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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-14825) Expose table schema for drivers
Date Mon, 12 Nov 2018 10:56:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-14825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16683564#comment-16683564
] 

Sylvain Lebresne commented on CASSANDRA-14825:
----------------------------------------------

bq. just to be clear if you query describe_keyspace table you can iterate through the result
set to get the entire schema (...)

And in case there was doubt, I didn't say it wasn't the case. I'm not saying you can't get
schema information through virtual tables.

What I'm asking is, why use virtual tables when we could just promote to CQL the `DESCRIBE`
statements every user is already familiar and which is, I think, a more fexible/direct approach?

By which I mean that you can both get the granular if you want, but also get a full schema
dump directly. With virtual tables, you get the granular, but a full schema dump requires
a small amount of post-processing (_not_ saying it's hard, but it is harder than no post-processing
at all). Additionally, it's very easy to add new options to statements, while once you settle
on some virtual table schema, it can harder to evolve.

What are the pros in favor of virtual tables that outweigh those 2 pros of promoting `DESCRIBE`
(existing familiarity and at least some form of better flexibility; to which I could add not
having 2 ways to do the same thing, since afaik, we're not going to remove `DESCRIBE` from
cqlsh)? I get that virtual tables are everyone's new shiny hammer, but it's not an objective
argument.

> Expose table schema for drivers
> -------------------------------
>
>                 Key: CASSANDRA-14825
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14825
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Chris Lohfink
>            Assignee: Chris Lohfink
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 0.5h
>  Remaining Estimate: 0h
>
> Currently the drivers recreate the CQL for the tables by putting together the system
table values. This is very difficult to keep up to date and buggy enough that its only even
supported in Java and Python drivers. Cassandra already has some limited output available
for snapshots that we could provide in a virtual table or new query that the drivers can fetch.
This can greatly reduce the complexity of drivers while also reducing bugs like CASSANDRA-14822
as the underlying schema and properties change.



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