Apache ZooKeeper is an open-source server which enables highly reliable distributed coordination.

Apache ZooKeeper Server Source Code files are provided in the source package file, apache-zookeeper-3.8.0.tar.gz.

You can download apache-zookeeper-3.8.0.tar.gz as described in the previous tutorial and go to the "zookeeper-server" sub-folder to view Apache ZooKeeper Server Source Code files.

You can also browse Apache ZooKeeper Server Source Code below:

⏎ org/apache/zookeeper/server/persistence/FileTxnSnapLog.java

/*
 * 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.zookeeper.server.persistence;

import java.io.File;
import java.io.FilenameFilter;
import java.io.IOException;
import java.nio.file.Files;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.jute.Record;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.KeeperException.Code;
import org.apache.zookeeper.ZooDefs.OpCode;
import org.apache.zookeeper.common.Time;
import org.apache.zookeeper.server.DataTree;
import org.apache.zookeeper.server.DataTree.ProcessTxnResult;
import org.apache.zookeeper.server.Request;
import org.apache.zookeeper.server.ServerMetrics;
import org.apache.zookeeper.server.ServerStats;
import org.apache.zookeeper.server.ZooTrace;
import org.apache.zookeeper.server.persistence.TxnLog.TxnIterator;
import org.apache.zookeeper.txn.CreateSessionTxn;
import org.apache.zookeeper.txn.TxnDigest;
import org.apache.zookeeper.txn.TxnHeader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * This is a helper class
 * above the implementations
 * of txnlog and snapshot
 * classes
 */
public class FileTxnSnapLog {

    //the directory containing the
    //the transaction logs
    final File dataDir;
    //the directory containing the
    //the snapshot directory
    final File snapDir;
    TxnLog txnLog;
    SnapShot snapLog;
    private final boolean autoCreateDB;
    private final boolean trustEmptySnapshot;
    public static final int VERSION = 2;
    public static final String version = "version-";

    private static final Logger LOG = LoggerFactory.getLogger(FileTxnSnapLog.class);

    public static final String ZOOKEEPER_DATADIR_AUTOCREATE = "zookeeper.datadir.autocreate";

    public static final String ZOOKEEPER_DATADIR_AUTOCREATE_DEFAULT = "true";

    static final String ZOOKEEPER_DB_AUTOCREATE = "zookeeper.db.autocreate";

    private static final String ZOOKEEPER_DB_AUTOCREATE_DEFAULT = "true";

    public static final String ZOOKEEPER_SNAPSHOT_TRUST_EMPTY = "zookeeper.snapshot.trust.empty";

    private static final String EMPTY_SNAPSHOT_WARNING = "No snapshot found, but there are log entries. ";

    /**
     * This listener helps
     * the external apis calling
     * restore to gather information
     * while the data is being
     * restored.
     */
    public interface PlayBackListener {

        void onTxnLoaded(TxnHeader hdr, Record rec, TxnDigest digest);

    }

    /**
     * Finalizing restore of data tree through
     * a set of operations (replaying transaction logs,
     * calculating data tree digests, and so on.).
     */
    private interface RestoreFinalizer {
        /**
         * @return the highest zxid of restored data tree.
         */
        long run() throws IOException;
    }

    /**
     * the constructor which takes the datadir and
     * snapdir.
     * @param dataDir the transaction directory
     * @param snapDir the snapshot directory
     */
    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);

        // by default create snap/log dirs, but otherwise complain instead
        // See ZOOKEEPER-1161 for more details
        boolean enableAutocreate = Boolean.parseBoolean(
            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(String.format(
                    "Missing data directory %s, automatic data directory creation is disabled (%s is false)."
                    + " Please create this directory manually.",
                    this.dataDir,
                    ZOOKEEPER_DATADIR_AUTOCREATE));
            }

            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()) {
            // by default create this directory, but otherwise complain instead
            // See ZOOKEEPER-1161 for more details
            if (!enableAutocreate) {
                throw new DatadirException(String.format(
                    "Missing snap directory %s, automatic data directory creation is disabled (%s is false)."
                    + "Please create this directory manually.",
                    this.snapDir,
                    ZOOKEEPER_DATADIR_AUTOCREATE));
            }

            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);
        }

        // check content of transaction log and snapshot dirs if they are two different directories
        // See ZOOKEEPER-2967 for more details
        if (!this.dataDir.getPath().equals(this.snapDir.getPath())) {
            checkLogDir();
            checkSnapDir();
        }

        txnLog = new FileTxnLog(this.dataDir);
        snapLog = new FileSnap(this.snapDir);

        autoCreateDB = Boolean.parseBoolean(
            System.getProperty(ZOOKEEPER_DB_AUTOCREATE, ZOOKEEPER_DB_AUTOCREATE_DEFAULT));
    }

    public void setServerStats(ServerStats serverStats) {
        txnLog.setServerStats(serverStats);
    }

    private void checkLogDir() throws LogDirContentCheckException {
        File[] files = this.dataDir.listFiles(new FilenameFilter() {
            @Override
            public boolean accept(File dir, String name) {
                return Util.isSnapshotFileName(name);
            }
        });
        if (files != null && files.length > 0) {
            throw new LogDirContentCheckException(
                "Log directory has snapshot files. Check if dataLogDir and dataDir configuration is correct.");
        }
    }

    private void checkSnapDir() throws SnapDirContentCheckException {
        File[] files = this.snapDir.listFiles(new FilenameFilter() {
            @Override
            public boolean accept(File dir, String name) {
                return Util.isLogFileName(name);
            }
        });
        if (files != null && files.length > 0) {
            throw new SnapDirContentCheckException(
                "Snapshot directory has log files. Check if dataLogDir and dataDir configuration is correct.");
        }
    }

    /**
     * get the datadir used by this filetxn
     * snap log
     * @return the data dir
     */
    public File getDataDir() {
        return this.dataDir;
    }

    /**
     * get the snap dir used by this
     * filetxn snap log
     * @return the snap dir
     */
    public File getSnapDir() {
        return this.snapDir;
    }

    /**
     * get information of the last saved/restored snapshot
     * @return info of last snapshot
     */
    public SnapshotInfo getLastSnapshotInfo() {
        return this.snapLog.getLastSnapshotInfo();
    }

    /**
     * whether to force the write of an initial snapshot after a leader election,
     * to address ZOOKEEPER-3781 after upgrading from Zookeeper 3.4.x.
     * @return true if an initial snapshot should be written even if not otherwise required, false otherwise.
     */
    public boolean shouldForceWriteInitialSnapshotAfterLeaderElection() {
        return trustEmptySnapshot && getLastSnapshotInfo() == null;
    }

    /**
     * this function restores the server
     * database after reading from the
     * snapshots and transaction logs
     * @param dt the datatree to be restored
     * @param sessions the sessions to be restored
     * @param listener the playback listener to run on the
     * database restoration
     * @return the highest zxid restored
     * @throws IOException
     */
    public long restore(DataTree dt, Map<Long, Integer> sessions, PlayBackListener listener) throws IOException {
        long snapLoadingStartTime = Time.currentElapsedTime();
        long deserializeResult = snapLog.deserialize(dt, sessions);
        ServerMetrics.getMetrics().STARTUP_SNAP_LOAD_TIME.add(Time.currentElapsedTime() - snapLoadingStartTime);
        FileTxnLog txnLog = new FileTxnLog(dataDir);
        boolean trustEmptyDB;
        File initFile = new File(dataDir.getParent(), "initialize");
        if (Files.deleteIfExists(initFile.toPath())) {
            LOG.info("Initialize file found, an empty database will not block voting participation");
            trustEmptyDB = true;
        } else {
            trustEmptyDB = autoCreateDB;
        }

        RestoreFinalizer finalizer = () -> {
            long highestZxid = fastForwardFromEdits(dt, sessions, listener);
            // The snapshotZxidDigest will reset after replaying the txn of the
            // zxid in the snapshotZxidDigest, if it's not reset to null after
            // restoring, it means either there are not enough txns to cover that
            // zxid or that txn is missing
            DataTree.ZxidDigest snapshotZxidDigest = dt.getDigestFromLoadedSnapshot();
            if (snapshotZxidDigest != null) {
                LOG.warn(
                        "Highest txn zxid 0x{} is not covering the snapshot digest zxid 0x{}, "
                                + "which might lead to inconsistent state",
                        Long.toHexString(highestZxid),
                        Long.toHexString(snapshotZxidDigest.getZxid()));
            }
            return highestZxid;
        };

        if (-1L == deserializeResult) {
            /* this means that we couldn't find any snapshot, so we need to
             * initialize an empty database (reported in ZOOKEEPER-2325) */
            if (txnLog.getLastLoggedZxid() != -1) {
                // ZOOKEEPER-3056: provides an escape hatch for users upgrading
                // from old versions of zookeeper (3.4.x, pre 3.5.3).
                if (!trustEmptySnapshot) {
                    throw new IOException(EMPTY_SNAPSHOT_WARNING + "Something is broken!");
                } else {
                    LOG.warn("{}This should only be allowed during upgrading.", EMPTY_SNAPSHOT_WARNING);
                    return finalizer.run();
                }
            }

            if (trustEmptyDB) {
                /* TODO: (br33d) we should either put a ConcurrentHashMap on restore()
                 *       or use Map on save() */
                save(dt, (ConcurrentHashMap<Long, Integer>) sessions, false);

                /* return a zxid of 0, since we know the database is empty */
                return 0L;
            } else {
                /* return a zxid of -1, since we are possibly missing data */
                LOG.warn("Unexpected empty data tree, setting zxid to -1");
                dt.lastProcessedZxid = -1L;
                return -1L;
            }
        }

        return finalizer.run();
    }

    /**
     * This function will fast forward the server database to have the latest
     * transactions in it.  This is the same as restore, but only reads from
     * the transaction logs and not restores from a snapshot.
     * @param dt the datatree to write transactions to.
     * @param sessions the sessions to be restored.
     * @param listener the playback listener to run on the
     * database transactions.
     * @return the highest zxid restored.
     * @throws IOException
     */
    public long fastForwardFromEdits(
        DataTree dt,
        Map<Long, Integer> sessions,
        PlayBackListener listener) throws IOException {
        TxnIterator itr = txnLog.read(dt.lastProcessedZxid + 1);
        long highestZxid = dt.lastProcessedZxid;
        TxnHeader hdr;
        int txnLoaded = 0;
        long startTime = Time.currentElapsedTime();
        try {
            while (true) {
                // iterator points to
                // the first valid txn when initialized
                hdr = itr.getHeader();
                if (hdr == null) {
                    //empty logs
                    return dt.lastProcessedZxid;
                }
                if (hdr.getZxid() < highestZxid && highestZxid != 0) {
                    LOG.error("{}(highestZxid) > {}(next log) for type {}", highestZxid, hdr.getZxid(), hdr.getType());
                } else {
                    highestZxid = hdr.getZxid();
                }
                try {
                    processTransaction(hdr, dt, sessions, itr.getTxn());
                    dt.compareDigest(hdr, itr.getTxn(), itr.getDigest());
                    txnLoaded++;
                } catch (KeeperException.NoNodeException e) {
                    throw new IOException("Failed to process transaction type: "
                                          + hdr.getType()
                                          + " error: "
                                          + e.getMessage(),
                                          e);
                }
                listener.onTxnLoaded(hdr, itr.getTxn(), itr.getDigest());
                if (!itr.next()) {
                    break;
                }
            }
        } finally {
            if (itr != null) {
                itr.close();
            }
        }

        long loadTime = Time.currentElapsedTime() - startTime;
        LOG.info("{} txns loaded in {} ms", txnLoaded, loadTime);
        ServerMetrics.getMetrics().STARTUP_TXNS_LOADED.add(txnLoaded);
        ServerMetrics.getMetrics().STARTUP_TXNS_LOAD_TIME.add(loadTime);

        return highestZxid;
    }

    /**
     * Get TxnIterator for iterating through txnlog starting at a given zxid
     *
     * @param zxid starting zxid
     * @return TxnIterator
     * @throws IOException
     */
    public TxnIterator readTxnLog(long zxid) throws IOException {
        return readTxnLog(zxid, true);
    }

    /**
     * Get TxnIterator for iterating through txnlog starting at a given zxid
     *
     * @param zxid starting zxid
     * @param fastForward true if the iterator should be fast forwarded to point
     *        to the txn of a given zxid, else the iterator will point to the
     *        starting txn of a txnlog that may contain txn of a given zxid
     * @return TxnIterator
     * @throws IOException
     */
    public TxnIterator readTxnLog(long zxid, boolean fastForward) throws IOException {
        FileTxnLog txnLog = new FileTxnLog(dataDir);
        return txnLog.read(zxid, fastForward);
    }

    /**
     * process the transaction on the datatree
     * @param hdr the hdr of the transaction
     * @param dt the datatree to apply transaction to
     * @param sessions the sessions to be restored
     * @param txn the transaction to be applied
     */
    public void processTransaction(
        TxnHeader hdr,
        DataTree dt,
        Map<Long, Integer> sessions,
        Record txn) throws KeeperException.NoNodeException {
        ProcessTxnResult rc;
        switch (hdr.getType()) {
        case OpCode.createSession:
            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());
            }
            // give dataTree a chance to sync its lastProcessedZxid
            rc = dt.processTxn(hdr, txn);
            break;
        case OpCode.closeSession:
            sessions.remove(hdr.getClientId());
            if (LOG.isTraceEnabled()) {
                ZooTrace.logTraceMessage(
                    LOG,
                    ZooTrace.SESSION_TRACE_MASK,
                    "playLog --- close session in log: 0x" + Long.toHexString(hdr.getClientId()));
            }
            rc = dt.processTxn(hdr, txn);
            break;
        default:
            rc = dt.processTxn(hdr, txn);
        }

        /*
         * Snapshots are lazily created. So when a snapshot is in progress,
         * there is a chance for later transactions to make into the
         * snapshot. Then when the snapshot is restored, NONODE/NODEEXISTS
         * errors could occur. It should be safe to ignore these.
         */
        if (rc.err != Code.OK.intValue()) {
            LOG.debug("Ignoring processTxn failure hdr: {}, error: {}, path: {}", hdr.getType(), rc.err, rc.path);
        }
    }

    /**
     * the last logged zxid on the transaction logs
     * @return the last logged zxid
     */
    public long getLastLoggedZxid() {
        FileTxnLog txnLog = new FileTxnLog(dataDir);
        return txnLog.getLastLoggedZxid();
    }

    /**
     * save the datatree and the sessions into a snapshot
     * @param dataTree the datatree to be serialized onto disk
     * @param sessionsWithTimeouts the session timeouts to be
     * serialized onto disk
     * @param syncSnap sync the snapshot immediately after write
     * @throws IOException
     */
    public void save(
        DataTree dataTree,
        ConcurrentHashMap<Long, Integer> sessionsWithTimeouts,
        boolean syncSnap) throws IOException {
        long lastZxid = dataTree.lastProcessedZxid;
        File snapshotFile = new File(snapDir, Util.makeSnapshotName(lastZxid));
        LOG.info("Snapshotting: 0x{} to {}", Long.toHexString(lastZxid), snapshotFile);
        try {
            snapLog.serialize(dataTree, sessionsWithTimeouts, snapshotFile, syncSnap);
        } catch (IOException e) {
            if (snapshotFile.length() == 0) {
                /* This may be caused by a full disk. In such a case, the server
                 * will get stuck in a loop where it tries to write a snapshot
                 * out to disk, and ends up creating an empty file instead.
                 * Doing so will eventually result in valid snapshots being
                 * removed during cleanup. */
                if (snapshotFile.delete()) {
                    LOG.info("Deleted empty snapshot file: {}", snapshotFile.getAbsolutePath());
                } else {
                    LOG.warn("Could not delete empty snapshot file: {}", snapshotFile.getAbsolutePath());
                }
            } else {
                /* Something else went wrong when writing the snapshot out to
                 * disk. If this snapshot file is invalid, when restarting,
                 * ZooKeeper will skip it, and find the last known good snapshot
                 * instead. */
            }
            throw e;
        }
    }

    /**
     * truncate the transaction logs the zxid
     * specified
     * @param zxid the zxid to truncate the logs to
     * @return true if able to truncate the log, false if not
     * @throws IOException
     */
    public boolean truncateLog(long zxid) {
        try {
            // close the existing txnLog and snapLog
            close();

            // truncate it
            try (FileTxnLog truncLog = new FileTxnLog(dataDir)) {
                boolean truncated = truncLog.truncate(zxid);

                // re-open the txnLog and snapLog
                // I'd rather just close/reopen this object itself, however that
                // would have a big impact outside ZKDatabase as there are other
                // objects holding a reference to this object.
                txnLog = new FileTxnLog(dataDir);
                snapLog = new FileSnap(snapDir);

                return truncated;
            }
        } catch (IOException e) {
            LOG.error("Unable to truncate Txn log", e);
            return false;
        }
    }

    /**
     * the most recent snapshot in the snapshot
     * directory
     * @return the file that contains the most
     * recent snapshot
     * @throws IOException
     */
    public File findMostRecentSnapshot() throws IOException {
        FileSnap snaplog = new FileSnap(snapDir);
        return snaplog.findMostRecentSnapshot();
    }

    /**
     * the n most recent snapshots
     * @param n the number of recent snapshots
     * @return the list of n most recent snapshots, with
     * the most recent in front
     * @throws IOException
     */
    public List<File> findNRecentSnapshots(int n) throws IOException {
        FileSnap snaplog = new FileSnap(snapDir);
        return snaplog.findNRecentSnapshots(n);
    }

    /**
     * the n recent valid snapshots
     * @param n the number of recent valid snapshots
     * @return the list of n recent valid snapshots, with
     * the most recent in front
     */
    public List<File> findNValidSnapshots(int n) {
        FileSnap snaplog = new FileSnap(snapDir);
        return snaplog.findNValidSnapshots(n);
    }

    /**
     * get the snapshot logs which may contain transactions newer than the given zxid.
     * This includes logs with starting zxid greater than given zxid, as well as the
     * newest transaction log with starting zxid less than given zxid.  The latter log
     * file may contain transactions beyond given zxid.
     * @param zxid the zxid that contains logs greater than
     * zxid
     * @return the snapshot logs which may contain transactions newer than the given zxid
     */
    public File[] getSnapshotLogs(long zxid) {
        return FileTxnLog.getLogFiles(dataDir.listFiles(), zxid);
    }

    /**
     * append the request to the transaction logs
     * @param si the request to be appended
     * @return true iff something appended, otw false
     * @throws IOException
     */
    public boolean append(Request si) throws IOException {
        return txnLog.append(si.getHdr(), si.getTxn(), si.getTxnDigest());
    }

    /**
     * commit the transaction of logs
     * @throws IOException
     */
    public void commit() throws IOException {
        txnLog.commit();
    }

    /**
     *
     * @return elapsed sync time of transaction log commit in milliseconds
     */
    public long getTxnLogElapsedSyncTime() {
        return txnLog.getTxnLogSyncElapsedTime();
    }

    /**
     * roll the transaction logs
     * @throws IOException
     */
    public void rollLog() throws IOException {
        txnLog.rollLog();
    }

    /**
     * close the transaction log files
     * @throws IOException
     */
    public void close() throws IOException {
        TxnLog txnLogToClose = txnLog;
        if (txnLogToClose != null) {
            txnLogToClose.close();
        }
        txnLog = null;
        SnapShot snapSlogToClose = snapLog;
        if (snapSlogToClose != null) {
            snapSlogToClose.close();
        }
        snapLog = null;
    }

    @SuppressWarnings("serial")
    public static class DatadirException extends IOException {

        public DatadirException(String msg) {
            super(msg);
        }
        public DatadirException(String msg, Exception e) {
            super(msg, e);
        }

    }

    @SuppressWarnings("serial")
    public static class LogDirContentCheckException extends DatadirException {

        public LogDirContentCheckException(String msg) {
            super(msg);
        }

    }

    @SuppressWarnings("serial")
    public static class SnapDirContentCheckException extends DatadirException {

        public SnapDirContentCheckException(String msg) {
            super(msg);
        }

    }

    public void setTotalLogSize(long size) {
        txnLog.setTotalLogSize(size);
    }

    public long getTotalLogSize() {
        return txnLog.getTotalLogSize();
    }
}

⏎ org/apache/zookeeper/server/persistence/FileTxnSnapLog.java

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