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From "Alex Baranau (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-2038) Coprocessors: Region level indexing
Date Fri, 06 Jan 2012 03:33:40 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2038?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13181069#comment-13181069
] 

Alex Baranau commented on HBASE-2038:
-------------------------------------

+1 for collaboration!
re HBASE-2037 (aka IHBase): it is the base for this effort. Yes, it doesn't require ITHBase,
it is alternative implementation. The refactored code I pointed above (https://github.com/abaranau/ihbase)
is also based on the IHBase code.

In short (sorry, the description is not tied to classes, don't have them in front of me currently):

As far as I remember (need to refresh my memory though) the point is that index is being kept
for each Region, it is loaded in RAM, not persistent. It is built during Region initialization
(after HBase restart or new region creation after split and such). When scan is performed
with indexed columns involved it uses the index when finding the next record to navigate to
and *fast forwards* to this next record (usually by skipping some other records without even
reading them). This is where it wins the speed.

As this was developed before CPs were added the special API was developed which is being used
by client.

Hope this helps a bit. I will refresh my memory from the code and we'll discuss that a bit
deeper.
                
> Coprocessors: Region level indexing
> -----------------------------------
>
>                 Key: HBASE-2038
>                 URL: https://issues.apache.org/jira/browse/HBASE-2038
>             Project: HBase
>          Issue Type: New Feature
>          Components: coprocessors
>            Reporter: Andrew Purtell
>            Priority: Minor
>
> HBASE-2037 is a good candidate to be done as coprocessor. It also serve as a good goalpost
for coprocessor environment design -- there should be enough of it so region level indexing
can be reimplemented as a coprocessor without any loss of functionality. 

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