Document zlib options

[ilanbiala]

Based on the zlib options, it seems like there are some extra properties that can be used but aren't very well documented there either (level, memLevel, and strategy). Does it make sense to at least show which ones can be accepted?

[Fishrock123]

All options are passed to zlib. You can look up the zlib docs separately if you need to know the details. :)

Usually you wouldn't touch those things, they already default to the optimal sweet spot levels on nearly every machine.

[dougwilson]

So I had thought about doing this back at the beginning of 2014, but gave up, because I couldn't just copy Node.js docs, had to read and come up with good explanations of the stuff from the zlib man page, and have to check that those explanations actually match what Node.js is doing.

@ilanbiala if you're willing to do this, I would happily add it/accept a PR :)

[ilanbiala]

@dougwilson how explanatory do you think it should be?

[dougwilson]

how explanatory do you think it should be?

Probably just good enough so you don't have to consult any other docs to understand what they mean, since that's what it does right now (points you to read another doc source). So like an explanation that makes sense, the type and range of values the option takes.

[hex7c0]

like this?
https://github.com/kesla/node-snappy/blob/master/benchmark/benchmark.js
level: zlib.Z_BEST_SPEED
memLevel: zlib.Z_MAX_MEMLEVEL

[hex7c0]

Usually you wouldn't touch those things, they already default to the optimal sweet spot levels on nearly every machine.

can I suggest these zlib options as default?
https://gist.github.com/hex7c0/25165f2f4650dfe16832

[Fishrock123]

Why would we use those as defaults? Those values are not going to be worth your while. :)

Max speed will be faster, but compress way too little. Max memory is also certainly unnecessary, otherwise it would be the default.

[Fishrock123]

@hex7c0 Hmmm, benchmarks look promising though. How big is the file you are transferring?

[hex7c0]

@Fishrock123 I use @kesla's benchmark
so the file is this 46Kb

from http://nodejs.org/api/zlib.html#zlib_memory_usage_tuning

memLevel = 8 (default values)

from http://zlib.net/manual.html#Constants

The memLevel parameter specifies how much memory should be allocated for the internal compression state. memLevel=1 uses minimum memory but is slow and reduces compression ratio; memLevel=9 uses maximum memory for optimal speed. The default value is 8. See zconf.h for total memory usage as a function of windowBits and memLevel.

with zlib.Z_MAX_MEMLEVEL (maybe) you can raise to 9

[hex7c0]

regard compression/speed
46155 bytes no compression
14105 bytes default compression
16481 bytes zlib.Z_BEST_SPEED compression

there isn't too much difference :) +2376 bytes

[ilanbiala]

@Fishrock123 do those settings make sense?

[dougwilson]

If someone wants them documented here, please see #28 (comment) . What I need is a specific list of the options and exactly what they do and what values they accept (and their complete value range).