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From "Tyler Hobbs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-10226) Support multiple non-PK cols in MV clustering key when partition key is shared
Date Mon, 31 Aug 2015 20:37:46 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-10226?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14723996#comment-14723996
] 

Tyler Hobbs commented on CASSANDRA-10226:
-----------------------------------------

bq. I'm assuming you will continue to filter out nulls?

Yes, the current {{IS NOT NULL}} restrictions will continue to apply for now.

bq. Also, how is this any different than a secondary index?

The two main differences are 1) that it doesn't require a scatter-gather query, and 2) only
a single read needs to be executed instead of reading the index table and then reading multiple
keys from the base table.  Is that what you're asking, or am I missing something?

> Support multiple non-PK cols in MV clustering key when partition key is shared
> ------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-10226
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10226
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Tyler Hobbs
>            Assignee: Tyler Hobbs
>              Labels: materializedviews
>             Fix For: 3.0.0 rc1
>
>
> This issue is similar to CASSANDRA-9928, but with one key limitation: the MV partition
key must match the base table's partition key.  This limitation results in the base replica
always pairing with itself as the MV replica.  Because of this pairing, if the base replica
is lost, any MV rows that would otherwise be ambiguous are also lost.  This allows us to avoid
the problem described in 9928 of not knowing which MV row to delete.
> Although this limitation has the potential to be a bit confusing for users, I believe
this improvement is still worthwhile because:
> * The base table's partition key will often be a good choice for the MV partition key
as well.  I expect it to be common for users to partition data the same way, but use a different
clustering order to optimize for (or allow for) different queries.
> * It may take a long time to solve the problems presented in 9928 in general (if we can
solve them at all).  On the other hand, this is straightforward and is a significant improvement
to the usability of MVs.
> I have a minimal prototype of this that works well, so I should be able to upload a patch
with thorough tests within the next few days.



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