What is locktype=transactionid ?

Hi

[Apologies for the long lines - not sure how to format them better]

I have a process that is waiting for a lock and the locktype of the lock is
"transactionid".

Despite a fair bit of googling I have been unable to find more information
on this type of lock.

Here are the relevant rows from pg_locks:

locktype | database | relation | page | tuple | virtualxid |
transactionid | classid | objid | objsubid | virtualtransaction | pid
| mode | granted
---------------+----------+----------+------+-------+------------+---------------+---------+-------+----------+--------------------+-------+---------------+---------
transactionid | | | | | |
83827390 | | | | 5/153427 | 20128 |
ExclusiveLock | t
transactionid | | | | | |
83827390 | | | | 8/171365 | 20289 |
ShareLock | f

And here are the relevant rows from pg_stat_activity:

client_addr | client_port | age | datid | datname |
procpid | usesysid | usename |
current_query | waiting |
xact_start | query_start |
backend_start | client_addr | client_port
-------------+-------------+-----------------+---------+-------------------+---------+----------+----------+----------------------------------------------------------------------+---------+-------------------------------+-------------------------------+-------------------------------+-------------+-------------
127.0.0.1 | 40926 | 05:28:08.349825 | 1569605 | nova_experimental
| 20128 | 10 | postgres | <IDLE> in
transaction | f |
2010-05-17 22:12:15.083799+00 | 2010-05-17 22:12:15.90937+00 | 2010-05-17
22:10:00.024239+00 | 127.0.0.1 | 40926
127.0.0.1 | 36054 | 05:28:08.345873 | 1569605 | nova_experimental
| 20289 | 10 | postgres | UPDATE
"users" | t | 2010-05-17
22:12:15.122643+00 | 2010-05-17 22:12:15.913322+00 | 2010-05-17
22:10:31.817664+00 | 127.0.0.1 | 36054

: SET "lock_version" = 2955, "previous_passwords" =
NULL

: WHERE id =
185

: AND "lock_version" =
2954

:

Can anybody point me to where I can find more information?

I am using PostgreSQL 8.3.9 on Ubuntu 9.04

Thanks

Regards, Tony