rajeshbabu created PHOENIX-17:
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Summary: 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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