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From "Jan Lukavsky (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5757) TableInputFormat should handle as many errors as possible
Date Tue, 15 May 2012 14:26:31 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5757?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13275793#comment-13275793
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Jan Lukavsky commented on HBASE-5757:
-------------------------------------

{quote}Note that we've been able to can set scanner caching on each individual scan in since
0.20 (HBASE-1759) – setting it for that job may be more 'correct'. {quote}

We are setting different caching for different jobs, the problem is that the rows may take
different time to process (based on job) and this cannot be told in advance. Currently, it
is only possible to set the caching for the whole job, but even if it was possible to change
the caching *during* the job, we would not know that we need to do it before we will get the
ScannerTimeoutException. So handling this error in the TableInputFormat seems right solution
to me.
                
> TableInputFormat should handle as many errors as possible
> ---------------------------------------------------------
>
>                 Key: HBASE-5757
>                 URL: https://issues.apache.org/jira/browse/HBASE-5757
>             Project: HBase
>          Issue Type: Bug
>          Components: mapred, mapreduce
>    Affects Versions: 0.90.6
>            Reporter: Jan Lukavsky
>         Attachments: HBASE-5757.patch, HBASE-5757.patch
>
>
> Prior to HBASE-4196 there was different handling of IOExceptions thrown from scanner
in mapred and mapreduce API. The patch to HBASE-4196 unified this handling so that if exception
is caught a reconnect is attempted (without bothering the mapred client). After that, HBASE-4269
changed this behavior back, but in both mapred and mapreduce APIs. The question is, is there
any reason not to handle all errors that the input format can handle? In other words, why
not try to reissue the request after *any* IOException? I see the following disadvantages
of current approach
>  * the client may see exceptions like LeaseException and ScannerTimeoutException if he
fails to process all fetched data in timeout
>  * to avoid ScannerTimeoutException the client must raise hbase.regionserver.lease.period
>  * timeouts for tasks is aready configured in mapred.task.timeout, so this seems to me
a bit redundant, because typically one needs to update both these parameters
>  * I don't see any possibility to get rid of LeaseException (this is configured on server
side)
> I think all of these issues would be gone, if the DoNotRetryIOException would not be
rethrown. -On the other hand, handling errors in InputFormat has disadvantage, that it may
hide from the user some inefficiency. Eg. if I have very big scanner.caching, and I manage
to process only a few rows in timeout, I will end up with single row being fetched many times
(and will not be explicitly notified about this). Could we solve this problem by adding some
counter to the InputFormat?-

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