Description:
Currently an ALTER TABLE that changes the UNION information for an existing MERGE table will block if there are any locks on the MERGE table itself or any of it's subtables.
It would be great if the blocking that occurs could be relaxed greatly so that the UNION information for active MERGE tables could be updated more easily.
How to repeat:
N/A
Suggested fix:
Here are some examples that illustrate how the locking could be relaxed.
Eg 1.
1. A long running UPDATE is occurring on the 'logs_20050101' table, which is one of many in the UNION that makes up the 'logs' table.
2. An ALTER is issued to add a new underlying table to the 'logs' MERGE.
If there are any queries acting on the underlying tables, this should not effect the ability to ALTER the MERGE table itself.
Eg 2.
1. A long running UPDATE is occurring on the 'logs' table, which is a MERGE of many log tables.
2. An ALTER is issued to add a new underlying table to the 'logs' MERGE.
The UPDATE should continue running using the pre-ALTER definition of the MERGE, the ALTER should complete and any new queries will see the newly defined UNION.
