Re: [HACKERS] SIGSEGV in BRIN autosummarize

On Sat, Oct 14, 2017 at 08:56:56PM -0500, Justin Pryzby wrote:
> On Fri, Oct 13, 2017 at 10:57:32PM -0500, Justin Pryzby wrote:
> > > Also notice the vacuum process was interrupted, same as yesterday (think
> > > goodness for full logs).  Our INSERT script is using python
> > > multiprocessing.pool() with "maxtasksperchild=1", which I think means we load
> > > one file and then exit the subprocess, and pool() creates a new subproc, which
> > > starts a new PG session and transaction.  Which explains why autovacuum starts
> > > processing the table only to be immediately interrupted.
> 
> On Sun, Oct 15, 2017 at 01:57:14AM +0200, Tomas Vondra wrote:
> > I don't follow. Why does it explain that autovacuum gets canceled? I
> > mean, merely opening a new connection/session should not cancel
> > autovacuum. That requires a command that requires table-level lock
> > conflicting with autovacuum (so e.g. explicit LOCK command, DDL, ...).
> 
> I was thinking that INSERT would do it, but I gather you're right about
> autovacuum.  Let me get back to you about this..

I confirmed that we're taking an explicit lock before creating new child tables
(as I recall, to avoid errors in the logs shortly after midnight when multiple
subprocesses see data for the new date for the first time):
2017-10-15 12:52:50.499-04 | 59e3925e.6951 | statement: LOCK TABLE cdrs_huawei_sgsnPDPRecord IN SHARE UPDATE EXCLUSIVE
MODE

Probably we can improve that with LOCK TABLE ONLY.

Justin


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