When does PostgreSQL create new cluster druing installation?

Question

I had PostgreSQL 9.5 installed on the server. I removed all postgres packages with

sudo apt remove '^postgres'

Then I stopped systemd postgresql service, removed the following directories:

/var/lib/postgresql/
/var/log/postgresql/
/etc/postgresql/

Also removed postgres user:

sudo deluser postgres

Removed systemd service (don't remember where it was)

After that I tried to install PostgreSQL 10, and it didn't create new cluster for version 10.

When I tried to install PostgreSQL 10 from the same source (http://apt.postgresql.org/pub/repos/apt/) on fresh server, new cluster was created.

As far as I remember, when I installed PostgreSQL 10 next to PostgreSQL 9.5 (and upgrading it using pg_upgradecluster), new cluster was created.

So, under what circumstances installation of PostgreSQL, particularly version 10, includes creation of a new cluster?

Answer 1

The Debian/Ubuntu packages have a postinstall step that essentially calls configure_version() in /usr/share/postgresql-common/maintscripts-functions (from the postgresql-common package) to create a new cluster.

The tests done by this function determine whether it should create a new cluster:

if [ ! -d "/etc/postgresql/$VERSION" ] || [ -z "$(ls /etc/postgresql/$VERSION)" ] || \
   [ -z "$(ls /etc/postgresql/$VERSION/*/postgresql.conf 2>/dev/null)" ]; then
    # skip creating the main cluster when this is not the first install, or
    # when explicitly disabled ($create is on/off/"")
    create=$(pg_conftool /etc/postgresql-common/createcluster.conf show -bs create_main_cluster || :)
    if [ -z "$2" ] && [ "$create" != "off" ]; then
        set_system_locale
        pg_createcluster -u postgres $VERSION main ||

So if there wasn't a pre-existing /etc/postgresql/10 directory, the next reason for not creating a cluster would be that the configuration in /etc/postgresql-common/createcluster.conf denies it.

Otherwise it might be that the environment had an invalid locale, but there would be a warning output about it, such as in Locale warning from Perl stops Postgres configuring.