Concurrent retry: same scope + key

Conceptual: A commits; if A rolls back, B can acquire the key

Concurrent retry: same scope + key Conceptual: A commits; if A rolls back, B can acquire the key BEGIN; reserve key K K acquired (uncommitted) BEGIN; reserve K (waits) INSERT order; save response COMMIT order + key + response ON CONFLICT: zero rows Next statement: SELECT K Compare request; replay saved result API A · Sequence participant API A PostgreSQL · Sequence participant PostgreSQL API B (retry) · Sequence participant API B (retry) Legend return default message