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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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