PHPLIB-1236 Implement Multi-Doc Benchmarks

[GromNaN]

Fix PHPLIB-1236

https://github.com/mongodb/specifications/blob/master/source/benchmarking/benchmarking.rst#multi-doc-benchmarks

• Find many and empty the cursor
• Small doc bulk insert
• Large doc bulk insert
• GridFS upload
• GridFS download

\MongoDB\Benchmark\DriverBench\MultiDocBench

    benchFindMany # Driver default typemap..I2 - Mo133.957ms (±0.20%)
    benchFindMany # Raw BSON................I2 - Mo17.109ms (±0.86%)
    benchBulkInsert # Small doc.............I2 - Mo53.328ms (±0.25%)
    benchBulkInsert # Small BSON doc........I2 - Mo53.180ms (±0.36%)
    benchBulkInsert # Large doc.............I2 - Mo242.104ms (±2.10%)
    benchBulkInsert # Large BSON doc........I2 - Mo239.291ms (±0.63%)

\MongoDB\Benchmark\DriverBench\GridFSBench

    benchUpload.............................I2 - Mo31.448ms (±0.47%)
    benchDownload...........................I2 - Mo67.099ms (±11.71%)

Subjects: 4, Assertions: 0, Failures: 0, Errors: 0

[GromNaN]

Extracted GridFS benchmarks into a specific class because they are very different that other collection benchmarks. They need some properties.

[GromNaN]

The dataset, designated GRIDFS_LARGE (disk file 'gridfs_large.bin'), consists of a single file containing about 50 MB of random data.

I don't need to commit a 50MB file full of NULL characters from the spec. I can generate it on-demand in-memory.

[alcaeus]

Agreed, thank you!

[GromNaN]

Refactored to give access to an instance of each library objects, and cache them.

[GromNaN]

50MB file takes a lot more than expected to be downloaded in-memory.

[GromNaN]

I need to profile why this is taking so much memory.

[GromNaN]

Profiling result: it's the substr that uses the most memory.

mongo-php-library/src/GridFS/ReadableStream.php

Lines 166 to 174 in ec6c431

	while (strlen($data) < $length) {
	if ($this->bufferOffset >= strlen($this->buffer) && ! $this->initBufferFromNextChunk()) {
	break;
	}
	$initialDataLength = strlen($data);
	$data .= substr($this->buffer, $this->bufferOffset, $length - $initialDataLength);
	$this->bufferOffset += strlen($data) - $initialDataLength;
	}