Test out the performance and memory usage of various ways to compose a gzip of streaming JSON log lines.

test-gzip-json-stream.js

/**
 * Test out the performance and memory usage of various ways to compose a gzip
 * of streaming JSON log lines.
 * 
 * One fun property of gzip is that a stream with multiple gzip chunks is
 * itself valid as a single gzip stream/file. That means there are lots of
 * interesting ways to break down how you build and stream out gzip data.
 */

const fs = require("fs");
const stream = require("stream");
const { pipeline } = require("stream/promises");
const zlib = require('zlib');
const { Buffer } = require('buffer');
const { promisify } = require('util');
const JSONStream = require("JSONStream");
const split2 = require("split2");
const streamChunker = require('stream-chunker');




// A reasonably large input file that matches the type of input we expect.
// ~3 GB of ND-JSON data. Most lines are pretty short (~150 bytes), but some
// are very long (~250 kB). All lines share the same structure, and lines of
// similar length tend to come together in chunks.
const inFilePath = "./data/univaf_raw/availability_log-2021-09-21.ndjson";


/**
 * Simplest implementation: just throw Node's built-in gzip stream in a stream
 * pipeline after we serialize the JSON.
 */
async function compressionSingleStream() {
  let i = 0;
  await pipeline(
    fs.createReadStream(inFilePath),
    split2(),
    async function* (source) {
      for await (const line of source) {
        if (line) {
          yield JSON.parse(line);
        }
      }
    },
    JSONStream.stringify(false),
    zlib.createGzip({ level: zlib.constants.Z_BEST_COMPRESSION }),
    fs.createWriteStream(`${inFilePath}.basicStream.gz`)
  );
}

/**
 * Possibly over-engineered: create a stream that outputs multiple gzips, one
 * after the other (which together form a valid gzip). There's a lot of messy
 * work here involved in making sure the whole thing continues to stream without
 * taking over a huge chunk of memory for the batching.
 */
async function compressionBatchSubStream() {
  class GzipBatchStream extends stream.Duplex {
    constructor(options) {
      super({
        readableObjectMode: false,
        writableObjectMode: true
      });
      this.createNewZipper();
      this.batchSize = options.batchSize || 10_000;
    }

    createNewZipper() {
      this.inputCount = 0;
      this.currentZipStream = zlib.createGzip({ level: zlib.constants.Z_BEST_COMPRESSION });
      this.currentZipStream.on("data", (chunk) => {
        if (!this.push(chunk)) {
          this.currentZipStream.pause();
        }
      })
    }

    _write(chunk, _encoding, callback) {
      return this.currentZipStream.write(JSON.stringify(chunk) + "\n", (error) => {
        if (error) {
          return callback(error);
        }

        this.inputCount++;
        if (this.inputCount === 10_000) {
          // Don't call back that we're done until the current batch stream has been consumed!
          this.currentZipStream.once("end", () => {
            this.createNewZipper();
            callback();
          });
          this.currentZipStream.end();
        } else {
          callback();
        }
      });
    }

    _final(callback) {
      this.currentZipStream.once("end", () => {
        this.currentZipStream = null;
        callback();
      });
      this.currentZipStream.end();
    }
  
    _read(_size) {
      if (this.currentZipStream) {
        this.currentZipStream.resume();
      }
    }
  }

  await pipeline(
    fs.createReadStream(inFilePath),
    split2(),
    async function* (source) {
      for await (const line of source) {
        if (line) {
          yield JSON.parse(line);
        }
      }
    },
    new GzipBatchStream({ batchSize: 10_000 }),
    fs.createWriteStream(`${inFilePath}.batchSubStream.gz`)
  );
}

/**
 * Simple batching: buffer up a large chunk of serialized output and then gzip
 * the whole chunk and output that on the stream. Like
 * `compressionBatchSubStream`, this winds up creating an output stream that is
 * a bunch of gzips one after the other (which together also form a valid gzip.)
 * This ought to take a lot more memory, and maybe also be slower. We'll see.
 */
async function compressionBatchChunks() {
  let i = 0;
  await pipeline(
    fs.createReadStream(inFilePath),
    split2(),
    async function* (source) {
      for await (const line of source) {
        if (line) {
          yield JSON.parse(line);
        }
      }
    },
    async function* (source) {
      const gzipPromise = promisify(zlib.gzip);

      let batch = "";
      let batchSize = 0;
      for await (const row of source) {
        batchSize++;
        batch += JSON.stringify(row) + "\n";

        if (batchSize === 10_000) {
          yield await gzipPromise(batch, { level: zlib.constants.Z_BEST_COMPRESSION });
          batch = "";
          batchSize = 0;
        }
      }

      if (batch.length) {
        yield await gzipPromise(batch, { level: zlib.constants.Z_BEST_COMPRESSION });
        batch = "";
        batchSize = 0;
      }
    },
    fs.createWriteStream(`${inFilePath}.batchChunkStream.gz`)
  );
}

/**
 * Like `compressionBatchChunks`, but separates the batching from the gzipping.
 * One steam outputs batches of 10,000 lines, and its output is consumed by a
 * normal gzip stream, rather than the single shot `gzip()` call for each batch.
 */
async function compressionBatchChunks2(batchSize) {
  await pipeline(
    fs.createReadStream(inFilePath),
    split2(),
    async function* (source) {
      for await (const line of source) {
        if (line) {
          yield JSON.parse(line);
        }
      }
    },
    async function* (source) {
      for await (const row of source) {
        yield JSON.stringify(row) + "\n";
      }
    },
    async function* (source) {
      let buffer = "";
      let bufferSize = 0;
      for await (const row of source) {
        bufferSize++;
        buffer += row;

        if (bufferSize === batchSize) {
          yield buffer;
          buffer = "";
          bufferSize = 0;
        }
      }

      yield buffer;
    },
    zlib.createGzip({ level: zlib.constants.Z_BEST_COMPRESSION }),
    fs.createWriteStream(`${inFilePath}.batchChunkStream2.gz`)
  );
}

/**
 * Like `compressionBatchChunks2`, but batches by bytes instead of by line.
 */
async function compressionBatchChunks2Bytes(batchSize) {
  await pipeline(
    fs.createReadStream(inFilePath),
    split2(),
    async function* (source) {
      for await (const line of source) {
        if (line) {
          yield JSON.parse(line);
        }
      }
    },
    async function* (source) {
      for await (const row of source) {
        yield Buffer.from(JSON.stringify(row) + "\n", "utf8");
      }
    },
    async function* (source) {
      let buffer = Buffer.allocUnsafe(batchSize);
      let bufferPosition = 0;

      for await (const input of source) {
        let inputPosition = 0;

        while (inputPosition < input.length) {
          const written = input.copy(buffer, bufferPosition, inputPosition);
          inputPosition += written;
          bufferPosition += written;

          if (bufferPosition === batchSize) {
            yield buffer;
            buffer = Buffer.alloc(batchSize);
            bufferPosition = 0;
          }
        }
      }

      // Emit any leftovers.
      if (bufferPosition > 0) {
        yield buffer.slice(0, bufferPosition);
      }
    },
    zlib.createGzip({ level: zlib.constants.Z_BEST_COMPRESSION }),
    fs.createWriteStream(`${inFilePath}.batchChunkStream2Bytes.gz`)
  );
}

/**
 * Like `compressionBatchChunks2Bytes`, but with proper streams instead of
 * async generators.
 */
async function compressionBatchChunks2BytesProper({ batchSize, setHighWaterMark = false, maxMemLevel = false, setChunkSize = false, setGzipHighWaterMark = false }) {
  // Couldn't find a good version of this on NPM (seems surprising, I'm probably
  // missing it). But the `stream-chunker` package performs *terribly* (it's
  // worse than no chunking at all!)
  class BufferedStream extends stream.Transform {
    constructor ({ size = 256 * 1024, setHighWaterMark = false } = {}) {
      const options = {};
      if (setHighWaterMark) options.readableHighWaterMark = size;

      super(options);
      this.size = size;
      this.resetBuffer();
    }

    resetBuffer () {
      this.buffer = Buffer.allocUnsafe(this.size);
      this.offset = 0;
    }

    _transform (input, encoding, callback) {
      if (typeof input === "string") {
        input = Buffer.from(input, encoding);
      } else if (!(input instanceof Buffer)) {
        callback(new TypeError(`BufferedStream input must be strings or buffers, not ${input.constructor.name}`));
        return;
      }

      let inputPosition = 0;
      while (inputPosition < input.length) {
        const written = input.copy(this.buffer, this.offset, inputPosition);
        inputPosition += written;
        this.offset += written;

        if (this.offset === this.size) {
          this.push(this.buffer);
          this.resetBuffer();
        }
      }
      callback();
    }

    _flush (callback) {
      if (this.offset > 0) {
        this.push(this.buffer.slice(0, this.offset));
      }
      callback();
    }

    _destroy (error, callback) {
      this.buffer = null;
      callback(error);
    }
  }

  await pipeline(
    fs.createReadStream(inFilePath),
    split2(),
    async function* (source) {
      for await (const line of source) {
        if (line) {
          yield JSON.parse(line);
        }
      }
    },
    JSONStream.stringify(false),
    new BufferedStream({ size: batchSize, setHighWaterMark }),
    zlib.createGzip({
      level: zlib.constants.Z_BEST_COMPRESSION,
      memLevel: maxMemLevel ? zlib.constants.Z_MAX_LEVEL : zlib.constants.Z_DEFAULT_MEMLEVEL,
      chunkSize: setChunkSize ? batchSize : undefined,
      highWaterMark: setGzipHighWaterMark ? batchSize : undefined
    }),
    fs.createWriteStream(`${inFilePath}.batchChunkStream2BytesProper.gz`)
  );
}

/**
 * Like `compressionBatchChunks2Bytes`, but with a third-party component
 * (stream-chunker).
 */
 async function compressionBatchChunks2Bytes3p(batchSize) {
  await pipeline(
    fs.createReadStream(inFilePath),
    split2(),
    async function* (source) {
      for await (const line of source) {
        if (line) {
          yield JSON.parse(line);
        }
      }
    },
    JSONStream.stringify(false),
    streamChunker(batchSize, { flush: true, align: false }),
    zlib.createGzip({ level: zlib.constants.Z_BEST_COMPRESSION }),
    fs.createWriteStream(`${inFilePath}.batchChunkStream2Bytes3p.gz`)
  );
}

async function main() {
  const sizeArgument = process.argv.find(x => x.startsWith("--size="));
  const batchSize = sizeArgument && parseInt(sizeArgument.match(/=(.*)$/)?.[1], 10) || 10_000;
  console.log("Batch size:", batchSize);
  const maxMemLevel = process.argv.includes('--max-mem-level');
  console.log("maxMemLevel:", maxMemLevel);
  const setHighWaterMark = process.argv.includes('--set-high-water-mark');
  console.log("setHighWaterMark:", setHighWaterMark);
  const setChunkSize = process.argv.includes('--set-chunk-size');
  console.log("setChunkSize:", setChunkSize);
  const setGzipHighWaterMark = process.argv.includes('--set-gzip-high-water-mark');
  console.log("setGzipHighWaterMark:", setGzipHighWaterMark);

  // Print memory usage every few seconds. This is optional so we can try a few
  // runs without it and make sure it's not impacting timing.
  if (process.argv.includes("--show-memory")) {
    const formatter = new Intl.NumberFormat();
    console.log("RSS\tHeap Total\tHeap Used\tExternal\tArrayBuffers")
    setInterval(() => {
      const usage = process.memoryUsage();
      console.log([
        formatter.format(usage.rss).padStart(11, " "),
        formatter.format(usage.heapTotal).padStart(11, " "),
        formatter.format(usage.heapUsed).padStart(11, " "),
        formatter.format(usage.external).padStart(11, " "),
        formatter.format(usage.arrayBuffers).padStart(11, " "),
      ].join("\t"));
    }, 5_000).unref();
  }

  if (process.argv.includes('single-stream')) {
    await compressionSingleStream();
  }
  if (process.argv.includes('batch-sub-stream')) {
    await compressionBatchSubStream();
  }
  if (process.argv.includes('batch-chunk-stream')) {
    await compressionBatchChunks();
  }
  if (process.argv.includes('batch-chunk-stream-2')) {
    await compressionBatchChunks2(batchSize);
  }
  if (process.argv.includes('batch-chunk-stream-2-bytes')) {
    await compressionBatchChunks2Bytes(batchSize);
  }
  if (process.argv.includes('batch-chunk-stream-2-bytes-proper')) {
    await compressionBatchChunks2BytesProper({
      batchSize,
      maxMemLevel,
      setHighWaterMark,
      setChunkSize,
      setGzipHighWaterMark
    });
  }
  if (process.argv.includes('batch-chunk-stream-2-bytes-3p')) {
    await compressionBatchChunks2Bytes3p(batchSize);
  }
}

main().catch(error => {
  console.log(error);
  process.exitCode = 1;
});

I came back again for one more round of testing on this.

Since compressionBatchChunks2 taught me that we really don’t need to do any chunking of the resulting gzips to get low-memory streaming and compression, it stands to reason that memory usage could be more optimized if we batch by bytes instead of by number of lines. The added tests here look at that, and (unsurprisingly) it improves memory usage in general and also makes the range between minimum and maximum memory usage much smaller — the memory footprint stays generally consistent.

In the new code, I’ve added 3 methods:

• compressionBatchChunks2Bytes works similarly to compressionBatchChunks2, except it creates buffers of N bytes instead of strings of N lines.

• compressionBatchChunks2BytesProper is the same as the above, but the batching code is written as a transform stream instead of as an async generator. I was curious whether the async generators supported by stream.pipeline() imposed any extra overhead (or maybe even had less overhead) compared to normal streams, but writing the code as a stream also allowed me to test some optimizations around high water marks (which you can’t set for the generator). Those optimizations are:

  • Setting highWaterMark on the batching stream to match the size of the batches. This had no notable impact. (On the other hand, I can imagine how this might make a difference is data is coming into the batching stream more slowly.)
  • Setting memLevel on the gzip stream to the maximum value (that is, 9 instead of 8). This maybe has some minor speed improvements when the batch size is 64 kB – 128 kB, but it seems as likely that this is just an artifact of the particular data file I was testing with. (I don’t think it was not doing enough runs to average out random jitter, since the same pattern repeats in the next test.)
  • Setting highWaterMark on the batching stream and memLevel on the gzip stream. This performs basically the same as just using memLevel.
  • Setting chunkSize to match the batch size (the default is 16 kB) in addition to the above optimizations. This had a small but consistent speed improvement for batch sizes above 64 kB. In reality, I think what’s happening here is that the highWaterMark for filesystem streams is 64 kB, so this is really more about how few reads are needed to fill the next stream’s buffer, rather than anything about gzipping. In any case, this does mean that optimizing the gzip stream for the high water mark of the next stream can have a pretty big impact on overall performance, which is good to keep in mind.
  • Setting highWaterMark on the gzip stream in addition to the previous optimization. This had no notable impact.

  It’s worth noting that none of the above optimizations made a consistent or notable impact on memory usage.

  One other minor advantage here is that the async generators don’t work with the old-style stream created by JSONStream, while an actual stream object does. This isn’t a huge deal, though.

• compressionBatchChunks2Bytes3p uses the stream-chunker package to batch up the data instead of custom code. It turns out to be incredibly inefficient, and actually makes the whole pipeline perform worse than anything else.

Overall, these approaches (excepting compressionBatchChunks2Bytes3p, which was just bad all around) improved both memory usage and time. I didn’t have a whole lot of time to dig into this, but I’m guessing most of the speed improvement between buffering by line and buffering by bytes is down doing more string operations in JS, which would generally be a bit more expensive that operating on bytes in buffers. It could also be that I made a poor estimation of average bytes per line and the comparison isn’t as comparable as I’d hope it to be. In any case, the memory improvements between them seem more obviously clear.

One interesting thing here is that user time tends to be pretty consistent between the different optimizations, so what the optimizations are affecting is likely to be mainly about a) how well zlib is able to spread its work across cores without bottlenecking and b) how much time is spent shuttling memory/data around between JS and zlib.

In most cases, performance seems pretty consistent with chunk sizes above 32 kB, and progressively slows down as the chunks get smaller. This makes sense, since the default windowBits for zlib is 15, which equates to a 32 kB data window to work with (note: the default is also the max; this can’t be made bigger). So as soon as the batches get smaller than that, we start wasting time waiting for data to fill zlib’s internal working buffer and things really to crawl.

Finally, memory usage between all the different byte buffering approaches here was pretty consistent, so I only included numbers from one of the methods in the tables below.

Overall Lessons Here

• Gzip streams can work over large streams of data pretty efficiently and really don’t need much memory at all. You don’t need to manually break up your data into multiple gzip blocks to get efficient streaming output. (I’m not sure if this is due to an implementation change from the early days, if I was just remembering something incorrectly, or if I’d never rigorously tested what I’d read about this way back early on. 🤷 )

• Batching data before it arrives at a gzip stream can massively improve both gzip speed and memory usage. Unless the timing of each byte on your stream is very inconsistent and very slow, you should probably always have a stream batch up data before piping/writing it to a gzip stream.

• Batches should ideally be >= the window size you are using in zlib (by default, this is 32 kB). You can calculate this as batchSizeBytes = 1 << windowBits.

• Setting zlib’s memLevel to the max did not make an appreciable difference on the data set I was working with.

• Setting the high water mark on a zlib stream doesn’t make any noticeable difference.

• When possible, matching a zlib stream’s chunkSize to the highWaterMark of whatever stream is reading from it can give a small but consistent speed boost.

Some Tables with Performance Measurements

All data comes from samples across 4 runs of of each method/optimization at each batch size. The timings in the table below are averages across all four runs.

-

	Batched Lines				Batched Bytes				Batched Bytes with HighWaterMark				Batched Bytes with MemLevel				Batched Bytes with HighWaterMark + MemLevel				Batched Bytes with HighWaterMark + MemLevel + ChunkSize				Batched Bytes with HighWaterMark + MemLevel + ChunkSize + Gzip HighWaterMark
	Real	User	System		Real	User	System		Real	User	System		Real	User	System		Real	User	System		Real	User	System		Real	User	System
384 kB	2m 20s 526ms	2m 24s 22ms	4s 866ms		1m 44s 560ms	2m 29s 972ms	4s 485ms		1m 43s 448ms	2m 28s 370ms	4s 438ms		1m 42s 825ms	2m 31s 257ms	4s 340ms		1m 42s 180ms	2m 30s 183ms	4s 237ms		1m 23s 670ms	2m 29s 53ms	3s 387ms		1m 23s 985ms	2m 29s 760ms	3s 197ms
256 kB	2m 21s 242ms	2m 24s 882ms	5s 72ms		1m 43s 938ms	2m 29s 910ms	4s 455ms		1m 43s 642ms	2m 29s 520ms	4s 480ms		1m 45s 635ms	2m 30s 167ms	4s 598ms		1m 45s 498ms	2m 30s 278ms	4s 242ms		1m 26s 427ms	2m 31s 428ms	3s 310ms		1m 25s 787ms	2m 30s 268ms	3s 188ms
128 kB	2m 23s 510ms	2m 27s 320ms	5s 840ms		1m 48s 245ms	2m 30s 265ms	4s 912ms		1m 46s 820ms	2m 28s 357ms	4s 603ms		1m 38s 127ms	2m 28s 260ms	4s 482ms		1m 38s 353ms	2m 28s 507ms	4s 465ms		1m 29s 922ms	2m 30s 255ms	3s 575ms		1m 29s 362ms	2m 29s 590ms	3s 485ms
64 kB	2m 20s 620ms	2m 24s 998ms	6s 408ms		1m 44s 953ms	2m 34s 810ms	6s 423ms		1m 40s 715ms	2m 28s 390ms	4s 978ms		1m 31s 557ms	2m 25s 590ms	4s 487ms		1m 32s 445ms	2m 26s 870ms	4s 713ms		1m 31s 490ms	2m 26s 605ms	3s 975ms		1m 31s 662ms	2m 27s 198ms	3s 925ms
32 kB	2m 23s 938ms	2m 27s 446ms	7s 226ms		1m 39s 337ms	2m 33s 993ms	6s 737ms		1m 34s 802ms	2m 28s 97ms	5s 648ms		1m 32s 365ms	2m 29s 35ms	5s 480ms		1m 32s 770ms	2m 29s 490ms	5s 848ms		1m 29s 265ms	2m 23s 547ms	5s 112ms		1m 29s 90ms	2m 23s 748ms	4s 875ms
16 kB	2m 28s 364ms	2m 30s 806ms	8s 576ms		1m 54s 538ms	2m 41s 300ms	8s 488ms		1m 48s 490ms	2m 34s 162ms	7s 725ms		1m 46s 892ms	2m 33s 405ms	7s 158ms		1m 46s 705ms	2m 33s 268ms	7s 178ms		1m 44s 40ms	2m 29s 938ms	7s 32ms		1m 42s 873ms	2m 28s 690ms	6s 702ms
8 kB	2m 17s 626ms	2m 47s 722ms	10s 930ms		2m 16s 752ms	2m 44s 192ms	10s 720ms		2m 16s 37ms	2m 43s 570ms	10s 705ms		2m 11s 238ms	2m 38s 775ms	9s 830ms		2m 15s 420ms	2m 43s 232ms	10s 477ms		2m 10s 97ms	2m 37s 523ms	10s 43ms		2m 5s 370ms	2m 35s 235ms	9s 987ms
4 kB	2m 45s 2ms	3m 1s 602ms	17s 54ms		2m 36s 107ms	2m 50s 768ms	15s 790ms		2m 38s 463ms	2m 53s 37ms	16s 12ms		2m 38s 15ms	2m 52s 218ms	15s 825ms		2m 39s 782ms	2m 53s 953ms	16s 157ms		2m 30s 865ms	2m 44s 75ms	16s 655ms		2m 26s 620ms	2m 41s 398ms	16s 450ms
2 kB	-	-	-		3m 5s 350ms	3m 10s 32ms	27s 670ms		3m 3s 373ms	3m 7s 813ms	27s 480ms		3m 5s 2ms	3m 9s 303ms	27s 490ms		3m 7s 102ms	3m 10s 857ms	27s 960ms		2m 59s 490ms	3m 1s 750ms	31s 335ms		2m 55s 855ms	2m 59s 183ms	30s 680ms
1 kB	4m 7s 480ms	3m 57s 560ms	55s 32ms		3m 57s 37ms	3m 46s 927ms	54s 477ms		3m 57s 162ms	3m 47s 25ms	54s 760ms		3m 53s 578ms	3m 44s 618ms	52s 545ms		3m 54s 555ms	3m 44s 322ms	52s 935ms		3m 47s 550ms	3m 35s 745ms	1m 0s 982ms		3m 46s 415ms	3m 34s 993ms	1m 0s 417ms

---

This is the memory usage from all 4 runs of compressionBatchChunks2BytesProper with all the optimizations on. It’s not appreciably different from any other combination of optimizations or from compressionBatchChunks2Bytes.

Buffer Size	Memory Type	Average	Min	Max
384 kB	RSS	104,030,272	97,927,168	118,628,352
	Heap Total	40,648,576	39,706,624	43,089,920
	Heap Used	12,176,966	4,901,440	20,850,632
	External	57,372,070	9,660,953	213,398,241
	ArrayBuffers	8,165,564	2,582,725	21,719,237
256 kB	RSS	100,179,486	96,157,696	106,569,728
	Heap Total	40,695,748	39,444,480	42,987,520
	Heap Used	11,943,601	5,173,792	20,279,872
	External	43,228,420	3,893,785	244,273,467
	ArrayBuffers	8,046,504	2,607,301	20,039,877
128 kB	RSS	94,362,564	91,574,272	98,009,088
	Heap Total	41,277,801	39,444,480	44,130,304
	Heap Used	12,596,829	5,155,880	20,859,848
	External	38,256,011	4,393,497	128,831,350
	ArrayBuffers	3,938,731	1,468,613	8,360,145
64 kB	RSS	90,714,804	83,144,704	94,695,424
	Heap Total	41,769,508	39,706,624	45,133,824
	Heap Used	13,905,169	5,619,832	23,282,328
	External	25,749,151	2,558,489	99,488,492
	ArrayBuffers	3,069,412	846,021	8,441,476
32 kB	RSS	91,643,362	87,035,904	96,342,016
	Heap Total	42,865,784	39,968,768	50,642,944
	Heap Used	13,651,218	7,118,320	21,181,032
	External	15,561,678	1,788,441	41,385,533
	ArrayBuffers	2,523,312	714,949	6,515,831
16 kB	RSS	92,032,307	88,014,848	98,107,392
	Heap Total	43,989,299	40,230,912	52,494,336
	Heap Used	15,607,441	6,186,752	27,250,312
	External	7,777,347	1,086,626	64,537,265
	ArrayBuffers	2,530,505	714,949	6,241,937
8 kB	RSS	92,965,282	87,474,176	100,810,752
	Heap Total	44,862,025	40,493,056	51,908,608
	Heap Used	16,094,696	6,113,592	26,453,416
	External	5,992,805	936,473	35,004,788
	ArrayBuffers	2,063,636	411,845	6,147,329
4 kB	RSS	92,521,303	86,949,888	100,409,344
	Heap Total	44,862,455	40,230,912	55,087,104
	Heap Used	16,232,215	7,344,272	27,337,672
	External	5,466,803	1,227,289	37,395,032
	ArrayBuffers	2,083,278	403,653	5,817,932
2 kB	RSS	91,437,513	86,269,952	98,705,408
	Heap Total	43,407,227	40,755,200	50,028,544
	Heap Used	14,673,008	4,878,200	27,261,088
	External	8,205,030	576,025	27,599,519
	ArrayBuffers	1,943,753	174,277	7,317,701
1 kB	RSS	90,928,378	85,712,896	95,481,856
	Heap Total	43,149,016	40,230,912	48,041,984
	Heap Used	13,615,629	5,325,600	23,040,816
	External	12,124,117	576,025	64,054,792
	ArrayBuffers	1,906,545	248,005	5,843,141