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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9425) Make node-local schema fully immutable
Date Fri, 27 Jan 2017 14:55:25 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9425?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15842944#comment-15842944
] 

Sylvain Lebresne commented on CASSANDRA-9425:
---------------------------------------------

bq. With both of these present in current trunk code, I'd prefer to commit what is here as
is, and move those into a separate ticket

Wfm.

Thanks for addressing the rest, +1, ship it (assuming clean CI, which we seem to have but
I checked quickly). Great work!

> Make node-local schema fully immutable
> --------------------------------------
>
>                 Key: CASSANDRA-9425
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9425
>             Project: Cassandra
>          Issue Type: Sub-task
>            Reporter: Aleksey Yeschenko
>            Assignee: Aleksey Yeschenko
>             Fix For: 4.0
>
>
> The way we handle schema changes currently is inherently racy.
> All of our {{SchemaAlteringStatement}} s perform validation on a schema state that's
won't necessarily be there when the statement gets executed and mutates schema.
> We should make all the *Metadata classes ({{KeyspaceMetadata, TableMetadata}}, {{ColumnMetadata}},
immutable, and local schema persistently snapshottable, with a single top-level {{AtomicReference}}
to the current snapshot. Have DDL statements perform validation and transformation on the
same state.
> In pseudo-code, think
> {code}
> public interface DDLStatement
> {
>     /**
>      * Validates that the DDL statement can be applied to the provided schema snapshot.
>      *
>      * @param schema snapshot of schema before executing CREATE KEYSPACE
>      */
>     void validate(SchemaSnapshot schema);
>  
>     /**
>      * Applies the DDL statement to the provided schema snapshot.
>      * Implies that validate() has already been called on the provided snapshot.
>      *
>      * @param schema snapshot of schema before executing the statement
>      * @return snapshot of schema as it would be after executing the statement
>      */
>     SchemaSnapshot transform(SchemaSnapshot schema);
> }
> {code}



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