ci: Test low-level DB code against PG12

Signed-off-by: Rémy Coutable <remy@rymai.me>

.gitlab/ci/rails.gitlab-ci.yml

@@ -300,6 +300,16 @@ rspec system pg11 minimal:
     - .minimal-rspec-tests
     - .rails:rules:ee-and-foss-system:minimal
 
+# Dedicated job to test DB library code against PG12.
+# Note that these are already tested against PG11 in the `rspec unit pg11` / `rspec-ee unit pg11` jobs.
+rspec db-library-code pg12:
+  extends:
+    - .rspec-base-pg12
+    - .rails:rules:ee-and-foss-db-library-code
+  script:
+    - *base-script
+    - rspec_simple_job "-- spec/lib/gitlab/database/ spec/support/helpers/database/ ee/spec/lib/gitlab/database/ ee/spec/lib/ee/gitlab/database_spec.rb"
+
 rspec fast_spec_helper:
   extends:
     - .rspec-base-pg11

.gitlab/ci/rules.gitlab-ci.yml

@@ -155,9 +155,15 @@
   - "{,ee/}{,spec/}lib/{,ee/}gitlab/database{,_spec}.rb"
   - "{,ee/}{,spec/}lib/{,ee/}gitlab/background_migration/**/*"
   - "{,ee/}{,spec/}lib/{,ee/}gitlab/background_migration{,_spec}.rb"
+  - "{,ee/}spec/support/helpers/database/**/*"
   - "config/prometheus/common_metrics.yml"  # Used by Gitlab::DatabaseImporters::CommonMetrics::Importer
   - "{,ee/}app/models/project_statistics.rb"  # Used to calculate sizes in migration specs
 
+.db-library-patterns: &db-library-patterns
+  - "{,ee/}{,spec/}lib/{,ee/}gitlab/database/**/*"
+  - "{,ee/}{,spec/}lib/{,ee/}gitlab/database{,_spec}.rb"
+  - "{,ee/}spec/support/helpers/database/**/*"
+
 .backstage-patterns: &backstage-patterns
   - "Dangerfile"
   - "danger/**/*"
@@ -775,6 +781,11 @@
     - <<: *if-merge-request-title-as-if-foss
       changes: *code-backstage-patterns
 
+.rails:rules:ee-and-foss-db-library-code:
+  rules:
+    - changes: *db-library-patterns
+    - <<: *if-merge-request-title-run-all-rspec
+
 .rails:rules:ee-mr-and-master-only:
   rules:
     - <<: *if-not-ee

doc/development/pipelines.md

@@ -422,24 +422,29 @@ We are using a custom mapping between source file to test files, maintained in t
 
 ### PostgreSQL versions testing
 
+Even though [Omnibus defaults to PG12 for new installs and upgrades](https://docs.gitlab.com/omnibus/package-information/postgresql_versions.md),
+our test suite is currently running against PG11, since GitLab.com still runs on PG11.
+
+We do run our test suite against PG12 on nightly scheduled pipelines as well as upon specific
+database library changes in MRs and `master` pipelines (with the `rspec db-library-code pg12` job).
+
 #### Current versions testing
 
 | Where? | PostgreSQL version |
-| ------ | ------ |
-| MRs | 11 |
-| `master` (non-scheduled pipelines) | 11 |
-| 2-hourly scheduled pipelines | 11 |
+| ------ | ------------------ |
+| MRs    | 11, 12 for DB library changes |
+| `master` (non-scheduled pipelines) | 11, 12 for DB library changes |
+| 2-hourly scheduled pipelines | 11, 12 for DB library changes |
 | `nightly` scheduled pipelines | 11, 12 |
 
 #### Long-term plan
 
 We follow the [PostgreSQL versions shipped with Omnibus GitLab](https://docs.gitlab.com/omnibus/package-information/postgresql_versions.html):
 
-| PostgreSQL version | 13.0 (May 2020) | 13.1 (June 2020) | 13.2 (July 2020) | 13.3 (August 2020) | 13.4, 13.5   | [13.7 (December 2020)](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5722) | 14.0 (May 2021?) |
-| ------ | --------------- | ---------------- | ---------------- | ------------------ | ------------ | -------------------- | ---------------- |
-| PG11   | MRs/`master`/`2-hour`/`nightly` | MRs/`master`/`2-hour`/`nightly` | MRs/`master`/`2-hour`/`nightly` | MRs/`master`/`2-hour`/`nightly` | MRs/`master`/`2-hour`/`nightly` | `nightly` | - |
-| PG12   | - | - | `nightly` | `2-hour`/`nightly` | `2-hour`/`nightly` | MRs/`2-hour`/`nightly` | `2-hour`/`nightly`     |
-| PG13   | - | - | -         | -                  | -                  | -                      | MRs/`2-hour`/`nightly` |
+| PostgreSQL version | 13.7 (December 2020) | 13.8 (January 2021) | 13.9 (February 2021) | 13.10 (March 2021) | 13.11 (April 2021) | 14.0 (May 2021?) |
+| -------------------| -------------------- | ------------------- | -------------------- | ------------------ | ------------------ | ---------------- |
+| PG11               | MRs/`2-hour`/`nightly` | MRs/`2-hour`/`nightly` | MRs/`2-hour`/`nightly` | MRs/`2-hour`/`nightly` | MRs/`2-hour`/`nightly` | MRs/`2-hour`/`nightly` |
+| PG12               | `nightly`            | `nightly`           | `nightly`           | `nightly`           | `nightly`           | `nightly`       |
 
 ### Test jobs