Tom Lane wrote:
> Adrian Klaver <aklaver@comcast.net> writes:
>> Nothing. I have created a Postgres instance on an EC2 virtual machine with
>> attached EBS(Elastic Block Storage)..[...]
>
> ... I wonder whether you have any guarantees about database consistency
> in that situation? PG has some pretty strong requirements about fsync
While I agree it shouldn't be taken on faith, their documentation
does take the time to point out that syncing of I/O's is pretty
expensive operation (even literally - they charge extra for individual
i/o operations and point out that those increase with syncs).
http://aws.amazon.com/ebs/
I have a couple databases there, and based on the rather high I/O-wait
times on their cheapest ($0.10/hr) instances, I'm wildly guessing that
they're doing something reasonable for sync :-). Their higher priced
instances supposedly have better I/O performance.
> behavior etc, and I'd not want to take it on faith that a cloud
> environment will meet those requirements.
That said, even apart from any SLA of fsync itself, I imagine there's
a concern that an entire hosted cloud might vanish for any number of
reasons.