Dropping unique constraint on PostgreSQL table taking 10+ hours We have a PostgreSQL database with a fairly large table (~50 million rows). The table has a unique constraint across several columns, each of which is indexed. For context, I recently deleted about half the rows in the table -- old data. Now I want to simply remove the multi-column unique constraint, so I executed this SQL:

alter table my_big_table drop constraint my_constraint_name


However, I started the command 10+ hours ago, and it's still running with no sign of abating. Why would dropping a constraint be taking so long? Is there anything I'm missing, or any way to perform actions like this with some kind of progress or status indication?

(I'm using PostgreSQL 9.0 on a Windows 64-bit system, and I generally connect to it using pgAdmin, though I can use the command-line client or connect programmatically too.)
Step one - go into task manager, have a look and see if anything is actually happening. If you can't see a lot of cpu and/or disk bandwidth then it's not doing anything.

Step two - check what PostgreSQL says is happening. There are two system views useful here: pg_stat_activity and pg_locks. See what's in both. The database/relation numbers in pg_locks are internal OIDs - try SELECT OID,* FROM pg_class to see which tables/indexes are being locked.

My guess is that the system is idle and it's just waiting for an exclusive lock on the table in question and something else is blocking it. The two system views should show you what is happening though.