Re: Query preparation

Tom Lane wrote:
> Oliver Jowett <oliver(at)opencloud(dot)com> writes:
>> Heikki Linnakangas wrote:
>>> Does anyone see a problem with caching the result set descriptor
>>> (RowDescription)? AFAICS it should never change after a statement is
>>> prepared. If not, I'll polish up and submit the patch.
>
>> If you tie it to the existing named statement mechanisms I think that
>> works. We invalidate the named statement anyway if the parameter types
>> change, and you want to invalidate any cached row description at the
>> same time. Schema changes could bite you, but I think they bite named
>> statements in other ways anyway. (Not sure how far the server-side
>> efforts to do plan invalidation progressed)
>
> It should be safe. The server is set up to throw an error if you try to
> re-use a prepared statement whose output tuple descriptor would have
> changed due to schema changes. So there's a backstop if the driver's
> invalidation logic misses anything.

Here's the patch. Describe message is only sent in the first invocation
of a query. The Field[] array constructed from the RowDescription
message is saved in the SimpleQuery object for reuse.

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