Re: Named advisory locks

On 5/04/2011 5:42 PM, rihad wrote:
> Hi, all. I'm looking for a way to lock on an arbitrary string, just how
> MySQL allows doing with GET_LOCK('foo.123') / RELEASE_LOCK('foo.123'). I
> know that at least Postgres 8.3 has pg_advisory_lock() /
> pg_advisory_unlock() but they seem to accept integer values only, and
> we're already using integer values elsewhere.

Already using _string_ values elsewhere?

Alas, I don't know of any way to use string based advisory locks directly.

You could store a mapping of lock strings to allocated ints in your app
or in the DB.

Alternately, you could maybe use the full 64 bits of the single-argument
form locks to pack in the initial chars of the lock ID strings if
they're short. If you can cheat and require that lock identifiers
contain only the "base 64" characters - or even less - you can pack 10
or more characters into the 64 bits rather than the 8 chars you'd get
with one byte per char. Of course, you can't do that if your strings are
in any way user-supplied or user-visible because you can't support
non-ascii charsets when doing ugly things like that.

--
Craig Ringer

Tech-related writing at http://soapyfrogs.blogspot.com/