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99 lines
3.0 KiB
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99 lines
3.0 KiB
Plaintext
$PostgreSQL: pgsql/contrib/pgrowlocks/README.pgrowlocks,v 1.1 2006/04/23 01:12:58 ishii Exp $
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pgrowlocks README Tatsuo Ishii
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1. What is pgrowlocks?
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pgrowlocks shows row locking information for specified table.
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pgrowlocks returns following data type:
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CREATE TYPE pgrowlocks_type AS (
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locked_row TID, -- row TID
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lock_type TEXT, -- lock type
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locker XID, -- locking XID
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multi bool, -- multi XID?
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xids xid[], -- multi XIDs
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pids INTEGER[] -- locker's process id
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);
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Here is a sample execution of pgrowlocks:
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test=# SELECT * FROM pgrowlocks('t1');
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locked_row | lock_type | locker | multi | xids | pids
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------------+-----------+--------+-------+-----------+---------------
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(0,1) | Shared | 19 | t | {804,805} | {29066,29068}
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(0,2) | Shared | 19 | t | {804,805} | {29066,29068}
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(0,3) | Exclusive | 804 | f | {804} | {29066}
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(0,4) | Exclusive | 804 | f | {804} | {29066}
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(4 rows)
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locked_row -- tuple ID(TID) of each locked rows
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lock_type -- "Shared" for shared lock, "Exclusive" for exclusive lock
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locker -- transaction ID of locker (note 1)
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multi -- "t" if locker is a multi transaction, otherwise "f"
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xids -- XIDs of lockers (note 2)
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pids -- process ids of locking backends
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note1: if the locker is multi transaction, it represents the multi ID
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note2: if the locker is multi, multiple data are shown
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2. Installing pgrowlocks
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Installing pgrowlocks requires PostgreSQL 8.0 or later source tree.
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$ cd /usr/local/src/postgresql-8.1/contrib
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$ tar xfz /tmp/pgrowlocks-1.0.tar.gz
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If you are using PostgreSQL 8.0, you need to modify pgrowlocks source code.
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Around line 61, you will see:
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#undef MAKERANGEVARFROMNAMELIST_HAS_TWO_ARGS
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change this to:
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#define MAKERANGEVARFROMNAMELIST_HAS_TWO_ARGS
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$ make
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$ make install
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$ psql -e -f pgrowlocks.sql test
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3. How to use pgrowlocks
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The calling sequence for pgrowlocks is as follows:
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CREATE OR REPLACE FUNCTION pgrowlocks(text) RETURNS pgrowlocks_type
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AS 'MODULE_PATHNAME', 'pgrowlocks'
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LANGUAGE 'c' WITH (isstrict);
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The parameter is a name of table. pgrowlocks returns type pgrowlocks_type.
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pgrowlocks grab AccessShareLock for the target table and read each
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row one by one to get the row locking information. You should
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notice that:
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1) if the table is exclusive locked by someone else, pgrowlocks
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will be blocked.
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2) pgrowlocks may show incorrect information if there's a new
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lock or a lock is freeed while its execution.
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pgrowlocks does not show the contents of locked rows. If you want
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to take a look at the row contents at the same time, you could do
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something like this:
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SELECT * FROM accounts AS a, pgrowlocks('accounts') AS p WHERE p.locked_ row = a.ctid;
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4. License
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pgrowlocks is distribute under (modified) BSD license described in
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the source file.
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5. History
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2006/03/21 pgrowlocks version 1.1 released (tested on 8.2 current)
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2005/08/22 pgrowlocks version 1.0 released
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