Re: PoC: Using Count-Min Sketch for join cardinality estimation - Mailing list pgsql-hackers

From John Naylor
Subject Re: PoC: Using Count-Min Sketch for join cardinality estimation
Date
Msg-id CAFBsxsHw-Z9vFSi7j1Yzxw7u_KcjA6c79n4QZiWwD=j4=LR_=Q@mail.gmail.com
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In response to Re: PoC: Using Count-Min Sketch for join cardinality estimation  (Tomas Vondra <tomas.vondra@enterprisedb.com>)
Responses Re: PoC: Using Count-Min Sketch for join cardinality estimation
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On Fri, Jun 18, 2021 at 3:43 PM Tomas Vondra <tomas.vondra@enterprisedb.com> wrote:

> Sorry, I'm not sure what you mean by "we set the number of MCVs to the
> number of histograms" :-(
>
> When you say "MCV limit" you mean that we limit the number of items to
> statistics target, right? I agree plan time is one concern - but it's
> also about analyze, as we need larger sample to build a larger MCV or
> histogram (as the paper you referenced shows).

Ah, I didn't realize the theoretical limit applied to the MCVs too, but that makes sense since they're basically singleton histogram buckets.

--
John Naylor
EDB: http://www.enterprisedb.com

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