Christopher B. Browne's Home Page
cbbrowne@acm.org

SLONIK MERGE SET

Name

MERGE SET --  Merge Slony-I replication sets together

Synopsis

MERGE SET (options);

Description

Merge a set of tables and sequences into another one. This function is a workaround for the problem that it is not possible to add tables/sequences to already-subscribed sets. One may create a temporary set, add the new objects to that, subscribe all nodes currently subscribed to the other set to this new one, and then merge the two together, eliminating the set ID that was being added.

This operation will refuse to be run if the two sets do not have exactly the same set of subscribers.

ID = ival

Unique ID of the set to contain the union of the two formerly separate sets.

ADD ID = ival

Unique ID of the set whose objects should be transferred into the above set.

ORIGIN = ival

Current origin node for both sets.

This uses mergeset(integer, integer).

Example

         # Assuming that node 1 is the origin of set 999 that has direct subscribers 2 and 3
         SUBSCRIBE SET (ID = 999, PROVIDER = 1, RECEIVER = 2);
         SYNC (ID=1);
         WAIT FOR EVENT (ORIGIN = 1, CONFIRMED = 2, WAIT ON=1);
         SUBSCRIBE SET (ID = 999, PROVIDER = 1, RECEIVER = 3);
         SYNC (ID=1);
         WAIT FOR EVENT (ORIGIN = 1, CONFIRMED = 3, WAIT ON=1);
         MERGE SET ( ID = 1, ADD ID = 999, ORIGIN = 1 );
        

Locking Behaviour

No application-visible locking should take place.

Dangerous/Unintuitive Behaviour

Merging takes place based on the configuration on the origin node. If a merge is requested while subscriptions are still being processed, this can cause in-progress subscribers' replication to break, as they'll be looking for configuration for this set which the merge request deletes. Do not be too quick to merge sets.

Version Information

This command was introduced in Slony-I 1.0.5. In 1.2.1, a race condition was rectified where the merge request would be submitted while subscriptions were still in process on subscribers; it refuses to merge before subscriptions are complete.

Google
Contact me at cbbrowne@acm.org