Re: [HACKERS] Speed up Clog Access by increasing CLOG buffers

On Wed, Aug 30, 2017 at 2:43 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Tue, Jul 4, 2017 at 12:33 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>> I have updated the patch to support wait events and moved it to upcoming CF.
>
> This patch doesn't apply any more, but I made it apply with a hammer
> and then did a little benchmarking (scylla, EDB server, Intel Xeon
> E5-2695 v3 @ 2.30GHz, 2 sockets, 14 cores/socket, 2 threads/core).
> The results were not impressive.  There's basically no clog contention
> to remove, so the patch just doesn't really do anything.
>

Yeah, in such a case patch won't help.

>  For example,
> here's a wait event profile with master and using Ashutosh's test
> script with 5 savepoints:
>
>       1  Lock            | tuple
>       2  IO              | SLRUSync
>       5  LWLock          | wal_insert
>       5  LWLock          | XidGenLock
>       9  IO              | DataFileRead
>      12  LWLock          | lock_manager
>      16  IO              | SLRURead
>      20  LWLock          | CLogControlLock
>      97  LWLock          | buffer_content
>     216  Lock            | transactionid
>     237  LWLock          | ProcArrayLock
>    1238  IPC             | ProcArrayGroupUpdate
>    2266  Client          | ClientRead
>
> This is just a 5-minute test; maybe things would change if we ran it
> for longer, but if only 0.5% of the samples are blocked on
> CLogControlLock without the patch, obviously the patch can't help
> much.  I did some other experiments too, but I won't bother
> summarizing the results here because they're basically boring.  I
> guess I should have used a bigger machine.
>

That would have been better. In any case, will do the tests on some
higher end machine and will share the results.

> Given that we've changed the approach here somewhat, I think we need
> to validate that we're still seeing a substantial reduction in
> CLogControlLock contention on big machines.
>

Sure will do so.  In the meantime, I have rebased the patch.


-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com

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