Re: Large Scale Aggregation (HashAgg Enhancement) - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Large Scale Aggregation (HashAgg Enhancement)
Date
Msg-id 10671.1137713891@sss.pgh.pa.us
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In response to Re: Large Scale Aggregation (HashAgg Enhancement)  (Simon Riggs <simon@2ndquadrant.com>)
Responses Re: Large Scale Aggregation (HashAgg Enhancement)  (Simon Riggs <simon@2ndquadrant.com>)
List pgsql-hackers
Simon Riggs <simon@2ndquadrant.com> writes:
> This seems to lead to a super-geometric progression in the number of
> files required,

But we double the number of batches at each step, so there are going to
be at most 20 or so levels, and that's only assuming a *horridly* wrong
initial guess by the planner.  In practice I think it's reasonable to
assume at most a couple rounds of doubling.  If you have more than that,
the extra data-shuffling is going to exhaust your patience anyway.
        regards, tom lane


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