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diff --git a/vendor/github.com/klauspost/compress/zstd/README.md b/vendor/github.com/klauspost/compress/zstd/README.md index ac3640dc9..ea3e51082 100644 --- a/vendor/github.com/klauspost/compress/zstd/README.md +++ b/vendor/github.com/klauspost/compress/zstd/README.md @@ -5,7 +5,6 @@ It offers a very wide range of compression / speed trade-off, while being backed A high performance compression algorithm is implemented. For now focused on speed. This package provides [compression](#Compressor) to and [decompression](#Decompressor) of Zstandard content. -Note that custom dictionaries are only supported for decompression. This package is pure Go and without use of "unsafe". @@ -232,41 +231,6 @@ nyc-taxi-data-10M.csv gzstd 1 3325605752 928656485 23876 132.83 nyc-taxi-data-10M.csv gzkp 1 3325605752 924718719 16388 193.53 ``` -### Converters - -As part of the development process a *Snappy* -> *Zstandard* converter was also built. - -This can convert a *framed* [Snappy Stream](https://godoc.org/github.com/golang/snappy#Writer) to a zstd stream. -Note that a single block is not framed. - -Conversion is done by converting the stream directly from Snappy without intermediate full decoding. -Therefore the compression ratio is much less than what can be done by a full decompression -and compression, and a faulty Snappy stream may lead to a faulty Zstandard stream without -any errors being generated. -No CRC value is being generated and not all CRC values of the Snappy stream are checked. -However, it provides really fast re-compression of Snappy streams. - - -``` -BenchmarkSnappy_ConvertSilesia-8 1 1156001600 ns/op 183.35 MB/s -Snappy len 103008711 -> zstd len 82687318 - -BenchmarkSnappy_Enwik9-8 1 6472998400 ns/op 154.49 MB/s -Snappy len 508028601 -> zstd len 390921079 -``` - - -```Go - s := zstd.SnappyConverter{} - n, err = s.Convert(input, output) - if err != nil { - fmt.Println("Re-compressed stream to", n, "bytes") - } -``` - -The converter `s` can be reused to avoid allocations, even after errors. - - ## Decompressor Staus: STABLE - there may still be subtle bugs, but a wide variety of content has been tested. @@ -337,6 +301,21 @@ A re-used Decoder will still contain the dictionaries registered. When registering multiple dictionaries with the same ID, the last one will be used. +It is possible to use dictionaries when compressing data. + +To enable a dictionary use `WithEncoderDict(dict []byte)`. Here only one dictionary will be used +and it will likely be used even if it doesn't improve compression. + +The used dictionary must be used to decompress the content. + +For any real gains, the dictionary should be built with similar data. +If an unsuitable dictionary is used the output may be slightly larger than using no dictionary. +Use the [zstd commandline tool](https://github.com/facebook/zstd/releases) to build a dictionary from sample data. +For information see [zstd dictionary information](https://github.com/facebook/zstd#the-case-for-small-data-compression). + +For now there is a fixed startup performance penalty for compressing content with dictionaries. +This will likely be improved over time. Just be aware to test performance when implementing. + ### Allocation-less operation The decoder has been designed to operate without allocations after a warmup. |