Re: max_expr_depth

Joseph Shraibman <jks(at)selectacast(dot)net> writes:
> I recently tried to do a big update with postgres 7.1.2. The update was
> something like
> UPDATE table SET status = 2 WHERE id IN (a few thousand entries) AND
> status = 1;
> and I got:
> ERROR: Expression too complex: nesting depth exceeds max_expr_depth =
> 10000

How many is "a few thousand"? About 10000 by any chance? That
"IN (a, b, ...)" will expand to "((id = a) OR (id = b) OR ...)"
which would set off the expression-too-complex detector right about
10000 ORs, if I'm not mistaken.

You could crank up the max_expr_depth SET variable if you are so
inclined, but frankly performance of this query is going to suck
anyway. I'd recommend sticking the target id values into a temp
table that you can join against, instead.

As for why we have an expression-too-complex check, it's because
mysql's crashme test used to provoke a stack overflow crash...

regards, tom lane