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From Jesse Yates <jesse.k.ya...@gmail.com>
Subject Re: Regarding support to make use of partial covered indexes in scan
Date Thu, 30 Jan 2014 16:12:56 GMT
AFAIK, no one is working on this, but it sounds pretty cool!

Mind filling a JIRA?

Thanks,
J
On Jan 30, 2014 7:28 AM, "rajeshbabu chintaguntla" <
rajeshbabu.chintaguntla@huawei.com> wrote:

> Hi,
>
> 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.
>
> Any one working to make use of partial covered indexes to avoid full table
> scan?
>
> We are interested to work on this in Phoenix.
>
> As part of our local indexing solution, we have similar kind of support.
> From index table first we fetch main table row key and from that we get
> projected columns data from main table so that we can skip most of records
> to scan from main table.
>
> Thanks,
> Rajeshbabu.
>
>
>
>
>
>
>

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