Re: Completely un-tuned Postgresql benchmark results: SSD vs desktop HDD

On 8/10/2010 12:21 PM, Greg Smith wrote:
> Scott Carey wrote:
>> Also, the amount of data at risk in a power loss varies between
>> drives. For Intel's drives, its a small chunk of data ( < 256K).
>> For some other drives, the cache can be over 30MB of outstanding writes.
>> For some workloads this is acceptable
>
> No, it isn't ever acceptable. You can expect the type of data loss
> you get when a cache fails to honor write flush calls results in
> catastrophic database corruption. It's not "I lost the last few
> seconds"; it's "the database is corrupted and won't start" after a
> crash. This is why we pound on this topic on this list. A SSD that
> fails to honor flush requests is completely worthless for anything
> other than toy databases. You can expect significant work to recover
> any portion of your data after the first unexpected power loss under
> heavy write load in this environment, during which you're down. We do
> database corruption recovery at 2ndQuadrant; while I can't talk about
> the details of some recent incidents, I am not speaking theoretically
> when I warn about this.
>

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.

--
Brad Nicholson 416-673-4106
Database Administrator, Afilias Canada Corp.