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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9681) Basic codec negotiation
Date Wed, 09 Oct 2013 04:01:42 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13790000#comment-13790000

ramkrishna.s.vasudevan commented on HBASE-9681:

Regarding the mapping, how should the server decide on the mapping?  Should it be from a configuration?
 If it is from a configuration then it is not generic because this may be context based.
One reason why the mapping is important because in some cases the client may ask for a codec
but it may not be right for the server to send out all the information say for example some
information stored in the tags.  So in that case the server should apply the context based
knowledge on what codec it should use.  This is where the mapping comes into picture.
In an internal discussion, there is a chance that for some cases like Export the server still
needs to send out information in tags too.  So in that case the mapping should deal this in
a different way.
So overall this mapping and usage of the codecs on the server side is more context based.
When we have sytem tags in future the above argument applies (generally here it is better
to suppress the tags from the clients).
So the connection negotiation part is a protocol that we can decide but the mapping is one
which is not very generic.  Can try to make this mapping a pluggable one?

> Basic codec negotiation
> -----------------------
>                 Key: HBASE-9681
>                 URL: https://issues.apache.org/jira/browse/HBASE-9681
>             Project: HBase
>          Issue Type: Sub-task
>    Affects Versions: 0.98.0
>            Reporter: Andrew Purtell
> Basic codec negotiation:
> There should be a default codec used for cell encoding over the RPC connection. This
should be configurable in the site file. 
> The client can optionally send a message, a manufactured "call" that would otherwise
be invalid in some way, to the server asking for a list of supported cell codecs. An older
server should simply send back an error because the request is invalid except to servers supporting
this feature. A server supporting this feature should send back the requested information
or an error indication if something went wrong.
> The client can optionally send a message, a manufactured "call" that would otherwise
be invalid in some way, to the server asking for it to use a given codec for all further communication.
Otherwise the server will continue to use the default codec. The server will send back a call
response acknowledging the change or an error indication if the request cannot be honored.
> Server configuration should support mappings from one codec type to another. We need
to handle the case where the server has a codec available that extends the requested type
but overrides some behavior in the base class, and this is what should be used in lieu of
the base type. It must also be possible to choose an alternate default codec which stands
in for the default codec, is compatible with client expectations, but changes the server side
behavior as needed in the absence of negotiation. 

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