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From "Matt Corgan (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5674) add support in HBase to overwrite hbase timestamp to a version number during major compaction
Date Fri, 30 Mar 2012 15:46:36 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5674?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13242460#comment-13242460
] 

Matt Corgan commented on HBASE-5674:
------------------------------------

I've been brainstorming something similar as a follow-on to HBASE-4676.  The more similar
timestamps you have in a block, the smaller the encoded version.  Most people doing a simple,
flat table with 1 version of each cell don't care about the timestamps.  They're only needed
to pick the latest cell.  If all timestamps in an HFile are the same then they will encode
down to nothing.

One possibility is to have an option "flattenTimestamps" where you grab t=currentTimeMillis()
at the beginning of a flush and overwrite all timestamps with it.  To support multiple versions
of a cell, you could use t-1, t-2, etc (as long as they don't go all the way back to the previous
hfile's timestamp).
                
> add support in HBase to overwrite hbase timestamp to a version number during major compaction
> ---------------------------------------------------------------------------------------------
>
>                 Key: HBASE-5674
>                 URL: https://issues.apache.org/jira/browse/HBASE-5674
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: He Yongqiang
>            Assignee: He Yongqiang
>
> Right now, a millisecond-level timestamp is attached to every record. 
> In our case, we only need a version number (mostly it will be just zero etc). A millisecond
timestamp is too heavy to carry. We should add support to overwrite it to zero during major
compaction. 
> KVs before major compaction will remain using system timestamp. And this should be configurable,
so that we should not mess up if the hbase timestamp is specified by application.

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