CASSANDRA-14366: Add prepared statement cache stats to nodetool info

Assisted-by: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

src/java/org/apache/cassandra/metrics/CQLMetrics.java

@@ -39,6 +39,7 @@ public class CQLMetrics
     public final Gauge<Integer> preparedStatementsCount;
     public final Gauge<Double> preparedStatementsRatio;
     public final Gauge<Long> preparedStatementsCacheSize;
+    public final Gauge<Long> preparedStatementsCacheCapacity;
 
     public CQLMetrics()
     {
@@ -67,5 +68,6 @@ public class CQLMetrics
             }
         });
         preparedStatementsCacheSize = Metrics.register(factory.createMetricName("PreparedStatementsCacheSize"), QueryProcessor::preparedStatementsCacheMemoryUsedBytes);
+        preparedStatementsCacheCapacity = Metrics.register(factory.createMetricName("PreparedStatementsCacheCapacity"), () -> QueryProcessor.PREPARED_STATEMENT_CACHE_SIZE_BYTES);
     }
 }

src/java/org/apache/cassandra/tools/NodeProbe.java

@@ -1939,6 +1939,38 @@ public class NodeProbe implements AutoCloseable
         }
     }
 
+    /**
+     * Retrieve CQL metrics by name.
+     * @param metricName PreparedStatementsCount, PreparedStatementsCacheSize, PreparedStatementsCacheCapacity,
+     *                   PreparedStatementsExecuted, or PreparedStatementsEvicted.
+     */
+    public Object getCQLMetric(String metricName)
+    {
+        try
+        {
+            switch (metricName)
+            {
+                case "PreparedStatementsCount":
+                case "PreparedStatementsCacheSize":
+                case "PreparedStatementsCacheCapacity":
+                    return JMX.newMBeanProxy(mbeanServerConn,
+                            new ObjectName("org.apache.cassandra.metrics:type=CQL,name=" + metricName),
+                            CassandraMetricsRegistry.JmxGaugeMBean.class).getValue();
+                case "PreparedStatementsExecuted":
+                case "PreparedStatementsEvicted":
+                    return JMX.newMBeanProxy(mbeanServerConn,
+                            new ObjectName("org.apache.cassandra.metrics:type=CQL,name=" + metricName),
+                            CassandraMetricsRegistry.JmxCounterMBean.class).getCount();
+                default:
+                    throw new RuntimeException("Unknown CQL metric name " + metricName);
+            }
+        }
+        catch (MalformedObjectNameException e)
+        {
+            throw new RuntimeException(e);
+        }
+    }
+
     private static Multimap<String, String> getJmxThreadPools(MBeanServerConnection mbeanServerConn)
     {
         try

src/java/org/apache/cassandra/tools/nodetool/Info.java

@@ -119,6 +119,15 @@ public class Info extends AbstractCommand
                 probe.getCacheMetric("CounterCache", "HitRate"),
                 cacheService.getCounterCacheSavePeriodInSeconds());
 
+        // Prepared Statement Cache: entries, size, capacity, executions, evictions
+        out.printf("%-23s: entries %d, size %s, capacity %s, %d executions, %d evictions%n",
+                "Prepared Stmt Cache",
+                probe.getCQLMetric("PreparedStatementsCount"),
+                FileUtils.stringifyFileSize((long) probe.getCQLMetric("PreparedStatementsCacheSize")),
+                FileUtils.stringifyFileSize((long) probe.getCQLMetric("PreparedStatementsCacheCapacity")),
+                probe.getCQLMetric("PreparedStatementsExecuted"),
+                probe.getCQLMetric("PreparedStatementsEvicted"));
+
         // Chunk Cache: Hits, Requests, RecentHitRate, SavePeriodInSeconds
         try
         {

test/distributed/org/apache/cassandra/distributed/mock/nodetool/InternalNodeProbe.java

@@ -174,6 +174,12 @@ public class InternalNodeProbe extends NodeProbe
         throw new UnsupportedOperationException();
     }
 
+    @Override
+    public Object getCQLMetric(String metricName)
+    {
+        throw new UnsupportedOperationException();
+    }
+
     @Override
     public Object getClientMetric(String metricName)
     {

test/unit/org/apache/cassandra/tools/nodetool/InfoTest.java

@@ -0,0 +1,46 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.cassandra.tools.nodetool;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import org.apache.cassandra.cql3.CQLTester;
+import org.apache.cassandra.tools.ToolRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class InfoTest extends CQLTester
+{
+    @BeforeClass
+    public static void setup() throws Exception
+    {
+        requireNetwork();
+        startJMXServer();
+    }
+
+    @Test
+    public void testInfoContainsPreparedStmtCache()
+    {
+        ToolRunner.ToolResult tool = ToolRunner.invokeNodetool("info");
+        tool.assertOnCleanExit();
+        String stdout = tool.getStdout();
+        assertThat(stdout).contains("Prepared Stmt Cache");
+        assertThat(stdout).containsPattern("Prepared Stmt Cache\\s+: entries \\d+, size .+, capacity .+, \\d+ executions, \\d+ evictions");
+    }
+}