jojochuang commented on code in PR #11085:
URL: https://github.com/apache/ozone/pull/11085#discussion_r3847159319
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hadoop-ozone/interface-storage/src/main/java/org/apache/hadoop/ozone/om/lock/OMLockMetrics.java:
##########
@@ -37,26 +36,24 @@ public final class OMLockMetrics implements MetricsSource {
private static final String SOURCE_NAME =
OMLockMetrics.class.getSimpleName();
- private final MetricsRegistry registry;
- private final MutableStat readLockWaitingTimeMsStat;
- private final MutableStat readLockHeldTimeMsStat;
- private final MutableStat writeLockWaitingTimeMsStat;
- private final MutableStat writeLockHeldTimeMsStat;
+ private final ConcurrentMutableStat readLockWaitingTimeMsStat;
+ private final ConcurrentMutableStat readLockHeldTimeMsStat;
+ private final ConcurrentMutableStat writeLockWaitingTimeMsStat;
+ private final ConcurrentMutableStat writeLockHeldTimeMsStat;
private OMLockMetrics() {
- registry = new MetricsRegistry(SOURCE_NAME);
- readLockWaitingTimeMsStat = registry.newStat("ReadLockWaitingTime",
+ readLockWaitingTimeMsStat = new
ConcurrentMutableStat("ReadLockWaitingTime",
"Time (in milliseconds) spent waiting for acquiring the read lock",
- "Ops", "Time", true);
- readLockHeldTimeMsStat = registry.newStat("ReadLockHeldTime",
+ "Ops", "Time", false);
Review Comment:
turning the extended field from true to false means extended stats (stdev,
min/max etc.) are not created by default. If ConcurrentMutableStat is not
expected to support extended stats, then let's remove this parameter.
##########
hadoop-hdds/common/src/main/java/org/apache/hadoop/ozone/util/ConcurrentMutableStat.java:
##########
@@ -0,0 +1,134 @@
+/*
+ * 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.hadoop.ozone.util;
+
+import java.util.concurrent.atomic.LongAccumulator;
+import java.util.concurrent.atomic.LongAdder;
+import org.apache.hadoop.metrics2.MetricsRecordBuilder;
+import org.apache.hadoop.metrics2.lib.MutableStat;
+import org.apache.hadoop.metrics2.util.SampleStat;
+
+/**
+ * A {@link MutableStat} whose hot-path {@link #add(long)} is non-blocking
+ * under concurrent callers. Each call accumulates in {@link LongAdder} /
+ * {@link LongAccumulator} cells and the pending totals are drained into the
+ * parent's running state lazily — only when metrics are read via
+ * {@link #snapshot}, {@link #lastStat}, or {@link #toString}.
+ *
+ * <p>This avoids the {@code synchronized} contention of the base class when
+ * many threads release locks simultaneously and all attempt to record a
+ * measurement on the same metric instance.
+ *
+ * <p><b>Standard deviation accuracy:</b> {@code drainPending()} batches all
+ * pending samples except the min and max into a single
+ * {@code super.add(n, sum)} call. {@link
org.apache.hadoop.metrics2.util.SampleStat}
+ * treats a batch as {@code n} identical samples equal to their mean, so the
+ * within-batch variance is lost. The reported standard deviation is therefore
+ * underestimated. Callers that need accurate standard deviation should use
+ * {@link org.apache.hadoop.metrics2.lib.MutableStat} directly, or pass
+ * {@code extended=false} to suppress the stdev metric.
+ */
+public class ConcurrentMutableStat extends MutableStat {
+
+ private final LongAdder pendingSum = new LongAdder();
+ private final LongAdder pendingCount = new LongAdder();
+ /** Cell-striped min accumulator: identity = Long.MAX_VALUE, function =
Math::min. */
+ private final LongAccumulator pendingMin = new LongAccumulator(Math::min,
Long.MAX_VALUE);
+ /** Cell-striped max accumulator: identity = Long.MIN_VALUE, function =
Math::max. */
+ private final LongAccumulator pendingMax = new LongAccumulator(Math::max,
Long.MIN_VALUE);
+
+ public ConcurrentMutableStat(String name, String description,
+ String sampleName, String valueName, boolean extended) {
+ super(name, description, sampleName, valueName, extended);
Review Comment:
```suggestion
String sampleName, String valueName) {
super(name, description, sampleName, valueName, false);
```
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