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From "Mck SembWever (JIRA)" <j...@apache.org>
Subject [jira] [Issue Comment Edited] (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 06:33:28 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-2388?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13057002#comment-13057002
] 

Mck SembWever edited comment on CASSANDRA-2388 at 6/29/11 6:31 AM:
-------------------------------------------------------------------

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

On a side note, 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 job may just as likely got to
a random c* node. At least now we can actually properly limit to the one DC and sort by proximity.


One thing we're not doing here is applying this same DC limit and sort by proximity in the
case when there isn't a localhost preference. See CFRR.initialize(..)
It would make sense to rewrite CFRR.getLocations(..) to
{noformat}    private Iterator<String> getLocations(final Configuration conf) throws
IOException
    {
        return new SplitEndpointIterator(conf);
    }{noformat} and then to move the finding-a-preference-to-localhost code into SplitEndpointIterator...

      was (Author: michaelsembwever):
    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.
I bet too that a fallback to a replica is faster than  a fallback to another TT. For example
a c* node may die in the middle of a TT...
  
> 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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