Subject: Re: BUG #14932: SELECT DISTINCT val FROM table gets stuck in an
 infinite loop
To: tcook@blackducksoftware.com, pgsql-bugs@postgresql.org
References: <20171127185700.1470.20362@wrigleys.postgresql.org>
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <fd924fd9-8f27-d945-04a9-57b503896107@2ndquadrant.com>
Date: Mon, 27 Nov 2017 20:17:25 +0100
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Hi,

On 11/27/2017 07:57 PM, tcook@blackducksoftware.com wrote:
> The following bug has been logged on the website:
> 
> Bug reference:      14932
> Logged by:          Todd Cook
> Email address:      tcook@blackducksoftware.com
> PostgreSQL version: 10.1
> Operating system:   CentOS Linux release 7.4.1708 (Core)
> Description:        
> 
> It hangs on a table with 167834 rows, though it works fine with only 167833
> rows.  When it hangs, CTRL-C does not interrupt it, and the backend has to
> be killed to stop it.
> 

Can you share the query and data, so that we can reproduce the issue?

Based on the stack traces this smells like a bug in the simplehash,
introduced in PostgreSQL 10. Perhaps somewhere in tuplehash_grow(),
which gets triggered for 167834 rows (but not for 167833).

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services