mirror of https://github.com/citusdata/citus.git
3eaff48114
Fixes #513 This change modifies the DDL Propagation logic so that DDL queries are propagated via 2-Phase Commit protocol. This way, failures during the execution of distributed DDL commands will not leave the table in an intermediate state and the pending prepared transactions can be commited manually. DDL commands are not allowed inside other transaction blocks or functions. DDL commands are performed with 2PC regardless of the value of `citus.multi_shard_commit_protocol` parameter. The workflow of the successful case is this: 1. Open individual connections to all shard placements and send `BEGIN` 2. Send `SELECT worker_apply_shard_ddl_command(<shardId>, <DDL Command>)` to all connections, one by one, in a serial manner. 3. Send `PREPARE TRANSCATION <transaction_id>` to all connections. 4. Sedn `COMMIT` to all connections. Failure cases: - If a worker problem occurs before sending of all DDL commands is finished, then all changes are rolled back. - If a worker problem occurs after all DDL commands are sent but not after `PREPARE TRANSACTION` commands are finished, then all changes are rolled back. However, if a worker node is failed, then the prepared transactions in that worker should be rolled back manually. - If a worker problem occurs during `COMMIT PREPARED` statements are being sent, then the prepared transactions on the failed workers should be commited manually. - If master fails before the first 'PREPARE TRANSACTION' is sent, then nothing is changed on workers. - If master fails during `PREPARE TRANSACTION` commands are being sent, then the prepared transactions on workers should be rolled back manually. - If master fails during `COMMIT PREPARED` or `ROLLBACK PREPARED` commands are being sent, then the remaining prepared transactions on the workers should be handled manually. This change also helps with #480, since failed DDL changes no longer mark failed placements as inactive. |
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