ZooKeeper Log Files: Transaction and Snapshot Logging System
This chapter analyzes ZooKeeper's logging system, focusing on transaction logs and snapshot logs rather than standard log.info output.
FileTxnSnapLog Analysis
Let's examine the FileTxnSnapLog class, which is responsible for storing transaction and snapshot logs. First, we'll analyze its constructor:
public FileTxnSnapLog(File dataDir, File snapDir) throws IOException {
LOG.debug("Opening datadir:{} snapDir:{}", dataDir, snapDir);
this.dataDir = new File(dataDir, version + VERSION);
this.snapDir = new File(snapDir, version + VERSION);
boolean enableAutocreate = Boolean.valueOf(
System.getProperty(ZOOKEEPER_DATADIR_AUTOCREATE,
ZOOKEEPER_DATADIR_AUTOCREATE_DEFAULT));
trustEmptySnapshot = Boolean.getBoolean(ZOOKEEPER_SNAPSHOT_TRUST_EMPTY);
LOG.info(ZOOKEEPER_SNAPSHOT_TRUST_EMPTY + " : " + trustEmptySnapshot);
if (!this.dataDir.exists()) {
if (!enableAutocreate) {
throw new DatadirException("Missing data directory "
+ this.dataDir
+ ", automatic data directory creation is disabled ("
+ ZOOKEEPER_DATADIR_AUTOCREATE
+ " is false). Please create this directory manually.");
}
if (!this.dataDir.mkdirs() && !this.dataDir.exists()) {
throw new DatadirException("Unable to create data directory "
+ this.dataDir);
}
}
if (!this.dataDir.canWrite()) {
throw new DatadirException("Cannot write to data directory " + this.dataDir);
}
if (!this.snapDir.exists()) {
if (!enableAutocreate) {
throw new DatadirException("Missing snap directory "
+ this.snapDir
+ ", automatic data directory creation is disabled ("
+ ZOOKEEPER_DATADIR_AUTOCREATE
+ " is false). Please create this directory manually.");
}
if (!this.snapDir.mkdirs() && !this.snapDir.exists()) {
throw new DatadirException("Unable to create snap directory "
+ this.snapDir);
}
}
if (!this.snapDir.canWrite()) {
throw new DatadirException("Cannot write to snap directory " + this.snapDir);
}
if (!this.dataDir.getPath().equals(this.snapDir.getPath())) {
checkLogDir();
checkSnapDir();
}
txnLog = new FileTxnLog(this.dataDir);
snapLog = new FileSnap(this.snapDir);
}
The constructor takes two key parameters:
dataDir: The directory for data filessnapDir: The directory for snapshot files
Note that these parameters represent top-level directories. ZooKeeper stores actual files in the version-2 subdirectory. The constructor performs several validation steps:
- Checks if automatic directory creation is enabled
- Verifies directory existence and creation success
- Validates write permissions
- Creates txnLog and snapLog member variables
After understanding the constructor, let's analyze the restore method, which recovers the database by reading snapshots and transaction logs:
public long restore(DataTree dt, Map<Long, Integer> sessions,
PlayBackListener listener) throws IOException {
// Get the last zxid
long deserializeResult = snapLog.deserialize(dt, sessions);
// Create transaction log
FileTxnLog txnLog = new FileTxnLog(dataDir);
RestoreFinalizer finalizer = () -> {
long highestZxid = fastForwardFromEdits(dt, sessions, listener);
return highestZxid;
};
// If the last zxid is -1
if (-1L == deserializeResult) {
// If the last zxid in transaction log is not -1
if (txnLog.getLastLoggedZxid() != -1) {
// Check if we trust empty snapshots
if (!trustEmptySnapshot) {
// Throw exception if we don't trust empty snapshots
throw new IOException(EMPTY_SNAPSHOT_WARNING + "Something is broken!");
} else {
LOG.warn("{}This should only be allowed during upgrading.",
EMPTY_SNAPSHOT_WARNING);
// Execute data recovery operation
return finalizer.run();
}
}
// Save snapshot
save(dt, (ConcurrentHashMap<Long, Integer>) sessions);
return 0;
}
// Execute data recovery operation
return finalizer.run();
}
In this method, we first get the last zxid. Then, we create a transaction log and a restore finalizer. If the last zxid is -1, we check if the last zxid in the transaction log is not -1. If it is not, we check if we trust empty snapshots. If we don't, we throw an exception. Otherwise, we execute the data recovery operation.
Next, let's analyze the fastForwardFromEdits method, which reads transaction logs and applies them to the database:
public long fastForwardFromEdits(DataTree dt, Map<Long, Integer> sessions,
PlayBackListener listener) throws IOException {
// Read transaction log
TxnIterator itr = txnLog.read(dt.lastProcessedZxid + 1);
// Get maximum zxid from data tree
long highestZxid = dt.lastProcessedZxid;
// Transaction header information
TxnHeader hdr;
try {
while (true) {
// Get transaction header
hdr = itr.getHeader();
// If header is null, return the maximum zxid from data tree
if (hdr == null) {
//empty logs
return dt.lastProcessedZxid;
}
// If transaction header has zxid less than highest zxid and highest zxid is not 0
if (hdr.getZxid() < highestZxid && highestZxid != 0) {
// Log error
LOG.error("{}(highestZxid) > {}(next log) for type {}",
highestZxid, hdr.getZxid(), hdr.getType());
} else {
// Update highest zxid
highestZxid = hdr.getZxid();
}
try {
// Process transaction
processTransaction(hdr, dt, sessions, itr.getTxn());
} catch (KeeperException.NoNodeException e) {
throw new IOException("Failed to process transaction type: " +
hdr.getType() + " error: " + e.getMessage(), e);
}
// Process transaction completion callback
listener.onTxnLoaded(hdr, itr.getTxn());
if (!itr.next())
break;
}
} finally {
if (itr != null) {
itr.close();
}
}
return highestZxid;
}
In this method, we read transaction logs from the last processed zxid + 1. We then iterate through the transaction logs, applying each transaction to the database. If a transaction has a lower zxid than the highest zxid, we log an error. Otherwise, we update the highest zxid and process the transaction.
Next, let's analyze the processTransaction method, which applies a transaction to the database:
public void processTransaction(TxnHeader hdr, DataTree dt,
Map<Long, Integer> sessions, Record txn)
throws KeeperException.NoNodeException {
// Transaction processing result storage object
ProcessTxnResult rc;
// Handle different transaction header types
switch (hdr.getType()) {
// Create session
case OpCode.createSession:
// Add session information to session container
sessions.put(hdr.getClientId(),
((CreateSessionTxn) txn).getTimeOut());
if (LOG.isTraceEnabled()) {
ZooTrace.logTraceMessage(LOG, ZooTrace.SESSION_TRACE_MASK,
"playLog --- create session in log: 0x"
+ Long.toHexString(hdr.getClientId())
+ " with timeout: "
+ ((CreateSessionTxn) txn).getTimeOut());
}
// Process transaction
rc = dt.processTxn(hdr, txn);
break;
// Close session
case OpCode.closeSession:
// Remove session from session container
sessions.remove(hdr.getClientId());
if (LOG.isTraceEnabled()) {
ZooTrace.logTraceMessage(LOG, ZooTrace.SESSION_TRACE_MASK,
"playLog --- close session in log: 0x"
+ Long.toHexString(hdr.getClientId()));
}
// Process transaction
rc = dt.processTxn(hdr, txn);
break;
// Default processing
default:
// Process transaction
rc = dt.processTxn(hdr, txn);
}
if (rc.err != Code.OK.intValue()) {
LOG.debug(
"Ignoring processTxn failure hdr: {}, error: {}, path: {}",
hdr.getType(), rc.err, rc.path);
}
}
In this method, we handle different types of transactions. For createSession transactions, we add the session to the sessions map. For closeSession transactions, we remove the session from the sessions map. For other transactions, we process the transaction using the DataTree's processTxn method.
Finally, let's analyze the addCommittedProposal method, which adds a committed proposal to the committed log:
public void addCommittedProposal(Request request) {
// Write lock
WriteLock wl = logLock.writeLock();
try {
// Lock
wl.lock();
// If committed log size exceeds default maximum commit count
if (committedLog.size() > commitLogCount) {
// Remove first element
committedLog.removeFirst();
// Set minimum committed log zxid to first transaction log
minCommittedLog = committedLog.getFirst().packet.getZxid();
}
// If committed log is empty
if (committedLog.isEmpty()) {
// Set both minimum and maximum committed log zxid to request zxid
minCommittedLog = request.zxid;
maxCommittedLog = request.zxid;
}
// Parse request data
byte[] data = SerializeUtils.serializeRequest(request);
// Construct data packet
QuorumPacket pp = new QuorumPacket(Leader.PROPOSAL, request.zxid, data, null);
// Create proposal
Proposal p = new Proposal();
p.packet = pp;
p.request = request;
// Add proposal to committed log
committedLog.add(p);
// Update maximum committed log zxid to proposal zxid
maxCommittedLog = p.packet.getZxid();
} finally {
// Unlock
wl.unlock();
}
}
In this method, we add a committed proposal to the committed log. If the log is full, we remove the oldest proposal and update the minimum committed log zxid. We then add the new proposal to the log and update the maximum committed log zxid.
TxnLog Analysis
The TxnLog interface defines the transaction log functionality. It has several methods for appending, reading, and truncating transaction logs.
append Method Analysis
The append method appends a transaction to the transaction log:
public synchronized boolean append(TxnHeader hdr, Record txn)
throws IOException {
if (hdr == null) {
return false;
}
if (hdr.getZxid() <= lastZxidSeen) {
LOG.warn("Current zxid " + hdr.getZxid()
+ " is <= " + lastZxidSeen + " for "
+ hdr.getType());
} else {
lastZxidSeen = hdr.getZxid();
}
// Log stream is empty
if (logStream == null) {
if (LOG.isInfoEnabled()) {
LOG.info("Creating new log file: " + Util.makeLogName(hdr.getZxid()));
}
// Create log file
logFileWrite = new File(logDir, Util.makeLogName(hdr.getZxid()));
// Create file output stream
fos = new FileOutputStream(logFileWrite);
// Initialize log stream
logStream = new BufferedOutputStream(fos);
// Initialize output archive
oa = BinaryOutputArchive.getArchive(logStream);
// Construct file header
FileHeader fhdr = new FileHeader(TXNLOG_MAGIC, VERSION, dbId);
// Serialize file header
fhdr.serialize(oa, "fileheader");
// Write to file
logStream.flush();
// Calculate current channel size and set to file padding
filePadding.setCurrentSize(fos.getChannel().position());
// Add file output stream to collection
streamsToFlush.add(fos);
}
// Pad file
filePadding.padFile(fos.getChannel());
// Serialize transaction header and transaction
byte[] buf = Util.marshallTxnEntry(hdr, txn);
// Check if serialization result is null or empty
if (buf == null || buf.length == 0) {
throw new IOException("Faulty serialization for header " +
"and txn");
}
// Get checksum algorithm
Checksum crc = makeChecksumAlgorithm();
// Update checksum
crc.update(buf, 0, buf.length);
// Write checksum to output archive
oa.writeLong(crc.getValue(), "txnEntryCRC");
// Write transaction to output archive
Util.writeTxnBytes(oa, buf);
return true;
}
In this method, we first check if the transaction header is null. If it is, we return false. We then check if the transaction zxid is less than or equal to the last seen zxid. If it is, we log a warning. Otherwise, we update the last seen zxid.
We then check if the log stream is null. If it is, we create a new log file and initialize the log stream and output archive. We serialize the transaction header and write it to the log file.
We then pad the file to ensure it is the correct size. We serialize the transaction and write it to the log file. We also update the checksum and write it to the log file.
read Method Analysis
The read method reads a transaction log from a given zxid:
public TxnIterator read(long zxid, boolean fastForward) throws IOException {
return new FileTxnIterator(logDir, zxid, fastForward);
}
In this method, we create a new FileTxnIterator object and return it.
getLastLoggedZxid Method Analysis
The getLastLoggedZxid method returns the last logged zxid:
public long getLastLoggedZxid() {
// Get all log files from log directory
File[] files = getLogFiles(logDir.listFiles(), 0);
// Determine maximum log number
// If log file count > 0, get zxid from name, otherwise return -1
long maxLog = files.length > 0 ?
Util.getZxidFromName(files[files.length - 1].getName(), LOG_FILE_PREFIX) : -1;
// Set zxid to maximum log number initially
long zxid = maxLog;
TxnIterator itr = null;
try {
// Convert log directory to transaction log
FileTxnLog txn = new FileTxnLog(logDir);
// Read TxnIterator from transaction log
itr = txn.read(maxLog);
// Process data in TxnIterator until no more entries
while (true) {
if (!itr.next()) {
break;
}
// Get header information and update zxid
TxnHeader hdr = itr.getHeader();
zxid = hdr.getZxid();
}
} catch (IOException e) {
LOG.warn("Unexpected exception", e);
} finally {
close(itr);
}
return zxid;
}
In this method, we first get all log files from the log directory. We then determine the maximum log number by getting the zxid from the last log file. We set the zxid to the maximum log number.
We then create a FileTxnLog object and read the transaction log from the maximum log number. We iterate through the transaction log and update the zxid to the last seen zxid.
truncate Method Analysis
The truncate method truncates the transaction log to a given zxid:
public boolean truncate(long zxid) throws IOException {
FileTxnIterator itr = null;
try {
// Create FileTxnIterator object
itr = new FileTxnIterator(this.logDir, zxid);
// Get input stream from FileTxnIterator
PositionInputStream input = itr.inputStream;
// If input stream is null, throw exception
if (input == null) {
throw new IOException("No log files found to truncate! This could " +
"happen if you still have snapshots from an old setup or " +
"log files were deleted accidentally or dataLogDir was changed in zoo.cfg.");
}
// Get position from input stream
long pos = input.getPosition();
// Truncate log file
RandomAccessFile raf = new RandomAccessFile(itr.logFile, "rw");
raf.setLength(pos);
raf.close();
// If there are subsequent log files, delete them
while (itr.goToNextLog()) {
// Delete log file
if (!itr.logFile.delete()) {
LOG.warn("Unable to truncate {}", itr.logFile);
}
}
} finally {
close(itr);
}
return true;
}
In this method, we first create a FileTxnIterator object and get the input stream. We then get the position from the input stream and truncate the log file to that position.
We then delete any subsequent log files.
commit Method Analysis
The commit method commits the transaction log:
public synchronized void commit() throws IOException {
// Log stream is not null, flush it
if (logStream != null) {
logStream.flush();
}
// Loop through file output streams and flush them
for (FileOutputStream log : streamsToFlush) {
// Flush output stream
log.flush();
// If force sync is enabled, force channel to write out data
if (forceSync) {
// Get current nanosecond time
long startSyncNS = System.nanoTime();
// Get channel
FileChannel channel = log.getChannel();
// Force channel to write out data
channel.force(false);
// Calculate time difference
syncElapsedMS = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startSyncNS);
// If time difference exceeds maximum allowed sync time, log warning
if (syncElapsedMS > fsyncWarningThresholdMS) {
// If server stats is not null, increment fsync threshold exceed count
if (serverStats != null) {
serverStats.incrementFsyncThresholdExceedCount();
}
LOG.warn("fsync-ing the write ahead log in "
+ Thread.currentThread().getName()
+ " took " + syncElapsedMS
+ "ms which will adversely effect operation latency. "
+ "File size is " + channel.size() + " bytes. "
+ "See the ZooKeeper troubleshooting guide");
}
}
}
// If file output stream collection size is greater than 1, remove first element and close it
while (streamsToFlush.size() > 1) {
streamsToFlush.removeFirst().close();
}
}
In this method, we first flush the log stream if it is not null. We then loop through the file output streams and flush each one. If force sync is enabled, we force the channel to write out the data and calculate the time difference. If the time difference exceeds the maximum allowed sync time, we log a warning.
We then remove and close the first file output stream if there are more than one.
SnapShot Analysis
The SnapShot interface defines the snapshot functionality. It has several methods for serializing and deserializing snapshots.
deserialize Method Analysis
The deserialize method deserializes a snapshot from a file:
public long deserialize(DataTree dt, Map<Long, Integer> sessions)
throws IOException {
// Find up to 100 valid snapshots
List<File> snapList = findNValidSnapshots(100);
// If no valid snapshots are found, return -1
if (snapList.size() == 0) {
return -1L;
}
File snap = null;
// Flag to indicate if a valid snapshot is found
boolean foundValid = false;
// Loop through snapshots
for (int i = 0, snapListSize = snapList.size(); i < snapListSize; i++) {
// Get current snapshot
snap = snapList.get(i);
LOG.info("Reading snapshot " + snap);
// Open snapshot input stream and checksum stream
try (InputStream snapIS = new BufferedInputStream(new FileInputStream(snap));
CheckedInputStream crcIn = new CheckedInputStream(snapIS, new Adler32())) {
// Convert checksum stream to input archive
InputArchive ia = BinaryInputArchive.getArchive(crcIn);
// Deserialize data tree from input archive
deserialize(dt, sessions, ia);
// Get checksum from checksum stream
long checkSum = crcIn.getChecksum().getValue();
// Get value from input archive
long val = ia.readLong("val");
// If value and checksum do not match, throw exception
if (val != checkSum) {
throw new IOException("CRC corruption in snapshot : " + snap);
}
// Set flag to indicate a valid snapshot is found
foundValid = true;
// Break out of loop
break;
} catch (IOException e) {
LOG.warn("problem reading snap file " + snap, e);
}
}
// If no valid snapshot is found, throw exception
if (!foundValid) {
throw new IOException("Not able to find valid snapshots in " + snapDir);
}
// Calculate zxid from snapshot file name and set it to data tree's last processed zxid
dt.lastProcessedZxid = Util.getZxidFromName(snap.getName(), SNAPSHOT_FILE_PREFIX);
// Return zxid
return dt.lastProcessedZxid;
}
In this method, we first find up to 100 valid snapshots. We then loop through the snapshots and deserialize each one. If we find a valid snapshot, we set the last processed zxid to the snapshot's zxid and return it.
serialize Method Analysis
The serialize method serializes a snapshot to a file:
public synchronized void serialize(DataTree dt, Map<Long, Integer> sessions, File snapShot)
throws IOException {
// Check if snapshot is closed
if (!close) {
// Open output stream and checksum output stream
try (OutputStream sessOS = new BufferedOutputStream(new FileOutputStream(snapShot));
CheckedOutputStream crcOut = new CheckedOutputStream(sessOS, new Adler32())) {
// Get output archive
OutputArchive oa = BinaryOutputArchive.getArchive(crcOut);
// Create file header
FileHeader header = new FileHeader(SNAP_MAGIC, VERSION, dbId);
// Serialize data
serialize(dt, sessions, oa, header);
// Get checksum
long val = crcOut.getChecksum().getValue();
// Write to archive
oa.writeLong(val, "val");
oa.writeString("/", "path");
sessOS.flush();
}
} else {
throw new IOException("FileSnap has already been closed");
}
}
In this method, we first check if the snapshot is closed. If it is not, we open the output stream and checksum output stream. We then create a file header and serialize the data. We get the checksum and write it to the output archive. We then flush the output stream.
findMostRecentSnapshot Method Analysis
The findMostRecentSnapshot method finds the most recent snapshot:
public File findMostRecentSnapshot() throws IOException {
// Find the single most recent valid snapshot
List<File> files = findNValidSnapshots(1);
if (files.size() == 0) {
return null;
}
return files.get(0);
}
In this method, we find the most recent snapshot by finding the first valid snapshot.
isValidSnapshot Method Analysis
The isValidSnapshot method checks if a snapshot is valid:
public static boolean isValidSnapshot(File f) throws IOException {
// Check if file is null or has invalid zxid
if (f == null || Util.getZxidFromName(f.getName(), FileSnap.SNAPSHOT_FILE_PREFIX) == -1)
return false;
// Convert file object to RandomAccessFile
try (RandomAccessFile raf = new RandomAccessFile(f, "r")) {
// Return false if file length is less than 10 bytes
if (raf.length() < 10) {
return false;
}
raf.seek(raf.length() - 5);
byte bytes[] = new byte[5];
int readlen = 0;
int l;
while (readlen < 5 &&
(l = raf.read(bytes, readlen, bytes.length - readlen)) >= 0) {
readlen += l;
}
// Return false if read length does not match byte array length
if (readlen != bytes.length) {
LOG.info("Invalid snapshot " + f
+ " too short, len = " + readlen);
return false;
}
// Convert byte array to ByteBuffer
ByteBuffer bb = ByteBuffer.wrap(bytes);
// Read fourth byte as integer
int len = bb.getInt();
// Read fifth byte
byte b = bb.get();
// Validate length and byte value
if (len != 1 || b != '/') {
LOG.info("Invalid snapshot " + f + " len = " + len
+ " byte = " + (b & 0xff));
return false;
}
}
return true;
}
In this method, we check if a snapshot file is valid by verifying several conditions:
- The file exists and has a valid zxid in its name
- The file size is at least 10 bytes
- The last 5 bytes contain specific validation data
- The fourth byte must be 1 and the fifth byte must be '/'
These checks ensure the integrity and validity of snapshot files before they are used for system recovery operations.
Summary
This chapter provides a comprehensive analysis of ZooKeeper's logging mechanisms, focusing on two primary types of logs:
-
Transaction Logs: Implemented through the TxnLog interface, these logs record all modifications to the ZooKeeper data tree in a sequential manner. They are crucial for maintaining consistency and enabling recovery in case of failures.
-
Snapshot Logs: Implemented through the SnapShot interface, these logs provide point-in-time snapshots of the entire ZooKeeper data tree. They optimize recovery time by providing a baseline state from which to replay transaction logs.
Key components analyzed include:
- FileTxnSnapLog: The central class managing both transaction and snapshot logs
- TxnLog Interface: Defines the contract for transaction log operations
- SnapShot Interface: Specifies the requirements for snapshot management
- File Management: Detailed examination of file naming, structure, and validation
- Data Integrity: Implementation of checksums and validation mechanisms
- Recovery Process: How logs are used to restore system state
This analysis demonstrates ZooKeeper's robust approach to maintaining data consistency and durability in a distributed system through careful log management and validation.
For further reading on distributed systems logging and consistency mechanisms, consider exploring:
- ZooKeeper's consensus protocol implementation
- Comparison with other distributed logging systems
- Performance optimization techniques for log management
- Advanced recovery scenarios and failure handling
// Check if the file is closed
if (!close) {
// Open output stream and checksum output stream
try (OutputStream sessOS = new BufferedOutputStream(new FileOutputStream(snapShot));
CheckedOutputStream crcOut = new CheckedOutputStream(sessOS, new Adler32())) {
// Get output archive
OutputArchive oa = BinaryOutputArchive.getArchive(crcOut);
// Create file header
FileHeader header = new FileHeader(SNAP_MAGIC, VERSION, dbId);
// Serialize data
serialize(dt, sessions, oa, header);
// Get checksum
long val = crcOut.getChecksum().getValue();
// Write to archive
oa.writeLong(val, "val");
oa.writeString("/", "path");
sessOS.flush();
}
} else {
throw new IOException("FileSnap has already been closed");
}
In this method, we first check if the snapshot is closed. If it is not, we open the output stream and checksum output stream. We then create a file header and serialize the data. We get the checksum and write it to the output archive. We then flush the output stream.
findMostRecentSnapshot Method Analysis
The findMostRecentSnapshot method finds the most recent snapshot:
public File findMostRecentSnapshot() throws IOException {
// Find the single most recent valid snapshot
List<File> files = findNValidSnapshots(1);
if (files.size() == 0) {
return null;
}
return files.get(0);
}
In this method, we find the most recent snapshot by finding the first valid snapshot.
isValidSnapshot Method Analysis
The isValidSnapshot method checks if a snapshot is valid:
public static boolean isValidSnapshot(File f) throws IOException {
// Check if file is null or has invalid zxid
if (f == null || Util.getZxidFromName(f.getName(), FileSnap.SNAPSHOT_FILE_PREFIX) == -1)
return false;
// Convert file object to RandomAccessFile
try (RandomAccessFile raf = new RandomAccessFile(f, "r")) {
// Return false if file length is less than 10 bytes
if (raf.length() < 10) {
return false;
}
raf.seek(raf.length() - 5);
byte bytes[] = new byte[5];
int readlen = 0;
int l;
while (readlen < 5 &&
(l = raf.read(bytes, readlen, bytes.length - readlen)) >= 0) {
readlen += l;
}
// Return false if read length does not match byte array length
if (readlen != bytes.length) {
LOG.info("Invalid snapshot " + f
+ " too short, len = " + readlen);
return false;
}
// Convert byte array to ByteBuffer
ByteBuffer bb = ByteBuffer.wrap(bytes);
// Read fourth byte as integer
int len = bb.getInt();
// Read fifth byte
byte b = bb.get();
// Validate length and byte value
if (len != 1 || b != '/') {
LOG.info("Invalid snapshot " + f + " len = " + len
+ " byte = " + (b & 0xff));
return false;
}
}
return true;
}
This method performs several validation checks on a snapshot file:
- Verifies that the file exists and has a valid zxid in its name
- Checks that the file size is at least 10 bytes
- Validates the last 5 bytes contain specific validation data
- Ensures the fourth byte is 1 and the fifth byte is '/'
These checks ensure the integrity and validity of snapshot files before they are used for system recovery operations.