0246 — deliveries stays one shared table across every topic, unlike message_log
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Context. With message_log split into per-topic physical tables, the
symmetric move would be per-topic deliveries tables too.
Decision. deliveries remains a single shared table; topic scoping is a
plain topic_id column plus the wider composite PK
(consumer_group, topic_id, message_id).
Consequences. topic.Register/Destroy stay cheap — they create and
drop only the topic’s own log tables, not N companion tables per topic.
Rejected: per-topic deliveries tables — message_log needs physical
separation for two structural reasons, its own BIGSERIAL sequence and
retention by DROP TABLE of topic-owned partition sets, and deliveries
has neither: rows are ephemeral (deleted or resolved continuously, no
retention-drop mechanism) and are not keyed by a shared sequence, so the
split would add real DDL-lifecycle cost for no matching benefit.