Reduce docker image size

[ebariaux]

When upgrading from PostgreSQL 15 to 17, our image size grew dramatically (5x) from about 350-400MB per architecture to 2.1GB

Double-check what is causing this size increase and what can be done to reduce the size.

[wborn]

I had a brief look and these dirs contain most data in an instance running the latest PostgreSQL image:

• 2.3G: /usr/local/lib/pgai
• 1.5G: /usr/lib/postgresql
• 1.4G: /usr/share/postgresql
• 1.3G: /home/postgres/.cache

---

Maybe pgai (https://github.com/timescale/pgai) can be removed because we currently don't use it, see also timescale/timescaledb-docker-ha#573:

# du -h --max-depth=1 /usr/local/lib/pgai
859M	/usr/local/lib/pgai/0.10.0
134M	/usr/local/lib/pgai/0.10.1
229M	/usr/local/lib/pgai/0.11.0
139M	/usr/local/lib/pgai/0.11.1
139M	/usr/local/lib/pgai/0.11.2
91M	/usr/local/lib/pgai/0.4.0
17M	/usr/local/lib/pgai/0.4.1
17M	/usr/local/lib/pgai/0.5.0
331M	/usr/local/lib/pgai/0.6.0
89M	/usr/local/lib/pgai/0.7.0
129M	/usr/local/lib/pgai/0.8.0
133M	/usr/local/lib/pgai/0.9.0
2.3G	/usr/local/lib/pgai

---

There are also 3 PostgreSQL versions in the image now for facilitating upgrades (#11):

# du -h --max-depth=1 /usr/lib/postgresql 
350M	/usr/lib/postgresql/17
575M	/usr/lib/postgresql/15
524M	/usr/lib/postgresql/14
1.5G	/usr/lib/postgresql

# du -h --max-depth=1 /usr/share/postgresql
341M	/usr/share/postgresql/17
588M	/usr/share/postgresql/15
491M	/usr/share/postgresql/14
1.4G	/usr/share/postgresql

We could also use a big image for doing upgrades and use a smaller one for instances that already upgraded.

---

Haven't looked yet if /home/postgres/.cache is part of the image or generated when it is run:

# du -h --max-depth=1 /home/postgres
1.3G	/home/postgres/.cache
16K	/home/postgres/pg_log
0	/home/postgres/pgdata
1.3G	/home/postgres

[Miggets7]

We can also consider providing an image without HA(High Availability) which also reduces the size of the image.