Add metric of log

### What changes are proposed in this pull request?

Add metric of log.

pr-link: #13839
change-id: cid-4275e40e7b1e126d3375c74abd0294740cf1bbfd

conf/log4j.properties

@@ -11,7 +11,7 @@
 
 # May get overridden by System Property
 
-log4j.rootLogger=INFO, ${alluxio.logger.type}, ${alluxio.remote.logger.type}
+log4j.rootLogger=INFO, ${alluxio.logger.type}, ${alluxio.remote.logger.type}, EventCounter
 
 log4j.category.alluxio.logserver=INFO, ${alluxio.logserver.logger.type}
 log4j.additivity.alluxio.logserver=false
@@ -34,6 +34,9 @@ log4j.appender.Console.layout.ConversionPattern=%d{ISO8601} %-5p %c{1} - %m%n
 log4j.logger.org.apache.parquet.hadoop.InternalParquetRecordWriter=WARN
 log4j.logger.org.apache.parquet.hadoop.InternalParquetRecordReader=WARN
 
+# Appender for EventCounter
+log4j.appender.EventCounter=alluxio.metrics.EventCounter
+
 # Appender for Job Master
 log4j.appender.JOB_MASTER_LOGGER=org.apache.log4j.RollingFileAppender
 log4j.appender.JOB_MASTER_LOGGER.File=${alluxio.logs.dir}/job_master.log

core/common/src/main/java/alluxio/metrics/EventCounter.java

@@ -0,0 +1,121 @@
+/*
+ * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
+ * (the "License"). You may not use this work except in compliance with the License, which is
+ * available at www.apache.org/licenses/LICENSE-2.0
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied, as more fully set forth in the License.
+ *
+ * See the NOTICE file distributed with this work for information regarding copyright ownership.
+ */
+
+package alluxio.metrics;
+
+import org.apache.log4j.AppenderSkeleton;
+import org.apache.log4j.Level;
+import org.apache.log4j.spi.LoggingEvent;
+
+/**
+ * A log4J Appender that simply counts logging events in four levels:
+ * FATAL, ERROR WARN and INFO. The class name is used in log4j.properties
+ */
+public class EventCounter extends AppenderSkeleton {
+  private static final int FATAL = 0;
+  private static final int ERROR = 1;
+  private static final int WARN = 2;
+  private static final int INFO = 3;
+  private static EventCounter.EventCounts sCount = new EventCounter.EventCounts();
+
+  /**
+   * The constructor of EventCounter.
+   */
+  public EventCounter() {
+  }
+
+  /**
+   * Gets the number of fatal log.
+   *
+   * @return the number of fatal log
+   */
+  public static long getFatal() {
+    return sCount.get(FATAL);
+  }
+
+  /**
+   * Gets the number of error log.
+   *
+   * @return the number of error log
+   */
+  public static long getError() {
+    return sCount.get(ERROR);
+  }
+
+  /**
+   * Gets the number of warn log.
+   *
+   * @return the number of warn log
+   */
+  public static long getWarn() {
+    return sCount.get(WARN);
+  }
+
+  /**
+   * Gets the number of info log.
+   *
+   * @return the number of info log
+   */
+  public static long getInfo() {
+    return sCount.get(INFO);
+  }
+
+  /**
+   * Add the number of corresponding level log.
+   *
+   * @param event event of generating log
+   */
+  public void append(LoggingEvent event) {
+    Level level = event.getLevel();
+    if (level.equals(Level.INFO)) {
+      sCount.incr(INFO);
+    } else if (level.equals(Level.WARN)) {
+      sCount.incr(WARN);
+    } else if (level.equals(Level.ERROR)) {
+      sCount.incr(ERROR);
+    } else if (level.equals(Level.FATAL)) {
+      sCount.incr(FATAL);
+    }
+  }
+
+  /**
+   * Release any resources allocated within the appender such as file
+   * handles, network connections, etc.
+   */
+  public void close() {
+  }
+
+  /**
+   * Configurators call this method to determine if the appender
+   * requires a layout.
+   *
+   * @return if the appender requires a layout
+   */
+  public boolean requiresLayout() {
+    return false;
+  }
+
+  private static class EventCounts {
+    private final long[] mCounts;
+
+    private EventCounts() {
+      mCounts = new long[]{0L, 0L, 0L, 0L};
+    }
+
+    private synchronized void incr(int i) {
+      mCounts[i]++;
+    }
+
+    private synchronized long get(int i) {
+      return mCounts[i];
+    }
+  }
+}

core/common/src/main/java/alluxio/metrics/LogStateCounterSet.java

@@ -0,0 +1,34 @@
+/*
+ * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
+ * (the "License"). You may not use this work except in compliance with the License, which is
+ * available at www.apache.org/licenses/LICENSE-2.0
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied, as more fully set forth in the License.
+ *
+ * See the NOTICE file distributed with this work for information regarding copyright ownership.
+ */
+
+package alluxio.metrics;
+
+import com.codahale.metrics.Gauge;
+import com.codahale.metrics.Metric;
+import com.codahale.metrics.MetricSet;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A set of counters for the log metric.
+ */
+public class LogStateCounterSet implements MetricSet {
+  @Override
+  public Map<String, Metric> getMetrics() {
+    final Map<String, Metric> gauges = new HashMap<>();
+    gauges.put("log.info.count", (Gauge<Long>) EventCounter::getInfo);
+    gauges.put("log.warn.count", (Gauge<Long>) EventCounter::getWarn);
+    gauges.put("log.error.count", (Gauge<Long>) EventCounter::getError);
+    gauges.put("log.fatal.count", (Gauge<Long>) EventCounter::getFatal);
+    return gauges;
+  }
+}

core/common/src/main/java/alluxio/metrics/MetricsSystem.java

@@ -147,6 +147,7 @@ public static InstanceType fromString(String text) {
     METRIC_REGISTRY.registerAll(new MemoryUsageGaugeSet());
     METRIC_REGISTRY.registerAll(new ClassLoadingGaugeSet());
     METRIC_REGISTRY.registerAll(new CachedThreadStatesGaugeSet(5, TimeUnit.SECONDS));
+    METRIC_REGISTRY.registerAll(new LogStateCounterSet());
   }
 
   @GuardedBy("MetricsSystem")