Re: [HACKERS] 6.5 cvs: can't drop table

Oleg Bartunov <oleg(at)sai(dot)msu(dot)su> writes:
> today I did some tests with current 6.5 from cvs and multiple joins.
> I did unpredictable server crashes, i.e. sometimes query works
> sometimes crashes.

I have a theory about why the results are random: the GEQO planner
deliberately uses random numbers to generate plans, so you don't
always get the same plan out of it. Whatever bug you are seeing
occurs only for a particular plan path. (I haven't had any luck
repeating your crash here, so the bug may be platform-specific.)

It bothers me that the GEQO results are not reliably reproducible
across platforms; that complicates debugging. I have been thinking
about suggesting that we ought to change GEQO to use a fixed random
seed value by default, with the variable random seed being available
only as a *non default* option. Comments anyone?

In the meantime, you could try setting up a pgsql/data/pg_geqo file
with a specific Random_Seed NNN line, and try different NNN values
until you find one that will reliably trigger the failure. That
would help in reproducing the problem elsewhere.

> After about a hour of my experiments I can't drop table in
> my test database:

If you crash the backend enough times, you shouldn't be too surprised
that your database gets corrupted ... I think this is just collateral
damage.

regards, tom lane