asyncMultiGet

异步读同一HashKey下的多行数据。

  1. public static class MultiGetResult {
  2.     /**
  3.      * return value for multiGet
  4.      * @param allFetched true if all data on the server are fetched; false if only partial data are fetched.
  5.      * @param values the got values. If sortKey in the input sortKeys is not found, it won't be in values.
  6.      *               The output values are ordered by the sortKey.
  7.      */
  8.     public boolean allFetched;
  9.     public List<Pair<byte[], byte[]>> values;
  10. }
  11.  
  12. public static interface MultiGetListener extends GenericFutureListener<Future<MultiGetResult>> {
  13.     /**
  14.      * This function will be called when listened asyncMultiGet future is done.
  15.      * @param future the listened future
  16.      * @throws Exception
  17.      *
  18.      * Notice: User shouldn't do any operations that may block or time-consuming
  19.      */
  20.     @Override
  21.     public void operationComplete(Future<MultiGetResult> future) throws Exception;
  22. }
  23.  
  24. /**
  25.  * get multiple key-values under the same hashKey, async version
  26.  * @param hashKey used to decide which partition the key may exist
  27.  *                should not be null or empty.
  28.  * @param sortKeys try to get values of sortKeys under the hashKey
  29.  *                 if null or empty, try to get all (sortKey,value) pairs under hashKey
  30.  * @param maxFetchCount max count of kv pairs to be fetched
  31.  *                      maxFetchCount <= 0 means no limit. default value is 100
  32.  * @param maxFetchSize max size of kv pairs to be fetched.
  33.  *                     maxFetchSize <= 0 means no limit. default value is 1000000.
  34.  * @param timeout how long will the operation timeout in milliseconds.
  35.  *                if timeout > 0, it is a timeout value for current op,
  36.  *                else the timeout value in the configuration file will be used.
  37.  *
  38.  * @return the future for current op
  39.  *
  40.  * Future return:
  41.  *      On success: An object of type MultiGetResult
  42.  *      On failure: a throwable, which is an instance of PException
  43.  *
  44.  * Thread safety:
  45.  *      All the listeners for the same table are guaranteed to be dispatched in the same thread, so all the
  46.  *      listeners for the same future are guaranteed to be executed as the same order as the listeners added.
  47.  *      But listeners for different tables are not guaranteed to be dispatched in the same thread.
  48.  */
  49. public Future<MultiGetResult> asyncMultiGet(byte[] hashKey, List<byte[]> sortKeys, int maxFetchCount, int maxFetchSize, int timeout/*ms*/);
  50. public Future<MultiGetResult> asyncMultiGet(byte[] hashKey, List<byte[]> sortKeys, int timeout/*ms*/);

注：

  • 提供了两个版本的接口，其中第一个接口可以指定maxFetchCount和maxFetchSize。
  • 参数：需传入HashKey、SortKeys、timeout；选择性传入maxFetchCount、maxFetchSize。
    • SortKeys如果非空，则只读取指定的数据；SortKeys如果为空，则表示读取该HashKey下的所有数据。
    • timeout单位为毫秒，如果<=0，表示使用配置文件中的默认超时。
    • maxFetchCount和maxFetchSize用于限制读取的数据量，maxFetchCount表示最多读取的数据条数，maxFetchSize表示最多读取的数据字节数，两者任一达到限制就停止读取。
  • 返回值：Future。
    • allFetched：如果用户指定了maxFetchCount或者maxFetchSize，单次查询可能只获取到部分结果。如果所有满足条件的数据都已经获取到，则设置为true；否则设置为false。asyncMultiGet还有另外一个版本的接口，可以支持SortKey的范围查询和条件过滤，只读取满足特定条件的数据。并且从1.8.0开始在MultiGetOptions中增加了reverse参数，支持逆向扫描数据。
  1.     /**
  2.      * get multiple key-values under the same hashKey with sortKey range limited, async version
  3.      * @param hashKey used to decide which partition the key may exist
  4.      *                should not be null or empty.
  5.      * @param startSortKey the start sort key.
  6.      *                     null means "".
  7.      * @param stopSortKey the stop sort key.
  8.      *                    null or "" means fetch to the last sort key.
  9.      * @param options multi-get options.
  10.      * @param maxFetchCount max count of kv pairs to be fetched
  11.      *                      maxFetchCount <= 0 means no limit. default value is 100
  12.      * @param maxFetchSize max size of kv pairs to be fetched.
  13.      *                     maxFetchSize <= 0 means no limit. default value is 1000000.
  14.      * @param timeout how long will the operation timeout in milliseconds.
  15.      *                if timeout > 0, it is a timeout value for current op,
  16.      *                else the timeout value in the configuration file will be used.
  17.      *
  18.      * @return the future for current op
  19.      *
  20.      * Future return:
  21.      *      On success: An object of type MultiGetResult
  22.      *      On failure: a throwable, which is an instance of PException
  23.      *
  24.      * Thread safety:
  25.      *      All the listeners for the same table are guaranteed to be dispatched in the same thread, so all the
  26.      *      listeners for the same future are guaranteed to be executed as the same order as the listeners added.
  27.      *      But listeners for different tables are not guaranteed to be dispatched in the same thread.
  28.      */
  29.     public Future<MultiGetResult> asyncMultiGet(byte[] hashKey, byte[] startSortKey, byte[] stopSortKey,
  30.                                                 MultiGetOptions options, int maxFetchCount, int maxFetchSize,
  31.                                                 int timeout/*ms*/);
  32.     public Future<MultiGetResult> asyncMultiGet(byte[] hashKey, byte[] startSortKey, byte[] stopSortKey,
  33.                                                 MultiGetOptions options, int timeout/*ms*/);

注：