Hi everybody!
Recently, I've discovered an interesting feature (or a bug?) of PostgreSql
(checked 7.4.x and 8.0.x):
One may define such tables:
create table ref(
id serial primary key,
name text);
create table dat(
id serial,
ref_id int references ref(id),
comment text);
Let us fill the ref table:
insert into ref(name) values('feature');
insert into ref(name) values('bug');
The test case:
For example we have 2 concurrent transactions (tr1 and tr2):
tr1: begin;
tr2: begin;
tr1: insert into dat(ref_id, comment) values (1, 'all ok');
tr2: insert into dat(ref_id, comment) values (2, 'all ok');
tr1: insert into dat(ref_id, comment) values (2, 'lockup');
tr2: insert into dat(ref_id, comment) values (1, 'deadlock');
... and we recieve a deadlock!
Easy to understand why: each insert statement generates query like:
SELECT 1 FROM ONLY "public"."ref" x WHERE "id" = $1 FOR UPDATE OF x
So, is this behaviour of postgresql is a bug or feature?
Thanks,
Eugene.
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