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From "rajeshbabu (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (PHOENIX-17) Support to make use of partial covered indexes in scan
Date Sat, 27 Sep 2014 19:44:33 GMT

     [ https://issues.apache.org/jira/browse/PHOENIX-17?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

rajeshbabu resolved PHOENIX-17.
-------------------------------
       Resolution: Duplicate
    Fix Version/s:     (was: 3.0.0)
         Assignee: rajeshbabu

Resolving this issue as duplicate because we can have partially covered local indexes and
local indexes helps in space constraint use cases. 

> Support to make use of partial covered indexes in scan
> ------------------------------------------------------
>
>                 Key: PHOENIX-17
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-17
>             Project: Phoenix
>          Issue Type: Improvement
>            Reporter: rajeshbabu
>            Assignee: rajeshbabu
>
> Normally when we want to use secondary indices we create index on one or very few
> columns of interest in query conditions. Index may not contain all the columns to retrieve.
> Currently Phoenix supporting full covered indexes only(where all or most of the columns
> should be in the index in many cases). When we run a query we will choose to scan from
user table
> or index table based on condition that  whether all projected columns in the index or
not.
> This approach may have some disadvantages mainly in case of wider tables.
> 1)If we did just store all the columns in the index, then it would be just like creating
another copy of the entire table
>  – which would take up way too much space and would be very inefficient for wider tables.
> 2) Some times if user creates index on few columns and observes that index is not getting
used
> and then he need to add all the projected columns to index(may be to the part of index
or included columns). 
> which is something like we are exposing design decisions to the users, especially when
we already
> target to simplify user's experience by giving SQL on top of a noSQL DB.
> 3) One more thing is as of now if we have an index table contains all projected columns
in the
> query then we are simply scanning index table only.This can also become full table scan
when we don't
> have any condition in the query or condition on non primary key column of index.
> Some times this might give bad performance than normal table full scan.
> This JIRA is to support making use of partial covered indexes to avoid full table scan.



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