Re: group locking: incomplete patch, just for discussion

Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Nov 13, 2014 at 3:38 AM, Jeff Davis <pgsql@j-davis.com> wrote:
>> If two backends both have an exclusive lock on the relation for a join
>> operation, that implies that they need to do their own synchronization,
>> because obviously the lock manager is not doing it for them.

> This doesn't make sense to me.  Why would they need to synchronize
> access to a relation in order to join it?

What's more to the point: why would you take an exclusive lock just to
do a join?
        regards, tom lane