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https://issues.apache.org/jira/browse/CASSANDRA-9415?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14548493#comment-14548493
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Carl Yeksigian commented on CASSANDRA-9415:
-------------------------------------------
There are a couple of problems with substituting materialized views in place of
base tables transparently:
# Unless the MV includes all of the columns exactly as the underlying table has
them, select statements which are valid on the base table will not be valid on
the MV
# When where clauses are allowed for the MV, the MV can't be used for the
select statement since it isn't a full copy of the base table
Also, using a different table was a benefit because the driver's will be able
to easily route the queries (CASSANDRA-8517).
Overall, I'm weary of transforming user's queries for them; I'd rather users
who use MV use the views directly. It is less likely that we would change the
rules surrounding queries to a MV directly versus base table query
transformations.
> Implicit use of Materialized Views on SELECT
> --------------------------------------------
>
> Key: CASSANDRA-9415
> URL: https://issues.apache.org/jira/browse/CASSANDRA-9415
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Brian Hess
>
> CASSANDRA-6477 introduces Materialized Views. This greatly simplifies the
> write path for the best-practice of "query tables". But it does not simplify
> the read path as much as our users want/need.
> We suggest to folks to create multiple copies of their base table optimized
> for certain queries - hence "query table". For example, we may have a USER
> table with two type of queries: lookup by userid and lookup by email address.
> We would recommend creating 2 tables USER_BY_USERID and USER_BY_EMAIL. Both
> would have the exact same schema, with the same PRIMARY KEY columns, but
> different PARTITION KEY - the first would be USERID and the second would be
> EMAIL.
> One complicating thing with this approach is that the application now needs
> to know that when it INSERT/UPDATE/DELETEs from the base table it needs to
> INSERT/UPDATE/DELETE from all of the query tables as well. CASSANDRA-6477
> covers this nicely.
> However, the other side of the coin is that the application needs to know
> which query table to leverage based on the selection criteria. Using the
> example above, if the query has a predicate such as "WHERE userid = 'bhess'",
> then USERS_BY_USERID is the better table to use. Similarly, when the
> predicate is "WHERE email = '[email protected]'", USERS_BY_EMAIL is
> appropriate.
> On INSERT/UPDATE/DELETE, Materialized Views essentially give a single "name"
> to the collection of tables. You do operations just on the base table. It
> is very attractive for the SELECT side as well. It would be very good to
> allow an application to simply do "SELECT * FROM users WHERE userid =
> 'bhess'" and have that query implicitly leverage the USERS_BY_USERID
> materialized view.
> For additional use cases, especially analytics use cases like in Spark, this
> allows the Spark code to simply push down the query without having to know
> about all of the MVs that have been set up. The system will route the query
> appropriately. And if additional MVs are necessary to make a query run
> better/faster, then those MVs can be set up and Spark will implicitly
> leverage them.
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