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From "Chandni Singh (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (APEXMALHAR-2063) Integrate WAL to FS WindowDataManager
Date Wed, 08 Jun 2016 06:36:20 GMT

    [ https://issues.apache.org/jira/browse/APEXMALHAR-2063?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15320102#comment-15320102
] 

Chandni Singh commented on APEXMALHAR-2063:
-------------------------------------------

I am close to completing the implementation of all  the methods supported in WindowDataManager
api.

WindowDataManager API extended the StorageAgent API and I am thinking of deprecating the following
methods which are not being used in any operator using WindowDataManager.
1. long[] getWindowIds(int operatorId)  
2. long[] getWindowIds() 
 
The reason to deprecate them is that the implementation to provide just the window ids is
not optimal. 
If all the window ids[] are expected without reading the data of those windows then we basically
re-read wal files.

> Integrate WAL to FS WindowDataManager
> -------------------------------------
>
>                 Key: APEXMALHAR-2063
>                 URL: https://issues.apache.org/jira/browse/APEXMALHAR-2063
>             Project: Apache Apex Malhar
>          Issue Type: Improvement
>            Reporter: Chandni Singh
>            Assignee: Chandni Singh
>
> FS Window Data Manager is used to save meta-data that helps in replaying tuples every
completed application window after failure. For this it saves meta-data in a file per window.
Having multiple small size files on hdfs cause issues as highlighted here:
> http://blog.cloudera.com/blog/2009/02/the-small-files-problem/
> Instead FS Window Data Manager can utilize the WAL to write data and maintain a mapping
of how much data was flushed to WAL each window. 
> In order to use FileSystemWAL for replaying data of a finished window, there are few
changes made to FileSystemWAL this is because of following:
> 1. WindowDataManager needs to reply data of every finished window. This window may not
be checkpointed. 
> FileSystemWAL truncates the WAL file to the checkpointed point after recovery so this
poses a problem. 
> WindowDataManager should be able to control recovery of FileSystemWAL.
> 2.  FileSystemWAL writes to temporary files. The mapping of temp files to actual file
is part of its state which is checkpointed. Since WindowDataManager replays data of a window
not yet checkpointed, it needs to know the actual temporary file the data is being persisted
to.



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