`adapt` is a new compression tool targeted at optimizing performance across network connections and pipelines. The tool is aimed at sensing network speeds and adapting compression level based on network or pipe speeds.
In situations where the compression level does not appropriately match the network/pipe speed, compression may be bottlenecking the entire pipeline or the files may not be compressed as much as they potentially could be, therefore losing efficiency. It also becomes quite impractical to manually measure and set an optimalcompression level (which could potentially change over time).
In order to build and use the tool, you can simply run `make adapt` in the `adaptive-compression` directory under `contrib`. This will generate an executable available for use. Another possible method of installation is running `make install`, which will create and install the binary as the command `zstd-adaptive`.
Similar to many other compression utilities, `zstd-adaptive` can be invoked by using the following format:
`zstd-adaptive [options] [file(s)]`
Supported options for the above format are described below.
`zstd-adaptive` also supports reading from `stdin` and writing to `stdout`, which is potentially more useful. By default, if no files are given, `zstd-adaptive` reads from and writes to standard I/O. Therefore, you can simply insert it within a pipeline like so:
If a file is provided, it is also possible to force writing to stdout using the `-c` flag like so:
`zstd-adaptive -c FILE | ssh "cat - > tmp.zst"`
Several options described below can be used to control the behavior of `zstd-adaptive`. More specifically, using the `-l#` and `-u#` flags will will set upper and lower bounds so that the compression level will always be within that range. The `-i#` flag can also be used to change the initial compression level. If an initial compression level is not provided, the initial compression level will be chosen such that it is within the appropriate range (it becomes equal to the lower bound).
`-l#` : set a lower bound on the compression level (default is 1)
`-u#` : set an upper bound on the compression level (default is 22)
### Benchmarking / Test results
#### Artificial Tests
These artificial tests were run by using the `pv` command line utility in order to limit pipe speeds (25 MB/s read and 5 MB/s write limits were chosen to mimic severe throughput constraints). A 40 GB backup file was sent through a pipeline, compressed, and written out to a file. Compression time, size, and ratio were computed. Data for `zstd -15` was excluded from these tests because the test runs quite long.
<table>
<tr><th> 25 MB/s read limit </th></tr>
<tr><td>
| Compressor Name | Ratio | Compressed Size | Compression Time |
The following tests were performed by piping a relatively large backup file (approximately 80 GB) through compression and over SSH to be stored on a server. The test data includes statistics for time and compressed size on `zstd` at several compression levels, as well as `zstd-adaptive`. The data highlights the potential advantages that `zstd-adaptive` has over using a low static compression level and the negative imapcts that using an excessively high static compression level can have on
pipe throughput.
| Compressor Name | Ratio | Compressed Size | Compression Time |
