org.iq80.leveldb.ReadOptions Java Examples

public static void print() throws IOException {
    //iterator，遍历，顺序读
    //读取当前snapshot，快照，读取期间数据的变更，不会反应出来       
    Snapshot snapshot = db.getSnapshot();
    //读选项        
    ReadOptions readOptions = new ReadOptions();
    readOptions.fillCache(false);//遍历中swap出来的数据，不应该保存在memtable中。        
    readOptions.snapshot(snapshot);//默认snapshot为当前。        
    DBIterator iterator = db.iterator(readOptions);
    while (iterator.hasNext()) {
        Map.Entry<byte[],byte[]> item = iterator.next();
        String key = new String(item.getKey(), Constants.CHARSET);
        String value = new String(item.getValue(), Constants.CHARSET);
        logger.debug("key:{}，value:{}", key, value);
    }
    iterator.close();
}
 

@Override
public DBIterator iterator(ReadOptions options) {
  if (null == options) {
    return iterator();
  }
  if (null != options.snapshot()) {
    throw new RuntimeException("Snapshots are unsupported.");
  }
  try {
    mutex.lockInterruptibly();
    pendingOps.incrementAndGet();
  } catch (InterruptedException ie) {
    throw new DBException("Interrupted while acquiring DB mutex.", ie);
  } finally {
    if (mutex.isHeldByCurrentThread()) {
      mutex.unlock();
    }
  }    
  return new WarpIterator(pendingOps, this.db.iterator(options));    
}
 

@Override
public Iterator<byte[]> keys() {
    check();

    try {
        ReadOptions readOptions = new ReadOptions();
        readOptions.snapshot(db.getSnapshot());
        return new LevelDBIteratorWrapper(readOptions, db.iterator(readOptions), LOG);
    } catch (Exception e) {
        LOG.error("Unable to extract keys from database " + this.toString() + ".", e);
    }

    // empty when retrieval failed
    return Collections.emptyIterator();
}
 

/**
 * @implNote Building two wrappers for the same {@link DBIterator} will lead to inconsistent
 *     behavior.
 */
LevelDBIteratorWrapper(final ReadOptions readOptions, final DBIterator iterator, final Logger log) {
    this.readOptions = readOptions;
    this.iterator = iterator;
    iterator.seekToFirst();
    closed = false;
    this.LOG = log;
}
 

/**
 * Create an iterator for the specified database
 */
public LeveldbIterator(DB db, ReadOptions options) {
  iter = db.iterator(options);
}
 

/**
 * Create an iterator for the specified database
 */
public LeveldbIterator(DB db, ReadOptions options) {
  iter = db.iterator(options);
}
 

@Override
public byte[] get(byte[] key, ReadOptions options) throws DBException {
  throw new RuntimeException("Unsupported operation get.");
  //return this.db.get(key, options);
}
 

@Override
public byte[] get(byte[] arg0, ReadOptions arg1) throws DBException {
    // TODO Auto-generated method stub
    return null;
}
 

@Override
public DBIterator iterator(ReadOptions arg0) {
    // TODO Auto-generated method stub
    return null;
}