17.0.6 release notes: ExecuteFetchAsDBA breaking change

Signed-off-by: Shlomi Noach <[email protected]>

changelog/17.0/17.0.6/release_notes.md

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+# Release of Vitess v17.0.6
+The entire changelog for this release can be found [here](https://github.com/vitessio/vitess/blob/main/changelog/17.0/17.0.6/changelog.md).
+
+### <a id="breaking-changes"/>Breaking Changes
+
+`vtctldclient ExecuteFetchAsDBA` (and similarly the `vtctl` and `vtctlclient` commands) now reject multi-statement SQL with error.
+
+For example, `vtctldclient ExecuteFetchAsDBA my-tablet "stop replica; change replication source to auto_position=1; start replica` will return an error, without attempting to execute any of these queries.
+
+Previously, `ExecuteFetchAsDBA` silently accepted multi statement SQL. It would (attempt to) execute all of them, but:
+
+- It would only indicate error for the first statement. Errors on 2nd, 3rd, ... statements were silently ignored.
+- It would not consume the result sets of the 2nd, 3rd, ... statements. It would then return the used connection to the pool in a dirty state. Any further query that happens to take that connection out of the pool could get unexpected results.
+- As another side effect, multi-statement schema changes would cause schema to be reloaded with only the 1st change, leaving the cached schema inconsistent with the underlying database.
+
+`ExecuteFetchAsDBA` does allow a specific use case of multi-statement SQL, which is where all statements are in the form of `CREATE TABLE` or `CREATE VIEW`. This is to support a common pattern of schema initialization.