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https://issues.apache.org/jira/browse/CASSANDRA-9425?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15840109#comment-15840109
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Aleksey Yeschenko commented on CASSANDRA-9425:
----------------------------------------------
bq. TableMetadataRef.to() feels like it could be misused easily so I'd suggest
making things a bit more explicit.
Done.
bq. for indexes, where we kind of hack around them not having their own ID.
Addressed by moving 2i {{TableMetadata}} s handling to {{Tables}} and
{{Schema}}.
bq. Also, the Schema ctor should probably be private.
Addressed.
bq. Some of Schema.createKeyspace() is actually redundant: Keyspace ctor
already initialize all tables and views, so it ends up being duplicated. It's
largely harmless though we do end up reloading each ColumnFamilyStore for no
reason.
Addressed.
bq. Schema.load and Schema.unload should probably be synchronized for their
modification of keyspaces.
Addressed.
bq. validateTable seems to replace Validation.validateColumnFamily but the
latter is still there and used in a few instances. Would be nice to clean up.
Validation.validateKeyspaceNotSystem could probably be migrated too for
consistency.
Addressed.
bq. In TableMetadata, validateCompatibility() should probably check more stuffs
(we can't alter non-PK column types as we want, nor change the partition key
size for instance).
Addressed.
The only unaddressed issues at this point are loading of schema and system
keyspaces in {{Schema}} static block and a proper refactoring of {{load()}}.
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 (I would also like to
separate out {{Keyspace}} instance handling and metadata handling into two
separate classes instead of overloading {{Schema}}, to address the issue
properly and not just put some lipstick on this pig).
> 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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