| PostgreSQL 9.1.14 Documentation | ||||
|---|---|---|---|---|
| Prev | Up | Appendix F. Additional Supplied Modules | Next | |
The pgrowlocks module provides a function to show row locking information for a specified table.
pgrowlocks(text) returns setof record
The parameter is the name of a table. The result is a set of records, with one row for each locked row within the table. The output columns are shown in Table F-19.
Table F-19. pgrowlocks Output Columns
| Name | Type | Description | 
|---|---|---|
| locked_row | tid | Tuple ID (TID) of locked row | 
| lock_type | text | Shared for shared lock, or Exclusive for exclusive lock | 
| locker | xid | Transaction ID of locker, or multixact ID if multi-transaction | 
| multi | boolean | True if locker is a multi-transaction | 
| xids | xid[] | Transaction IDs of lockers (more than one if multi-transaction) | 
| pids | integer[] | Process IDs of locking backends (more than one if multi-transaction) | 
   pgrowlocks takes AccessShareLock for the
   target table and reads each row one by one to collect the row locking
   information.  This is not very speedy for a large table.  Note that:
  
    If the table as a whole is exclusive-locked by someone else,
    pgrowlocks will be blocked.
    
     pgrowlocks is not guaranteed to produce a
     self-consistent snapshot.  It is possible that a new row lock is taken,
     or an old lock is freed, during 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;Be aware however that (as of PostgreSQL 8.3) such a query will be very inefficient.
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)Tatsuo Ishii