Date: Tue, 3 Apr 2018 16:01:50 -0700
From: Andres Freund <andres@anarazel.de>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: amul sul <sulamul@gmail.com>, Stephen Frost <sfrost@snowman.net>,
	Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Restrict concurrent update/delete with UPDATE of
 partition key
Message-ID: <20180403230150.b564ihenfuktt7cp@alap3.anarazel.de>
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On 2018-03-06 19:57:03 +0530, Amit Kapila wrote:
> On Tue, Mar 6, 2018 at 4:53 AM, Andres Freund <andres@anarazel.de> wrote:
> > Hi,
> >
> >> diff --git a/src/backend/executor/nodeLockRows.c b/src/backend/executor/nodeLockRows.c
> >> index 7961b4be6a..b07b7092de 100644
> >> --- a/src/backend/executor/nodeLockRows.c
> >> +++ b/src/backend/executor/nodeLockRows.c
> >> @@ -218,6 +218,11 @@ lnext:
> >>                                       ereport(ERROR,
> >>                                                       (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
> >>                                                        errmsg("could not serialize access due to concurrent update")));
> >> +                             if (!BlockNumberIsValid(BlockIdGetBlockNumber(&((hufd.ctid).ip_blkid))))
> >> +                                     ereport(ERROR,
> >> +                                                     (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
> >> +                                                      errmsg("tuple to be locked was already moved to another partition due to concurrent update")));
> >> +
> >
> > Why are we using ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE rather than
> > ERRCODE_T_R_SERIALIZATION_FAILURE?  A lot of frameworks have builtin
> > logic to retry serialization failures, and this kind of thing is going
> > to resolved by retrying, no?
> >
> 
> I think it depends, in some cases retry can help in deleting the
> required tuple, but in other cases like when the user tries to perform
> delete on a particular partition table, it won't be successful as the
> tuple would have been moved.

So? In that case the retry will not find the tuple, which'll also
resolve the issue. Preventing frameworks from dealing with this seems
like a way worse issue than that.

Greetings,

Andres Freund