"Thomas F.O'Connell" <tfo@sitening.com> writes:
> The linking table is a pure linking table. It has a user_id and a
> group_id, each a foreign key. The user_id ties to the appropriate
> subclass user table. The group_id ties to the groups table, which is
> not part of an inheritance hierarchy. A multicolumn primary key covers
> both foreign keys in the linking table, and the secondary column of the
> key also has its own index.
Inserts/updates in a table that has a foreign key result in locks on the
referenced rows in the master table. Could this explain your problem?
regards, tom lane