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From "Douglas Creager (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AVRO-986) Avro files generated from avro-c dont work with the Java mapred implementation.
Date Thu, 22 Dec 2011 18:27:30 GMT

    [ https://issues.apache.org/jira/browse/AVRO-986?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13174955#comment-13174955

Douglas Creager commented on AVRO-986:

+1  Should we apply the patch to 1.5, too?

Also, it'll still be the case that any existing C-produced files will be unreadable in Java
mapred.  Should we also provide a fixup script of some kind?
> Avro files generated from avro-c dont work with the Java mapred implementation.
> -------------------------------------------------------------------------------
>                 Key: AVRO-986
>                 URL: https://issues.apache.org/jira/browse/AVRO-986
>             Project: Avro
>          Issue Type: Bug
>          Components: c, java
>         Environment: avro-c 1.6.2-SNAPSHOT
> avro-java 1.6.2-SNAPSHOT
> hadoop 0.20.2
>            Reporter: Michael Cooper
>            Priority: Critical
>              Labels: c, hadoop, java, mapreduce
>         Attachments: 0001-Remove-sync-marker-from-metadata-in-header.patch
> When a file generated from the Avro-C implementation is fed into Hadoop, it will fail
with "Block size invalid or too large for this implementation: -49".
> This is caused by the sync marker, namely the one that Avro-C puts into the header...
> The org.apache.avro.mapred.AvroRecordReader uses a FileSplit object to work out where
it should read from, but this class is not particularly smart, it just divides the file up
into equal size chunks, the first being with position 0.
> So org.apache.avro.mapred.AvroRecordReader gets 0 as the start of its chunk, and calls
> {code:title=AvroRecordReader.java}reader.sync(split.getStart());   // sync to start{code}
> Then the org.apache.avro.file.DataFileReader::seek() goes to 0, then searches for a sync
> It encounters one at position 32, the one in the header metadata map, "avro.sync"
> No other implementations add the sync marker in the metadata map, and none read it from
there, not even the C version.
> I suggest we remove this from the header as the simplest solution.
> Another solution would be to create an AvroFileSplit class in mapred that knows where
the blocks are, and provides the correct locations in the first place.

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