MINOR: Add test to ensure log metrics are removed after deletion (#7750)

Reviewers: Jason Gustafson <jason@confluent.io>

core/src/main/scala/kafka/log/Log.scala

@@ -465,25 +465,25 @@ class Log(@volatile var dir: File,
     Map("topic" -> topicPartition.topic, "partition" -> topicPartition.partition.toString) ++ maybeFutureTag
   }
 
-  newGauge("NumLogSegments",
+  newGauge(LogMetricNames.NumLogSegments,
     new Gauge[Int] {
       def value = numberOfSegments
     },
     tags)
 
-  newGauge("LogStartOffset",
+  newGauge(LogMetricNames.LogStartOffset,
     new Gauge[Long] {
       def value = logStartOffset
     },
     tags)
 
-  newGauge("LogEndOffset",
+  newGauge(LogMetricNames.LogEndOffset,
     new Gauge[Long] {
       def value = logEndOffset
     },
     tags)
 
-  newGauge("Size",
+  newGauge(LogMetricNames.Size,
     new Gauge[Long] {
       def value = size
     },
@@ -2297,10 +2297,10 @@ class Log(@volatile var dir: File,
    * remove deleted log metrics
    */
   private[log] def removeLogMetrics(): Unit = {
-    removeMetric("NumLogSegments", tags)
-    removeMetric("LogStartOffset", tags)
-    removeMetric("LogEndOffset", tags)
-    removeMetric("Size", tags)
+    removeMetric(LogMetricNames.NumLogSegments, tags)
+    removeMetric(LogMetricNames.LogStartOffset, tags)
+    removeMetric(LogMetricNames.LogEndOffset, tags)
+    removeMetric(LogMetricNames.Size, tags)
   }
 
   /**
@@ -2624,3 +2624,14 @@ object Log {
     file.getPath.endsWith(LogFileSuffix)
 
 }
+
+object LogMetricNames {
+  val NumLogSegments: String = "NumLogSegments"
+  val LogStartOffset: String = "LogStartOffset"
+  val LogEndOffset: String = "LogEndOffset"
+  val Size: String = "Size"
+
+  def allMetricNames: List[String] = {
+    List(NumLogSegments, LogStartOffset, LogEndOffset, Size)
+  }
+}

core/src/test/scala/unit/kafka/log/LogTest.scala

@@ -4145,6 +4145,27 @@ class LogTest {
     assertEquals(1, log.numberOfSegments)
   }
 
+  @Test
+  def testMetricsRemovedOnLogDeletion(): Unit = {
+    TestUtils.clearYammerMetrics()
+
+    val logConfig = LogTest.createLogConfig(segmentBytes = 1024 * 1024)
+    val log = createLog(logDir, logConfig)
+    val topicPartition = Log.parseTopicPartitionName(logDir)
+    val metricTag = s"topic=${topicPartition.topic},partition=${topicPartition.partition}"
+
+    val logMetrics = metricsKeySet.filter(_.getType == "Log")
+    assertEquals(LogMetricNames.allMetricNames.size, logMetrics.size)
+    logMetrics.foreach { metric =>
+      assertTrue(metric.getMBeanName.contains(metricTag))
+    }
+
+    // Delete the log and validate that corresponding metrics were removed.
+    log.delete()
+    val logMetricsAfterDeletion = metricsKeySet.filter(_.getType == "Log")
+    assertTrue(logMetricsAfterDeletion.isEmpty)
+  }
+
   private def allAbortedTransactions(log: Log) = log.logSegments.flatMap(_.txnIndex.allAbortedTxns)
 
   private def appendTransactionalAsLeader(log: Log, producerId: Long, producerEpoch: Short): Int => Unit = {