## Name

LOCK SET — Guard Slony-I replication set to prepare for `MOVE SET`

## Synopsis

`LOCK SET (options);`

## Description

Guards a replication set against client application updates in preparation for a MOVE SET command.

This command must be the first in a possible statement group (`try`). The reason for this is that it needs to commit the changes made to the tables (adding a special trigger function) before it can wait for every concurrent transaction to finish. At the same time it cannot hold an open transaction to the same database itself since this would result in blocking itself forever.

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

The operation waits for transaction IDs to advance in order that data is not missed on the new origin. Thus, if you have long-running transactions running on the source node, this operation will wait for those transactions to complete. Unfortunately, if you have another database on the same postmaster as the origin node, long running transactions on that database will also be considered even though they are essentially independent.

`ID = ival`

  ID of the set to lock

`ORIGIN = ival`

  Node ID of the current set origin

This uses schemadoclockset( integer ).

## Example

    LOCK SET (
       ID = 1,
       RECEIVER = 3
    );

## Locking Behaviour

Exclusive locks on each replicated table will be taken out on the origin node, and triggers are added to each such table that reject table updates.

## Version Information

This command was introduced in Slony-I 1.0