Re: hardware upgrade, performance degrade?

On Fri, Mar 1, 2013 at 1:52 AM, Steven Crandell
<steven(dot)crandell(at)gmail(dot)com>wrote:

> Recently I moved my ~600G / ~15K TPS database from a
> 48 core(at)2(dot)0GHz server with 512GB RAM on 15K RPM disk
> to a newer server with
> 64 core(at)2(dot)2Ghz server with 1T of RAM on 15K RPM disks
>
> The move was from v9.1.4 to v9.1.8 (eventually also tested with v9.1.4 on
> the new hardware) and was done via base backup followed by slave promotion.
> All postgres configurations were matched exactly as were system and kernel
> parameters.
>
> On the first day that this server saw production load levels it absolutely
> fell on its face. We ran an exhaustive battery of tests including failing
> over to the new (hardware matched) slave only to find the problem happening
> there also.
>
> After several engineers all confirmed that every postgres and system
> setting matched, we eventually migrated back onto the original hardware
> using exactly the same methods and settings that had been used while the
> data was on the new hardware. As soon as we brought the DB live on the
> older (supposedly slower) hardware, everything started running smoothly
> again.
>
> As far as we were able to gather in the frantic moments of downtime,
> hundreds of queries were hanging up while trying to COMMIT. This in turn
> caused new queries backup as they waited for locks and so on.
>
> Prior to failing back to the original hardware, we found interesting posts
> about people having problems similar to ours due to NUMA and several
> suggested that they had solved their problem by setting
> vm.zone_reclaim_mode = 0
>
> Unfortunately we experienced the exact same problems even after turning
> off the zone_reclaim_mode. We did extensive testing of the i/o on the new
> hardware (both data and log arrays) before it was put into service and
> have done even more comprehensive testing since it came out of service.
> The short version is that the disks on the new hardware are faster than
> disks on the old server. In one test run we even set the server to write
> WALs to shared memory instead of to the log LV just to help rule out i/o
> problems and only saw a marginal improvement in overall TPS numbers.
>
> At this point we are extremely confident that if we have a configuration
> problem, it is not with any of the usual postgresql.conf/sysctl.conf
> suspects. We are pretty sure that the problem is being caused by the
> hardware in some way but that it is not the result of a hardware failure
> (e.g. degraded array, raid card self tests or what have you).
>
> Given that we're dealing with new hardware and the fact that this still
> acts a lot like a NUMA issue, are there other settings we should be
> adjusting to deal with possible performance problems associated with NUMA?
>
> Does this sound like something else entirely?
>
> Any thoughts appreciated.
>

One piece of information that you didn't supply ... sorry if this is
obvious, but did you run the usual range of performance tests using
pgbench, bonnie++ and so forth to confirm that the new server was working
well before you put it into production? Did it compare well on those same
tests to your old hardware?

Craig

> thanks,
> Steve
>