Re: patch: SQL/MED(FDW) DDL

On 05.10.2010 17:56, Robert Haas wrote:
> On Tue, Oct 5, 2010 at 10:41 AM, Tom Lane<tgl@sss.pgh.pa.us>  wrote:
>> (I'd also say that your performance estimate is miles in advance of any
>> facts; but even if it's true, the caching ought to be inside the FDW,
>> because we have no clear idea of what it will need to cache.)
>
> I can't imagine how an FDW could possibly be expected to perform well
> without some persistent local data storage.  Even assume the remote
> end is PG.  To return a cost, it's going to need the contents of
> pg_statistic cached locally, for each remote table.  Do you really
> think it's going to work to incur that overhead once per table per
> backend startup?

It doesn't seem completely out of the question to me. Sure, it's 
expensive, but it's only incurred the first time a remote table is 
accessed in a session. Local persistent storage would be nice, but a lot 
of applications might prefer to not use it anyway, to ensure that fresh 
statistics are used.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com