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https://issues.apache.org/jira/browse/PHOENIX-29?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13906094#comment-13906094
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James Taylor commented on PHOENIX-29:
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[~anoop.hbase] - keep your filter at the end like you had it before and make
the ExplainTable more forgiving of the FilterList order. It's better to have
the PageFilter before yours so that it reduces the number of rows over which
you're mucking with the KeyValues.
> 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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