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Optimize percentile calculation #67

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Jan 3, 2019
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Optimize percentile calculation #67

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bcf701b
Optimize percentile calculation by optimizing binary heap clone
shuhei Dec 24, 2018
81b5bc7
Return unsorted heap items to optimize percentile calculation
shuhei Dec 29, 2018
9196aa3
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shuhei Dec 30, 2018
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7 changes: 2 additions & 5 deletions lib/binary_heap.js
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Original file line number Diff line number Diff line change
Expand Up @@ -11,11 +11,8 @@ var BinaryHeap = module.exports = function BinaryHeap(scoreFunction){

BinaryHeap.prototype = {

clone: function() {
var heap = new BinaryHeap(this.scoreFunction);
// A little hacky, but effective.
heap.content = JSON.parse(JSON.stringify(this.content));
return heap;
getValues: function() {
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One thing that is odd to me is why it does:

heap.content = JSON.parse(JSON.stringify(this.content));

This looks really inefficient, instead this should work better:

heap.content = this.content.slice(0);

I updated percentiles.js benchmark to try this out, changing the cycle method to:

  .on("cycle", function(event) {
        console.log(String(event.target));
        BinaryHeap.prototype.clone = function() {
          var heap = new BinaryHeap(this.scoreFunction);
          heap.content = this.content.slice(0);
          return heap;
        };
      })

Results:

original x 755 ops/sec ±2.86% (89 runs sampled)
updated x 3,365 ops/sec ±2.01% (93 runs sampled)

The performance is not as good as the non-copy approach, but it's definitely better than before. If we go the route of adding the snapshot parameter, we can retain a clone implementation and change it to use slice instead of using the JSON trick.

return this.content;
},

push: function(element) {
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10 changes: 2 additions & 8 deletions stats/exponentially_decaying_sample.js
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Expand Up @@ -14,15 +14,9 @@ var ExponentiallyDecayingSample = module.exports = function ExponentiallyDecayin

ExponentiallyDecayingSample.prototype = new Sample();

// This is a relatively expensive operation
// The result is not sorted in a meaningful order.
ExponentiallyDecayingSample.prototype.getValues = function() {
var values = []
, elt
, heap = this.values.clone();
while(elt = heap.pop()) {
values.push(elt.val);
}
return values;
return this.values.getValues().map(function(v) { return v.val; });
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D'oh, now that I think of it, this very line here of using map and returning the underlying value works fine! We still essentially get a snapshot, so ignore my previous comments as this is sufficient. Sorry for any confusion!

}

ExponentiallyDecayingSample.prototype.size = function() {
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