From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Oleksii Kliukin <alexk@hintbits.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: pgsql: Avoid spurious deadlocks when upgrading a tuple lock
Date: Tue, 18 Jun 2019 12:26:32 -0400
Message-ID: <20190618162632.GA9141@alvherre.pgsql> (raw)
In-Reply-To: <20190616190441.GA30993@alvherre.pgsql>
On 2019-Jun-16, Alvaro Herrera wrote:
> So, I'm too lazy today to generate a case that fully reproduces the
> deadlock, because you need to stall 's2' a little bit using the
> well-known advisory lock trick, but this one hits the code that would
> re-initialize the variable.
Here's such a case. I was unable to reproduce the condition with a
smaller sequence of commands. This one does hit the deadlock when used
with the previous code, as expected; with the fixed code (ie.
skip_tuple_lock in the outer scope and same lifetime as "first_time")
then it works fine, no deadlock.
I'm going to push the fixed commit this afternoon, including this as an
additional permutation in the spec file.
setup
{
drop table if exists tlu_job;
create table tlu_job (id integer primary key, name text);
insert into tlu_job values(1, 'a');
}
teardown
{
drop table tlu_job;
}
session "s0"
setup { begin; }
step "s0_keyshare" { select id from tlu_job where id = 1 for key share; }
step "s0_share" { select id from tlu_job where id = 1 for share; }
step "s0_rollback" { rollback; }
session "s1"
setup { begin; }
step "s1_keyshare" { select id from tlu_job where id = 1 for key share; }
step "s1_savept_e" { savepoint s1_e; }
step "s1_share" { select id from tlu_job where id = 1 for share; }
step "s1_savept_f" { savepoint s1_f; }
step "s1_fornokeyupd" { select id from tlu_job where id = 1 for no key update; }
step "s1_rollback_f" { rollback to s1_f; }
step "s1_rollback_e" { rollback to s1_e; }
step "s1_rollback" { rollback; }
session "s2"
setup { begin; }
step "s2_keyshare" { select id from tlu_job where id = 1 for key share; }
step "s2_fornokeyupd" { select id from tlu_job where id = 1 for no key update; }
step "s2_rollback" { rollback; }
session "s3"
setup { begin; }
step "s3_for_update" { select id from tlu_job where id = 1 for update; }
step "s3_rollback" { rollback; }
permutation "s1_keyshare" "s3_for_update" "s2_keyshare" "s1_savept_e" "s1_share" "s1_savept_f" "s1_fornokeyupd" "s2_fornokeyupd" "s0_keyshare" "s1_rollback_f" "s0_share" "s1_rollback_e" "s1_rollback" "s2_rollback" "s0_rollback" "s3_rollback"
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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To: pgsql-committers@postgresql.org
Cc: alvherre@2ndquadrant.com, alexk@hintbits.com, tgl@sss.pgh.pa.us, pgsql-hackers@lists.postgresql.org
Subject: Re: pgsql: Avoid spurious deadlocks when upgrading a tuple lock
In-Reply-To: <20190618162632.GA9141@alvherre.pgsql>
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