Support for larger dictionary sizes

  • Supercilious Dude


    Is there any possibility to implement larger dictionary sizes 2GB or 4GB for example? It would be a tremendous help in improving the compression ratio for large archives containing virtual machines for example.

    I frequently find that programs like exdupe or pcompress massively outperform 7zip in compression ratio and the do so in much less time, primarily due to their larger block sizes being able to find matches that are more than 1GB apart.


  • Anonymous - 2013-12-02

    I have 32GB of RAM in my laptop and could handle above 2GB of dictionary size. How to enable that? What do I have to change in the source code in order to manage that? (mkay I admit I don't know how to compile it for Ubuntu). I imagine that it can have some use to compress some DVD ISOs with similar files below the dictionary size or virtual machines of the same operating systems (mostly fresh installed).

  • Anonymous - 2013-12-04

    Mkay, my result on some fresh installed Windows virtual machines of totally 35GB:
    5,6GB: 7za a -t7z -m0=lzma2 -y -mhe=on -mx=9 -mfb=1024 -ms=on -mmt=3 -md=1024m 1G.7z
    4,3GB: exdupe -g8 volume/ g8.xdp
    2,8GB: 7za a -t7z -m0=lzma2 -y -mhe=on -mx=9 -mfb=1024 -ms=on -mmt=3 -md=1024m g8_1024.7z g8.xdp

    Compressing KDE partition manager partition images I had the result:
    4 7zip-archives with 7-zip using 1gb dictionary size: 18GB
    Whole content of that archives (72GB) compressed using exdupe: 14,7GB
    Compressed the exdupe archive with 7zip with 1GB dictionary size: 11,2GB

    Conclusion: I'll always use Exdupe aftercompressing that with 7zip after it when handling huge files.

    • john lee

      john lee - 2013-12-05

      Andreas, why exdupe? did you try zpaq or pcompress in place of exdupe? John

  • Igor Pavlov

    Igor Pavlov - 2013-12-05

    I plan to work for dictionary size increasing in next 2-4 weeks.

    • Supercilious Dude

      That's great to hear! I would be very happy to help test and debug any builds supporting larger dictionaries.

    • Supercilious Dude

      Has there been any progress on this?

      • Igor Pavlov

        Igor Pavlov - 2014-03-01

        There were another tasks.
        So that feature will be not implemented in nearest version.


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