PG Bug reporting form <noreply@postgresql.org> writes:
> I don't understand how such excessive memory consumption is produced by such
> a "simple" query.
Compare
regression=# select row(row(1));
row
---------
("(1)")
(1 row)
regression=# select row(row(row(1)));
row
---------------
("(""(1)"")")
(1 row)
regression=# select row(row(row(row(1))));
row
-------------------------
("(""(""""(1)"""")"")")
(1 row)
Each layer of ROW() has to quote the string representing the next
lower layer, so it doubles all the double-quotes per the quoting
rules at
https://www.postgresql.org/docs/current/rowtypes.html#ROWTYPES-IO-SYNTAX
So the output length nearly doubles for each layer of ROW(), and yes
it doesn't take that many layers to get to something excessive.
Maybe we could redefine the quoting rules in a way that's friendlier
to this sort of thing, but it would surely make them a lot more
complicated, which would likely introduce enough client-side bugs
to make the change unattractive. Not to mention the whole backwards
compatibility question.
On the whole I can't get excited about this, since I see no very
good reason to use such a data structure.
regards, tom lane
