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From "Brandon Williams (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-2388) ColumnFamilyRecordReader fails for a given split because a host is down, even if records could reasonably be read from other replica.
Date Wed, 29 Jun 2011 18:42:28 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-2388?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13057392#comment-13057392
] 

Brandon Williams commented on CASSANDRA-2388:
---------------------------------------------

{quote}
This does happen already (i've seen it while testing initial patches that were no good).
Problem is that the TT is blacklisted, reducing hadoop's throughput for all jobs running.
{quote}

If the cassandra node where the TT resides isn't working, then throughput is reduced regardless.


bq. I bet too that a fallback to a replica is faster than a fallback to another TT.

I doubt that for any significant job.  Locality is important.

{quote}
There is no guarantee that any given TT will have its split accessible via a local c* node
- this is only a preference in CFRR. A failed task may just as likely go to a random c* node.
At least now we can actually properly limit to the one DC and sort by proximity.
{quote}

This sounds like the thing we need to fix, then.  Ensuring that the TT assigned to the map
has a local replica.

> ColumnFamilyRecordReader fails for a given split because a host is down, even if records
could reasonably be read from other replica.
> -------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-2388
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2388
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Hadoop
>    Affects Versions: 0.7.6, 0.8.0
>            Reporter: Eldon Stegall
>            Assignee: Jeremy Hanna
>              Labels: hadoop, inputformat
>             Fix For: 0.7.7, 0.8.2
>
>         Attachments: 0002_On_TException_try_next_split.patch, CASSANDRA-2388-addition1.patch,
CASSANDRA-2388.patch, CASSANDRA-2388.patch, CASSANDRA-2388.patch
>
>
> ColumnFamilyRecordReader only tries the first location for a given split. We should try
multiple locations for a given split.

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