Merge pull request #209 from datajoint/docs/db-version-support-policy

docs(backends): state DB version support policy — LTS-targeted, scope out MySQL 9.x

Author: dimitri-yatsenko

src/reference/specs/database-backends.md

@@ -7,10 +7,24 @@ DataJoint supports multiple database backends through a unified adapter architec
 
 ## Supported Backends
 
-| Backend | Minimum Version | Default Port | Status |
-|---------|-----------------|--------------|--------|
-| MySQL | 8.0.13 | 3306 | Production |
-| PostgreSQL | 15 | 5432 | Production |
+| Backend | Minimum Version | Tested in CI | Default Port | Status |
+|---------|-----------------|--------------|--------------|--------|
+| MySQL | 8.0.13 | 8.0, 8.4 (LTS) | 3306 | Production |
+| PostgreSQL | 15 | 15 | 5432 | Production |
+| MariaDB | — | — | — | **Not supported** |
+
+### Version support policy
+
+DataJoint targets **long-term-support (LTS) database releases** — the versions offered by managed
+services such as AWS RDS:
+
+- **MySQL** — the **8.0** and **8.4** LTS lines; CI exercises both (see
+  [datajoint-python#1498](https://github.com/datajoint/datajoint-python/pull/1498)).
+- **PostgreSQL** — **15** and later.
+- **MySQL 9.x is not a supported target.** The 9.x series is a sequence of short-lived *Innovation*
+  releases — there is no 9.x LTS, and it is not offered as a standard managed-service engine. DataJoint
+  may run on it, but it is untested and support is best-effort only.
+- **MariaDB is not officially supported** in DataJoint 2.x; the client emits a warning on connection.
 
 ## Configuration