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# Databases family — first release

## Added

| Document | What it carries |
|---|---|
| `reference/databases/cloud-sql.md` | three engines, Enterprise Plus, the HA shape, four connection paths, the restarting update category |
| `reference/databases/alloydb.md` | the cluster/instance/node model, three instance types, the columnar engine |
| `reference/databases/spanner.md` | the three configurations with their stated availability and write-latency trade |
| `reference/databases/firestore.md` | the two modes, real-time updates, MongoDB compatibility |
| `reference/databases/bigtable.md` | the data model, data on Colossus not on nodes, the consistency-by-cluster-count rule, HBase |
| `reference/databases/errors.md` | indexed by symptom and configuration, with an explicit note on missing vendor strings |
| `guides/databases/connect-to-cloud-sql-with-iam-auth.md` | seven steps to a connection with no stored credential |
| `guides/parity/databases.md` | the two rows where no counterpart is honest, and the provisioned-capacity against request-unit trap |

## The two headline facts

1. **Adding a second Bigtable cluster changes consistency** from strong to eventually consistent by default.
   It produces no error, which makes it the hardest class of failure in this family to diagnose.
2. **Spanner has no like-for-like counterpart on AWS or Azure** — Microsoft's own table offers two unrelated
   services for it. A move off Spanner is an architecture change and must be costed as one.

## Absences recorded rather than filled in

1. **The Cloud SQL pages publish no verbatim connection error messages.** The error catalogue says so and is
   indexed by symptom instead, rather than inventing strings.
2. The Cloud SQL overview **states no version end-of-support information**, which is normally one of the
   highest-value facts in a database migration.
3. The Firestore modes page **does not say whether a database's mode can be changed** after creation.
4. The Spanner instance-configurations page **states no minimum** for nodes or processing units.

## Known missing

- Memorystore and Azure/AWS cache parity beyond the name row.
- Backups, point-in-time recovery and retention on every engine.
- Read replicas on Cloud SQL (as distinct from AlloyDB read pools).
- Firestore security rules and index management.
- Spanner schema design, interleaved tables and the PostgreSQL interface.
- Engine-level error catalogues: these come from MySQL, PostgreSQL and SQL Server, not from Google Cloud.


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