SOLR-12683: HashQuery will throw an exception if more than 4 partitionKeys is specified. Earlier after the 4th partitionKey the keys would be silently ignored.

solr/CHANGES.txt

@@ -251,6 +251,9 @@ Bug Fixes
 
 * SOLR-12598: Do not fetch non-stored fields (Nikolay Khitrin, Erick Erickson)
 
+* SOLR-12683: HashQuery will throw an exception if more than 4 partitionKeys is specified.
+  Earlier after the 4th partitionKey the keys would be silently ignored. (Varun Thacker)
+
 Optimizations
 ----------------------
 

solr/core/src/java/org/apache/solr/search/HashQParserPlugin.java

@@ -73,15 +73,18 @@ public class HashQParserPlugin extends QParserPlugin {
         throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, "workers needs to be more than 1");
       }
       int worker = localParams.getInt("worker", 0);
-      String keys = params.get("partitionKeys");
+      String keyParam = params.get("partitionKeys");
-      keys = keys.replace(" ", "");
+      String[] keys = keyParam.replace(" ", "").split(",");
+      if (keys.length > 4) {
+        throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, "HashQuery supports upto 4 partitionKeys");
+      }
       return new HashQuery(keys, workers, worker);
     }
   }
 
   private static class HashQuery extends ExtendedQueryBase implements PostFilter {
 
-    private String keysParam;
+    private String[] keys;
     private int workers;
     private int worker;
 
@@ -95,7 +98,7 @@ public class HashQParserPlugin extends QParserPlugin {
 
     public int hashCode() {
       return classHash() + 
-          31 * keysParam.hashCode() + 
+          31 * keys.hashCode() +
           31 * workers + 
           31 * worker;
     }
@@ -106,13 +109,13 @@ public class HashQParserPlugin extends QParserPlugin {
     }
 
     private boolean equalsTo(HashQuery other) {
-      return keysParam.equals(other.keysParam) && 
+      return keys.equals(other.keys) &&
              workers == other.workers && 
              worker == other.worker;
     }
 
-    public HashQuery(String keysParam, int workers, int worker) {
+    public HashQuery(String[] keys, int workers, int worker) {
-      this.keysParam = keysParam;
+      this.keys = keys;
       this.workers = workers;
       this.worker = worker;
     }
@@ -120,7 +123,6 @@ public class HashQParserPlugin extends QParserPlugin {
     @Override
     public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost) throws IOException {
 
-      String[] keys = keysParam.split(",");
       SolrIndexSearcher solrIndexSearcher = (SolrIndexSearcher)searcher;
       IndexReaderContext context = solrIndexSearcher.getTopReaderContext();
 
@@ -224,7 +226,6 @@ public class HashQParserPlugin extends QParserPlugin {
     }
 
     public DelegatingCollector getFilterCollector(IndexSearcher indexSearcher) {
-      String[] keys = keysParam.split(",");
       HashKey[] hashKeys = new HashKey[keys.length];
       SolrIndexSearcher searcher = (SolrIndexSearcher)indexSearcher;
       IndexSchema schema = searcher.getSchema();

solr/core/src/test/org/apache/solr/search/TestHashQParserPlugin.java

@@ -18,6 +18,7 @@ package org.apache.solr.search;
 
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.solr.SolrTestCaseJ4;
+import org.apache.solr.common.SolrException;
 import org.apache.solr.common.params.ModifiableSolrParams;
 import org.junit.Before;
 import org.junit.BeforeClass;
@@ -54,6 +55,36 @@ public class TestHashQParserPlugin extends SolrTestCaseJ4 {
     }
   }
 
+  @Test
+  public void testManyHashPartitions() throws Exception {
+    ModifiableSolrParams params = new ModifiableSolrParams();
+    params.add("q", "*:*");
+    params.add("fq", "{!hash worker=0 workers=2 cost="+getCost(random())+"}");
+    params.add("partitionKeys", "a_i,a_s,a_i,a_s");
+    params.add("wt", "xml");
+    String response = h.query(req(params));
+    h.validateXPath(response, "//*[@numFound='0']");
+
+    params = new ModifiableSolrParams();
+    params.add("q", "*:*");
+    params.add("fq", "{!hash worker=0 workers=2 cost="+getCost(random())+"}");
+    params.add("partitionKeys", "a_i,a_s,a_i,a_s,a_i");
+    params.add("wt", "xml");
+    ModifiableSolrParams finalParams = params;
+    expectThrows(SolrException.class, () -> h.query(req(finalParams)));
+  }
+
+  @Test
+  public void testLessWorkers() {
+    ModifiableSolrParams params = new ModifiableSolrParams();
+    params.add("q", "*:*");
+    params.add("fq", "{!hash worker=0 workers=1 cost="+getCost(random())+"}");
+    params.add("partitionKeys", "a_i");
+    params.add("wt", "xml");
+    ModifiableSolrParams finalParams = params;
+    expectThrows(SolrException.class, () -> h.query(req(finalParams)));
+  }
+
   @Test
   public void testHashPartitionWithEmptyValues() throws Exception {