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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5827) [Coprocessors] Observer notifications on exceptions
Date Wed, 27 Jun 2012 00:11:44 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13401820#comment-13401820
] 

Andrew Purtell commented on HBASE-5827:
---------------------------------------

bq. I'll have to take some time to see if a bigger redesign is warranted. 

In the abstract I'd be all for a "coprocessors v2" if the result is more elegant. We are still
pre Singularity. (But that does imply a time horizon.) The current framework design is the
familiar upcall model, akin to kernel extensions, or a VFS interface. It counts simplicity
and familiarity as pluses. But it is by no means the last word I'd say.

bq. TL;DR +1 on an onXXXXFailure method + a deprecated postXXX with error in context for compatibility

Ack.
                
> [Coprocessors] Observer notifications on exceptions
> ---------------------------------------------------
>
>                 Key: HBASE-5827
>                 URL: https://issues.apache.org/jira/browse/HBASE-5827
>             Project: HBase
>          Issue Type: Improvement
>          Components: coprocessors
>            Reporter: Andrew Purtell
>            Assignee: Andrew Purtell
>
> Benjamin Busjaeger wrote on dev@:
> {quote}
> Is there a reason that RegionObservers are not notified when a get/put/delete fails?
Suppose I maintain some (transient) state in my Coprocessor that is created during preGet
and discarded during postGet. If the get fails, postGet is not invoked, so I cannot remove
the state.
> If there is a good reason, is there any other way to achieve the same thing? If not,
would  it be possible to add something the snippet below to the code base?
> {code}
>     // pre-get CP hook
>     if (withCoprocessor && (coprocessorHost != null)) {
>       if (coprocessorHost.preGet(get, results)) {
>         return results;
>       }
>     }
> +    try{
>     ...
> +    } catch (Throwable t) {
> +        // failed-get CP hook
> +        if (withCoprocessor && (coprocessorHost != null)) {
> +          coprocessorHost.failedGet(get, results);
> +        }
> +        rethrow t;
> +    }
>     // post-get CP hook
>     if (withCoprocessor && (coprocessorHost != null)) {
>       coprocessorHost.postGet(get, results);
>     }
> {code}
> {quote}

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