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From: Todd A. Cook <tcook@blackducksoftware.com>
To: Andres Freund <andres@anarazel.de>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: PostgreSQL Bugs <pgsql-bugs@postgresql.org>
Subject: Re: BUG #14932: SELECT DISTINCT val FROM table gets stuck in an infinite loop
Date: Wed, 6 Dec 2017 16:38:18 -0500
Message-ID: <21d507d9-9024-33a8-37c8-b472b3dce7df@blackducksoftware.com> (raw)
In-Reply-To: <20171206211225.zcp2crfr3bssn3xr@alap3.anarazel.de>
References: <17357.1511841783@sss.pgh.pa.us>
	<9cd29b81-7ba1-91a2-f491-9014f4ac87e6@blackducksoftware.com>
	<2a76784c-06cb-46ec-35be-9895d144b839@2ndquadrant.com>
	<263b03b1-3e1c-49ca-165a-8ac6751419c4@2ndquadrant.com>
	<20171206193545.3imvbfwjgrmuho3s@alap3.anarazel.de>
	<ebe8b411-006e-7863-3c60-67ddafe1c636@2ndquadrant.com>
	<790BC80E-D8E5-499B-A1E3-8EE0752B53ED@anarazel.de>
	<06523583-b9c5-1424-ef0a-1fc8063e9ed7@2ndquadrant.com>
	<20171206204616.wcect35fuj5gjde2@alap3.anarazel.de>
	<67e5af9b-f509-7b9e-f7a1-e01112f6c18d@2ndquadrant.com>
	<20171206211225.zcp2crfr3bssn3xr@alap3.anarazel.de>

On 12/06/17 16:12, Andres Freund wrote:
> 
>> The datasets I shared are somewhat extreme in the sense that there are
>> many contiguous sequences of hash values, but it only takes one such
>> sequence with at least SH_GROW_MAX_MOVE values to trigger the issue. So
>> the hash table may still be perfectly fine for most keys, and only
>> slightly slower for the keys in the sequence.
> 
> Meh, we're talking about adversarial attacks here.

Hmmmmm...

I found this problem when I dropped 10.1 into a test environment to see
what would happen.  There was no deliberate attempt to break anything.

-- todd




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  Subject: Re: BUG #14932: SELECT DISTINCT val FROM table gets stuck in an infinite loop
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