A large table.
A non-batch commit update.
Run 15mins,kill the session.
No active session.
Server Load becomes high.
Pick 28107 to check.
See event ‘PX Deq: Txn Recovery Start; and ‘wait for a undo record’.
Check parallel activity.
Top wait event for last 5 mins shows lots of ‘wait for a undo record’.
See high CPU/high active session/parallel execution in the same time window.
So above 256(128*2) PX sessions/processes are as expected.