聊聊chronos的BackupDB

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本文主要研究一下chronos的BackupDB

BackupDB

DDMQ/carrera-chronos/src/main/java/com/xiaojukeji/chronos/db/BackupDB.java

public class BackupDB {    private static final Logger LOGGER = LogUtils.BACKUP_RESTORE_LOGGER;    public static final String DB_PATH_BACKUP = ConfigManager.getConfig().getDbConfig().getDbPathBackup();    public static final String DB_PATH_RESTORE = ConfigManager.getConfig().getDbConfig().getDbPathRestore();    private static volatile boolean backuping = false;    private static volatile boolean restoring = false;    public static BackupState backup() {        if (backuping) {            LOGGER.info("is backuping, return");            return BackupState.BEING_BACKUP;        }        LOGGER.info("start backup");        backuping = true;        try (final BackupableDBOptions bopt = new BackupableDBOptions(DB_PATH_BACKUP);             final BackupEngine be = BackupEngine.open(Env.getDefault(), bopt)) {            /**             * Captures the state of the database in the latest backup             *             * @param db The database to backup             * @param flushBeforeBackup When true, the Backup Engine will first issue a             *                          memtable flush and only then copy the DB files to             *                          the backup directory. Doing so will prevent log             *                          files from being copied to the backup directory             *                          (since flush will delete them).             *                          When false, the Backup Engine will not issue a             *                          flush before starting the backup. In that case,             *                          the backup will also include log files             *                          corresponding to live memtables. The backup will             *                          always be consistent with the current state of the             *                          database regardless of the flushBeforeBackup             *                          parameter.             *             * Note - This method is not thread safe             *             * @throws RocksDBException thrown if a new backup could not be created             */            boolean flushBeforeBackup = false;            be.createNewBackup(RDB.DB, flushBeforeBackup);            List<BackupInfo> backupInfos = be.getBackupInfo();            for (int i = 0; i < backupInfos.size(); i++) {                LOGGER.info("backupInfo[{}}, backupId:{}, timestamp:{}, size:{}, numberFiles:{}", i, backupInfos.get(i).backupId(),                        backupInfos.get(i).timestamp(), backupInfos.get(i).size(), backupInfos.get(i).numberFiles());            }            return BackupState.SUCCESS;        } catch (RocksDBException e) {            LOGGER.error("error while backup, path:{}, err:{}", DB_PATH_BACKUP, e.getMessage(), e);            return BackupState.FAIL;        } finally {            backuping = false;            LOGGER.info("end backup");        }    }    public static RestoreState restore() throws RocksDBException {        if (restoring) {            LOGGER.info("is restoring, return");            return RestoreState.BEING_RESTORE;        }        LOGGER.info("start restore");        restoring = true;        RocksDB restoreDB = null;        try (final BackupableDBOptions bopt = new BackupableDBOptions(DB_PATH_BACKUP);             final BackupEngine be = BackupEngine.open(Env.getDefault(), bopt)) {            // restore db from first backup            /**             * @param keepLogFiles If true, restore won't overwrite the existing log files             *   in wal_dir. It will also move all log files from archive directory to             *   wal_dir. Use this option in combination with             *   BackupableDBOptions::backup_log_files = false for persisting in-memory             *   databases.             *   Default: false             */            boolean keepLogFiles = false;            be.restoreDbFromLatestBackup(DB_PATH_RESTORE, DB_PATH_RESTORE, new RestoreOptions(keepLogFiles));            // open database again.            restoreDB = RocksDB.open(OptionsConfig.DB_OPTIONS, DB_PATH_RESTORE, CFManager.CF_DESCRIPTORS, CFManager.CF_HANDLES);            int i = 0;            try (RocksIterator it = restoreDB.newIterator()) {                for (it.seekToFirst(); it.isValid(); it.next()) {                    LOGGER.info("i:{}, key:{}, value:{}", i++, new String(it.key()), new String(it.value()));                    if (i == 10) {                        break;                    }                }            }            return RestoreState.SUCCESS;        } catch (RocksDBException e) {            LOGGER.error("error while restore, path:{}, err:{}", DB_PATH_RESTORE, e.getMessage(), e);            return RestoreState.FAIL;        } finally {            if (restoreDB != null) {                restoreDB.close();            }            restoring = false;            LOGGER.info("end restore");        }    }}

• BackupDB提供了两个静态方法，分别是backup及restore；backup方法通过BackupEngine的createNewBackup来进行backup；restore方法通过BackupEngine的restoreDbFromLatestBackup来进行restore

BackupEngine

rocksdbjni-5.7.2-sources.jar!/org/rocksdb/BackupEngine.java

public class BackupEngine extends RocksObject implements AutoCloseable {  protected BackupEngine(final long nativeHandle) {    super(nativeHandle);  }  public void createNewBackup(      final RocksDB db, final boolean flushBeforeBackup)      throws RocksDBException {    assert (isOwningHandle());    createNewBackup(nativeHandle_, db.nativeHandle_, flushBeforeBackup);  }  private native void createNewBackup(final long handle, final long dbHandle,      final boolean flushBeforeBackup) throws RocksDBException;  public void restoreDbFromLatestBackup(      final String dbDir, final String walDir,      final RestoreOptions restoreOptions) throws RocksDBException {    assert (isOwningHandle());    restoreDbFromLatestBackup(nativeHandle_, dbDir, walDir,        restoreOptions.nativeHandle_);  }  private native void restoreDbFromLatestBackup(final long handle,      final String dbDir, final String walDir, final long restoreOptionsHandle)      throws RocksDBException;  //......}

• createNewBackup方法接收RocksDB及flushBeforeBackup参数；restoreDbFromLatestBackup接收dbDir、walDir、restoreOptions参数

小结

BackupDB提供了两个静态方法，分别是backup及restore；backup方法通过BackupEngine的createNewBackup来进行backup；restore方法通过BackupEngine的restoreDbFromLatestBackup来进行restore

doc

• carrera-chronos