diff options
| -rw-r--r-- | src/compression.rs | 50 |
1 files changed, 38 insertions, 12 deletions
diff --git a/src/compression.rs b/src/compression.rs index 7e20a94..9b17698 100644 --- a/src/compression.rs +++ b/src/compression.rs @@ -39,14 +39,37 @@ impl CompressionFormat { Ok(match self { CompressionFormat::Gz => Box::new(GzEncoder::new(file, flate2::Compression::best())), CompressionFormat::Xz => { - // Note that preset 6 takes about 173MB of memory per thread, so we limit the number of - // threads to not blow out 32-bit hosts. (We could be more precise with - // `MtStreamBuilder::memusage()` if desired.) - let stream = xz2::stream::MtStreamBuilder::new() - .threads(Ord::min(num_cpus::get(), 8) as u32) - .preset(6) - .encoder()?; - Box::new(XzEncoder::new_stream(file, stream)) + let mut filters = xz2::stream::Filters::new(); + // the preset is overridden by the other options so it doesn't matter + let mut lzma_ops = xz2::stream::LzmaOptions::new_preset(9).unwrap(); + // This sets the overall dictionary size, which is also how much memory (baseline) + // is needed for decompression. + lzma_ops.dict_size(64 * 1024 * 1024); + // Use the best match finder for compression ratio. + lzma_ops.match_finder(xz2::stream::MatchFinder::BinaryTree4); + lzma_ops.mode(xz2::stream::Mode::Normal); + // Set nice len to the maximum for best compression ratio + lzma_ops.nice_len(273); + // Set depth to a reasonable value, 0 means auto, 1000 is somwhat high but gives + // good results. + lzma_ops.depth(1000); + // 2 is the default and does well for most files + lzma_ops.position_bits(2); + // 0 is the default and does well for most files + lzma_ops.literal_position_bits(0); + // 3 is the default and does well for most files + lzma_ops.literal_context_bits(3); + + filters.lzma2(&lzma_ops); + let compressor = XzEncoder::new_stream( + std::io::BufWriter::new(file), + xz2::stream::MtStreamBuilder::new() + .threads(1) + .filters(filters) + .encoder() + .unwrap(), + ); + Box::new(compressor) } }) } @@ -94,10 +117,13 @@ impl fmt::Display for CompressionFormats { if i != 0 { write!(f, ",")?; } - fmt::Display::fmt(match format { - CompressionFormat::Xz => "xz", - CompressionFormat::Gz => "gz", - }, f)?; + fmt::Display::fmt( + match format { + CompressionFormat::Xz => "xz", + CompressionFormat::Gz => "gz", + }, + f, + )?; } Ok(()) } |