Re: Re: [WIP] Performance Improvement by reducing WAL for Update Operation

> On Thursday, October 04, 2012 12:54 PM Heikki Linnakangas
> On 03.10.2012 19:03, Amit Kapila wrote:
> > Any comments/suggestions regarding performance/functionality test?
> 
> Hmm. Doing a lot of UPDATEs concurrently can be limited by the
> WALInsertLock, which each inserter holds while copying the WAL record to
> the buffer. Reducing the size of the WAL records, by compression or
> delta encoding, alleviates that bottleneck: when WAL records are
> smaller, the lock needs to be held for a shorter duration. That improves
> throughput, even if individual backends need to do more CPU work to
> compress the records, because that work can be done in parallel. I
> suspect much of the benefit you're seeing in these tests might be
> because of that effect.
> 
> As it happens, I've been working on making WAL insertion scale better in
> general:
> http://archives.postgresql.org/message-id/5064779A.3050407@vmware.com.
> That should also help most when inserting large WAL records. The
> question is: assuming we commit the xloginsert-scale patch, how much
> benefit is there left from the compression? It will surely still help to
> reduce the size of WAL, which can certainly help if you're limited by
> the WAL I/O, but I suspect the results from the pgbench tests you run
> might look quite different.
> 
> So, could you rerun these tests with the xloginsert-scale patch applied?

I shall take care of doing the performance test with xloginsert-scale patch
as well
both for single and multi-thread.

With Regards,
Amit Kapila.