Re: ALTER TABLE .. DETACH PARTITION CONCURRENTLY - Mailing list pgsql-hackers
From | Amit Langote |
---|---|
Subject | Re: ALTER TABLE .. DETACH PARTITION CONCURRENTLY |
Date | |
Msg-id | CA+HiwqH9eD7gUVt_VH2CU43w=SZx=uKKQbBjh--4-i=2xD54NQ@mail.gmail.com Whole thread Raw |
In response to | Re: ALTER TABLE .. DETACH PARTITION CONCURRENTLY (Tom Lane <tgl@sss.pgh.pa.us>) |
Responses |
Re: ALTER TABLE .. DETACH PARTITION CONCURRENTLY
(Amit Langote <amitlangote09@gmail.com>)
|
List | pgsql-hackers |
On Mon, Apr 12, 2021 at 6:20 AM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote: > On 2021-Mar-31, Tom Lane wrote: > > > diff -U3 /home/buildfarm/trilobite/buildroot/HEAD/pgsql.build/src/test/isolation/expected/detach-partition-concurrently-4.out /home/buildfarm/trilobite/buildroot/HEAD/pgsql.build/src/test/isolation/output_iso/results/detach-partition-concurrently-4.out > > --- /home/buildfarm/trilobite/buildroot/HEAD/pgsql.build/src/test/isolation/expected/detach-partition-concurrently-4.out 2021-03-29 20:14:21.258199311 +0200 > > +++ /home/buildfarm/trilobite/buildroot/HEAD/pgsql.build/src/test/isolation/output_iso/results/detach-partition-concurrently-4.out 2021-03-30 18:54:34.272839428 +0200 > > @@ -324,6 +324,7 @@ > > 1 > > 2 > > step s1insert: insert into d4_fk values (1); > > +ERROR: insert or update on table "d4_fk" violates foreign key constraint "d4_fk_a_fkey" > > step s1c: commit; > > > > starting permutation: s2snitch s1b s1s s2detach s1cancel s3vacfreeze s1s s1insert s1c > > Hmm, actually, looking at this closely, I think the expected output is > bogus and trilobite is doing the right thing by throwing this error > here. The real question is why isn't this case behaving in that way in > every *other* animal. Indeed. I can see a wrong behavior of RelationGetPartitionDesc() in a case that resembles the above test case. drop table if exists d4_primary, d4_primary1, d4_fk, d4_pid; create table d4_primary (a int primary key) partition by list (a); create table d4_primary1 partition of d4_primary for values in (1); create table d4_primary2 partition of d4_primary for values in (2); insert into d4_primary values (1); insert into d4_primary values (2); create table d4_fk (a int references d4_primary); insert into d4_fk values (2); create table d4_pid (pid int); Session 1: begin isolation level serializable; select * from d4_primary; a --- 1 2 (2 rows) Session 2: alter table d4_primary detach partition d4_primary1 concurrently; <waits> Session 1: -- can see d4_primary1 as detached at this point, though still scans! select * from d4_primary; a --- 1 2 (2 rows) insert into d4_fk values (1); INSERT 0 1 end; Session 2: <alter-finishes> ALTER TABLE Session 1: -- FK violated select * from d4_primary; a --- 2 (1 row) select * from d4_fk; a --- 1 (1 row) The 2nd select that session 1 performs adds d4_primary1, whose detach it *sees* is pending, to the PartitionDesc, but without setting its includes_detached. The subsequent insert's RI query, because it uses that PartitionDesc as-is, returns 1 as being present in d4_primary, leading to the insert succeeding. When session 1's transaction commits, the waiting ALTER proceeds with committing the 2nd part of the DETACH, without having a chance again to check if the DETACH would lead to the foreign key of d4_fk being violated. It seems problematic to me that the logic of setting includes_detached is oblivious of the special check in find_inheritance_children() to decide whether "force"-include a detach-pending child based on cross-checking its pg_inherit tuple's xmin against the active snapshot. Maybe fixing that would help, although I haven't tried that myself yet. -- Amit Langote EDB: http://www.enterprisedb.com
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