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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.utils;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.lang.management.ManagementFactory;
import java.nio.file.FileStore;
import java.nio.file.Path;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import javax.management.MBeanServer;
import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.text.StrBuilder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.sun.management.HotSpotDiagnosticMXBean;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.io.util.File;
import org.apache.cassandra.io.util.PathUtils;
import static org.apache.cassandra.config.CassandraRelevantEnv.JAVA_HOME;
import static org.apache.cassandra.utils.Clock.Global.currentTimeMillis;
/**
* Utility to log heap histogram.
*
*/
public final class HeapUtils
{
private static final Logger logger = LoggerFactory.getLogger(HeapUtils.class);
private static final Lock DUMP_LOCK = new ReentrantLock();
/**
* Generates a HEAP histogram in the log file.
*/
public static void logHeapHistogram()
{
try
{
logger.info("Trying to log the heap histogram using jcmd");
Long processId = getProcessId();
if (processId == null)
{
logger.error("The process ID could not be retrieved. Skipping heap histogram generation.");
return;
}
String jcmdPath = getJcmdPath();
// The jcmd file could not be found. In this case let's default to jcmd in the hope that it is in the path.
String jcmdCommand = jcmdPath == null ? "jcmd" : jcmdPath;
String[] histoCommands = new String[] {jcmdCommand,
processId.toString(),
"GC.class_histogram"};
logProcessOutput(Runtime.getRuntime().exec(histoCommands));
}
catch (Throwable e)
{
logger.error("The heap histogram could not be generated due to the following error: ", e);
}
}
/**
* @return full path to the created heap dump file
*/
public static String maybeCreateHeapDump()
{
// Make sure that only one heap dump can be in progress across all threads, and abort for
// threads that cannot immediately acquire the lock, allowing them to fail normally.
if (DUMP_LOCK.tryLock())
{
try
{
if (DatabaseDescriptor.getDumpHeapOnUncaughtException())
{
MBeanServer server = ManagementFactory.getPlatformMBeanServer();
Path absoluteBasePath = DatabaseDescriptor.getHeapDumpPath();
// We should never reach this point with this value null as we initialize the bool only after confirming
// the -XX param / .yaml conf is present on initial init and the JMX entry point, but still worth checking.
if (absoluteBasePath == null)
{
DatabaseDescriptor.setDumpHeapOnUncaughtException(false);
throw new RuntimeException("Cannot create heap dump unless -XX:HeapDumpPath or cassandra.yaml:heap_dump_path is specified.");
}
long maxMemoryBytes = Runtime.getRuntime().maxMemory();
long freeSpaceBytes = PathUtils.tryGetSpace(absoluteBasePath, FileStore::getUnallocatedSpace);
// Abort if there isn't enough room on the target disk to dump the entire heap and then copy it.
if (freeSpaceBytes < 2 * maxMemoryBytes)
throw new RuntimeException("Cannot allocated space for a heap dump snapshot. There are only " + freeSpaceBytes + " bytes free at " + absoluteBasePath + '.');
HotSpotDiagnosticMXBean mxBean = ManagementFactory.newPlatformMXBeanProxy(server, "com.sun.management:type=HotSpotDiagnostic", HotSpotDiagnosticMXBean.class);
String filename = String.format("pid%s-epoch%s.hprof", HeapUtils.getProcessId().toString(), currentTimeMillis());
String fullPath = File.getPath(absoluteBasePath.toString(), filename).toString();
logger.info("Writing heap dump to {} on partition w/ {} free bytes...", absoluteBasePath, freeSpaceBytes);
mxBean.dumpHeap(fullPath, false);
logger.info("Heap dump written to {}", fullPath);
// Disable further heap dump creations until explicitly re-enabled.
DatabaseDescriptor.setDumpHeapOnUncaughtException(false);
return fullPath;
}
else
{
logger.debug("Heap dump creation on uncaught exceptions is disabled.");
}
}
catch (Throwable e)
{
logger.warn("Unable to create heap dump.", e);
}
finally
{
DUMP_LOCK.unlock();
}
}
else
{
logger.debug("Heap dump creation is already in progress. Request aborted.");
}
return null;
}
/**
* Retrieve the path to the JCMD executable.
* @return the path to the JCMD executable or null if it cannot be found.
*/
private static String getJcmdPath()
{
// Searching in the JAVA_HOME is safer than searching into System.getProperty("java.home") as the Oracle
// JVM might use the JRE which do not contains jmap.
String javaHome = JAVA_HOME.getString();
if (javaHome == null)
return null;
File javaBinDirectory = new File(javaHome, "bin");
File[] files = javaBinDirectory.tryList((dir, name) -> name.startsWith("jcmd"));
return ArrayUtils.isEmpty(files) ? null : files[0].path();
}
/**
* Logs the output of the specified process.
*
* @param p the process
* @throws IOException if an I/O problem occurs
*/
private static void logProcessOutput(Process p) throws IOException
{
try (BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream())))
{
StrBuilder builder = new StrBuilder();
String line;
while ((line = input.readLine()) != null)
{
builder.appendln(line);
}
logger.info(builder.toString());
}
}
/**
* Retrieves the process ID or null if the process ID cannot be retrieved.
* @return the process ID or null if the process ID cannot be retrieved.
*/
private static Long getProcessId()
{
long pid = NativeLibrary.getProcessID();
if (pid >= 0)
return pid;
return getProcessIdFromJvmName();
}
/**
* Retrieves the process ID from the JVM name.
* @return the process ID or null if the process ID cannot be retrieved.
*/
private static Long getProcessIdFromJvmName()
{
// the JVM name in Oracle JVMs is: '@' but this might not be the case on all JVMs
String jvmName = ManagementFactory.getRuntimeMXBean().getName();
try
{
return Long.valueOf(jvmName.split("@")[0]);
}
catch (NumberFormatException e)
{
// ignore
}
return null;
}
/**
* The class must not be instantiated.
*/
private HeapUtils()
{
}
}