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From "Tathagata Das (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-7139) Allow received block metadata to be saved to WAL and recovered on driver failure
Date Mon, 27 Apr 2015 22:04:39 GMT

    [ https://issues.apache.org/jira/browse/SPARK-7139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14515105#comment-14515105
] 

Tathagata Das commented on SPARK-7139:
--------------------------------------

[~hshreedharan][~jerryshao]

> Allow received block metadata to be saved to WAL and recovered on driver failure
> --------------------------------------------------------------------------------
>
>                 Key: SPARK-7139
>                 URL: https://issues.apache.org/jira/browse/SPARK-7139
>             Project: Spark
>          Issue Type: Improvement
>          Components: Streaming
>            Reporter: Tathagata Das
>            Assignee: Tathagata Das
>            Priority: Critical
>
> The received API allows arbitrary metadata to be added for each block. However that information
is not saved in the WAL as part of the block information in the driver. 
> To fix this, the following needs to be done. 
> 1. Forward the metadata to the ReceivedBlockTracker in the driver.
> 2. ReceivedBlockTracker saves the metadata and recovers it on restart. 
> However there is one tricky thing. The ReceivedBlockTracker WAL is enabled only when
`spark.streaming.receiver.writeAheadLog.enable = true`. This means that only when  receiver
WAL is enabled is the driver WAL enabled. This is not desired as the one may want to save
and recovered block metadata information (especially information like Kafka offsets or Kinesis
sequence numbers) that can be used to recover data without actually saving the data to the
receiver WAL. So we have to always enable the tracker WAL. 
> 3. Always enable the ReceivedBlockTracker WAL. However, make sure that the blockIds are
not recovered as they will not be useful after driver restart (the blocks are gone!). 



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