PX Deq wait event

Question

Hi,
Statspack report me that on our database, there is wait event about this PX Deq :
PX Deq: Table Q Normal
PX Deq: Execute Reply
PX Deq Credit: send blkd
What is this exactly ?
Nicolas.

Answer 1

Here is some additional info from metalink.
PX Deq: Table Q Normal
Indicates that the slave wait for data to arrive on its input table queue.
In a parallel execution environment we have a producer consumer model.
One slave set works on the data ( e.g. read data from disk , do a join )
called the produces slave set and the other slave set waits to get the data
that the can start the work. The slaves in this slave set are called consumer.
The wait event "PX Deq: Table Q Normal" means that the slaves in the consumer
slave have to wait for rows( data ) from the other slave set that they can
start there work.
PX Deq: Execute Reply
The QC is expecting a response (acknowledgement) to a control message
from the slaves or is expecting to dequeue data from the producer slave set.
This means he waits that the slaves finished to execute the SQL statement
and that they send the result of the query back to the QC.