[jira] [Created] (LUCENE-10103) QueryCache not estimating query size properly

["Haoyu Zhai (Jira)" <ji...@apache.org>]

Haoyu Zhai created LUCENE-10103:
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             Summary: QueryCache not estimating query size properly
                 Key: LUCENE-10103
                 URL: https://issues.apache.org/jira/browse/LUCENE-10103
             Project: Lucene - Core
          Issue Type: Improvement
          Components: core/search
            Reporter: Haoyu Zhai


QueryCache seems estimating the cached query size using a [constant|https://github.com/apache/lucene/blob/main/lucene/core/src/java/org/apache/lucene/search/LRUQueryCache.java#L302], it will cause OOM error in some extreme cases where queries cached will use far more memories than assumed. (The default QueryCache tries to use [only 5% of heap|https://github.com/apache/lucene/blob/main/lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java#L89]) One example of such memory-eating query is AutomatonQuery, it will each carry a [RunAutomaton|https://github.com/apache/lucene/blob/main/lucene/core/src/java/org/apache/lucene/util/automaton/RunAutomaton.java#L42] , which consumes a good amount of memory in exchange for the speed.

On the other hand, we actually have a good implementation of {{Accountable}} interface for AutomatonQuery (though it will become a bit more complicated later since this query will eventually be rewritten to something else), so maybe QueryCache could use those estimation directly (using an {{instanceof}} check)? Or moreover we could make all {{Query}} implement {Accountable}}, and maybe the default implementation could just be returning the current constant we're using, and only override the method of the potential troublesome queries?



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