The queue size for ConcurrentUpdateSolrClient should default to 10 instead of throwing an IllegalArgumentException

solr/CHANGES.txt

@@ -153,6 +153,9 @@ Bug Fixes
 * SOLR-11608: Correctly parse the new core-name in the V2 core rename API.
   (Jason Gerlowski via Anshum Gupta)
 
+* SOLR-11256: The queue size for ConcurrentUpdateSolrClient should default to 10 instead of throwing an
+  IllegalArgumentException. (Jason Gerlowski, Anshum Gupta)
+
 Optimizations
 ----------------------
 * SOLR-11285: Refactor autoscaling framework to avoid direct references to Zookeeper and Solr

solr/solrj/src/java/org/apache/solr/client/solrj/impl/ConcurrentUpdateSolrClient.java

@@ -772,7 +772,7 @@ public class ConcurrentUpdateSolrClient extends SolrClient {
    */
   public static class Builder extends SolrClientBuilder<Builder> {
     protected String baseSolrUrl;
-    protected int queueSize;
+    protected int queueSize = 10;
     protected int threadCount;
     protected ExecutorService executorService;
     protected boolean streamDeletes;
@@ -803,7 +803,7 @@ public class ConcurrentUpdateSolrClient extends SolrClient {
     }
     
     /**
-     * The number of documents to batch together before sending to Solr.
+     * The number of documents to batch together before sending to Solr. If not set, this defaults to 10.
      */
     public Builder withQueueSize(int queueSize) {
       if (queueSize <= 0) {

solr/solrj/src/test/org/apache/solr/client/solrj/impl/ConcurrentUpdateSolrClientBuilderTest.java

@@ -30,4 +30,12 @@ public class ConcurrentUpdateSolrClientBuilderTest extends LuceneTestCase {
   public void testRejectsMissingBaseSolrUrl() {
     new Builder(null).build();
   }
+
+  @Test
+  public void testMissingQueueSize() {
+    try (ConcurrentUpdateSolrClient client = new Builder("someurl").build()){
+      // Do nothing as we just need to test that the only mandatory parameter for building the client
+      // is the baseSolrUrl
+    }
+  }
 }