On 8/10/2010 2:28 PM, 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.
>
The case where I'm thinking they may be of use is for indexes you can
afford to lose. I'm thinking of ones that are needed by nightly batch
jobs, down stream systems or reporting - the sorts of things that you
can turn off during a rebuild, and where the data sets are not likely
to be in cache.
We have a few such cases, but we don't need the speed of SSD's for them.
Personally, I wouldn't entertain any SSD with a capacitor backing it for
anything, even indexes. Not worth the hassle to me.
--
Brad Nicholson 416-673-4106
Database Administrator, Afilias Canada Corp.