| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | James Coleman <jtc331(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: sqlsmith crash incremental sort |
| Date: | 2020-04-17 01:26:40 |
| Message-ID: | 20403.1587086800@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> I think we have essentially three options:
> 1) assuming there's just a single group
> 2) assuming each row is a separate group
> 3) something in between
> If (1) and (2) are worst/best-case scenarios, maybe we should pick
> something in between. We have DEFAULT_NUM_DISTINCT (200) which
> essentially says "we don't know what the number of groups is" so maybe
> we should use that.
I wouldn't recommend picking either the best or worst cases.
Possibly DEFAULT_NUM_DISTINCT is a sane choice, though it's fair to
wonder if it's quite applicable to the case where we already know
we've grouped by some columns.
regards, tom lane
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