Re: [HACKERS] Everything leaks; How it mm suppose to work?

>
> Bruce:
> > Maurice:
> > > >Running postgresql in interactive mode shows that for each query I
> > > >type there is memory lost. The exact amount of memory lost depends on
> > > >the query I use. The amount of memory not freed is also a function
> > > >of the number of tuples returned.
> > > >
> > >
> > > Oops, it seems some palloced memory is not freed by pfree but
> > > using some other function(s).
> > > My mistake, sorry.
> > >
> >
> > One thing I have found is that:
> >
> >     select * from test where 1=0;
> >
> > do not leak memory while
> >
> >     select * from test where x=-999;
> >
> > does leak memory, even though neither returns any rows.  Strange.  Would
> > seem to point to the optimizer or executor.
>
> In the first case, the where clause is constant and evaluates false, so
> not much is done. In the second case, the table is scanned and presumably
> some memory is allocated for each row, probably to evaluate the expression.
> Since this memory is allocated into a per statement duration, it will not
> be freed until the end of the statement when the context is destroyed.
>
> -dg
>

Does it make sense to have a 'row' context which is released just before
starting with a new tuple ? The total number or free is the same but they
are distributed over the query and unused memory should not accumulate.
I have seen backends growing to 40-60MB with queries which scan a very
large number of rows.

Massimo Dal Zotto

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