Add PostgreSQL in-place upgrade note

Signed-off-by: Anatoli Nicolae <[email protected]>

notes/in-place-mariadb-upgrade.md

@@ -37,11 +37,11 @@ If you still chose to proceed with an in-place migration, **make sure your data
 ## Procedure
 
 ```bash
-# Run bootstrapper
-upcp -sb
+# Temporarily disable Monit
+systemctl stop monit.service
 
 # Set new MariaDB version
-cpcmd scope:set cp.bootstrapper mariadb_version 10.11
+cpcmd scope:set cp.bootstrapper mariadb_version "10.11"
 
 # Make a copy of the repo definition
 mysql -v

notes/in-place-psotgresql-upgrade.md

@@ -0,0 +1,106 @@
+---
+title: In-place PostgreSQL upgrade
+tags:
+  - postgres
+  - database
+  - systemd
+emoji: 🐘
+queries:
+  - in-place postgres upgrade
+---
+
+<Warning>
+
+WIP: this is a **draft guide**. Make sure you know what you're doing before following this guide as **it's NOT a supported procedure**.
+
+</Warning>
+
+
+<Warning>
+
+This procedure is **highly discouraged** as it may lead to serious data loss.
+
+</Warning>
+
+<Note>
+
+Take advantage of the [zero downtime migration tool](https://docs.apiscp.com/admin/Migrations%20-%20server/#migration-components) to get those sites over that need the newer PostgreSQL release while evaluating the impact it can have.
+
+</Note>
+
+<Warning>
+
+If you still chose to proceed with an in-place migration, **make sure your data is backed up before proceeding.**
+
+</Warning>
+
+## Checklist
+- [ ] Set maintenance window
+- [ ] upcp -sb 1 hour before maintenance, to make sure everything works
+- [ ] Do all steps in exact order
+- [ ] Take notes on behaviour
+
+
+## Procedure
+
+```bash
+export PG_FROM_VERSION="14"
+export PG_TO_VERSION="16"
+export PG_UPGRADE_TIME=$(date +%F-%T)
+export LC_ALL="en_US.UTF-8"
+export LC_CTYPE="en_US.UTF-8"
+
+# Perform a backup of all databases
+pg_dumpall > "/home/pg-all-$PG_UPGRADE_TIME.sql"
+
+# Temporarily disable Monit
+systemctl stop monit.service apiscp.service
+
+# Set new Postgres version
+cpcmd scope:set cp.bootstrapper pgsql_version "$PG_TO_VERSION"
+
+# Remove pgdg repo to fetch fresh one
+mv /etc/yum.repos.d/pgdg-redhat-all.repo{,.old}
+mv /etc/yum.repos.d/timescaledb.repo{,.old}
+
+# Install new packages
+upcp -sbf packages/install
+
+upcp -sbf pgsql/install
+systemctl stop postgresql-$PG_FROM_VERSION
+systemctl stop postgresql-$PG_TO_VERSION
+systemctl reset-failed
+upcp -sbf pgsql/install
+
+# Login as Postgres to initdb and upgrade
+su postgres
+
+# Initialize a new DB
+/usr/pgsql-$PG_TO_VERSION/bin/initdb -D /var/lib/pgsql/$PG_TO_VERSION/data
+
+# Add timescale to shared libs, otherwise install will fail
+echo "shared_preload_libraries = 'timescaledb'" >> /var/lib/pgsql/$PG_TO_VERSION/data/postgresql.conf
+
+# Reset WAL
+/usr/pgsql-16/bin/pg_resetwal -f /var/lib/pgsql/16/data/
+
+# Perform the upgrade with the command that fits your OS version
+# RHEL <8
+/usr/pgsql-$PG_TO_VERSION/bin/pg_upgrade -b /var/lib/pgsql/$PG_FROM_VERSION/bin -B /var/lib/pgsql/$PG_TO_VERSION/bin -d /var/lib/pgsql/$PG_FROM_VERSION/data -D /var/lib/pgsql/$PG_TO_VERSION/data -j 4
+# RHEL 8+
+/usr/pgsql-$PG_TO_VERSION/bin/pg_upgrade -b /usr/pgsql-$PG_FROM_VERSION/bin -B /usr/pgsql-$PG_TO_VERSION/bin -d /var/lib/pgsql/$PG_FROM_VERSION/data -D /var/lib/pgsql/$PG_TO_VERSION/data -j 4
+
+exit
+
+# Start new Postgres
+systemctl start postgresql-$PG_TO_VERSION
+
+# Start Monit service again
+systemctl start monit.service apiscp.service
+```
+
+<Warning>
+
+In case anything goes wrong, **after switching back version and reinstalling packages**, you can try restoring the databases with the following command: `psql --clean -f "/home/pg-all-$PG_UPGRADE_TIME.sql" postgres`
+
+</Warning>