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From iyerr3 <...@git.apache.org>
Subject [GitHub] incubator-madlib issue #120: DT: Assign memory only for reachable nodes
Date Fri, 21 Apr 2017 22:21:44 GMT
Github user iyerr3 commented on the issue:

    https://github.com/apache/incubator-madlib/pull/120
  
    @ivannovick Here's an example of how much memory can be saved. The numbers below are for
a tree built for the [Poker hand dataset](https://archive.ics.uci.edu/ml/datasets/Poker+Hand),
mostly using default parameters and setting `min_splits` and `min_bucket` to `1` to build
a deep tree. 
    
    Currently, memory is allocated for the maximum possible nodes, but only a fraction of
that is actually used (indicated in `% usage` column). As expected, this `%` decreases as
depth increases, since some nodes stop branching further. With this work, memory will be allocated
at each depth only for the fraction of nodes that are actually used. 
    
    Note, this is for a specific problem/data and results will vary for other datasets. In
general, problems that are so big that they hit the 1 GB agg state limit within a couple of
tree levels will not benefit for this. 
    
    | depth | Nodes used | Max nodes (2^k - 1) | % usage | 
    |-------|-------------|---------------------|---------|
    | 2 | 3 | 3 | 100 | 
    | 3 | 7 | 7 | 100 | 
    | 4 | 11 | 15 | 73.3 | 
    | 5 | 17 | 31 | 54.8 | 
    | 6 | 25 | 63 | 39.7 | 
    | 7 | 41 | 127 | 32.2 | 
    | 8 | 73 | 255 | 28.6 | 
    | 9 | 135 | 511 | 26.4 | 
    | 10 | 251 | 1023 | 24.5 | 
    | 11 | 447 | 2047 | 21.8  | 


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