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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (APEXMALHAR-1965) Create a WAL in Malhar
Date Mon, 28 Mar 2016 05:37:25 GMT

    [ https://issues.apache.org/jira/browse/APEXMALHAR-1965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15213829#comment-15213829
] 

ASF GitHub Bot commented on APEXMALHAR-1965:
--------------------------------------------

Github user chandnisingh commented on a diff in the pull request:

    https://github.com/apache/incubator-apex-malhar/pull/204#discussion_r57546194
  
    --- Diff: library/src/main/java/org/apache/apex/malhar/lib/wal/WAL.java ---
    @@ -0,0 +1,130 @@
    +/**
    + * 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.apex.malhar.lib.wal;
    +
    +import java.io.Closeable;
    +import java.io.IOException;
    +
    +/**
    + * This interface represents a write ahead log that can be used by operator.
    + * the WAL is split into two interfaces, a WALWriter which allows writing
    + * data, and WALReader which provides iterator like interface to read entries
    + * writen to the WAL.
    + *
    + * @param <T> Tuple type
    + * @param <P> WAL Pointer Type.
    + */
    +public interface WAL<T, P>
    +{
    +  WALReader<T, P> getReader() throws IOException;
    +
    +  WALWriter<T, P> getWriter() throws IOException;
    +
    +  /**
    +   * Provides iterator like interface to read entries from the WAL.
    +   * @param <T> type of WAL entries
    +   * @param <P> type of Pointer in the WAL
    +   */
    +  interface WALReader<T, P> extends Closeable
    +  {
    +    /**
    +     * Close WAL after read.
    +     *
    +     * @param offset seek offset.
    --- End diff --
    
    there isn't any offset argument in close method


> Create a WAL in Malhar
> ----------------------
>
>                 Key: APEXMALHAR-1965
>                 URL: https://issues.apache.org/jira/browse/APEXMALHAR-1965
>             Project: Apache Apex Malhar
>          Issue Type: Task
>            Reporter: Chandni Singh
>            Assignee: Tushar Gosavi
>
> In Malhar we have an IdempotentStorageManager which we use like a Write Ahead Logger.
There have been some other places where we have created a different flavor of Write Ahead
Logger. 
> We need to find overlap between all these flavors and create a common Write Ahead Logger
for use in Apex core and Apex malhar.



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