mikemccand commented on issue #854: Shared PQ Based Early Termination for 
Concurrent Search
URL: https://github.com/apache/lucene-solr/pull/854#issuecomment-530549495
 
 
   I agree the "maximum minimum" score (for all local PQs that are full) is 
compelling as it'd require minimum synchronization.  Maybe it performs best 
overall for most use cases.
   
   It's downside is that it's collecting N * M (N = requested topN, M = number 
of thread work units).  When N is smallish (common case) maybe the tradeoff is 
worthwhile?
   
   The "minimum minimum" score (once N hits have been collected sum'd across 
all thread work units) is closer to optimal, since it only collects N before 
skipping/pruning, but requires more work to update the "minimum minimum" any 
time any thread collects a newly competitive hit.  If it's a simple array 
that's an O(M) scan each time; if it's a PQ then O(log(M)).

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