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Does cascading do anything without replanning?

For cascading pools, does cascading really do anything if we don't have the following parameter set to 1? If a query cascades without replanning, will the memory acquired for the query get returned to the original pool and then be taken from the new pool it cascaded too?

select set_config('CascadeResourcePoolAlwaysReplan', 1)

Question from Optimizing Query Performance and Resource Pool Tuning @rbankula @bat

Answers

  • AFAIK replan does not happen, if it is not necessary - if the query has to go into queue, because target pool is overloaded.
    Without replan even dc_resource_acquisitions table does not contain a record related to cascade, so it looks like the query was running in the source pool all the time. This complicates monitoring a little ;-)
    Anyway, from my point of view it is valuable to do not force such replans - replan always mean the query must start from the beginning.
    Will watch this discussion curious about more details....

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