Update query started hanging on merge table

[Ronald Rudy]

I have a data warehouse type application in which I have one large merge table that I manage through an application (adding/removing tables from it as I get new data, etc.). An update query that was working with no issues previously has just started hanging (data was added).

That merge table itself is comprised of about 55 tables right now, and the total records in the table are about 11 million. It's not an even distribution across the 55 tables; some are quite large, others are smaller. The table has 49 columns, which are of virtually all types (smallint, int, decimal, varchars).

The update query joins this merge table to another table, which itself is 50-60k long. The join expression consists of an int (though it should be a smallint or could probably even be a tinyint) and a varchar (this is for mapping data from external sources to internal domain data). Both are indexed properly; the query itself is actually not particularly slow when it runs.

This update query has just started hanging, where it was not before. The status is "Sending data...". If I run this query individually against all the tables within the merge union it will execute perfectly fine, but when it is run against the large merge table it simply hangs on the 'Sending data...' status.

Any thoughts?