Re: [SQL] How to avoid "Out of memory" using aggregate functions?

Well, not silly at all . . . regrouping
the order of the WHERE clause does the trick!

Cheers,

Frank

On Mon, Dec 06, 1999 at 11:23:27AM -0500, Tom Lane wrote:
> Frank Joerdens <frank(at)x9media(dot)com> writes:
> > [ complex query ]
> > which stopped working after the table grew over the 1 million mark
> > (approximately) - I get the error
>
> > FATAL 1: Memory exhausted in AllocSetAlloc()
>
> > This sounds to me like the problem described below . . . my question is:
> > Would the changes you already made to the current sources fix it for me?
>
> Afraid not. I think what's killing you is all those date_part() and
> date_trunc() operations --- the resultant datetime or float8 value from
> each one occupies memory that won't get reclaimed till end of statement
> :-(.
>
> Silly as it sounds, you might be able to put off the problem by
> rearranging the order of the WHERE clauses, remembering that AND stops
> evaluating its subclauses as soon as it finds a FALSE. Presumably the
> day check eliminates many more rows than the time-of-day checks, so
>
> WHERE
> domains.internet = stunde_test.destination
> AND
> date_trunc('day', stunde_test.date) = 'yesterday'
> AND
> date_part('hour', stunde_test.date) > 6
> AND
> date_part('hour', stunde_test.date) < 23
>
> would probably about halve the number of date_part+date_trunc
> calculations done.
>
> Of course the real fix is to recycle temporary memory for all
> expressions intra-query, but I do not know if that will get done for
> 7.0. It will get done eventually.
>
> regards, tom lane
>
> ************