[jira] [Commented] (PHOENIX-17) Support to make use of partial covered indexes in scan

["Anoop Sam John (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-17?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13891989#comment-13891989 ] 

Anoop Sam John commented on PHOENIX-17:
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bq.With this approach, the dead lock issue discussed during put may also come.
So what is the proposal here [~rajesh23]?

> 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
>             Fix For: 3.0.0
>
>
> 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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