The init lifecycle

init performs these steps in order (you can see each in the console output):

1. Database DDLs: pre_ddls, then DROP/CREATE TABLE for every table (with access_method / storage). Run in one transaction.
2. Pre-loading: pre_load_script, if present (single connection).
3. Data loading: -j parallel jobs. The 1..scalefactor unit ids are round-robin distributed across jobs; each job runs the template loaders or load_script for its ids.
4. Primary keys: ALTER TABLE ... ADD PRIMARY KEY.
5. Foreign keys: unless --no-fkey.
6. Indexes: all indexes.
7. Vacuum: VACUUM FREEZE ANALYZE per table, then post_ddls.
8. Checkpoint: forces a checkpoint so the run starts from a clean state.

Keys and indexes are created after loading for speed. This ordering is why your row templates / load_script only need to produce raw column data: the constraints are applied afterwards.