Re: BUG #6200: standby bad memory allocations on SELECT

"Daniel Farina" <daniel(at)heroku(dot)com> writes:
> A huge thanks to Conrad Irwin of Rapportive for furnishing virtually all the
> details of this bug report.

This isn't really enough information to reproduce the problem ...

> The occurrence rate is somewhere in the one per tens-of-millions of
> queries.

... and that statement is going to discourage anyone from even trying,
since with such a low occurrence rate it's going to be impossible to be
sure whether the setup to reproduce the problem is correct. So if you'd
like this to be fixed, you're either going to need to show us exactly
how to reproduce it, or investigate it yourself.

The way that I'd personally proceed to investigate it would probably be
to change the "invalid memory alloc request size" size errors (in
src/backend/utils/mmgr/mcxt.c; there are about four occurrences) from
ERROR to PANIC so that they'll provoke a core dump, and then use gdb
to get a stack trace, which would provide at least a little more
information about what happened. However, if you are only able to
reproduce it in a production server, you might not like that approach.
Perhaps you can set up an extra standby that's only there for testing,
so you don't mind if it crashes?

regards, tom lane