7-Zip LZMA2 vs pigz Speed Comparison

When comparing 7-Zip's LZMA2 algorithm to pigz (parallel gzip), the fundamental trade-off lies between raw execution speed and compression efficiency. Pigz is dramatically faster at both compressing and decompressing data across multi-core systems because it utilizes the lightweight Deflate algorithm. In contrast, 7-Zip LZMA2 is significantly slower—often by an order of magnitude—because it performs deep, complex pattern matching to achieve substantially smaller file sizes.

Compression Speed and Architecture

Pigz functions as a fully multi-threaded replacement for standard gzip. It breaks input files into chunks (typically 128 KB) and distributes the Deflate compression workload across all available CPU threads simultaneously. Because Deflate is computationally lightweight, pigz routinely saturates high-core processors and achieves speeds limited only by storage drive throughput (often hundreds of megabytes per second).

LZMA2 also supports multi-threading, but its algorithmic workload per byte is far heavier. It uses large dictionary sizes (typically 16 MB to 64 MB or more) and complex Markov chain modeling to identify repeating patterns. Even with multi-threading fully engaged, LZMA2 requires massive CPU cycles per chunk, making its compression throughput roughly 5 to 20 times slower than pigz on the same hardware.

Decompression Speed

Decompression performance widens the gap between the two tools:

  • pigz: Decompresses data near memory and disk speeds. While single-threaded by default during decompression (unless compiled with specific extensions), the simplicity of Deflate makes it exceptionally fast.
  • LZMA2: While LZMA2 decompresses much faster than it compresses, it still requires more CPU overhead and memory than Deflate to reconstruct files from large dictionary buffers.

If fast extraction times on end-user systems are critical, pigz holds a distinct performance advantage.

Memory Consumption

  • pigz: Extremely memory-efficient. Each thread only requires a few megabytes to process its chunk buffer.
  • LZMA2: Highly memory-intensive. LZMA2 assigns a full dictionary buffer to every active thread. Running an LZMA2 compression task with a 64 MB dictionary across 16 threads can easily consume several gigabytes of RAM.

Compression Ratio vs. Speed Trade-Off

The primary reason to accept LZMA2's slower speed is its compression ratio.

  • pigz (Deflate): Produces standard .gz archives. It achieves modest compression ratios suitable for general text, logs, and basic data archives.
  • 7-Zip (LZMA2): Typically produces archives that are 20% to 50% smaller than those created by pigz, particularly on large software builds, source code repositories, and raw datasets.

Which Should You Choose?

  • Use pigz when: You need fast backups, real-time log rotation, rapid data pipelines, or when CPU time and compression windows are limited. It is best suited for scenarios where fast completion matters more than conserving storage space.
  • Use 7-Zip LZMA2 when: You are preparing software distributions, cold storage archives, or files intended for download over limited-bandwidth networks. The extra compression time pays off in significantly lower transfer costs and smaller disk footprints.