db-dump: set sequence values when importing a database dump

[LawnGnome]

By default, the import script recreates the database schema, which includes creating new sequences with zero values. This results in the lazy crates.io developer occasionally receiving obscure errors when inserting records into tables that use sequences, often not on the first or second insert due to IDs in the database dump not always being continuous.

Rather than dumping the real sequence values from the database, we can just recreate them based on the maximum ID in each table. Works well enough, and means we don't have to tinker with the export script or ship extra data.

This commit only configures the database tables that actually include data in the database dump. There are other sequences, but since those tables won't have data imported, it doesn't matter if they remain zero after import.

[Turbo87]

instead of manually declaring them here, would it be possible to derive them from the database schema in some way?

[eth3lbert]

This is doable as follows, which is modified from https://stackoverflow.com/a/55414721:

select tbl.relname as table_name, 
       col.attname as column_name,
       s.relname as sequence_name
from pg_class s
  join pg_namespace sn on sn.oid = s.relnamespace 
  join pg_depend d on d.refobjid = s.oid and d.refclassid='pg_class'::regclass 
  join pg_attrdef ad on ad.oid = d.objid and d.classid = 'pg_attrdef'::regclass
  join pg_attribute col on col.attrelid = ad.adrelid and col.attnum = ad.adnum
  join pg_class tbl on tbl.oid = ad.adrelid 
  join pg_namespace ts on ts.oid = tbl.relnamespace 
where s.relkind = 'S'
--  and s.relname = 'your_sequence_name_her'
  and d.deptype in ('a', 'n');

From the result, you should see something similar to the following:

      table_name       | column_name |        sequence_name         
-----------------------+-------------+------------------------------
 api_tokens            | id          | api_tokens_id_seq
 background_jobs       | id          | background_jobs_id_seq
 categories            | id          | categories_id_seq
 crates                | id          | packages_id_seq
 deleted_crates        | id          | deleted_crates_id_seq
 dependencies          | id          | dependencies_id_seq
 emails                | id          | emails_id_seq
 keywords              | id          | keywords_id_seq
 teams                 | id          | teams_id_seq
 users                 | id          | users_id_seq
 version_owner_actions | id          | version_owner_actions_id_seq
 versions              | id          | versions_id_seq
(12 rows)

[Turbo87]

I think this needs an update of the corresponding test snapshot :)