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From "Appy (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18898) Provide way for the core flow to know whether CP implemented each of the hooks
Date Mon, 16 Oct 2017 19:41:01 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16206459#comment-16206459

Appy commented on HBASE-18898:

Thinking about it more:

By annotated methods, i assume you mean something like this
boolean myPreDeleteHook(...) {
where we'll expose a set of enums which can be passed as a parameter to the annotation to
denote which type of observer hook that function is.
Then, using reflection,  we can get all methods marked @ObserverHook.

But we'll still have to 1)  Expose reference method signatures somewhere 2) Verify that the
annotated methods have correct signature. So that, if someone annotates {{void foo()}} by
mistake (note that all observer hooks at least take one param - environment), we can report
Maybe our current *Observer interfaces will become reference for the method signatures?

But then, why not let implementations use method override?
That'll at least give power of compile time checks. Checking  correctness for arguments, return
types, exceptions, etc of an impl should not require running a cluster and loading the coprocessor.

And if we have method overrides, having an extra annotation in implementations is completely
redundant. (is it not?)

The one +ve i see with annotated methods is, we can support say multiple hooks of one type
in single implementation i.e. multiple fns can be annotated PRE_DELETE. But is it worth that

> Provide way for the core flow to know whether CP implemented each of the hooks
> ------------------------------------------------------------------------------
>                 Key: HBASE-18898
>                 URL: https://issues.apache.org/jira/browse/HBASE-18898
>             Project: HBase
>          Issue Type: Improvement
>          Components: Coprocessors, Performance
>            Reporter: Anoop Sam John
>            Assignee: Anoop Sam John
>            Priority: Critical
> This came as a discussion topic at the tale of HBASE-17732
> Can we have a way in the code (before trying to call the hook) to know whether the user
has implemented one particular hook or not? eg: On write related hooks only prePut() might
be what the user CP implemented. All others are just dummy impl from the interface. Can we
have a way for the core code to know this and avoid the call to other dummy hooks fully? Some
times we do some processing for just calling CP hooks (Say we have to make a POJO out of PB
object for calling) and if the user CP not impl this hook, we can avoid this extra work fully.
The pain of this will be more when we have to later deprecate one hook and add new. So the
dummy impl in new hook has to call the old one and that might be doing some extra work normally.
> If the CP f/w itself is having a way to tell this, the core code can make use. What am
expecting is some thing like in PB way where we can call 
> CPObject.hasPreXXXX(), then CPObject. preXXXX ().. Should not like asking users to impl
this extra ugly thing. When the CP instance is loaded in the RS/HM, that object will be having
this info also. 

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