Re: Patch to couch_btree:chunkify

[Adam Kocoloski]

I'd like to see some more concrete numbers on the performance  
difference the two versions.  I wasn't able to reproduce Chris' 10%+  
speedup using hovercraft:lightning; in fact, the two versions seem to  
be compatible within measurement variance.

I tried messing around with fprof for a while today, and if anything  
it indicates that the original version might actually be faster  
(though I find that hard to believe).  Anyway, I think we should get  
in the habit of having some quantitative, reproducible way of  
evaluating performance-related patches.

+1 for Bob's suggestion of stripping out Bt from the arguments, though.

Adam

On May 11, 2009, at 3:28 PM, Damien Katz wrote:

+1 for committing.

-Damien


On May 10, 2009, at 9:49 PM, Paul Davis wrote:

Chris reminded me that I had an optimization patch laying around for
couch_btree:chunkify and his tests show that it gets a bit of a speed
increase when running some tests with hovercraft. The basic outline  
of
what I did was to swap a call like term_to_binary([ListOfTuples])  
to a
sequence of ListOfSizes = lists:map(term_to_binary, ListOfTuples),
Size = sum(ListOfSizes), and then when we go through the list of
tuples to split them into chunks I use the pre calculated sizes.

Anyway, I just wanted to run it across the list before I commit it in
case anyone sees anything subtle I might be missing.

chunkify(_Bt, []) ->
  [];
chunkify(Bt, InList) ->
  ToSize = fun(X) -> size(term_to_binary(X)) end,
  SizeList = lists:map(ToSize, InList),
  TotalSize = lists:sum(SizeList),
  case TotalSize of
  Size when Size > ?CHUNK_THRESHOLD ->
      NumberOfChunksLikely = ((Size div ?CHUNK_THRESHOLD) + 1),
      ChunkThreshold = Size div NumberOfChunksLikely,
      chunkify(Bt, InList, SizeList, ChunkThreshold, [], 0, []);
  _Else ->
      [InList]
  end.

chunkify(_Bt, [], [], _Threshold, [], 0, Chunks) ->
  lists:reverse(Chunks);
chunkify(_Bt, [], [], _Threshold, OutAcc, _OutAccSize, Chunks) ->
  lists:reverse([lists:reverse(OutAcc) | Chunks]);
chunkify(Bt, [InElement | RestInList], [InSize | RestSizes],  
Threshold, OutAcc,
      OutAccSize, Chunks) ->
  case InSize of
  InSize when (InSize + OutAccSize) > Threshold andalso OutAcc /=  
[] ->
      chunkify(Bt, RestInList, RestSizes, Threshold, [], 0,
          [lists:reverse([InElement | OutAcc]) | Chunks]);
  InSize ->
      chunkify(Bt, RestInList, RestSizes, Threshold, [InElement |  
OutAcc],
          OutAccSize + InSize, Chunks)
  end.