Hi,
On 06/11/15 16:20, Jan Wieck wrote:
> On 06/11/2015 09:53 AM, Kouhei Kaigai wrote:
>>> curious: what was work_mem set to?
>>>
>> work_mem=48GB
>>
>> My machine mounts 256GB physical RAM.
>
> work_mem can be allocated several times per backend. Nodes like sort
> and hash_aggregate may each allocate that much. You should set
> work_mem to a fraction of physical-RAM / concurrent-connections
> depending on the complexity of your queries. 48GB does not sound
> reasonable.
That's true, but there are cases where values like this may be useful
(e.g. for a particular query). We do allow such work_mem values, so I
consider this failure to be a bug.
It probably existed in the past, but was amplified by the hash join
improvements I did for 9.5, because that uses NTUP_PER_BUCKET=1 instead
of NTUP_PER_BUCKET=10. So the arrays of buckets are much larger, and we
also much more memory than we had in the past.
Interestingly, the hash code checks for INT_MAX overflows on a number of
places, but does not check for this ...
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
