The equation above is essentially correct, but there are two additional considerations which factor in which are - (1) the query degree can be configured and (2) that very short queries bypass admission control.
So the general behavior would be summarized by:
# of concurrent sqls <= ((# processor cores * wlm_agent_load_trgt) / effective_query_degree) + # very short queries
And in the case some sessions were doing something like SET CURRENT DEGREE '1' you would potentially get more concurrent queries.
As a final note - the reasoning behind the default wlm_agent_load_trgt value of 32 threads per core - the goal is to let in sufficient work to drive a healthy load on the CPUs but not let them get overloaded the point where we lose efficiency (basically maximize throughput as much as possible).
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DAVID KALMUK
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Original Message:
Sent: 02-24-2019 06:47 PM
From: Daniel Wang
Subject: Concurrency Limit
I am interested in knowing this as well, so, can I continue asking for a followup question?
Without considering the sort memory limitation and the locking factor, does the following calculation make any sense?
# of concurrent sqls <= (total of agents) / effective_query_degree
where total of agents = # of processor cores * wlm_agent_load_trgt
If this formula does not a sense in some circumstances, my question is what value/how to set for the wlm_agent_load_trgt, 32; and which value/how to set for effective_query_degree?
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Daniel Wang
Original Message:
Sent: 02-18-2019 09:09 AM
From: Juliet Sigmann
Subject: Concurrency Limit
Hi -
I received the following information from some team members:
No specific limit - our adaptive workload manager does fit based admission - so concurrency achieved will depend on the resource demands of the jobs being run. With lightweight jobs it's possible to run 100's simultaneously. For heavier jobs we'll target 32 threads per core by default which typically means that if memory is not a limiting factor we'll try to execute approximately 32 queries at at time. HTH.
Without Adaptive (Row organized IIAS) we were able to run 150+ concurrent of mix workload queries
Check out the Adaptive WLM page in the manual: https://www.ibm.com/support/knowledgecenter/SS6NHC/com.ibm.swg.im.dashdb.doc/adaptive_wlm/adaptive_wlm.html
Thank you!
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Juliet Sigmann
Community Marketing Manager
IBM
FL
Original Message:
Sent: 02-12-2019 04:29 PM
From: Chandhra Vadlamudi
Subject: Concurrency Limit
Hi,
May I know if there is any query concurrency limit in IIAS like in Netezza, if so, what is the limit?
Thanks,
Chandhra Vadlamudi
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chandhra vadlamudi
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