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

On 11/27/17 14:17, Tomas Vondra wrote:
> Hi,
>
> On 11/27/2017 07:57 PM, tcook(at)blackducksoftware(dot)com wrote:
>> The following bug has been logged on the website:
>>
>> Bug reference: 14932
>> Logged by: Todd Cook
>> Email address: tcook(at)blackducksoftware(dot)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).

I've attached a reproducer using real data. (FWIW, I wasn't able to reproduce with
fake data made with generate_series().)

Also, I forgot to mention that this problem is not present in 9.6 or 9.5.

-- todd