[jira] [Created] (LUCENE-5052) bitset codec for off heap filters

["Mikhail Khludnev (JIRA)" <ji...@apache.org>]

Mikhail Khludnev created LUCENE-5052:
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             Summary: bitset codec for off heap filters
                 Key: LUCENE-5052
                 URL: https://issues.apache.org/jira/browse/LUCENE-5052
             Project: Lucene - Core
          Issue Type: New Feature
          Components: core/codecs
            Reporter: Mikhail Khludnev
             Fix For: 5.0


Colleagues,

When we filter we don’t care any of scoring factors i.e. norms, positions, tf, but it should be fast. The obvious way to handle this is to decode postings list and cache it in heap (CachingWrappingFilter, Solr’s DocSet). Both of consuming a heap and decoding as well are expensive. 
Let’s write a posting list as a bitset, if df is greater than segment's maxdocs/8  (what about skiplists? and overall performance?). 
Beside of the codec implementation, the trickiest part to me is to design API for this. How we can let the app know that a term query don’t need to be cached in heap, but can be held as an mmaped bitset?

WDYT?  

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