Tuesday, September 18, 2007

Jackson is Fast... but how fast?

Faster Than The Speeding Bullet?

Nope: that would be Superman. But perhaps Jackson can at least sting like a bee? Anyway, to try to answer the question, I decided to repurpose code from StaxTest (loose set of performance test components used for Woodstox development) and see how Jackson compares to the venerable Json.org reference implementation. Test classes in question will be available as part of the next Jackson source code bundle (under src/perf), and others can check out their experiences. But here are some choice tidbits until then.

First of all, I decided to use sample documents from http://www.json.org/example.html. The documents are quite short (from less than 1 kB to about 4), but since there do not seem to be similar sample document repositories as there are for xml, these would have to do. The test consists of repeated parsing of specified document. Document is first read into a byte array before running tests (to minimize I/O overhead), and then feed using implementation dependant mechanism.

For repetition count of 2500 over the largest (4 kB) of sample JSON documents, on my (t)rusty old single-CPU Athlon box, I got following numbers:

  • Jackson, fully streaming: 224 milliseconds
  • Jackson using simple Java type mapper: 333 milliseconds
  • Json.org reference implementation: 883 milliseconds

(I also did test out the other documets; numbers I saw were similar)

Fully streaming case will just iterate over all tokens of the input, without further processing. Java mapper, on the other hand, will actually construct in-memory representation (Lists, Maps, Numbers, Strings, Booleans). So for this particular case, Jackson would be about 4 times as fast as the reference implementation, when using the fastest mode. This comparison is not completely fair, of course, since the reference implementation does actually build an in-memory representation. Of course it is not necessarily true that one always needs such "tree", so your mileage may vary.

At any rate, a simplified and somewhat naive answer would be that Jackson may be 3 - 4 times as fast as the reference implementation if you use the fastest access mode (streaming); and 2 - 3 times as fast if you need an Object representation of JSON data. The usual disclaimers apply, of course: it is not always easy to give fair comparison; different kind of input might give different results and so forth. But hopefully this gives some perspective on kinds of improvements one could get. And I would love to see others doing similar measurements.

But how about the absolute speed?

So it seems like Jackson might be a wee bit faster than the most commonly used alternative. But beyond this, how would JSON compare to, say, equivalent XML parsing? Well, given the input document size and repetition counts, streaming parsing with JSON appears to proceed with respectable rate of about 50 MBps on this particular system. The usual XML processing rates using Woodstox, on same machine, is anywhere between 10 and 30 MBps, depending on complexity of the document (plain text and elements are fastest to process, attribute slower and so forth). So assuming similar information density (some people claim JSON has less fluff, but this seems debatable -- however, I haven't heard anyone claim that XML would have more compact representation in its textual serialization) it would appear that processing JSON is indeed somewhat faster, which is to be expected given simplifity of JSON as a data (transfer) format.

The real question is whether this advantage can be converted to even more significant speed boost at higher level, like when doing full Java data binding (a la JAXB). We should find it in near future once people get more serious about building toolkits on top of efficient JSON parsers...

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