Explanation of a parallel wait

GokhanVarol 2013-07-08 01:45:43

What does this wait type mean? Does it mean that producing rows from the right is slow?

Waittype: CXPACKET
resource description: exchangeEvent id=Pipe8c2e3ac480
    WaitType=e_waitPipeGetRow nodeId=0
PhysicalOp: Parallelism
LogicalOp: Gather Streams

I attached the currently running query plan. I am guessing the hash table is being built and root has to just wait maybe?

Analysis File

Screenshot

SQLkiwi 2013-07-08 02:09:06
The wait occurs when the consumer thread at the Gather Streams is waiting for a packet of rows. The consumer is doing very little work (the result output is assigned to variables) so it is not surprising that it processes all available packets very quickly.

The number of packets buffered at the exchange is limited, and the parallel threads are doing much more work per row, so they produce packets more slowly than the consumer could read them. These waits are therefore expected and harmless.

GokhanVarol 2013-07-08 02:19:19
I see, contextid = 0 blocked by all other context id at the same time, that's the coordinator. Thank you