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Date: Wed, 1 Jan 2014 22:22:50 +0000 (UTC)
From: "Micah Whitacre (JIRA)" <jira@apache.org>
To: crunch-dev@incubator.apache.org
Message-ID: <JIRA.12686860.1388509336728.29203.1388614970577@arcas>
In-Reply-To: <JIRA.12686860.1388509336728@arcas>
References: <JIRA.12686860.1388509336728@arcas>
Subject: [jira] [Updated] (CRUNCH-316) Data Corruption when
 DatumWriter.write() throws MapBufferTooSmallException when called by
 SafeAvroSerialization
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     [ https://issues.apache.org/jira/browse/CRUNCH-316?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Micah Whitacre updated CRUNCH-316:
----------------------------------

    Attachment: CRUNCH-316.patch

Patch with the change to DirectBinaryEncoder.  [~ben.roling] is going to want this patched back to 0.8.x more than likely.

> Data Corruption when DatumWriter.write() throws MapBufferTooSmallException when called by SafeAvroSerialization
> ---------------------------------------------------------------------------------------------------------------
>
>                 Key: CRUNCH-316
>                 URL: https://issues.apache.org/jira/browse/CRUNCH-316
>             Project: Crunch
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 0.9.0, 0.8.2
>            Reporter: Ben Roling
>            Assignee: Josh Wills
>         Attachments: ArrayIndexOutOfBoundsException.txt, CRUNCH-316.patch
>
>
> Recently we encountered an issue when processing a crunch join with a large Avro record.  The job was failing in the reduce phase with the attached ArrayIndexOutOfBoundsException deserializing an Avro record.
> One of the first things I noticed when looking into the problem was the following message:
> 2013-12-31 10:33:02,489 INFO  [pool-1-thread-1] org.apache.hadoop.mapred.MapTask Record too large for in-memory buffer: 99615133 bytes
> The message indicates a record is too large to fit in the sort buffer (per io.sort.mb -- which defaults to 100MB).  I increased io.sort.mb and the problem went away, but I was curious to figure out the root cause of the issue.
> After some lengthy debugging, I was able to figure out that the problem is in SafeAvroSerialization.  When a record is too small to fit in the sort buffer, org.apache.hadoop.mapred.MapTask$MapOutputBuffer$Buffer.write() throws MapBufferTooSmallException.  This exception is handled in MapTask.collect() by spilling the record to disk.  The problem is that the BufferedBinaryEncoder used by SafeAvroSerialization is never flushed and as a result corruption occurs when the next record is processed due to data still in the buffer from the previous record getting flushed into the new record.
> I was able to prove further to myself that this was the problem by leaving io.sort.mb at default and modifying SafeAvroSerialization to use a DirectBinaryEncoder instead of a BufferedBinaryEncoder.
> It could be argued that the problem is actually in MapTask with the way it is handling the exception.  Perhaps it should discard the key and value serializers and get new ones when handling this exception.  Doing that would acknowledge that the Serializers might be stateful like SafeAvroSerialization.  I don't see any documentation that suggests they must be stateless.


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