Re: 9.5: Better memory accounting, towards memory-bounded HashAgg

On Sun, 2014-12-28 at 12:37 -0800, Jeff Davis wrote:
> I feel like I made a mistake -- can someone please do a
> sanity check on my numbers?

I forgot to randomize the inputs, which doesn't matter much for hashagg
but does matter for sort. New data script attached. The results are even
*better* for disk-based hashagg than the previous numbers suggest. Here
are some new numbers:

work_mem='1MB':
                  sort+group (s)    hashagg (s)
   singleton q1           21             10
   singleton q2           12              8
   even q1                20              7
   even q2                13              5
   skew q1                22              6
   skew q2                16              4

work_mem='4MB':
                  sort+group (s)    hashagg (s)
   singleton q1           17             10
   singleton q2           11              6
   even q1                16              7
   even q2                11              5
   skew q1                19              6
   skew q2                13              4

work_mem='16MB':
                  sort+group (s)    hashagg (s)
   singleton q1           16             11
   singleton q2           11              7
   even q1                15              8
   even q2                12              6
   skew q1                15              6
   skew q2                12              4

work_mem='64MB':
                  sort+group (s)    hashagg (s)
   singleton q1           18             12
   singleton q2           13              8
   even q1                17             10
   even q2                13              6
   skew q1                17              6
   skew q2                14              4

work_mem='256MB':
                  sort+group (s)    hashagg (s)
   singleton q1           18             12
   singleton q2           14              7
   even q1                16              9
   even q2                14              5
   skew q1                18              6
   skew q2                13              4

work_mem='512MB':
                  sort+group (s)    hashagg (s)
   singleton q1           18             12
   singleton q2           14              7
   even q1                17              9
   even q2                14              5
   skew q1                17              6
   skew q2                13              4

work_mem='2GB':
                  sort+group (s)    hashagg (s)
   singleton q1           11             11
   singleton q2            7              6
   even q1                10              9
   even q2                 7              5
   skew q1                 7              6
   skew q2                 4              4


Regards,
    Jeff Davis