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From mbalassi <...@git.apache.org>
Subject [GitHub] flink pull request: [streaming] New Source and state checkpointing...
Date Mon, 04 May 2015 08:26:34 GMT
Github user mbalassi commented on a diff in the pull request:

    https://github.com/apache/flink/pull/643#discussion_r29571516
  
    --- Diff: flink-staging/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/checkpoint/Checkpointed.java
---
    @@ -0,0 +1,53 @@
    +/*
    + * 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.flink.streaming.api.checkpoint;
    +
    +import org.apache.flink.runtime.state.OperatorState;
    +
    +/**
    + * This method must be implemented by functions that have state that needs to be
    + * checkpointed. The functions get a call whenever a checkpoint should take place
    + * and return a snapshot of their state, which will be checkpointed.
    + * 
    + * <p>This interface marks a function as <i>synchronously</i> checkpointed.
While the
    + * state is written, the function is not called, so the function needs not return a
    + * copy of its state, but may return a reference to its state. Functions that can
    + * continue to work and mutate the state, even while the state snapshot is being accessed,
    + * can implement the {@link org.apache.flink.streaming.api.checkpoint.CheckpointedAsynchronously}
    + * interface.</p>
    + */
    +public interface Checkpointed {
    +
    +	/**
    +	 * Gets the current operator state as a checkpoint. The state must reflect all operations
    +	 * from all prior operations if this function. 
    +	 * 
    +	 * @param checkpointId The ID of the checkpoint.
    +	 * @param checkpointTimestamp The timestamp of the checkpoint, as derived by
    +	 *                            System.currentTimeMillis() on the JobManager.
    +	 *                            
    +	 * @return A snapshot of the operator state.
    +	 * 
    +	 * @throws Exception Thrown if the creation of the state object failed. This causes
the
    +	 *                   checkpoint to fail. The system may decide to fail the operation
(and trigger
    +	 *                   recovery), or to discard this checkpoint attempt and to continue
running
    +	 *                   and to try again with the next checkpoint attempt.
    +	 */
    +	OperatorState<?> snapshotState(long checkpointId, long checkpointTimestamp) throws
Exception;
    +}
    --- End diff --
    
    If the `checkpointTimestamp` is also derived at the JobManager why do we need both here?
Maybe I am missing something. :)


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