Changes between Version 112 and Version 113 of FAQ

2015-10-04T01:00:30Z (5 years ago)

current status of MDMF


  • FAQ

    v112 v113  
    101101'''[=#Q13_modify_a_section_of_mutable_file Q13:] Is it possible to modify a mutable file by "patching" it? Also... if I have a file stored and I want to update a section of the file in the middle, is that possible or would be file need to be downloaded, patched and re-uploaded?'''
    103 A: Not at present. We've implemented only "Small Distributed Mutable Files" (SDMF) so far, which have the property that the whole file must be
    104 downloaded or uploaded at once. We have plans for "medium" MDMF files, which will fix this. MDMF files are broken into segments (default size
    105 is 128KiB), and you only have to replace the segments that are dirtied by the write, so changing a single byte would only require the upload of
    106 N/k*128KiB or about 440KiB for the default {{{3-of-10}}} encoding.
    108 Kevan Carstensen has implemented MDMF, thanks in part to the sponsorship of Google Summer Of Code. Ticket #393 is tracking this work.
     103A: Some steps have been taken toward implementing this. There are two kinds of mutable file: "Small Distributed Mutable Files" (SDMF), and "Medium Distributed Mutable Files" (MDMF). MDMF files are broken into segments (default size 128 KiB), and are designed to allow replacing only the segments changed by a write. However, although MDMF files work correctly and are the preferred format (soon to be the default in Tahoe-LAFS v1.11), writes to them currently (as of Tahoe-LAFS v1.10.1) still replace the whole file. Once writing individual segments is implemented, a write within a single segment will only require the upload of N/k*128KiB or about 440KiB, for the default segment size and {{{3-of-10}}} encoding.
     105Kevan Carstensen implemented MDMF thanks in part to the sponsorship of Google Summer Of Code.
    110107'''[=#Q14_unique_node_id Q14:] How can Tahoe-LAFS ensure that every node ID is unique?'''