Hi list, I've got massive wait events named "PX Deq Credit: send blkd". As far as I know, that's a parallel query issue, a producer is faster then the consumer. But thats a textbook explanantion I simply don't understand. The obvious option, to increase PARALLEL_EXECUTION_MESSAGE_SIZE, does not fit since it's set to the (x86_64) architecture's maximum, 64k. The system is rather capable, and CPU load is less than 30%, disk IO around 100MB/s, the underlying ASM diskgroups have been successfully tested with nearly 1GB/s. The query in question is a huge MERGE statement with APPEND PARALLEL hints, a little abstracted form here: MERGE /* APPEND PARALLEL ("TABLE_A") */ INTO "WA_FILBU_BEARB" USING (SELECT /*+ PARALLEL ("TABLE_B") PARALLEL ("TABLE_B") PARALLEL ("TABLE_B") PARALLEL ("TABLE_B") PARALLEL ("TABLE_B")*/ <fields> from (SELECT /*+ PARALLEL ("TABLE_B") PARALLEL ("TABLE_B") PARALLEL ("TABLE_B") PARALLEL ("TABLE_B") PARALLEL ("TABLE_B") <other fields> from <likewise select again>)) It comes from a warehouse builder application by oracle, and I have no clue if there is another SQL solution, and my question does not touch this aspect: I've got no chance to change this at the moment, and if, I am no SQL developer. But I'd like to know for improving my personal knowledge and for further issues, how I can track down the wait event (PX Deq Credit: send blkd) to a root cause, and maybe, avoid it. Any chance? :) Thanks in Advance! Martin Klier -- Usn's IT Blog for Linux, Oracle, Asterisk http://www.usn-it.de -- //www.freelists.org/webpage/oracle-l