Subject: Re: [HACKERS] pg_locks view and user locks

From: "Merlin Moncure" <[email-masked]>
Date: Mon, 13 Sep 2004 16:12:32 -0400

> Merlin Moncure wrote:
> > Second,
> > Is there a reason why user level locks are completely undocumented?
> > AFAICT, There is no mention of them in anywhere in the docs,
> > particularly 12.4, which describes methods for application managed
> > concurrency.  The availability of cooperative long term locks is
> > (IMO) a really nice feature, particularly for people porting legacy
> > applications which depend on explicit locking (there is some good
> > info in the user lock module which is unfortunately under the GPL).
> 
> That's the whole problem.  I don't think anyone objects to the user
lock
> principle, but as long as it's GPL, we won't support it.  It was
> probably a mistake to accept this module in the first place.  I
believe
> some people have been trying to get the module relicensed, but that
> evidently never happened.

Well, the lock module itself is nothing more than some wrappers for the
system lock manager functions (LockAcquire,etc) in C and wrappers for
those in SQL, plus a makefile and some basic documentation...in other
words almost nothing.

If the 'userlock' module author can't be found or refuses to open his
module, why not simply rewrite it?  It's extremely small.  This also
gives an opportunity to add some missing parts, like resolving a lock to
a pid and better error handling.

In any case, IMHO it is worthwhile to flesh out 12.3, adding user locks
(simply listing as a lock type), 12.4 with usage of above, perhaps with
an example.  Also a mention of userlocks in 43.32 and possibly a new
entry in this section, depending on how they get handled per my
suggestion wrt pg_locks.  Also possibly a note in 16.4.8
(postgresql.conf entry for max_locks_per_transaction) describing the
interaction between this parameter and user locks (aside: is there
any?).  Certain aspects of these changes would of course depend on the
feasibility of moving some of the lock interfaces into the main project.

I'd be willing to have a stab at the above, is it worthwhile?

Merlin