SLONIK EXECUTE SCRIPT

Description

Executes a script containing arbitrary SQL statements on all nodes that are subscribed to a set at a common controlled point within the replication transaction stream.

The specified event origin must be the origin of the set. The script file must not contain any START or COMMIT TRANSACTION calls. (This changes somewhat in PostgreSQL 8.0 once nested transactions, aka savepoints, are supported) In addition, non-deterministic DML statements (like updating a field with CURRENT_TIMESTAMP) must be avoided, since the data changes done by the script are explicitly not replicated.

See also the warnings in Section 3.2.

Note that this is a potentially heavily-locking operation, which means that it can get stuck behind other database activity.

Note that if you need to make reference to the cluster name, you can use the token @CLUSTERNAME@; if you need to make reference to the Slony-I namespace, you can use the token @NAMESPACE@; both will be expanded into the appropriate replacement tokens.

This uses schemadocddlscript_complete(integer, text, integer).

Example

EXECUTE SCRIPT (
   SET ID = 1,
   FILENAME = '/tmp/changes_2008-04-01.sql',
   EVENT NODE = 1
);
    

Locking Behaviour

Up until the 2.0 branch, each replicated table received an exclusive lock, on the origin node, in order to remove the replication triggers; after the DDL script completes, those locks will be cleared. In the 2.0 branch this is no longer the case. EXECUTE SCRIPT won't obtain any locks on your application tables though the script that you executing probably will. Due to bug #137 you should avoid concurrent writes to the tables being modified by the script while the script is running.

After the DDL script has run on the origin node, it will then run on subscriber nodes, where replicated tables will be similarly altered to remove replication triggers, therefore requiring that exclusive locks be taken out on each node, in turn.

Version Information

This command was introduced in Slony-I 1.0.

Before Slony-I version 1.2, the entire DDL script was submitted as one PQexec() request, with the implication that the entire script was parsed based on the state of the database before invokation of the script. This means statements later in the script cannot depend on DDL changes made by earlier statements in the same script. Thus, you cannot add a column to a table and add constraints to that column later in the same request.

In Slony-I version 1.2, the DDL script is split into statements, and each statement is submitted separately. As a result, it is fine for later statements to refer to objects or attributes created or modified in earlier statements. Furthermore, in version 1.2, the slonik output includes a listing of each statement as it is processed, on the set origin node. Similarly, the statements processed are listed in slon logs on the other nodes.

In Slony-I version 1.0, this would only lock the tables in the specified replication set. As of 1.1 (until 2.0), all replicated tables are locked (e.g. - triggers are removed at the start, and restored at the end). This deals with the risk that one might request DDL changes on tables in multiple replication sets. With version 2.0 no locks on application tables are obtained by Slony-I

In version 2.0, the default value for EVENT NODE was removed, so a node must be specified.

As of version 2.0.7, the log triggers on all replicated tables are checked to ensure their parameters match the primary key on the table. If they do not match, those tables that are exclusively locked as a result of the DDL request will have the triggers recreated to match the primary key. Tables that do not have an exclusive lock will not be corrected, but a warning message will be generated. The function repair_log_triggers(only_locked boolean) may be used manually to correct the triggers on those tables.