| From: | John Naylor <john(dot)naylor(at)enterprisedb(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
| Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: PoC: Using Count-Min Sketch for join cardinality estimation |
| Date: | 2021-06-18 19:54:40 |
| Message-ID: | CAFBsxsHw-Z9vFSi7j1Yzxw7u_KcjA6c79n4QZiWwD=j4=LR_=Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Jun 18, 2021 at 3:43 PM Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)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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