Re: [PATCH 4/4] Add tests to dblink covering use of COPY TO FUNCTION

On Tue, Nov 24, 2009 at 2:51 AM, Daniel Farina <drfarina@gmail.com> wrote:
> On Tue, Nov 24, 2009 at 2:50 AM, Hannu Krosing <hannu@2ndquadrant.com> wrote:
>> Can't you use existing aggregate function design ?
>>
>> CREATE AGGREGATE name ( input_data_type [ , ... ] ) (
>>    SFUNC = sfunc,
>>    STYPE = state_data_type
>>    [ , FINALFUNC = ffunc ]
>>    [ , INITCOND = initial_condition ]
>>    [ , SORTOP = sort_operator ]
>> )
>
> Actually, yes.  I just thought that this was an idea so crazy that no
> one would like it.

Oh, and the other elephant in the room: error handling.  How to handle
error conditions...try/catch/finally type stuff.  Aggregates do not
necessarily provide a slot for this one.  I did consider using
aggregates though, but somehow it felt to me like "I need at least a
three-tuple, why not fish around for any random bundling of three
functions..."

After all, I would not want to actually call the nodeAgg stuff to
apply the function anyway...so it'd basically be abused as a
three-tuple of functions.

Also, what if you wanted, say, replace the mechanism for COPY TO
'file'?  It'd be nice to make the following interaction (which uses
some implied global variables) not use such global variables:

BEGIN;
select open_file('/tmp/file', 'w+');
copy foo to function write_to_file;
-- what happens here if COPY aborts?  Does the transaction being in
the error state mean that files will not get closed?
select close_file();
COMMIT;

fdr