From: | Scott Carey <scott(at)richrelevance(dot)com> |
---|---|
To: | Greg Smith <greg(at)2ndquadrant(dot)com> |
Cc: | Brad Nicholson <bnichols(at)ca(dot)afilias(dot)info>, Michael March <mmarch(at)gmail(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: Completely un-tuned Postgresql benchmark results: SSD vs desktop HDD |
Date: | 2010-08-11 23:10:29 |
Message-ID: | 6FDD30A3-FEA2-45D3-8B09-2D28C6588185@richrelevance.com |
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Thread: | |
Lists: | pgsql-performance |
On Aug 10, 2010, at 11:28 AM, Greg Smith wrote:
> Brad Nicholson wrote:
>> What about putting indexes on them? If the drive fails and drops
>> writes on those, they could be rebuilt - assuming your system can
>> function without the index(es) temporarily.
>
> Dumping indexes on SSD is one of the better uses for them, presuming you
> can survive what is likely to be an outage from a "can the site handle
> full load?" perspective while they rebuild after a crash. As I'm sure
> Brad is painfully aware of already, index rebuilding in PostgreSQL can
> take a while. To spin my broken record here again, the main thing to
> note when you consider that--relocate indexes onto SSD--is that the ones
> you are most concerned about the performance of were likely to be
> already sitting in RAM anyway, meaning the SSD speedup doesn't help
> reads much. So the giant performance boost just isn't there in that case.
>
For an OLTP type system, yeah. But for DW/OLAP and batch processing the gains are pretty big. Those indexes get kicked out of RAM and then pulled back in a lot. I'm talking about a server with 72GB of RAM that can't keep enough indexes in memory to avoid a lot of random access. Putting the indexes on an SSD has lowered the random I/O load on the other drives a lot, letting them get through sequential scans a lot faster.
Estimated power failure, once every 18 months (mostly due to human error). Rebuild indexes offline for 40 minutes every 18 months? No problem.
> --
> Greg Smith 2ndQuadrant US Baltimore, MD
> PostgreSQL Training, Services and Support
> greg(at)2ndQuadrant(dot)com www.2ndQuadrant.us
>
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