Memory usage tuning

From zlib/zconf.h, modified for Node.js usage:

The memory requirements for deflate are (in bytes):

(1 << (windowBits + 2)) + (1 << (memLevel + 9));

That is: 128K for windowBits = 15 + 128K for memLevel = 8 (default values) plus a few kilobytes for small objects.

For example, to reduce the default memory requirements from 256K to 128K, the options should be set to:

const options = { windowBits: 14, memLevel: 7 };

This will, however, generally degrade compression.

The memory requirements for inflate are (in bytes) 1 << windowBits. That is, 32K for windowBits = 15 (default value) plus a few kilobytes for small objects.

This is in addition to a single internal output slab buffer of size chunkSize, which defaults to 16K.

The speed of zlib compression is affected most dramatically by the level setting. A higher level will result in better compression, but will take longer to complete. A lower level will result in less compression, but will be much faster.

In general, greater memory usage options will mean that Node.js has to make fewer calls to zlib because it will be able to process more data on each write operation. So, this is another factor that affects the speed, at the cost of memory usage.

There are equivalents to the zlib options for Brotli-based streams, although these options have different ranges than the zlib ones:

• zlib's level option matches Brotli's BROTLI_PARAM_QUALITY option.
• zlib's windowBits option matches Brotli's BROTLI_PARAM_LGWIN option.

See below for more details on Brotli-specific options.

There are equivalents to the zlib options for Zstd-based streams, although these options have different ranges than the zlib ones:

• zlib's level option matches Zstd's ZSTD_c_compressionLevel option.
• zlib's windowBits option matches Zstd's ZSTD_c_windowLog option.

See below for more details on Zstd-specific options.