The problem
Source positions reach the engine as an opaque u64 token. That fits an LSN and a GTID-derived offset, but not every change stream: SQL Server's LSN is binary(10) (80 bits), MongoDB resume tokens are strings. Any source whose position does not fit cannot be written without touching core first — and if one is written around the limit, every later installation inherits a migration.
Proposed behaviour
Generalise the position token to an opaque byte string end to end: the core checkpoint type, the comparison the engine needs (ordering stays the source's business), and the checkpoint document format in every target. One epic, not one PR, because the stored format changes: the sinks must read an existing u64 checkpoint and write the new form, so a live installation restarts without losing its position. Proven by the failover probe and the kill -9 e2e sections in all three targets.
What you tried instead
Deferring until the first non-u64 source: that turns a planned migration into a forced one, written under pressure inside an unrelated source PR.
The problem
Source positions reach the engine as an opaque
u64token. That fits an LSN and a GTID-derived offset, but not every change stream: SQL Server's LSN isbinary(10)(80 bits), MongoDB resume tokens are strings. Any source whose position does not fit cannot be written without touching core first — and if one is written around the limit, every later installation inherits a migration.Proposed behaviour
Generalise the position token to an opaque byte string end to end: the core checkpoint type, the comparison the engine needs (ordering stays the source's business), and the checkpoint document format in every target. One epic, not one PR, because the stored format changes: the sinks must read an existing
u64checkpoint and write the new form, so a live installation restarts without losing its position. Proven by the failover probe and thekill -9e2e sections in all three targets.What you tried instead
Deferring until the first non-u64 source: that turns a planned migration into a forced one, written under pressure inside an unrelated source PR.