[jira] [Created] (CASSANDRA-9425) Make node-local schema fully immutable

["Aleksey Yeschenko (JIRA)" <ji...@apache.org>]

Aleksey Yeschenko created CASSANDRA-9425:
--------------------------------------------

             Summary: Make node-local schema fully immutable
                 Key: CASSANDRA-9425
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9425
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Aleksey Yeschenko
             Fix For: 3.x


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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