| From: | "Todd A(dot) Cook" <tcook(at)blackducksoftware(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, PostgreSQL Bugs <pgsql-bugs(at)postgresql(dot)org> |
| Subject: | Re: BUG #14932: SELECT DISTINCT val FROM table gets stuck in an infinite loop |
| Date: | 2017-12-06 19:04:56 |
| Message-ID: | 359db34e-2bb1-8bee-4709-2b23ac7b22bd@blackducksoftware.com |
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| Lists: | pgsql-bugs |
On 12/06/17 12:19, Andres Freund wrote:
> On 2017-12-06 12:14:24 -0500, Tom Lane wrote:
>> Checking out hashint8() on random data shows no such obvious fault.
>> You've apparently got a data set that exposes a weakness in hashint8,
>> but it's not very clear what that is.
>
> It's intentionally designed to cause problems afaict:
>
> http://archives.postgresql.org/message-id/861b9f1f-cdc0-bc49-2595-80bc39c37dc3%40blackducksoftware.com
Definitely not intentionally. My wording there could have been better;
perhaps "we expect to get lots of duplicates in that column and we then
need to find the unique values". Eventually, a substantial number of
the duplicates will be deleted, but that's further along in the process.
-- todd
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