rocksdb/java/org/rocksdb/WriteBatch.java

// Copyright (c) 2014, Facebook, Inc.  All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.

package org.rocksdb;

import java.util.*;

/**
 * WriteBatch holds a collection of updates to apply atomically to a DB.
 *
 * The updates are applied in the order in which they are added
 * to the WriteBatch.  For example, the value of "key" will be "v3"
 * after the following batch is written:
 *
 *    batch.put("key", "v1");
 *    batch.remove("key");
 *    batch.put("key", "v2");
 *    batch.put("key", "v3");
 *
 * Multiple threads can invoke const methods on a WriteBatch without
 * external synchronization, but if any of the threads may call a
 * non-const method, all threads accessing the same WriteBatch must use
 * external synchronization.
 */
public class WriteBatch {
  public WriteBatch() {
    nativeHandle_ = 0;
    newWriteBatch(0);
  }

  public WriteBatch(int reserved_bytes) {
    nativeHandle_ = 0;
    newWriteBatch(reserved_bytes);
  }

  /**
   * Returns the number of updates in the batch.
   */
  public native int count();

  /**
   * Store the mapping "key->value" in the database.
   */
  public void put(byte[] key, byte[] value) {
    put(key, key.length, value, value.length);
  }

  /**
   * Merge "value" with the existing value of "key" in the database.
   * "key->merge(existing, value)"
   */
  public void merge(byte[] key, byte[] value) {
    merge(key, key.length, value, value.length);
  }

  /**
   * If the database contains a mapping for "key", erase it.  Else do nothing.
   */
  public void remove(byte[] key) {
    remove(key, key.length);
  }

  /**
   * Append a blob of arbitrary size to the records in this batch. The blob will
   * be stored in the transaction log but not in any other file. In particular,
   * it will not be persisted to the SST files. When iterating over this
   * WriteBatch, WriteBatch::Handler::LogData will be called with the contents
   * of the blob as it is encountered. Blobs, puts, deletes, and merges will be
   * encountered in the same order in thich they were inserted. The blob will
   * NOT consume sequence number(s) and will NOT increase the count of the batch
   *
   * Example application: add timestamps to the transaction log for use in
   * replication.
   */
  public void putLogData(byte[] blob) {
    putLogData(blob, blob.length);
  }

  /**
   * Clear all updates buffered in this batch
   */
  public native void clear();

  /**
   * Delete the c++ side pointer.
   */
  public synchronized void dispose() {
    if (nativeHandle_ != 0) {
      dispose0();
    }
  }

  @Override protected void finalize() {
    dispose();
  }

  private native void newWriteBatch(int reserved_bytes);
  private native void put(byte[] key, int keyLen,
                          byte[] value, int valueLen);
  private native void merge(byte[] key, int keyLen,
                            byte[] value, int valueLen);
  private native void remove(byte[] key, int keyLen);
  private native void putLogData(byte[] blob, int blobLen);
  private native void dispose0();

  long nativeHandle_;
}

/**
 * Package-private class which provides java api to access
 * c++ WriteBatchInternal.
 */
class WriteBatchInternal {
  static native void setSequence(WriteBatch batch, long sn);
  static native long sequence(WriteBatch batch);
  static native void append(WriteBatch b1, WriteBatch b2);
}