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https://issues.apache.org/jira/browse/HBASE-2038?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13201205#comment-13201205
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Anoop Sam John commented on HBASE-2038:
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Hi Lars,
I am also trying for a secondary index and I have seen the IHBase
concept being good.. But we need this to be moved to coprocessor based so that
the kernel code of HBase need not be different for the secondary index. IHBase
makes the scan go through all the regions ( as u said ) but they will skip and
seek to the later positions in the heap avoid so many possible data read from
HDFS etc...
When I saw the current co processor, we call preScannerNext() from
HRegionServer next(final long scannerId, int nbRows) and pass the
RegionScanner here to the co processor. But as per the IHBase way, within the
co processor we should be able to seek to the correct row where the indexed col
val equals our value. But we can not do this as of now as RegionScanner seek()
not there.
Also this preScannerNext() will be called once before the actual next(final
long scannerId, int nbRows) call happening on the region. Here as per the cache
value at the client side the nbRows might be more than one. Now suppose this is
nbRows=2 and in the region we have 2 rows one at some what in the middle part
of an HFile and the other at another HFile. Now as per IHBase we should 1st
seek to the 1st position of the row and after reading this data should seek to
the next position. Now as per the current way of calling of preScannerNext()
this wont be possible. So I think we might need some change in these area?
What do u say?
Mean while what is your plan to continue with the way of IHBase storing the
index in memory for each of the region or some change in this?
> 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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