Add Switch The Running Postgres Server Version as a Postgres til

postgres/switch-the-running-postgres-server-version.md

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+# Switch The Running Postgres Server Version
+
+I use [asdf](https://github.com/asdf-vm/asdf) install and manage multiple
+versions of Postgres on my Mac OSX machine. With `asdf` and project-based
+`.tools-versions` files, I can control what version of Postgres (`psql`) I use
+at a project-level.
+
+The one snag with this workflow is managing the currently running server
+version.  Lets say I need to switch from a project using `12.3` to a project
+using `13.1`. If the Postgres server running on my machine is using the
+Postgres server 12.3, then I'll need to manually stop that server and start up
+the Postgres server 13.1.
+
+This can be done like so:
+
+```bash
+# stop the 12.3 server
+$ $HOME/.asdf/installs/postgres/12.3/bin/pg_ctl \
+    -D $HOME/.asdf/installs/postgres/12.3/data \
+    stop
+
+# start the 13.1 server
+$ $HOME/.asdf/installs/postgres/13.1/bin/pg_ctl \
+    -D $HOME/.asdf/installs/postgres/13.1/data \
+    start
+```
+
+This uses the specific asdf-versioned `pg_ctl` command to stop and start the
+servers.
+
+I've found it tedious to dig up these commands each time I need to switch, so I
+added a [`switch_pg` function to my `~/.zshrc`
+config](https://gist.github.com/jbranchaud/3cda6be6e1dc69c6f55435a387018dac).