Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager

On Thu, Mar 12, 2020 at 11:15 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> I have fixed this in the attached patch set.
>

I have modified your
v4-0003-Conflict-Extension-Page-lock-in-group-member patch. The
modifications are (a) Change src/backend/storage/lmgr/README to
reflect new behaviour, (b) Introduce a new macro LOCK_LOCKTAG which
slightly simplifies the code, (c) moved the deadlock.c check a few
lines up and (d) changed a few comments.

It might be better if we can move the checks related to extension and
page lock in a separate API or macro. What do you think?

I have also used an extension to test this patch. This is the same
extension that I have used to test the group locking patch. It will
allow backends to form a group as we do for parallel workers. The
extension is attached to this email.

Test without patch:
Session-1
Create table t1(c1 int, c2 char(500));
Select become_lock_group_leader();

Insert into t1 values(generate_series(1,100),'aaa'); -- stop this
after acquiring relation extension lock via GDB.

Session-2
Select become_lock_group_member();
Insert into t1 values(generate_series(101,200),'aaa');
- Debug LockAcquire and found that it doesn't generate conflict for
Relation Extension lock.

The above experiment has shown that without patch group members can
acquire relation extension lock if the group leader has that lock.
After patch the second session waits for the first session to release
the relation extension lock. I know this is not a perfect way to test,
but it is better than nothing. I think we need to do some more
testing either using this extension or some other way for extension
and page locks.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com