I wrote:
> ... enabling LWLOCK_STATS shows that the contention
> rate on the sinval locks is now completely negligible --- one block
> per thousand acquisitions on SInvalWriteLock, and less than one in
> 10000 on SInvalReadLock.  The vast majority of the LWLock contention
> now comes from WALInsertLock and the LockMgr locks:

>       Lock                    # acquisitions  # times blocked

>       SInvalReadLock          6469840         380
>       SInvalWriteLock         240567          163
>       WALInsertLock           2388805         89142
>       LockMgr partition locks 8253142         177715

For comparison's sake I rebuilt CVS HEAD with LWLOCK_STATS enabled
and repeated the same test.  I got

        SInvalLock              81090044        505750
        WALInsertLock           2382254         62747
        LockMgr locks           10657480        171799

The change in sinval numbers is gratifying, but for awhile I didn't
believe these results because of the discrepancy in LockMgr acquisition
figures.  I think though that what we are seeing here is that CVS HEAD
has the reset-everyone-on-sinval-queue-overflow behavior, which results
in a whole lot of useless cache resets, which results in a lot of
unnecessary cache reloads, and every one of those requires taking
AccessShareLock on one or more system catalogs in order to suck the data
back in.  So the reduction in LockMgr traffic is explained by not doing
so many cache resets.

                        regards, tom lane

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