Creating an index on a live database

[John McCawley <nospam@xxxxxxxxxxxx>]

I have a table with a few million rows which has inserts performed on it 
roughly 50 or so times a minute.  It contains a heavily-queried column 
that I would like to add an index to, but I am concerned about a 
deadlock occurring.  Should I wait until downtime to add the index, or 
is the Postgres add index command "nice" enough to avoid deadlocks?