What is the value of p1 in parallel query wait event?

A trace file from a parallel query indicates a wait event on a write to file# 1509. But there is no datafile or tempfile with that number. What is this p1 and where is it coming from?

WAIT #1: nam='direct path write' ela= 107 p1=1509 p2=368263 p3=127

WAIT #1: nam='direct path write' ela= 109 p1=1509 p2=192517 p3=127

WAIT #1: nam='direct path write' ela= 135 p1=1509 p2=480649 p3=127

WAIT #1: nam='direct path write' ela= 110 p1=1509 p2=480776 p3=127

WAIT #1: nam='direct path write' ela= 116 p1=1509 p2=480903 p3=127

WAIT #1: nam='direct path write' ela= 123 p1=1509 p2=481030 p3=127

p1 = 1509 is the temporary tablespace data file.

1509 = (value in db_files parameter in init.ora)+abs.file_number from v$tempfile.

What is the current value you set for db_files?

Example:
show parameter db_files

NAME TYPE VALUE
-------------------- ----------- ------------------------------
db_files integer 900

grep "direct path write" test_ora_1405102.trc
WAIT #1: nam='direct path write' ela= 2236 p1=901 p2=98628 p3=10
WAIT #1: nam='direct path write' ela= 2 p1=901 p2=98638 p3=2

Tamil

Thanks Tamil.

db_files is set to 1500 and temp tablespace has 10 temp files and it is trying to write to file number 9.