title: Increase the precision of a numeric datatype without locking the table
body: <p>I would like to increase the precision of a numeric column on a large tableof  10+ million records. The standard way being <code>ALTER TABLE mytable ALTER COLUMN mycolumn TYPE numeric(15,6)</code> will lock the table. This is a highly transactional table. Is there a way to do this without locking the table and without recreating the table, copying the data, and renaming/swapping the tables? I'm currently running a dockerized postgres 9.5 </p>