[GitHub] [lucene-solr] jgq2008303393 commented on a change in pull request #940: LUCENE-9002: Query caching leads to absurdly slow queries

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jgq2008303393 commented on a change in pull request #940: LUCENE-9002: Query caching leads to absurdly slow queries
URL: https://github.com/apache/lucene-solr/pull/940#discussion_r333815178
 
 

 ##########
 File path: lucene/core/src/java/org/apache/lucene/search/LRUQueryCache.java
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 @@ -732,8 +741,39 @@ public ScorerSupplier scorerSupplier(LeafReaderContext context) throws IOExcepti
 
       if (docIdSet == null) {
         if (policy.shouldCache(in.getQuery())) {
-          docIdSet = cache(context);
-          putIfAbsent(in.getQuery(), docIdSet, cacheHelper);
+          final ScorerSupplier supplier = in.scorerSupplier(context);
+          if (supplier == null) {
+            putIfAbsent(in.getQuery(), DocIdSet.EMPTY, cacheHelper);
+            return null;
+          }
+
+          final long cost = supplier.cost();
+          return new ScorerSupplier() {
+            @Override
+            public Scorer get(long leadCost) throws IOException {
+              // skip cache operation which would slow query down too much
+              if (cost > skipCacheCost && cost > leadCost * skipCacheFactor
+                  && in.getQuery() instanceof IndexOrDocValuesQuery) {
 
 Review comment:
   This PR is mainly for IndexOrDocValuesQuery now. 
   
   As discussed earlier, the reason why IndexOrDocValuesQuery slow down is that a large amount of data will be read during caching action, while only a small amount of data will be read from doc values when not caching. I don't find any other type of query that reads much more data for caching than it really needs. 
   
   Looking forward to more discussions.

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