Re: Need help understanding pg_locks

Tom Lane wrote:
> Florian Pflug <fgp(at)phlo(dot)org> writes:
> > On Jul11, 2011, at 05:47 , Bruce Momjian wrote:
> >> Thank you. I think my confusion is that virtualtransaction is the lock
> >> holder/waiter, and the other two are actual locks. The attached doc
> >> patch clarifies that. I had actually realized this a few weeks ago and
> >> forgot, meaning this is pretty confusing.
>
> > For consistency, I guess it should say "lock object" instead of simply
> > "object" the description of all the columns up to (and including)
> > "objsubid", not only those of "virtualxid" and "transactionid".
>
> Yeah, I think this patch is going in the wrong direction altogether.
> It would be better to modify the description of virtualtransaction
> and pid to say that those are the "locking" entity.

OK, so as I understand it, in pg_locks:

Column | Type | Modifiers
--------------------+----------+-----------
locktype | text |
database | oid |
relation | oid |
page | integer |
tuple | smallint |
virtualxid | text |
transactionid | xid |
classid | oid |
objid | oid |
objsubid | smallint |

virtualtransaction | text |
pid | integer |
mode | text |
granted | boolean |

It is the last four that are related to the "locking entity". I don't
see a way of improving the description of the last four columns:

http://developer.postgresql.org/pgdocs/postgres/view-pg-locks.html

What was unclear to me was that the earlier columns (illogically)
vaguely represented the locked object.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +