Uploaded image for project: 'Lucene - Core'
  1. Lucene - Core
  2. LUCENE-5743

new 4.9 norms format



    • New Feature
    • Status: Resolved
    • Major
    • Resolution: Fixed
    • None
    • 4.9, 6.0
    • None
    • None
    • New


      Norms can eat up a lot of RAM, since by default its 8 bits per field per document. We rely upon users to omit them to not blow up RAM, but its a constant trap.

      Previously in 4.2, I tried to compress these by default, but it was too slow. My mistakes were:

      • allowing slow bits per value like bpv=5 that are implemented with expensive operations.
      • trying to wedge norms into the generalized docvalues numeric case
      • not handling "simple" degraded cases like "constant norm" the same norm value for every document.

      Instead, we can just have a separate norms format that is very careful about what it does, since we understand in general the patterns in the data:

      • uses CONSTANT compression (just writes the single value to metadata) when all values are the same.
      • only compresses to bitsPerValue = 1,2,4 (this also happens often, for very short text fields like person names and other stuff in structured data)
      • otherwise, if you would need 5,6,7,8 bits per value, we just continue to do what we do today, encode as byte[]. Maybe we can improve this later, but this ensures we don't have a performance impact.


        1. LUCENE-5743.patch
          26 kB
          Robert Muir



            Unassigned Unassigned
            rcmuir Robert Muir
            0 Vote for this issue
            6 Start watching this issue