Bug Report: Unable to execute a DDL twice in a same client connection

[earayu]

Overview of the Issue

I've observed that the introduced session_uuid from this issue (#7263) is being used as a migration_context for OnlineDDL. Nevertheless, a consequence of this is that it prevents the execution of a DDL statement more than once for a single client connection.

Reproduction Steps

create table t3 (c1 int primary);

drop table t3;

-- won't be executed as the migration_context is unchanged
create table t3 (c1 int primary); 

Binary Version

main

Operating System and Environment details

main

Log Fragments

No response

[earayu]

Maybe this problem can be fixed like this:

[shlomi-noach]

The behavior is actually intentional, with multi-sharded environments in mind, and where some shards may succeed a migration and some may fail. See details in https://vitess.io/docs/18.0/user-guides/schema-changes/advanced-usage/#duplicate-migration-detection. As per the docs (and a recent addition), you may explicitly set @@migration_context to override @@session_uuid:

mysql> set @@migration_context = uuid();
Query OK, 0 rows affected (0.00 sec)

mysql> select @@migration_context;
+--------------------------------------+
| @@migration_context                  |
+--------------------------------------+
| 53374dec-58a9-11ee-9d5b-0a43f95f28a3 |
+--------------------------------------+
1 row in set (0.00 sec)

This value is then used in your next submitted migrations. So, the following will work:

> create table t3 (c1 int primary);

> drop table t3;

> set @@migration_context = uuid();
> create table t3 (c1 int primary); 

[shlomi-noach]

If there's no more comments I will go ahead and close this issue.

[earayu]

If there's no more comments I will go ahead and close this issue.

Thank you for your reply, there's no more comments.