Temp files on Commit

Hi,

I’m seeing cases where I have temp files being written on commit, such as.

2013-08-16 12:09:02 GMT [14480]: [588-1] user=dbuser,db=dbname STATEMENT:  COMMIT

2013-08-16 12:09:02 GMT [14480]: [589-1] user= dbuser,db=dbname LOG:  temporary file: path "base/pgsql_tmp/pgsql_tmp14480.263", size 814822

Is this a case of having work_mem set to low, or something else?  I haven’t seen temp files on commit before.

Thanks,

Brad.