SQL Wait Event: PX Deq Credit: send blkd
Oracle Tips by Burleson Consulting
May 1, 2008
I'm running a 20 SQL count batch job on a 4-node RAC
cluster, and one of the queries takes much longer to complete when run as part
of a 20 SQL batch job count. (It completes successfully when run on it's own)
The Top User wait event that I'm seeing is PX Deq Credit: send blkd..
Is there any way I could reduce the time taken for these last few queries to
complete (or reduce this wait event)?
To start make sure you are dedicating 5 to each node. The
goal with batch jobs is to load-down the server without overloading it.
See the following on tuning large batch jobs to help reduce your wait event:
Also, we can assume that there may have been contention for
a shared resource increasing your wait event. You will have to determine
exactly what that is:
Having PX Deq Credit: send blkd as your top user wait event
is normal. My guess would be that you have maxed the CPU's with the parallel
You can take a five minute STATSPACK report and paste it into
There are ways to reduce the time taken for these last few
queries to complete, but we would have to open it up and have a look at the
Also, Take a look at these tips for tuning Oracle parallel query execution
as a means of reducing the PX Deq Credit: send blkd wait event when running DW
SQL on RAC here: