Horton

Re: pg_restore causing deadlocks on partitioned tables

Amit Langote <amitlangote09@gmail.com>

View thread View on postgr.es
From: Amit Langote <amitlangote09@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Domagoj Smoljanovic <domagoj.smoljanovic@oradian.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2020-09-15T14:07:30Z
Lists: pgsql-hackers 
On Tue, Sep 15, 2020 at 10:47 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Amit Langote <amitlangote09@gmail.com> writes:
> > On Tue, Sep 15, 2020 at 9:09 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> I wrote a quick patch for this part.  It seems pretty safe and probably
> >> could be back-patched without fear.
>
> > The patch's theory that if the parent column has NOT NULL set then it
> > must be set in child tables too does not actually hold for plain
> > inheritance cases, because as shown above, NOT NULL can be dropped in
> > children independently of the parent.
>
> Ah, right.  That seems like a bug but we have not attempted to fix it.

IIRC, when this behavior was brought up as a bug in past discussions,
it was decided that it will be fixed when NOT NULL constraints are
represented using pg_constraint entries.

> But we could restrict the optimization to partitioned tables, where
> the assumption does hold, no?

Yeah, seems safe in their case.

-- 
Amit Langote
EnterpriseDB: http://www.enterprisedb.com

Commits

  1. Don't fetch partition check expression during InitResultRelInfo.

  2. Avoid unnecessary recursion to child tables in ALTER TABLE SET NOT NULL.