How do I measure user disk usage on Postgresql table?

["Dave" <withheld@xxxxxxxxxxxxx>]

Lets say I have a Postgresql table where I store uploaded data for all users, identified by user_id column. Is it possible to run a query to measure the storage a user is consuming?

Ideally this would be a SELECT query with WHERE clause on user_id and will only return size of the data field(s), rather then the overhead.

Any other ideas?

 

Thanks