock Exclusive 62
ProcArrayLock Exclusive 79
Lock Id Mode Combined Time (ns)
CLogControlLock Exclusive 325200
CLogControlLock Shared 4509200
XidGenLock Exclusive 11839600
ProcArrayLock Shared 40506600
XidGenLock Shared 119013700
WALInsertLock Exclusive 148063100
WALWriteLock Exclusive 347052100
ProcArrayLock Exclusive 1054780600
Here is another one at higher user count 1600:
bash-3.00# ./4_lwlock_waits.d 9208
Lock Id Mode Count
CLogControlLock Exclusive 1
CLogControlLock Shared 2
XidGenLock Shared 7
WALInsertLock Exclusive 12
WALWriteLock Exclusive 50
ProcArrayLock Exclusive 82
Lock Id Mode Combined Time (ns)
CLogControlLock Exclusive 27300
XidGenLock Shared 14689300
CLogControlLock Shared 72664900
WALInsertLock Exclusive 101431300
WALWriteLock Exclusive 534357400
ProcArrayLock Exclusive 4110350300
Now I will try with your second patch.
Regards,
Jignesh
Simon Riggs wrote:
On Thu, 2007-07-26 at 17:17 -0400, Jignesh K. Shah wrote:
Lock Id Combined Time (ns)
XidGenLock 194966200
WALInsertLock 517955000
CLogControlLock 679665100
WALWriteLock 2838716200
ProcArrayLock 44181002600
Is this the time the lock is held for or the time that we wait for that
lock? It would be good to see the break down of time separately for
shared and exclusive.
Can we have a table like this:
LockId,LockMode,SumTimeLockHeld,SumTimeLockWait
Top Wait time seems to come from the following code path for
ProcArrayLock:
Lock Id Mode Count
ProcArrayLock Exclusive 21
Lock Id Combined Time (ns)
ProcArrayLock 5255937500
Lock Id Combined Time (ns)
postgres`LWLockAcquire+0x1f0
postgres`CommitTransaction+0x104
postgres`CommitTransactionCommand+0xbc
postgres`finish_xact_command+0x78
Well thats pretty weird. That code path clearly only happens once per
transaction and ought to be fast. The other code paths that take
ProcArrayLock like TransactionIdIsInProgress() and GetSnapshotData()
ought to spend more time holding the lock. Presumably you are running
with a fair number of SERIALIZABLE transactions?
Are you running with commit_delay > 0? Its possible that the call to
CountActiveBackends() is causing pinging of the procarray by other
backends while we're trying to read it during CommitTransaction(). If
so, try the attached patch.
------------------------------------------------------------------------
Index: src/backend/access/transam/xact.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/access/transam/xact.c,v
retrieving revision 1.245
diff -c -r1.245 xact.c
*** src/backend/access/transam/xact.c 7 Jun 2007 21:45:58 -0000 1.245
--- src/backend/access/transam/xact.c 27 Jul 2007 09:09:08 -0000
***************
*** 820,827 ****
* are fewer than CommitSiblings other backends with active
* transactions.
*/
! if (CommitDelay > 0 && enableFsync &&
! CountActiveBackends() >= CommitSiblings)
pg_usleep(CommitDelay);
XLogFlush(recptr);
--- 820,826 ----
* are fewer than CommitSiblings other backends with active
* transactions.
*/
! if (CommitDelay > 0 && enableFsync)
pg_usleep(CommitDelay);
XLogFlush(recptr);
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