Re: [PERFORM] psql -A (unaligned format) eats too much

> Mark Woodward wrote:
>>> "Jim C. Nasby" <jnasby(at)pervasive(dot)com> writes:
>>>
>>>> On Mon, Jun 05, 2006 at 11:27:30AM -0400, Tom Lane wrote:
>>>>
>>>>> I'm reading this as just another uninformed complaint about libpq's
>>>>> habit of buffering the whole query result. It's possible that
>>>>> there's
>>>>> a memory leak in the -A path specifically, but nothing said so far
>>>>> provided any evidence for that.
>>>>>
>>>> Certainly seems like it. It seems like it would be good to allow for
>>>> libpq not to buffer, since there's cases where it's not needed...
>>>>
>>> See past discussions. The problem is that libpq's API says that when
>>> it
>>> hands you back the completed query result, the command is complete and
>>> guaranteed not to fail later. A streaming interface could not make
>>> that
>>> guarantee, so it's not a transparent substitution.
>>>
>>> I wouldn't have any strong objection to providing a separate API that
>>> operates in a streaming fashion, but defining it is something no one's
>>> bothered to do yet. In practice, if you have to code to a variant API,
>>> it's not that much more trouble to use a cursor...
>>>
>>>
>>
>> Wouldn't the "COPY (select ...) TO STDOUT" format being discussed solve
>> this for free?
>>
>>
>>
>
> It won't solve it in the general case for clients that expect a result
> set. ISTM that "use a cursor" is a perfectly reasonable answer, though.

I'm not sure I agree -- surprise!

psql is often used as a command line tool and using a cursor is not
acceptable.

Granted, with an unaligned output, perhaps psql should not buffer the
WHOLE result at once, but without rewriting that behavior, a COPY from
query may be close enough.