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https://issues.apache.org/jira/browse/CASSANDRA-9425?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15828320#comment-15828320
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Aleksey Yeschenko commented on CASSANDRA-9425:
----------------------------------------------
Anyway, thanks. Addressed the points in the last comment. The remained of the
original ones later tonight.
> 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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