On Tue, Feb 22, 2011 at 1:31 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> I wrote: > > Ugh. That quick little "ExecRemoveJunk" is a lot more dangerous than it > > looks. I had actually looked at this before, but concluded it was OK > > because I couldn't reproduce the problem with a trigger in place. > > I guess I wasn't unlucky enough to have the chance pointer equality > > occur. > > On closer inspection, the palloc collision is actually extremely likely, > because what will happen is we'll pfree the old tuple and immediately > palloc the new one, and if the new one is of sufficiently similar size > that it needs the same size of alloc chunk, it's *guaranteed* to get > that same chunk back, because of the LIFO free-chunk chains in aset.c. > > The reason that the problem is hard to reproduce is that most triggers > (certainly those written in plpgsql) will give back newly allocated > tuples even when you return the unmodified NEW tuple. The only way to > expose the problem is for ExecBRUpdateTrigger's trigger-calling loop to > not replace the "newtuple", and the easiest way for that to happen is if > all the triggers are disabled. So that's why you're seeing it when > fooling with the replication-role setting. I was able to reproduce the > failure by creating a trigger with a false WHEN condition, and of course > there are other ways to prevent a trigger from being called too. > > regards, tom lane > Thank you very much for fixing that issue. I apologize for not providing critical details at start of the discussion (until yesterday they seems unimportant for me), I will try provide all possible details in future if I find anything else like that. Now for me start digging next strange problem described here: http://archives.postgresql.org/pgsql-admin/2011-01/msg00055.php -- Maxim Boguk Senior Postgresql DBA.
