Add a 'defunct' tag for Index definitions

[skywhat]

Cassandra doesn’t support changing columns of the materialized view. Therefore It introduces the concern that how to handle the existing index table since the goal of the feature is to reduce the large partition.
The current solution is to educate users to mark their old index table as defunct and then create a new index table with limited columns.
The next time users use range query, the gateway would skip the lookup in defunct index table.

[phliar]

The title can be shorted to Add a 'defunct' tag for Index definitions

[phliar]

Does it have to be defunct=true? I'd like to be able to simply say something like

   Index `dosa:"key=(foo,bar),defunct"`

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

Gang Zhang seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}