V$PX_PROCESS contains information about the sessions running parallel execution.

Column Datatype Description
SERVER_NAME VARCHAR2(4) The name of the PX server (P000, P001, and so on)
STATUS VARCHAR2(9) The state of the PX server (IN USE|AVAILABLE)
PID NUMBER The process identifier
SPID VARCHAR2(12) OS process ID
SID NUMBER The session ID of the PX server, if in use
SERIAL# NUMBER The session serial number of the PX server, if in use