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  1. WiredTiger
  2. WT-370

WiredTiger cannot change compression algorithms without dump/load.

    • Type: Icon: Task Task
    • Resolution: Done
    • WT1.3.5
    • Affects Version/s: None
    • Component/s: None

      WiredTiger's file format doesn't note the compression algorithm that was used anywhere in the page, which means applications cannot use multiple compression algorithms in the same application (pretty unlikely, I suspect), or change from one compression algorithm to another between releases, without a full dump/load cycle (yeah, that could happen).

      We could use the WT_PAGE_HEADER.unused field for this purpose, but there's no obvious name mapping for each configured compressor.

      We also have built-in support for bzip2 and snappy, so we'll need to split the name-space somehow so we can give the built-in compressors their own IDs without colliding with application compressor extensions.

      Finally, there's no way to specify multiple compression engines for a single file: the compression engine's name is stored in the metadata file, but there's no method of replacing that value. (I suspect that's all we'd need: we could use the compression engine ID to identify the compression engine to use for decompression, and the named compression engine would be used to compress all newly created pages.)

            Assignee:
            keith.bostic@mongodb.com Keith Bostic (Inactive)
            Reporter:
            keith.bostic@mongodb.com Keith Bostic (Inactive)
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              Created:
              Updated:
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