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From "Chris Lohfink (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-7622) Implement virtual tables
Date Fri, 27 Apr 2018 13:40:00 GMT


Chris Lohfink commented on CASSANDRA-7622:

> I do think it would be worth separating the discussion on the system view/virtual table
mechanism from the one on the exact schema of metrics tables for the sake of focus

agreed, I removed table_stats from system_view and it can be discussed in another ticket.
That leaves {{settings}}, {{compaction_stats}}, {{ring_state}}. Thats 2 essentially copies
of the nodetool output and a new table that lets you see current state of the configuration
(with a few updatable).

> I am strongly in favor of not shipping syntax for creating virtual tables

Removing CQL syntax change and {{CreateTableStatement}} changes. Will build the tablemetadata
from builder instead in the {{SystemViewKeyspace}}.

> The patch seems to disable the {{ALLOW FILTERING}} check for virtual tables

The patch allows each virtual table to enable or disable the restrictions that normally would
require {{ALLOW FILTERING}} to make

     * If the table allows unrestricted queries (ie filter on clustering key with no partition).
Since These tables are
     * not backed by the C* data model, this restriction isnt always necessary.
    public boolean allowFiltering()
        return true;

I will change default to have same behavior as normal C* tables, but I actually really would
like to remove those restrictions on queries for the {{SystemView}} tables since they dont
need them and it makes querying interesting things a lot easier.

> naming is important 

agreed but its hard to have 100% foresight, the goal of this ticket shifted dramatically through
its lifetime even. I went with {{VirtualTable}} being the base abstract class for a custom
backend, but the one implementation provided is a {{SystemView}} to make it easier to make
internal system state/metrics tables.

> 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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