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From "David Smiley (JIRA)" <>
Subject [jira] [Commented] (LUCENE-7304) Doc values based block join implementation
Date Thu, 26 May 2016 15:26:12 GMT


David Smiley commented on LUCENE-7304:

This is interesting. I wonder... instead couldn't we get a DocIdSetIterator of parent docs
and kind of intersect it with the child DISI?  (no bitset, no potentially fragile encoding
of relative doc ID offsets). This is a half-baked idea and I'm not sure if it even makes any
sense :-P so take it with a grain of salt!

> Doc values based block join implementation
> ------------------------------------------
>                 Key: LUCENE-7304
>                 URL:
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Martijn van Groningen
>            Priority: Minor
>         Attachments: LUCENE_7304.patch
> At query time the block join relies on a bitset for finding the previous parent doc during
advancing the doc id iterator. On large indices these bitsets can consume large amounts of
jvm heap space.  Also typically due the nature how these bitsets are set, the 'FixedBitSet'
implementation is used.
> The idea I had was to replace the bitset usage by a numeric doc values field that stores
offsets. Each child doc stores how many docids it is from its parent doc and each parent stores
how many docids it is apart from its first child. At query time this information can be used
to perform the block join.
> I think another benefit of this approach is that external tools can now easily determine
if a doc is part of a block of documents and perhaps this also helps index time sorting?

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