Add section for removing Zero leftovers

[saturnonearth]

Added a quick workup for a section on how and what to remove from Postgres when trying to get rid of Zero.

Feel free to change the section name if you don't like it (I am not in love with it either).

Please also check all commands as I don't have any experience with psql and did not actually test any of this lol.

See: https://bugs.rocicorp.dev/issue/3262

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Name	Status	Preview	Comments	Updated (UTC)
zero-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Dec 18, 2024 7:07pm

[saturnonearth]

Note: Add section for publications removal as well:

[darkgnotic]

Thank you @saturnonearth !

One thing I think we've missed is replication slots, which are also "cluster"-wide (in pg parlance) and thus also not covered by schemas.

SELECT slot_name FROM pg_replication_slots;

will list the replication slots in the pg cluster. Zero creates slots of the format "zero_{shard-id}". These can be dropped with, e.g.:

SELECT pg_drop_replication_slot('zero_0');

[darkgnotic]

Another database-level artifact is publications.

SELECT pubname FROM pg_publication;

In addition to the default zero_public publication (or whatever the user overrides with --shard-publications, zero creates an internal publication for each shard, of the form _zero_metadata_{shard-id}.

These can be dropped with, e.g.:

DROP PUBLICATION IF EXISTS zero_public;
DROP PUBLICATION IF EXISTS _zero_metadata_0;