Clarify that MOLT Fetch does not migrate sequences (#20644)

* Clarify that MOLT Fetch does not migrate sequences

* made changes based on Tuan's feedback

* made changes based on Ryan's feedback

Author: bsanchez-the-roach

src/current/_includes/molt/migration-schema-design-practices.md

@@ -32,6 +32,10 @@ Convert the source schema into a CockroachDB-compatible schema. CockroachDB supp
 
 - Every table **must** have an explicit primary key. For more information, refer to [Primary key best practices]({% link {{ site.current_cloud_version }}/schema-design-table.md %}#primary-key-best-practices).
 
+	{{site.data.alerts.callout_danger}}
+	Avoid using sequential keys. To learn more about the performance issues that can result from their use, refer to the [guidance on indexing with sequential keys]({% link {{site.current_cloud_version}}/sql-faqs.md %}#how-do-i-generate-unique-slowly-increasing-sequential-numbers-in-cockroachdb). If a sequential key is necessary in your CockroachDB table, you must create it manually, after using [MOLT Fetch]({% link molt/molt-fetch.md %}) to load and replicate the data.
+	{{site.data.alerts.end}}
+
 - Review [Transformations]({% link molt/molt-fetch.md %}#transformations) to understand how computed columns and partitioned tables can be mapped to the target, and how target tables can be renamed.
 
 - By default on CockroachDB, `INT` is an alias for `INT8`, which creates 64-bit signed integers. PostgreSQL and MySQL default to 32-bit integers. Depending on your source database or application requirements, you may need to change the integer size to `4`. For more information, refer to [Considerations for 64-bit signed integers]({% link {{ site.current_cloud_version }}/int.md %}#considerations-for-64-bit-signed-integers).

src/current/molt/molt-fetch.md

@@ -125,6 +125,8 @@ To verify that your connections and configuration work properly, run MOLT Fetch
 
 - {% include molt/molt-drop-constraints-indexes.md %}
 
+- MOLT Fetch does not support migrating sequences. If your source database contains sequences, refer to the [guidance on indexing with sequential keys]({% link {{site.current_cloud_version}}/sql-faqs.md %}#how-do-i-generate-unique-slowly-increasing-sequential-numbers-in-cockroachdb). If a sequential key is necessary in your CockroachDB table, you must create it manually. After using MOLT Fetch to load and replicate the data onto the target, but before cutover, make sure to update each sequence's current value using [`setval()`]({% link {{site.current_cloud_version}}/functions-and-operators.md %}#sequence-functions) so that new inserts continue from the correct point.
+
 ## Security recommendations
 
 Cockroach Labs **strongly** recommends the following: