Re: SQL/MED - core functionality

On 25.11.2010 18:28, Tom Lane wrote:
> Heikki Linnakangas<heikki.linnakangas@enterprisedb.com>  writes:
>> Hmm, I see, cached plans are planned in a shorter-lived context first,
>> and copied to permanent storage afterwards. Needs more thought then.
>> Maybe the FDW needs to provide a copyFdwPlan() function to copy FdwPlans
>> returned by that FDW.
>
> Or just specify a format for the extra information.  Perhaps it could be
> thought of as being a value of type bytea?  Obviously we can't just have
> a fixed amount of info, but maybe a blob with a length word is enough.

That seems quite awkward to work with. Let's at least make it a Node *, 
so that you can store a Value or List there, or anything else that 
already has copyObject support.

I think the PostgreSQL FDW would want to store the remote query there. 
But it's not a stretch that you want to use parameter markers in the 
remote query, with the parameter values determined at runtime. In that 
case you'd also store a list of Exprs for the parameter values (Hmm, 
BeginScan needs an ExprContext for that..). This is very hand-wavy, but 
I think we'll hit the wall with a single blob pretty quickly.

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