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

On 11/28/17 13:14, Andres Freund wrote:
> On 2017-11-28 09:55:13 -0500, Todd A. Cook wrote:
>> On 11/27/17 23:03, Tom Lane wrote:
>>>
>>> Note that the sample data has a lot of collisions:
>>>
>>> regression=# select hashint8(val), count(*) from reproducer group by 1 order by 2 desc;
>>>     hashint8   | count
>>> -------------+-------
>>>      441526644 |  2337
>>>    -1117776826 |  1221
>>>    -1202007016 |   935
>>>    -2068831050 |   620
>>>     1156644653 |   538
>>>      553783815 |   510
>>>      259780770 |   444
>>>      371047036 |   394
>>>      915722575 |   359
>>>    ... etc etc ...
>>
>> In case it matters, the complete data set will have some outlier values with 10k to 100k
>> collisions in this column.
> 
> To make sure we're on the same page, this is data intentionally created
> to have a lot of hash collisions, is that right?

More or less.  It might be more accurate to say that it's created in such a way that
we expect to get lots of collisions.

-- todd