FAQ

Is 5.0 compatible with 4.x? No (D1): not the API, the configuration, nor the stored data. The offline migration tool moves data and configuration once; 4.x and 5.0 never run in one namespace.

Will ids continue after a migration, or jump? They continue. 5.0 keeps the 4.x default layout and epoch (D16), segments continue past the 4.x maximum, and time-based ids continue after the migration time W.

Do clocks have to be synchronized? Not for uniqueness: it rests on the store-side window invariant alone (D22). Skew costs availability. A host ahead of the store by more than tolerance pauses near its window ceiling, and a host behind it waits longer to pass a new floor. Run NTP anyway.

What happens if my process freezes for a minute? When it resumes, its timestamps lie past its window ceiling: it refuses to issue (SlotWindowExceededException) until it has renewed or acquired a new slot. Meanwhile another instance may hold the slot, with a window that starts after the frozen one's ceiling.

Can I keep issuing when the store is down? Segments: until the ids at hand and the ready ranges run out, which is about lookahead (1s) of traffic. A longer lookahead buys more. Snowflake: until the window ceiling, about ttl − ttl/3 + tolerance after the last renewal. There is no option to issue past a lost lease (P1).

Why are there gaps in my segment ids? Gaps are allowed, duplicates never (D19). A restart drops the rest of a range, and so do a timed-out wait and a range-ttl expiry.

How many instances can share a namespace?2^bits with leased slots (1024 by default). Segments need no slot.

Can I delete a generator at run time? No (D17): generators are fixed at start-up. Mark one disabled: true, or change the spec with a RuntimeSpecCustomizer before start.

How do I remove old period keys? Offline: cosid-migration purge --to … --namespace … --before 20250101, first with --dry-run. Run-time code never deletes a key (D23).

Which store should I use? JDBC if you have a database: transactional and simple. ZooKeeper if you run one. Redis for speed, with its durability precondition. MongoDB on a replica set. cosid-server when applications should not reach the store directly, or are not on the JVM.