PX Deq Credit: send blkd - wait for what?（ZT)
Detail as below
http://www.asktherealtom.ch/?p=8
"If a query is run in parallel there is a query coordinator (QC) and the query slaves. The slaves do the actual work an send the result to the query coordinator. This is done through message buffers which you specified with the parallel_execution_message_size.
This buffer exists in the large or in the shared pool depending how PARALLEL_AUTOMATIC_TUNING is set."
http://www.asktherealtom.ch/?p=8
"If a query is run in parallel there is a query coordinator (QC) and the query slaves. The slaves do the actual work an send the result to the query coordinator. This is done through message buffers which you specified with the parallel_execution_message_size.
This buffer exists in the large or in the shared pool depending how PARALLEL_AUTOMATIC_TUNING is set."
In this case the waits were cause by a query which look similar to this:
insert into tablex values (select /*+ parallel(32) */ from tabley);
Now it pretty clear from where the waits are coming. Since parallel query is enabled by default, but parallel dml is disabled, you feed a single insert process with 32 slaves. the insert process can never consume that much.
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/3637/viewspace-628286/ ，如需转载，请注明出处，否则将追究法律责任。
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