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$PostgreSQL: pgsql/contrib/pgrowlocks/README.pgrowlocks,v 1.2 2007/08/27 00:13:51 tgl Exp $
pgrowlocks README Tatsuo Ishii
1. What is pgrowlocks?
pgrowlocks shows row locking information for specified table.
pgrowlocks returns following columns:
locked_row TID, -- row TID
lock_type TEXT, -- lock type
locker XID, -- locking XID
multi bool, -- multi XID?
xids xid[], -- multi XIDs
pids INTEGER[] -- locker's process id
Here is a sample execution of pgrowlocks:
test=# SELECT * FROM pgrowlocks('t1');
locked_row | lock_type | locker | multi | xids | pids
------------+-----------+--------+-------+-----------+---------------
(0,1) | Shared | 19 | t | {804,805} | {29066,29068}
(0,2) | Shared | 19 | t | {804,805} | {29066,29068}
(0,3) | Exclusive | 804 | f | {804} | {29066}
(0,4) | Exclusive | 804 | f | {804} | {29066}
(4 rows)
locked_row -- tuple ID(TID) of each locked rows
lock_type -- "Shared" for shared lock, "Exclusive" for exclusive lock
locker -- transaction ID of locker (note 1)
multi -- "t" if locker is a multi transaction, otherwise "f"
xids -- XIDs of lockers (note 2)
pids -- process ids of locking backends
note1: if the locker is multi transaction, it represents the multi ID
note2: if the locker is multi, multiple data are shown
2. Installing pgrowlocks
Installing pgrowlocks requires PostgreSQL 8.0 or later source tree.
$ cd /usr/local/src/postgresql-8.1/contrib
$ tar xfz /tmp/pgrowlocks-1.0.tar.gz
If you are using PostgreSQL 8.0, you need to modify pgrowlocks source code.
Around line 61, you will see:
#undef MAKERANGEVARFROMNAMELIST_HAS_TWO_ARGS
change this to:
#define MAKERANGEVARFROMNAMELIST_HAS_TWO_ARGS
$ make
$ make install
$ psql -e -f pgrowlocks.sql test
3. How to use pgrowlocks
pgrowlocks grab AccessShareLock for the target table and read each
row one by one to get the row locking information. You should
notice that:
1) if the table is exclusive locked by someone else, pgrowlocks
will be blocked.
2) pgrowlocks may show incorrect information if there's a new
lock or a lock is freeed while its execution.
pgrowlocks does not show the contents of locked rows. If you want
to take a look at the row contents at the same time, you could do
something like this:
SELECT * FROM accounts AS a, pgrowlocks('accounts') AS p WHERE p.locked_ row = a.ctid;
4. License
pgrowlocks is distribute under (modified) BSD license described in
the source file.
5. History
2006/03/21 pgrowlocks version 1.1 released (tested on 8.2 current)
2005/08/22 pgrowlocks version 1.0 released