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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* 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.metrics;
import java.io.PrintStream;
import java.io.Serializable;
import java.util.List;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.function.BiFunction;
import org.apache.cassandra.concurrent.ExecutorPlus;
import org.apache.cassandra.net.MessagingService;
import org.apache.cassandra.net.Verb;
import org.apache.cassandra.utils.ExecutorUtils;
import org.apache.cassandra.utils.MonotonicClock;
import com.google.common.annotations.VisibleForTesting;
import static org.apache.cassandra.concurrent.ExecutorFactory.Global.executorFactory;
public abstract class Sampler
{
private static long DISABLED = -1L;
private static final BiFunction
FrequencySamplerFomatter = (type, resultBuilder) ->
resultBuilder.forType(type, type.description)
.addColumn("Table", "table")
.addColumn("Partition", "value")
.addColumn("Count", "count")
.addColumn("+/-", "error");
public enum SamplerType
{
READS("Frequency of reads by partition", FrequencySamplerFomatter),
WRITES("Frequency of writes by partition", FrequencySamplerFomatter),
LOCAL_READ_TIME("Longest read query times", ((samplerType, resultBuilder) ->
resultBuilder.forType(samplerType, samplerType.description)
.addColumn("Query", "value")
.addColumn("Microseconds", "count"))),
READ_ROW_COUNT("Partitions read with the most rows", ((samplerType, resultBuilder) ->
resultBuilder.forType(samplerType, samplerType.description)
.addColumn("Table", "table")
.addColumn("Partition", "value")
.addColumn("Rows", "count"))),
READ_TOMBSTONE_COUNT("Partitions read with the most tombstones", ((samplerType, resultBuilder) ->
resultBuilder.forType(samplerType, samplerType.description)
.addColumn("Table", "table")
.addColumn("Partition", "value")
.addColumn("Tombstones", "count"))),
READ_SSTABLE_COUNT("Partitions read with the most sstables", ((samplerType, resultBuilder) ->
resultBuilder.forType(samplerType, samplerType.description)
.addColumn("Table", "table")
.addColumn("Partition", "value")
.addColumn("SSTables", "count"))),
WRITE_SIZE("Max mutation size by partition", ((samplerType, resultBuilder) ->
resultBuilder.forType(samplerType, samplerType.description)
.addColumn("Table", "table")
.addColumn("Partition", "value")
.addColumn("Bytes", "count"))),
CAS_CONTENTIONS("Frequency of CAS contention by partition", FrequencySamplerFomatter);
private final String description;
private final BiFunction formatter;
SamplerType(String description, BiFunction formatter)
{
this.description = description;
this.formatter = formatter;
}
void format(SamplingManager.ResultBuilder resultBuilder, PrintStream ps)
{
formatter.apply(this, resultBuilder).print(ps);
}
}
@VisibleForTesting
MonotonicClock clock = MonotonicClock.Global.approxTime;
@VisibleForTesting
static final ExecutorPlus samplerExecutor = executorFactory()
.withJmxInternal()
.configureSequential("Sampler")
.withQueueLimit(1000)
.withRejectedExecutionHandler((runnable, executor) -> MessagingService.instance().metrics.recordSelfDroppedMessage(Verb._SAMPLE))
.build();
private long endTimeNanos = -1;
public void addSample(final T item, final int value)
{
if (isEnabled())
samplerExecutor.submit(() -> insert(item, value));
}
protected abstract void insert(T item, long value);
/**
* A sampler is enabled between {@link this#beginSampling} and {@link this#finishSampling}
* @return true if the sampler is enabled.
*/
public boolean isEnabled()
{
return endTimeNanos != DISABLED;
}
public void disable()
{
endTimeNanos = DISABLED;
}
/**
* @return true if the sampler is active.
* A sampler is active only if it is enabled and the current time is within the `durationMillis` when beginning sampling.
*/
public boolean isActive()
{
return isEnabled() && clock.now() <= endTimeNanos;
}
/**
* Update the end time for the sampler. Implicitly, calling this method enables the sampler.
*/
public void updateEndTime(long endTimeMillis)
{
this.endTimeNanos = endTimeMillis;
}
/**
* Begin sampling with the configured capacity and duration
* @param capacity Number of sample items to keep in memory, the lower this is
* the less accurate results are. For best results use value
* close to cardinality, but understand the memory trade offs.
* @param durationMillis Upperbound duration in milliseconds for sampling. The sampler
* stops accepting new samples after exceeding the duration
* even if {@link #finishSampling(int)}} is not called.
*/
public abstract void beginSampling(int capacity, long durationMillis);
/**
* Stop sampling and return the results
* @param count The number of the samples requested to retrieve from the sampler
* @return a list of samples, the size is the minimum of the total samples and {@param count}.
*/
public abstract List> finishSampling(int count);
public abstract String toString(T value);
/**
* Represents the ranked items collected during a sample period
*/
public static class Sample implements Serializable
{
public final S value;
public final long count;
public final long error;
public Sample(S value, long count, long error)
{
this.value = value;
this.count = count;
this.error = error;
}
@Override
public String toString()
{
return "Sample [value=" + value + ", count=" + count + ", error=" + error + "]";
}
}
public static void shutdownNowAndWait(long time, TimeUnit units) throws InterruptedException, TimeoutException
{
ExecutorUtils.shutdownNowAndWait(time, units, samplerExecutor);
}
}