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From "Jeff Jirsa (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-7622) Implement virtual tables
Date Fri, 27 Apr 2018 17:00:00 GMT


Jeff Jirsa commented on CASSANDRA-7622:

No disagreement here. We don't want it to be exposed in regular DDL. However, we would like
this to be at least a little bit generic, so that one could plug-in extra virtual keyspaces
on C* startup, similar to how some folks/forks add extra system keyspaces and system tables.
There are some use cases for virtual tables that we want to experiment with (Jeff Jirsa gave
a few examples in his NGCC talk) that are compelling enough to at least allow this possibility.

Just to expand on this: the metrics/config stuff I think is a no brainer and not really contentious.
There are a few other things I think are useful to operators that we'll likely be experimenting
with (privately) in the near future, as a proof-of-concept before we attempt to suggest they're
suitable or relevent for the larger audience. An example in this space is something like a
table that inspects unfiltered cells of a partition (a la {{sstabledump}} , but over CQL)
for troubleshooting purposes ('which sstables have this key' and 'why does this partition
have so many tombstones?' type virtual table implementations). Further down the road (in the
6.x/7.x timeframe), leaving these as virtual tables instead of system views may allow future
uses like , so long term I'd like to
consider leaving the door open for that if possible, but I'm happy to set that desire aside
if necessary in order to get the first two steps (metrics/config and an extension point for
the debugging tables/views) in properly. 

> Implement virtual tables
> ------------------------
>                 Key: CASSANDRA-7622
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: CQL
>            Reporter: Tupshin Harper
>            Assignee: Chris Lohfink
>            Priority: Major
>             Fix For: 4.x
>         Attachments: screenshot-1.png
> There are a variety of reasons to want virtual tables, which would be any table that
would be backed by an API, rather than data explicitly managed and stored as sstables.
> One possible use case would be to expose JMX data through CQL as a resurrection of CASSANDRA-3527.
> Another is a more general framework to implement the ability to expose yaml configuration
information. So it would be an alternate approach to CASSANDRA-7370.
> A possible implementation would be in terms of CASSANDRA-7443, but I am not presupposing.

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