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https://issues.apache.org/jira/browse/PHOENIX-29?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13907264#comment-13907264
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Anoop Sam John commented on PHOENIX-29:
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Got it clearly now James.. What is the need/use of this empty KV. Let me
think and see how we can support this case also. Right now in patch V2, in
case of this mapped view also, we will be adding the new filter. So if we can
not do the dynamic empty KV, we will have to add checks and avoid the addition
of new filter (as u said)..
Any way I will try for solving this also and come up with next version of patch.
> Add custom filter to more efficiently navigate KeyValues in row
> ---------------------------------------------------------------
>
> Key: PHOENIX-29
> URL: https://issues.apache.org/jira/browse/PHOENIX-29
> Project: Phoenix
> Issue Type: Bug
> Reporter: James Taylor
> Attachments: PHOENIX-29.patch, PHOENIX-29_V2.patch
>
>
> Currently HBase is 50% faster at selecting the first KV in a row than in
> selecting any other column. The reason is that when you project a column into
> a Scan, HBase uses its ExplicitColumTracker which does a reseek to the
> column. The only case where this is not necessary is when the column is the
> first one.
> In most cases (unless you have thousands of versions), it'd be more efficient
> to just do a NEXT instead of a reseek (especially if your KV is the next
> one). We can provide our own custom filter through which we pass two lists:
> 1) all KVs referenced in the select expressions. These are the only ones that
> need to be returned back to the client which is another advantage we'd get
> writing this custom filter.
> 2) all KVs referenced in the WHERE clause.
> The filter could sort the KVs using the standard KeyValue.COMPARATOR and
> merge between them and the incoming KVs, using NEXT instead of a reseek. We
> could potentially use a reseek if the number of columns in the table is
> beyond a certain threshold.
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