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https://issues.apache.org/jira/browse/PHOENIX-29?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Anoop Sam John updated PHOENIX-29:
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Attachment: PHOENIX-29_V2.patch
Seems we have to make bit of trick with the ordering of filters in the
FilterList. The code in ExplainTable#explain() expects PageFilter to be the
last Filter in the list (and that might make sense too).
V2 patch adds the new filter towards the end in the FilterList but before
PageFilter (If there is any). Also done bit of change in
ExplainTable#explain() to explain the PageFilter correctly.
UTs pass with this.
> 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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