On Sun, Nov 11, 2012 at 12:22 PM, Tom Lane
<tgl@sss.pgh.pa.us> wrote:
>> How long is "long"?
> I was seeing queries with around 5000-7000 "UNION ALL" statements.
Hm. I experimented with test queries created like so:
perl -e 'print "SELECT 1 a, 2 b, 3 c\n"; print "UNION ALL SELECT 1 a, 2 b, 3 c\n" foreach (1..8200);' | psql
On the machine I tried this on, it works up to about 8200 and then fails
in the way I'd expect:
ERROR: stack depth limit exceeded
HINT: Increase the configuration parameter "max_stack_depth" (currently 2048kB), after ensuring the platform's stack depth limit is adequate.
But then when I cranked it up to 80000, kaboom:
connection to server was lost
Inspection of the core dump shows transformSetOperationTree is the
problem --- it's recursing but lacks a check_stack_depth test.
So that's easy to fix, but I wonder why the critical depth limit seems
to be so much less on your machine. I get the expected error up to
about 65000 UNION ALLs --- why is yours crashing at a tenth of that?
Tom,
Interesting. I really have no idea why mine seemed to fail so much sooner. I recalled my 5k-7k figure from memory, so I might be off on that, but probably not by an order of magnitude. In any case, it sounds like you know how to fix the problem. Should I file this as a bug report or will you take care of it from here?
Best,
Matt
