/**
* 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.hdfs.server.namenode;
import static org.apache.hadoop.util.Time.now;
import java.io.Closeable;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.net.URI;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hdfs.DFSConfigKeys;
import org.apache.hadoop.hdfs.DFSUtil;
import org.apache.hadoop.hdfs.HAUtil;
import org.apache.hadoop.hdfs.protocol.HdfsConstants;
import org.apache.hadoop.hdfs.protocol.LayoutVersion;
import org.apache.hadoop.hdfs.server.common.HdfsServerConstants.NamenodeRole;
import org.apache.hadoop.hdfs.server.common.HdfsServerConstants.RollingUpgradeStartupOption;
import org.apache.hadoop.hdfs.server.common.HdfsServerConstants.StartupOption;
import org.apache.hadoop.hdfs.server.common.InconsistentFSStateException;
import org.apache.hadoop.hdfs.server.common.Storage;
import org.apache.hadoop.hdfs.server.common.Storage.FormatConfirmable;
import org.apache.hadoop.hdfs.server.common.Storage.StorageDirectory;
import org.apache.hadoop.hdfs.server.common.Storage.StorageState;
import org.apache.hadoop.hdfs.server.common.Util;
import org.apache.hadoop.hdfs.server.namenode.FSImageStorageInspector.FSImageFile;
import org.apache.hadoop.hdfs.server.namenode.NNStorage.NameNodeDirType;
import org.apache.hadoop.hdfs.server.namenode.NNStorage.NameNodeFile;
import org.apache.hadoop.hdfs.server.namenode.snapshot.Snapshot;
import org.apache.hadoop.hdfs.server.namenode.startupprogress.Phase;
import org.apache.hadoop.hdfs.server.namenode.startupprogress.StartupProgress;
import org.apache.hadoop.hdfs.server.protocol.CheckpointCommand;
import org.apache.hadoop.hdfs.server.protocol.NamenodeCommand;
import org.apache.hadoop.hdfs.server.protocol.NamenodeProtocol;
import org.apache.hadoop.hdfs.server.protocol.NamenodeRegistration;
import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
import org.apache.hadoop.hdfs.util.Canceler;
import org.apache.hadoop.hdfs.util.MD5FileUtils;
import org.apache.hadoop.io.MD5Hash;
import org.apache.hadoop.util.Time;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Joiner;
import com.google.common.base.Preconditions;
import com.google.common.collect.Lists;
/**
* FSImage handles checkpointing and logging of the namespace edits.
*
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class FSImage implements Closeable {
public static final Log LOG = LogFactory.getLog(FSImage.class.getName());
protected FSEditLog editLog = null;
private boolean isUpgradeFinalized = false;
protected NNStorage storage;
/**
* The last transaction ID that was either loaded from an image
* or loaded by loading edits files.
*/
protected long lastAppliedTxId = 0;
final private Configuration conf;
protected NNStorageRetentionManager archivalManager;
/**
* Construct an FSImage
* @param conf Configuration
* @throws IOException if default directories are invalid.
*/
public FSImage(Configuration conf) throws IOException {
this(conf,
FSNamesystem.getNamespaceDirs(conf),
FSNamesystem.getNamespaceEditsDirs(conf));
}
/**
* Construct the FSImage. Set the default checkpoint directories.
*
* Setup storage and initialize the edit log.
*
* @param conf Configuration
* @param imageDirs Directories the image can be stored in.
* @param editsDirs Directories the editlog can be stored in.
* @throws IOException if directories are invalid.
*/
protected FSImage(Configuration conf,
Collection<URI> imageDirs,
List<URI> editsDirs)
throws IOException {
this.conf = conf;
storage = new NNStorage(conf, imageDirs, editsDirs);
if(conf.getBoolean(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_RESTORE_KEY,
DFSConfigKeys.DFS_NAMENODE_NAME_DIR_RESTORE_DEFAULT)) {
storage.setRestoreFailedStorage(true);
}
this.editLog = new FSEditLog(conf, storage, editsDirs);
archivalManager = new NNStorageRetentionManager(conf, storage, editLog);
}
void format(FSNamesystem fsn, String clusterId) throws IOException {
long fileCount = fsn.getTotalFiles();
// Expect 1 file, which is the root inode
Preconditions.checkState(fileCount == 1,
"FSImage.format should be called with an uninitialized namesystem, has " +
fileCount + " files");
NamespaceInfo ns = NNStorage.newNamespaceInfo();
LOG.info("Allocated new BlockPoolId: " + ns.getBlockPoolID());
ns.clusterID = clusterId;
storage.format(ns);
editLog.formatNonFileJournals(ns);
saveFSImageInAllDirs(fsn, 0);
}
/**
* Check whether the storage directories and non-file journals exist.
* If running in interactive mode, will prompt the user for each
* directory to allow them to format anyway. Otherwise, returns
* false, unless 'force' is specified.
*
* @param force format regardless of whether dirs exist
* @param interactive prompt the user when a dir exists
* @return true if formatting should proceed
* @throws IOException if some storage cannot be accessed
*/
boolean confirmFormat(boolean force, boolean interactive) throws IOException {
List<FormatConfirmable> confirms = Lists.newArrayList();
for (StorageDirectory sd : storage.dirIterable(null)) {
confirms.add(sd);
}
confirms.addAll(editLog.getFormatConfirmables());
return Storage.confirmFormat(confirms, force, interactive);
}
/**
* Analyze storage directories.
* Recover from previous transitions if required.
* Perform fs state transition if necessary depending on the namespace info.
* Read storage info.
*
* @throws IOException
* @return true if the image needs to be saved or false otherwise
*/
boolean recoverTransitionRead(StartupOption startOpt, FSNamesystem target,
MetaRecoveryContext recovery)
throws IOException {
assert startOpt != StartupOption.FORMAT :
"NameNode formatting should be performed before reading the image";
Collection<URI> imageDirs = storage.getImageDirectories();
Collection<URI> editsDirs = editLog.getEditURIs();
// none of the data dirs exist
if((imageDirs.size() == 0 || editsDirs.size() == 0)
&& startOpt != StartupOption.IMPORT)
throw new IOException(
"All specified directories are not accessible or do not exist.");
// 1. For each data directory calculate its state and
// check whether all is consistent before transitioning.
Map<StorageDirectory, StorageState> dataDirStates =
new HashMap<StorageDirectory, StorageState>();
boolean isFormatted = recoverStorageDirs(startOpt, dataDirStates);
if (LOG.isTraceEnabled()) {
LOG.trace("Data dir states:\n " +
Joiner.on("\n ").withKeyValueSeparator(": ")
.join(dataDirStates));
}
if (!isFormatted && startOpt != StartupOption.ROLLBACK
&& startOpt != StartupOption.IMPORT) {
throw new IOException("NameNode is not formatted.");
}
int layoutVersion = storage.getLayoutVersion();
if (layoutVersion < Storage.LAST_PRE_UPGRADE_LAYOUT_VERSION) {
NNStorage.checkVersionUpgradable(storage.getLayoutVersion());
}
if (startOpt != StartupOption.UPGRADE
&& !RollingUpgradeStartupOption.STARTED.matches(startOpt)
&& layoutVersion < Storage.LAST_PRE_UPGRADE_LAYOUT_VERSION
&& layoutVersion != HdfsConstants.NAMENODE_LAYOUT_VERSION) {
throw new IOException(
"\nFile system image contains an old layout version "
+ storage.getLayoutVersion() + ".\nAn upgrade to version "
+ HdfsConstants.NAMENODE_LAYOUT_VERSION + " is required.\n"
+ "Please restart NameNode with the \""
+ RollingUpgradeStartupOption.STARTED.getOptionString()
+ "\" option if a rolling upgraded is already started;"
+ " or restart NameNode with the \""
+ StartupOption.UPGRADE + "\" to start a new upgrade.");
}
storage.processStartupOptionsForUpgrade(startOpt, layoutVersion);
// 2. Format unformatted dirs.
for (Iterator<StorageDirectory> it = storage.dirIterator(); it.hasNext();) {
StorageDirectory sd = it.next();
StorageState curState = dataDirStates.get(sd);
switch(curState) {
case NON_EXISTENT:
throw new IOException(StorageState.NON_EXISTENT +
" state cannot be here");
case NOT_FORMATTED:
LOG.info("Storage directory " + sd.getRoot() + " is not formatted.");
LOG.info("Formatting ...");
sd.clearDirectory(); // create empty currrent dir
break;
default:
break;
}
}
// 3. Do transitions
switch(startOpt) {
case UPGRADE:
doUpgrade(target);
return false; // upgrade saved image already
case IMPORT:
doImportCheckpoint(target);
return false; // import checkpoint saved image already
case ROLLBACK:
throw new AssertionError("Rollback is now a standalone command, "
+ "NameNode should not be starting with this option.");
case REGULAR:
default:
// just load the image
}
return loadFSImage(target, startOpt, recovery);
}
/**
* For each storage directory, performs recovery of incomplete transitions
* (eg. upgrade, rollback, checkpoint) and inserts the directory's storage
* state into the dataDirStates map.
* @param dataDirStates output of storage directory states
* @return true if there is at least one valid formatted storage directory
*/
private boolean recoverStorageDirs(StartupOption startOpt,
Map<StorageDirectory, StorageState> dataDirStates) throws IOException {
boolean isFormatted = false;
// This loop needs to be over all storage dirs, even shared dirs, to make
// sure that we properly examine their state, but we make sure we don't
// mutate the shared dir below in the actual loop.
for (Iterator<StorageDirectory> it =
storage.dirIterator(); it.hasNext();) {
StorageDirectory sd = it.next();
StorageState curState;
try {
curState = sd.analyzeStorage(startOpt, storage);
// sd is locked but not opened
switch(curState) {
case NON_EXISTENT:
// name-node fails if any of the configured storage dirs are missing
throw new InconsistentFSStateException(sd.getRoot(),
"storage directory does not exist or is not accessible.");
case NOT_FORMATTED:
break;
case NORMAL:
break;
default: // recovery is possible
sd.doRecover(curState);
}
if (curState != StorageState.NOT_FORMATTED
&& startOpt != StartupOption.ROLLBACK) {
// read and verify consistency with other directories
storage.readProperties(sd);
isFormatted = true;
}
if (startOpt == StartupOption.IMPORT && isFormatted)
// import of a checkpoint is allowed only into empty image directories
throw new IOException("Cannot import image from a checkpoint. "
+ " NameNode already contains an image in " + sd.getRoot());
} catch (IOException ioe) {
sd.unlock();
throw ioe;
}
dataDirStates.put(sd,curState);
}
return isFormatted;
}
/** Check if upgrade is in progress. */
void checkUpgrade(FSNamesystem target) throws IOException {
// Upgrade or rolling upgrade is allowed only if there are
// no previous fs states in any of the directories
for (Iterator<StorageDirectory> it = storage.dirIterator(false); it.hasNext();) {
StorageDirectory sd = it.next();
if (sd.getPreviousDir().exists())
throw new InconsistentFSStateException(sd.getRoot(),
"previous fs state should not exist during upgrade. "
+ "Finalize or rollback first.");
}
}
/**
* @return true if there is rollback fsimage (for rolling upgrade) in NameNode
* directory.
*/
public boolean hasRollbackFSImage() throws IOException {
final FSImageStorageInspector inspector = new FSImageTransactionalStorageInspector(
EnumSet.of(NameNodeFile.IMAGE_ROLLBACK));
storage.inspectStorageDirs(inspector);
try {
List<FSImageFile> images = inspector.getLatestImages();
return images != null && !images.isEmpty();
} catch (FileNotFoundException e) {
return false;
}
}
void doUpgrade(FSNamesystem target) throws IOException {
checkUpgrade(target);
// load the latest image
this.loadFSImage(target, StartupOption.UPGRADE, null);
// Do upgrade for each directory
target.checkRollingUpgrade("upgrade namenode");
long oldCTime = storage.getCTime();
storage.cTime = now(); // generate new cTime for the state
int oldLV = storage.getLayoutVersion();
storage.layoutVersion = HdfsConstants.NAMENODE_LAYOUT_VERSION;
List<StorageDirectory> errorSDs =
Collections.synchronizedList(new ArrayList<StorageDirectory>());
assert !editLog.isSegmentOpen() : "Edits log must not be open.";
LOG.info("Starting upgrade of local storage directories."
+ "\n old LV = " + oldLV
+ "; old CTime = " + oldCTime
+ ".\n new LV = " + storage.getLayoutVersion()
+ "; new CTime = " + storage.getCTime());
// Do upgrade for each directory
for (Iterator<StorageDirectory> it = storage.dirIterator(false); it.hasNext();) {
StorageDirectory sd = it.next();
try {
NNUpgradeUtil.doPreUpgrade(sd);
} catch (Exception e) {
LOG.error("Failed to move aside pre-upgrade storage " +
"in image directory " + sd.getRoot(), e);
errorSDs.add(sd);
continue;
}
}
if (target.isHaEnabled()) {
editLog.doPreUpgradeOfSharedLog();
}
storage.reportErrorsOnDirectories(errorSDs);
errorSDs.clear();
saveFSImageInAllDirs(target, editLog.getLastWrittenTxId());
// upgrade shared edit storage first
if (target.isHaEnabled()) {
editLog.doUpgradeOfSharedLog();
}
for (Iterator<StorageDirectory> it = storage.dirIterator(false); it.hasNext();) {
StorageDirectory sd = it.next();
try {
NNUpgradeUtil.doUpgrade(sd, storage);
} catch (IOException ioe) {
errorSDs.add(sd);
continue;
}
}
storage.reportErrorsOnDirectories(errorSDs);
isUpgradeFinalized = false;
if (!storage.getRemovedStorageDirs().isEmpty()) {
// during upgrade, it's a fatal error to fail any storage directory
throw new IOException("Upgrade failed in "
+ storage.getRemovedStorageDirs().size()
+ " storage directory(ies), previously logged.");
}
}
void doRollback(FSNamesystem fsns) throws IOException {
// Rollback is allowed only if there is
// a previous fs states in at least one of the storage directories.
// Directories that don't have previous state do not rollback
boolean canRollback = false;
FSImage prevState = new FSImage(conf);
try {
prevState.getStorage().layoutVersion = HdfsConstants.NAMENODE_LAYOUT_VERSION;
for (Iterator<StorageDirectory> it = storage.dirIterator(false); it.hasNext();) {
StorageDirectory sd = it.next();
if (!NNUpgradeUtil.canRollBack(sd, storage, prevState.getStorage(),
HdfsConstants.NAMENODE_LAYOUT_VERSION)) {
continue;
}
LOG.info("Can perform rollback for " + sd);
canRollback = true;
}
if (fsns.isHaEnabled()) {
// If HA is enabled, check if the shared log can be rolled back as well.
editLog.initJournalsForWrite();
boolean canRollBackSharedEditLog = editLog.canRollBackSharedLog(
prevState.getStorage(), HdfsConstants.NAMENODE_LAYOUT_VERSION);
if (canRollBackSharedEditLog) {
LOG.info("Can perform rollback for shared edit log.");
canRollback = true;
}
}
if (!canRollback)
throw new IOException("Cannot rollback. None of the storage "
+ "directories contain previous fs state.");
// Now that we know all directories are going to be consistent
// Do rollback for each directory containing previous state
for (Iterator<StorageDirectory> it = storage.dirIterator(false); it.hasNext();) {
StorageDirectory sd = it.next();
LOG.info("Rolling back storage directory " + sd.getRoot()
+ ".\n new LV = " + prevState.getStorage().getLayoutVersion()
+ "; new CTime = " + prevState.getStorage().getCTime());
NNUpgradeUtil.doRollBack(sd);
}
if (fsns.isHaEnabled()) {
// If HA is enabled, try to roll back the shared log as well.
editLog.doRollback();
}
isUpgradeFinalized = true;
} finally {
prevState.close();
}
}
/**
* Load image from a checkpoint directory and save it into the current one.
* @param target the NameSystem to import into
* @throws IOException
*/
void doImportCheckpoint(FSNamesystem target) throws IOException {
Collection<URI> checkpointDirs =
FSImage.getCheckpointDirs(conf, null);
List<URI> checkpointEditsDirs =
FSImage.getCheckpointEditsDirs(conf, null);
if (checkpointDirs == null || checkpointDirs.isEmpty()) {
throw new IOException("Cannot import image from a checkpoint. "
+ "\"dfs.namenode.checkpoint.dir\" is not set." );
}
if (checkpointEditsDirs == null || checkpointEditsDirs.isEmpty()) {
throw new IOException("Cannot import image from a checkpoint. "
+ "\"dfs.namenode.checkpoint.dir\" is not set." );
}
FSImage realImage = target.getFSImage();
FSImage ckptImage = new FSImage(conf,
checkpointDirs, checkpointEditsDirs);
target.dir.fsImage = ckptImage;
// load from the checkpoint dirs
try {
ckptImage.recoverTransitionRead(StartupOption.REGULAR, target, null);
} finally {
ckptImage.close();
}
// return back the real image
realImage.getStorage().setStorageInfo(ckptImage.getStorage());
realImage.getEditLog().setNextTxId(ckptImage.getEditLog().getLastWrittenTxId()+1);
realImage.initEditLog(StartupOption.IMPORT);
target.dir.fsImage = realImage;
realImage.getStorage().setBlockPoolID(ckptImage.getBlockPoolID());
// and save it but keep the same checkpointTime
saveNamespace(target);
getStorage().writeAll();
}
void finalizeUpgrade(boolean finalizeEditLog) throws IOException {
LOG.info("Finalizing upgrade for local dirs. " +
(storage.getLayoutVersion() == 0 ? "" :
"\n cur LV = " + storage.getLayoutVersion()
+ "; cur CTime = " + storage.getCTime()));
for (Iterator<StorageDirectory> it = storage.dirIterator(false); it.hasNext();) {
StorageDirectory sd = it.next();
NNUpgradeUtil.doFinalize(sd);
}
if (finalizeEditLog) {
// We only do this in the case that HA is enabled and we're active. In any
// other case the NN will have done the upgrade of the edits directories
// already by virtue of the fact that they're local.
editLog.doFinalizeOfSharedLog();
}
isUpgradeFinalized = true;
}
boolean isUpgradeFinalized() {
return isUpgradeFinalized;
}
public FSEditLog getEditLog() {
return editLog;
}
@VisibleForTesting
void setEditLogForTesting(FSEditLog newLog) {
editLog = newLog;
}
void openEditLogForWrite() throws IOException {
assert editLog != null : "editLog must be initialized";
editLog.openForWrite();
storage.writeTransactionIdFileToStorage(editLog.getCurSegmentTxId());
};
/**
* Toss the current image and namesystem, reloading from the specified
* file.
*/
void reloadFromImageFile(File file, FSNamesystem target) throws IOException {
target.clear();
LOG.debug("Reloading namespace from " + file);
loadFSImage(file, target, null);
}
/**
* Choose latest image from one of the directories,
* load it and merge with the edits.
*
* Saving and loading fsimage should never trigger symlink resolution.
* The paths that are persisted do not have *intermediate* symlinks
* because intermediate symlinks are resolved at the time files,
* directories, and symlinks are created. All paths accessed while
* loading or saving fsimage should therefore only see symlinks as
* the final path component, and the functions called below do not
* resolve symlinks that are the final path component.
*
* @return whether the image should be saved
* @throws IOException
*/
private boolean loadFSImage(FSNamesystem target, StartupOption startOpt,
MetaRecoveryContext recovery)
throws IOException {
final boolean rollingRollback
= RollingUpgradeStartupOption.ROLLBACK.matches(startOpt);
final EnumSet<NameNodeFile> nnfs;
if (rollingRollback) {
// if it is rollback of rolling upgrade, only load from the rollback image
nnfs = EnumSet.of(NameNodeFile.IMAGE_ROLLBACK);
} else {
// otherwise we can load from both IMAGE and IMAGE_ROLLBACK
nnfs = EnumSet.of(NameNodeFile.IMAGE, NameNodeFile.IMAGE_ROLLBACK);
}
final FSImageStorageInspector inspector = storage.readAndInspectDirs(nnfs);
isUpgradeFinalized = inspector.isUpgradeFinalized();
List<FSImageFile> imageFiles = inspector.getLatestImages();
StartupProgress prog = NameNode.getStartupProgress();
prog.beginPhase(Phase.LOADING_FSIMAGE);
File phaseFile = imageFiles.get(0).getFile();
prog.setFile(Phase.LOADING_FSIMAGE, phaseFile.getAbsolutePath());
prog.setSize(Phase.LOADING_FSIMAGE, phaseFile.length());
boolean needToSave = inspector.needToSave();
Iterable<EditLogInputStream> editStreams = null;
initEditLog(startOpt);
if (NameNodeLayoutVersion.supports(
LayoutVersion.Feature.TXID_BASED_LAYOUT, getLayoutVersion())) {
// If we're open for write, we're either non-HA or we're the active NN, so
// we better be able to load all the edits. If we're the standby NN, it's
// OK to not be able to read all of edits right now.
// In the meanwhile, for HA upgrade, we will still write editlog thus need
// this toAtLeastTxId to be set to the max-seen txid
// For rollback in rolling upgrade, we need to set the toAtLeastTxId to
// the txid right before the upgrade marker.
long toAtLeastTxId = editLog.isOpenForWrite() ? inspector
.getMaxSeenTxId() : 0;
if (rollingRollback) {
// note that the first image in imageFiles is the special checkpoint
// for the rolling upgrade
toAtLeastTxId = imageFiles.get(0).getCheckpointTxId() + 2;
}
editStreams = editLog.selectInputStreams(
imageFiles.get(0).getCheckpointTxId() + 1,
toAtLeastTxId, recovery, false);
} else {
editStreams = FSImagePreTransactionalStorageInspector
.getEditLogStreams(storage);
}
int maxOpSize = conf.getInt(DFSConfigKeys.DFS_NAMENODE_MAX_OP_SIZE_KEY,
DFSConfigKeys.DFS_NAMENODE_MAX_OP_SIZE_DEFAULT);
for (EditLogInputStream elis : editStreams) {
elis.setMaxOpSize(maxOpSize);
}
for (EditLogInputStream l : editStreams) {
LOG.debug("Planning to load edit log stream: " + l);
}
if (!editStreams.iterator().hasNext()) {
LOG.info("No edit log streams selected.");
}
FSImageFile imageFile = null;
for (int i = 0; i < imageFiles.size(); i++) {
try {
imageFile = imageFiles.get(i);
loadFSImageFile(target, recovery, imageFile);
break;
} catch (IOException ioe) {
LOG.error("Failed to load image from " + imageFile, ioe);
target.clear();
imageFile = null;
}
}
// Failed to load any images, error out
if (imageFile == null) {
FSEditLog.closeAllStreams(editStreams);
throw new IOException("Failed to load an FSImage file!");
}
prog.endPhase(Phase.LOADING_FSIMAGE);
if (!rollingRollback) {
long txnsAdvanced = loadEdits(editStreams, target, startOpt, recovery);
needToSave |= needsResaveBasedOnStaleCheckpoint(imageFile.getFile(),
txnsAdvanced);
if (RollingUpgradeStartupOption.DOWNGRADE.matches(startOpt)) {
// rename rollback image if it is downgrade
renameCheckpoint(NameNodeFile.IMAGE_ROLLBACK, NameNodeFile.IMAGE);
}
} else {
// Trigger the rollback for rolling upgrade. Here lastAppliedTxId equals
// to the last txid in rollback fsimage.
rollingRollback(lastAppliedTxId + 1, imageFiles.get(0).getCheckpointTxId());
needToSave = false;
}
editLog.setNextTxId(lastAppliedTxId + 1);
return needToSave;
}
/** rollback for rolling upgrade. */
private void rollingRollback(long discardSegmentTxId, long ckptId)
throws IOException {
// discard discard unnecessary editlog segments starting from the given id
this.editLog.discardSegments(discardSegmentTxId);
// rename the special checkpoint
renameCheckpoint(ckptId, NameNodeFile.IMAGE_ROLLBACK, NameNodeFile.IMAGE,
true);
// purge all the checkpoints after the marker
archivalManager.purgeCheckpoinsAfter(NameNodeFile.IMAGE, ckptId);
String nameserviceId = DFSUtil.getNamenodeNameServiceId(conf);
if (HAUtil.isHAEnabled(conf, nameserviceId)) {
// close the editlog since it is currently open for write
this.editLog.close();
// reopen the editlog for read
this.editLog.initSharedJournalsForRead();
}
}
void loadFSImageFile(FSNamesystem target, MetaRecoveryContext recovery,
FSImageFile imageFile) throws IOException {
LOG.debug("Planning to load image :\n" + imageFile);
StorageDirectory sdForProperties = imageFile.sd;
storage.readProperties(sdForProperties);
if (NameNodeLayoutVersion.supports(
LayoutVersion.Feature.TXID_BASED_LAYOUT, getLayoutVersion())) {
// For txid-based layout, we should have a .md5 file
// next to the image file
loadFSImage(imageFile.getFile(), target, recovery);
} else if (NameNodeLayoutVersion.supports(
LayoutVersion.Feature.FSIMAGE_CHECKSUM, getLayoutVersion())) {
// In 0.22, we have the checksum stored in the VERSION file.
String md5 = storage.getDeprecatedProperty(
NNStorage.DEPRECATED_MESSAGE_DIGEST_PROPERTY);
if (md5 == null) {
throw new InconsistentFSStateException(sdForProperties.getRoot(),
"Message digest property " +
NNStorage.DEPRECATED_MESSAGE_DIGEST_PROPERTY +
" not set for storage directory " + sdForProperties.getRoot());
}
loadFSImage(imageFile.getFile(), new MD5Hash(md5), target, recovery);
} else {
// We don't have any record of the md5sum
loadFSImage(imageFile.getFile(), null, target, recovery);
}
}
public void initEditLog(StartupOption startOpt) throws IOException {
Preconditions.checkState(getNamespaceID() != 0,
"Must know namespace ID before initting edit log");
String nameserviceId = DFSUtil.getNamenodeNameServiceId(conf);
if (!HAUtil.isHAEnabled(conf, nameserviceId)) {
// If this NN is not HA
editLog.initJournalsForWrite();
editLog.recoverUnclosedStreams();
} else if (HAUtil.isHAEnabled(conf, nameserviceId)
&& (startOpt == StartupOption.UPGRADE
|| RollingUpgradeStartupOption.ROLLBACK.matches(startOpt))) {
// This NN is HA, but we're doing an upgrade or a rollback of rolling
// upgrade so init the edit log for write.
editLog.initJournalsForWrite();
if (startOpt == StartupOption.UPGRADE) {
long sharedLogCTime = editLog.getSharedLogCTime();
if (this.storage.getCTime() < sharedLogCTime) {
throw new IOException("It looks like the shared log is already " +
"being upgraded but this NN has not been upgraded yet. You " +
"should restart this NameNode with the '" +
StartupOption.BOOTSTRAPSTANDBY.getName() + "' option to bring " +
"this NN in sync with the other.");
}
}
editLog.recoverUnclosedStreams();
} else {
// This NN is HA and we're not doing an upgrade.
editLog.initSharedJournalsForRead();
}
}
/**
* @param imageFile the image file that was loaded
* @param numEditsLoaded the number of edits loaded from edits logs
* @return true if the NameNode should automatically save the namespace
* when it is started, due to the latest checkpoint being too old.
*/
private boolean needsResaveBasedOnStaleCheckpoint(
File imageFile, long numEditsLoaded) {
final long checkpointPeriod = conf.getLong(
DFSConfigKeys.DFS_NAMENODE_CHECKPOINT_PERIOD_KEY,
DFSConfigKeys.DFS_NAMENODE_CHECKPOINT_PERIOD_DEFAULT);
final long checkpointTxnCount = conf.getLong(
DFSConfigKeys.DFS_NAMENODE_CHECKPOINT_TXNS_KEY,
DFSConfigKeys.DFS_NAMENODE_CHECKPOINT_TXNS_DEFAULT);
long checkpointAge = Time.now() - imageFile.lastModified();
return (checkpointAge > checkpointPeriod * 1000) ||
(numEditsLoaded > checkpointTxnCount);
}
/**
* Load the specified list of edit files into the image.
*/
public long loadEdits(Iterable<EditLogInputStream> editStreams,
FSNamesystem target) throws IOException {
return loadEdits(editStreams, target, null, null);
}
private long loadEdits(Iterable<EditLogInputStream> editStreams,
FSNamesystem target, StartupOption startOpt, MetaRecoveryContext recovery)
throws IOException {
LOG.debug("About to load edits:\n " + Joiner.on("\n ").join(editStreams));
StartupProgress prog = NameNode.getStartupProgress();
prog.beginPhase(Phase.LOADING_EDITS);
long prevLastAppliedTxId = lastAppliedTxId;
try {
FSEditLogLoader loader = new FSEditLogLoader(target, lastAppliedTxId);
// Load latest edits
for (EditLogInputStream editIn : editStreams) {
LOG.info("Reading " + editIn + " expecting start txid #" +
(lastAppliedTxId + 1));
try {
loader.loadFSEdits(editIn, lastAppliedTxId + 1, startOpt, recovery);
} finally {
// Update lastAppliedTxId even in case of error, since some ops may
// have been successfully applied before the error.
lastAppliedTxId = loader.getLastAppliedTxId();
}
// If we are in recovery mode, we may have skipped over some txids.
if (editIn.getLastTxId() != HdfsConstants.INVALID_TXID) {
lastAppliedTxId = editIn.getLastTxId();
}
}
} finally {
FSEditLog.closeAllStreams(editStreams);
// update the counts
updateCountForQuota(target.dir.rootDir);
}
prog.endPhase(Phase.LOADING_EDITS);
return lastAppliedTxId - prevLastAppliedTxId;
}
/**
* Update the count of each directory with quota in the namespace.
* A directory's count is defined as the total number inodes in the tree
* rooted at the directory.
*
* This is an update of existing state of the filesystem and does not
* throw QuotaExceededException.
*/
static void updateCountForQuota(INodeDirectory root) {
updateCountForQuotaRecursively(root, Quota.Counts.newInstance());
}
private static void updateCountForQuotaRecursively(INodeDirectory dir,
Quota.Counts counts) {
final long parentNamespace = counts.get(Quota.NAMESPACE);
final long parentDiskspace = counts.get(Quota.DISKSPACE);
dir.computeQuotaUsage4CurrentDirectory(counts);
for (INode child : dir.getChildrenList(Snapshot.CURRENT_STATE_ID)) {
if (child.isDirectory()) {
updateCountForQuotaRecursively(child.asDirectory(), counts);
} else {
// file or symlink: count here to reduce recursive calls.
child.computeQuotaUsage(counts, false);
}
}
if (dir.isQuotaSet()) {
// check if quota is violated. It indicates a software bug.
final Quota.Counts q = dir.getQuotaCounts();
final long namespace = counts.get(Quota.NAMESPACE) - parentNamespace;
final long nsQuota = q.get(Quota.NAMESPACE);
if (Quota.isViolated(nsQuota, namespace)) {
LOG.error("BUG: Namespace quota violation in image for "
+ dir.getFullPathName()
+ " quota = " + nsQuota + " < consumed = " + namespace);
}
final long diskspace = counts.get(Quota.DISKSPACE) - parentDiskspace;
final long dsQuota = q.get(Quota.DISKSPACE);
if (Quota.isViolated(dsQuota, diskspace)) {
LOG.error("BUG: Diskspace quota violation in image for "
+ dir.getFullPathName()
+ " quota = " + dsQuota + " < consumed = " + diskspace);
}
dir.getDirectoryWithQuotaFeature().setSpaceConsumed(namespace, diskspace);
}
}
/**
* Load the image namespace from the given image file, verifying
* it against the MD5 sum stored in its associated .md5 file.
*/
private void loadFSImage(File imageFile, FSNamesystem target,
MetaRecoveryContext recovery) throws IOException {
MD5Hash expectedMD5 = MD5FileUtils.readStoredMd5ForFile(imageFile);
if (expectedMD5 == null) {
throw new IOException("No MD5 file found corresponding to image file "
+ imageFile);
}
loadFSImage(imageFile, expectedMD5, target, recovery);
}
/**
* Load in the filesystem image from file. It's a big list of
* filenames and blocks.
*/
private void loadFSImage(File curFile, MD5Hash expectedMd5,
FSNamesystem target, MetaRecoveryContext recovery) throws IOException {
// BlockPoolId is required when the FsImageLoader loads the rolling upgrade
// information. Make sure the ID is properly set.
target.setBlockPoolId(this.getBlockPoolID());
FSImageFormat.LoaderDelegator loader = FSImageFormat.newLoader(conf, target);
loader.load(curFile);
// Check that the image digest we loaded matches up with what
// we expected
MD5Hash readImageMd5 = loader.getLoadedImageMd5();
if (expectedMd5 != null &&
!expectedMd5.equals(readImageMd5)) {
throw new IOException("Image file " + curFile +
" is corrupt with MD5 checksum of " + readImageMd5 +
" but expecting " + expectedMd5);
}
long txId = loader.getLoadedImageTxId();
LOG.info("Loaded image for txid " + txId + " from " + curFile);
lastAppliedTxId = txId;
storage.setMostRecentCheckpointInfo(txId, curFile.lastModified());
}
/**
* Save the contents of the FS image to the file.
*/
void saveFSImage(SaveNamespaceContext context, StorageDirectory sd,
NameNodeFile dstType) throws IOException {
long txid = context.getTxId();
File newFile = NNStorage.getStorageFile(sd, NameNodeFile.IMAGE_NEW, txid);
File dstFile = NNStorage.getStorageFile(sd, dstType, txid);
FSImageFormatProtobuf.Saver saver = new FSImageFormatProtobuf.Saver(context);
FSImageCompression compression = FSImageCompression.createCompression(conf);
saver.save(newFile, compression);
MD5FileUtils.saveMD5File(dstFile, saver.getSavedDigest());
storage.setMostRecentCheckpointInfo(txid, Time.now());
}
/**
* FSImageSaver is being run in a separate thread when saving
* FSImage. There is one thread per each copy of the image.
*
* FSImageSaver assumes that it was launched from a thread that holds
* FSNamesystem lock and waits for the execution of FSImageSaver thread
* to finish.
* This way we are guaranteed that the namespace is not being updated
* while multiple instances of FSImageSaver are traversing it
* and writing it out.
*/
private class FSImageSaver implements Runnable {
private final SaveNamespaceContext context;
private final StorageDirectory sd;
private final NameNodeFile nnf;
public FSImageSaver(SaveNamespaceContext context, StorageDirectory sd,
NameNodeFile nnf) {
this.context = context;
this.sd = sd;
this.nnf = nnf;
}
@Override
public void run() {
try {
saveFSImage(context, sd, nnf);
} catch (SaveNamespaceCancelledException snce) {
LOG.info("Cancelled image saving for " + sd.getRoot() +
": " + snce.getMessage());
// don't report an error on the storage dir!
} catch (Throwable t) {
LOG.error("Unable to save image for " + sd.getRoot(), t);
context.reportErrorOnStorageDirectory(sd);
}
}
@Override
public String toString() {
return "FSImageSaver for " + sd.getRoot() +
" of type " + sd.getStorageDirType();
}
}
private void waitForThreads(List<Thread> threads) {
for (Thread thread : threads) {
while (thread.isAlive()) {
try {
thread.join();
} catch (InterruptedException iex) {
LOG.error("Caught interrupted exception while waiting for thread " +
thread.getName() + " to finish. Retrying join");
}
}
}
}
/**
* @see #saveNamespace(FSNamesystem, Canceler)
*/
public synchronized void saveNamespace(FSNamesystem source)
throws IOException {
saveNamespace(source, NameNodeFile.IMAGE, null);
}
/**
* Save the contents of the FS image to a new image file in each of the
* current storage directories.
* @param canceler
*/
public synchronized void saveNamespace(FSNamesystem source, NameNodeFile nnf,
Canceler canceler) throws IOException {
assert editLog != null : "editLog must be initialized";
LOG.info("Save namespace ...");
storage.attemptRestoreRemovedStorage();
boolean editLogWasOpen = editLog.isSegmentOpen();
if (editLogWasOpen) {
editLog.endCurrentLogSegment(true);
}
long imageTxId = getLastAppliedOrWrittenTxId();
try {
saveFSImageInAllDirs(source, nnf, imageTxId, canceler);
storage.writeAll();
} finally {
if (editLogWasOpen) {
editLog.startLogSegment(imageTxId + 1, true);
// Take this opportunity to note the current transaction.
// Even if the namespace save was cancelled, this marker
// is only used to determine what transaction ID is required
// for startup. So, it doesn't hurt to update it unnecessarily.
storage.writeTransactionIdFileToStorage(imageTxId + 1);
}
}
}
/**
* @see #saveFSImageInAllDirs(FSNamesystem, long, Canceler)
*/
protected synchronized void saveFSImageInAllDirs(FSNamesystem source, long txid)
throws IOException {
saveFSImageInAllDirs(source, NameNodeFile.IMAGE, txid, null);
}
private synchronized void saveFSImageInAllDirs(FSNamesystem source,
NameNodeFile nnf, long txid, Canceler canceler) throws IOException {
StartupProgress prog = NameNode.getStartupProgress();
prog.beginPhase(Phase.SAVING_CHECKPOINT);
if (storage.getNumStorageDirs(NameNodeDirType.IMAGE) == 0) {
throw new IOException("No image directories available!");
}
if (canceler == null) {
canceler = new Canceler();
}
SaveNamespaceContext ctx = new SaveNamespaceContext(
source, txid, canceler);
try {
List<Thread> saveThreads = new ArrayList<Thread>();
// save images into current
for (Iterator<StorageDirectory> it
= storage.dirIterator(NameNodeDirType.IMAGE); it.hasNext();) {
StorageDirectory sd = it.next();
FSImageSaver saver = new FSImageSaver(ctx, sd, nnf);
Thread saveThread = new Thread(saver, saver.toString());
saveThreads.add(saveThread);
saveThread.start();
}
waitForThreads(saveThreads);
saveThreads.clear();
storage.reportErrorsOnDirectories(ctx.getErrorSDs());
if (storage.getNumStorageDirs(NameNodeDirType.IMAGE) == 0) {
throw new IOException(
"Failed to save in any storage directories while saving namespace.");
}
if (canceler.isCancelled()) {
deleteCancelledCheckpoint(txid);
ctx.checkCancelled(); // throws
assert false : "should have thrown above!";
}
renameCheckpoint(txid, NameNodeFile.IMAGE_NEW, nnf, false);
// Since we now have a new checkpoint, we can clean up some
// old edit logs and checkpoints.
purgeOldStorage(nnf);
} finally {
// Notify any threads waiting on the checkpoint to be canceled
// that it is complete.
ctx.markComplete();
ctx = null;
}
prog.endPhase(Phase.SAVING_CHECKPOINT);
}
/**
* Purge any files in the storage directories that are no longer
* necessary.
*/
void purgeOldStorage(NameNodeFile nnf) {
try {
archivalManager.purgeOldStorage(nnf);
} catch (Exception e) {
LOG.warn("Unable to purge old storage " + nnf.getName(), e);
}
}
/**
* Rename FSImage with the specific txid
*/
private void renameCheckpoint(long txid, NameNodeFile fromNnf,
NameNodeFile toNnf, boolean renameMD5) throws IOException {
ArrayList<StorageDirectory> al = null;
for (StorageDirectory sd : storage.dirIterable(NameNodeDirType.IMAGE)) {
try {
renameImageFileInDir(sd, fromNnf, toNnf, txid, renameMD5);
} catch (IOException ioe) {
LOG.warn("Unable to rename checkpoint in " + sd, ioe);
if (al == null) {
al = Lists.newArrayList();
}
al.add(sd);
}
}
if(al != null) storage.reportErrorsOnDirectories(al);
}
/**
* Rename all the fsimage files with the specific NameNodeFile type. The
* associated checksum files will also be renamed.
*/
void renameCheckpoint(NameNodeFile fromNnf, NameNodeFile toNnf)
throws IOException {
ArrayList<StorageDirectory> al = null;
FSImageTransactionalStorageInspector inspector =
new FSImageTransactionalStorageInspector(EnumSet.of(fromNnf));
storage.inspectStorageDirs(inspector);
for (FSImageFile image : inspector.getFoundImages()) {
try {
renameImageFileInDir(image.sd, fromNnf, toNnf, image.txId, true);
} catch (IOException ioe) {
LOG.warn("Unable to rename checkpoint in " + image.sd, ioe);
if (al == null) {
al = Lists.newArrayList();
}
al.add(image.sd);
}
}
if(al != null) {
storage.reportErrorsOnDirectories(al);
}
}
/**
* Deletes the checkpoint file in every storage directory,
* since the checkpoint was cancelled.
*/
private void deleteCancelledCheckpoint(long txid) throws IOException {
ArrayList<StorageDirectory> al = Lists.newArrayList();
for (StorageDirectory sd : storage.dirIterable(NameNodeDirType.IMAGE)) {
File ckpt = NNStorage.getStorageFile(sd, NameNodeFile.IMAGE_NEW, txid);
if (ckpt.exists() && !ckpt.delete()) {
LOG.warn("Unable to delete cancelled checkpoint in " + sd);
al.add(sd);
}
}
storage.reportErrorsOnDirectories(al);
}
private void renameImageFileInDir(StorageDirectory sd, NameNodeFile fromNnf,
NameNodeFile toNnf, long txid, boolean renameMD5) throws IOException {
final File fromFile = NNStorage.getStorageFile(sd, fromNnf, txid);
final File toFile = NNStorage.getStorageFile(sd, toNnf, txid);
// renameTo fails on Windows if the destination file already exists.
if(LOG.isDebugEnabled()) {
LOG.debug("renaming " + fromFile.getAbsolutePath()
+ " to " + toFile.getAbsolutePath());
}
if (!fromFile.renameTo(toFile)) {
if (!toFile.delete() || !fromFile.renameTo(toFile)) {
throw new IOException("renaming " + fromFile.getAbsolutePath() + " to " +
toFile.getAbsolutePath() + " FAILED");
}
}
if (renameMD5) {
MD5FileUtils.renameMD5File(fromFile, toFile);
}
}
CheckpointSignature rollEditLog() throws IOException {
getEditLog().rollEditLog();
// Record this log segment ID in all of the storage directories, so
// we won't miss this log segment on a restart if the edits directories
// go missing.
storage.writeTransactionIdFileToStorage(getEditLog().getCurSegmentTxId());
return new CheckpointSignature(this);
}
/**
* Start checkpoint.
* <p>
* If backup storage contains image that is newer than or incompatible with
* what the active name-node has, then the backup node should shutdown.<br>
* If the backup image is older than the active one then it should
* be discarded and downloaded from the active node.<br>
* If the images are the same then the backup image will be used as current.
*
* @param bnReg the backup node registration.
* @param nnReg this (active) name-node registration.
* @return {@link NamenodeCommand} if backup node should shutdown or
* {@link CheckpointCommand} prescribing what backup node should
* do with its image.
* @throws IOException
*/
NamenodeCommand startCheckpoint(NamenodeRegistration bnReg, // backup node
NamenodeRegistration nnReg) // active name-node
throws IOException {
LOG.info("Start checkpoint at txid " + getEditLog().getLastWrittenTxId());
String msg = null;
// Verify that checkpoint is allowed
if(bnReg.getNamespaceID() != storage.getNamespaceID())
msg = "Name node " + bnReg.getAddress()
+ " has incompatible namespace id: " + bnReg.getNamespaceID()
+ " expected: " + storage.getNamespaceID();
else if(bnReg.isRole(NamenodeRole.NAMENODE))
msg = "Name node " + bnReg.getAddress()
+ " role " + bnReg.getRole() + ": checkpoint is not allowed.";
else if(bnReg.getLayoutVersion() < storage.getLayoutVersion()
|| (bnReg.getLayoutVersion() == storage.getLayoutVersion()
&& bnReg.getCTime() > storage.getCTime()))
// remote node has newer image age
msg = "Name node " + bnReg.getAddress()
+ " has newer image layout version: LV = " +bnReg.getLayoutVersion()
+ " cTime = " + bnReg.getCTime()
+ ". Current version: LV = " + storage.getLayoutVersion()
+ " cTime = " + storage.getCTime();
if(msg != null) {
LOG.error(msg);
return new NamenodeCommand(NamenodeProtocol.ACT_SHUTDOWN);
}
boolean needToReturnImg = true;
if(storage.getNumStorageDirs(NameNodeDirType.IMAGE) == 0)
// do not return image if there are no image directories
needToReturnImg = false;
CheckpointSignature sig = rollEditLog();
return new CheckpointCommand(sig, needToReturnImg);
}
/**
* End checkpoint.
* <p>
* Validate the current storage info with the given signature.
*
* @param sig to validate the current storage info against
* @throws IOException if the checkpoint fields are inconsistent
*/
void endCheckpoint(CheckpointSignature sig) throws IOException {
LOG.info("End checkpoint at txid " + getEditLog().getLastWrittenTxId());
sig.validateStorageInfo(this);
}
/**
* This is called by the 2NN after having downloaded an image, and by
* the NN after having received a new image from the 2NN. It
* renames the image from fsimage_N.ckpt to fsimage_N and also
* saves the related .md5 file into place.
*/
public synchronized void saveDigestAndRenameCheckpointImage(NameNodeFile nnf,
long txid, MD5Hash digest) throws IOException {
// Write and rename MD5 file
List<StorageDirectory> badSds = Lists.newArrayList();
for (StorageDirectory sd : storage.dirIterable(NameNodeDirType.IMAGE)) {
File imageFile = NNStorage.getImageFile(sd, nnf, txid);
try {
MD5FileUtils.saveMD5File(imageFile, digest);
} catch (IOException ioe) {
badSds.add(sd);
}
}
storage.reportErrorsOnDirectories(badSds);
CheckpointFaultInjector.getInstance().afterMD5Rename();
// Rename image from tmp file
renameCheckpoint(txid, NameNodeFile.IMAGE_NEW, nnf, false);
// So long as this is the newest image available,
// advertise it as such to other checkpointers
// from now on
if (txid > storage.getMostRecentCheckpointTxId()) {
storage.setMostRecentCheckpointInfo(txid, Time.now());
}
}
@Override
synchronized public void close() throws IOException {
if (editLog != null) { // 2NN doesn't have any edit log
getEditLog().close();
}
storage.close();
}
/**
* Retrieve checkpoint dirs from configuration.
*
* @param conf the Configuration
* @param defaultValue a default value for the attribute, if null
* @return a Collection of URIs representing the values in
* dfs.namenode.checkpoint.dir configuration property
*/
static Collection<URI> getCheckpointDirs(Configuration conf,
String defaultValue) {
Collection<String> dirNames = conf.getTrimmedStringCollection(
DFSConfigKeys.DFS_NAMENODE_CHECKPOINT_DIR_KEY);
if (dirNames.size() == 0 && defaultValue != null) {
dirNames.add(defaultValue);
}
return Util.stringCollectionAsURIs(dirNames);
}
static List<URI> getCheckpointEditsDirs(Configuration conf,
String defaultName) {
Collection<String> dirNames = conf.getTrimmedStringCollection(
DFSConfigKeys.DFS_NAMENODE_CHECKPOINT_EDITS_DIR_KEY);
if (dirNames.size() == 0 && defaultName != null) {
dirNames.add(defaultName);
}
return Util.stringCollectionAsURIs(dirNames);
}
public NNStorage getStorage() {
return storage;
}
public int getLayoutVersion() {
return storage.getLayoutVersion();
}
public int getNamespaceID() {
return storage.getNamespaceID();
}
public String getClusterID() {
return storage.getClusterID();
}
public String getBlockPoolID() {
return storage.getBlockPoolID();
}
public synchronized long getLastAppliedTxId() {
return lastAppliedTxId;
}
public long getLastAppliedOrWrittenTxId() {
return Math.max(lastAppliedTxId,
editLog != null ? editLog.getLastWrittenTxId() : 0);
}
public void updateLastAppliedTxIdFromWritten() {
this.lastAppliedTxId = editLog.getLastWrittenTxId();
}
// Should be OK for this to not be synchronized since all of the places which
// mutate this value are themselves synchronized so it shouldn't be possible
// to see this flop back and forth. In the worst case this will just return an
// old value.
public long getMostRecentCheckpointTxId() {
return storage.getMostRecentCheckpointTxId();
}
}