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Date: Fri, 18 Oct 2013 04:27:44 +0000 (UTC)
From: "ramkrishna.s.vasudevan (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.12646149.1367811953072.85172.1382070464967@arcas>
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Subject: [jira] [Commented] (HBASE-8496) Implement tags and the internals of
 how a tag should look like
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    [ https://issues.apache.org/jira/browse/HBASE-8496?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13798775#comment-13798775 ] 

ramkrishna.s.vasudevan commented on HBASE-8496:
-----------------------------------------------

bq.Shouldn't this issue have a release note? I marked it as reviewed and an incompatible change (is that right?). What should we add to the refguide on tags? Or, we are not ready to add anything there just yet?
I can add a release note and reference guide on tags.
bq.The below should be 0 or more... right?
Intention was to say tags can be 1 or more in the sense we support more than 1.  Ya per KV it is 0 or more tags.
bq. It looks like this design doc. is a long way from what was implemented
The implementation is not much deviated as per the design. But the thing is we added terms like HFileContext just to have a POJO for all the hfile file related attributes.  Mainly that avoids the problem that was once pointed out in the older review requests where inorder to include/exclude tags we were passing booleans in method parameters like how includeMemstoreTS is passed through out the code flow.
bq.On slide #3 you don't say what a tag is? Just a run of bytes?
I can add them.  
bq.The tag structure on slide #5 is different from what is on #3. On #5 it talks of a tagarray (am I being too literal)?
The slide on #3 describes how per KV the tag looks like.  As every KV can have one or more tags we are having a format that gives the length, type and the tag bytes.
When we write it in the HFile we need to write the total tag length and all the tags that is available. I cannot say that as a different format, it is the way it is persisted in HFile.
bq.Are there big changes between hfilev2 and hfilev3?
Agree that the change is not much.  But the fact that changing the exising HFileV2 was looked upon as a risky area for accomodating tags and hence decided to go with V3.


> Implement tags and the internals of how a tag should look like
> --------------------------------------------------------------
>
>                 Key: HBASE-8496
>                 URL: https://issues.apache.org/jira/browse/HBASE-8496
>             Project: HBase
>          Issue Type: New Feature
>    Affects Versions: 0.98.0, 0.95.2
>            Reporter: ramkrishna.s.vasudevan
>            Assignee: ramkrishna.s.vasudevan
>            Priority: Critical
>             Fix For: 0.98.0
>
>         Attachments: Comparison.pdf, HBASE-8496_2.patch, HBASE-8496_3.patch, HBASE-8496_3.patch, HBASE-8496_3.patch, HBASE-8496_4.patch, HBASE-8496_5.patch, HBASE-8496_6.patch, HBASE-8496.patch, Performance_report.xlsx, Tag design.pdf, Tag design_updated.pdf, Tag_In_KV_Buffer_For_reference.patch
>
>
> The intent of this JIRA comes from HBASE-7897.
> This would help us to decide on the structure and format of how the tags should look like. 


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