Re: BUG #13490: Segmentation fault on pg_stat_activity

This particular instance is from pghero, which is a monitoring tool.   It
can be reproduced simply by querying stat_activity in psql as well.  Pghero
is using prepared statements via ruby from a quick skim on their github
repo.

We have pg_stat_statements enabled, and can reproduce without pghero setup
as well.  No other extensions loaded.
On Jul 12, 2015 2:37 PM, "Tom Lane" <tgl@sss.pgh.pa.us> wrote:

> Michael Bommarito <michael@bommaritollc.com> writes:
> > Here's the session with debug_query_string:
> > (gdb) printf "%s\n", debug_query_string
> > SELECT application_name AS source, client_addr AS ip, COUNT(*) AS
> > total_connections FROM pg_stat_activity WHERE pid <> pg_backend_pid()
> GROUP
> > BY application_name, ip ORDER BY COUNT(*) DESC, application_name ASC,
> > client_addr ASC
>
> Thanks.  This still doesn't match the stack trace: in particular, this
> stack frame
>
> #3  0x00007fd0d478152c in expression_tree_mutator (node=0x7fd0d5d9e908,
> mutator=0x7fd0d481c390 <replace_rte_variables_mutator>,
> context=0x7fff52170620) at
>
> /tmp/buildd/postgresql-9.5-9.5~alpha1/build/../src/backend/nodes/nodeFuncs.c:2769
>
> indicates that we found a PlaceHolderInfo node in the expression tree that
> pullup_replace_vars() was applied to, but so far as I can see no such node
> should exist in the query tree generated by this query.  The most likely
> theory seems to be that something clobbered the query tree while it was
> sitting in the plancache, causing this recursive function to follow a
> bogus pointer.  But that doesn't leave us with a lot to go on.
>
> What can you tell us about the environment this is happening in?
> How is the client-side code executing the failing queries?  (We know
> it's using extended query protocol, but is it preparing a statement
> and then executing it repeatedly, or just using a one-shot unnamed
> prepared statement?)  What nondefault settings are in use on the
> server side?  Do you have any extensions loaded, such as
> pg_stat_statements or auto_explain?
>
>                         regards, tom lane
>