Tracking issue for sink returning inaccurate checkpoints

[overvenus]

In the current implementation (11/20/2021), when a table flushes its' sink, sink may return a checkpoint that is larger than resolved ts.
It can easily be reproduced when tables in a "slow" TiCDC node, whose checkpoint is Tca, are scheduled to a "faster" TiCDC node, whose checkpoint is Tcb, and Tca < Tcb .

Combine with #3029 and #2617, it can easily cause data lose and changefeed stuck when a "slow" is killed, e.g.,

• https://github.com/pingcap/ticdc/issues/3531
• https://github.com/pingcap/ticdc/issues/3521
• https://github.com/pingcap/ticdc/issues/3503

Sink must return accurate checkpoint for each table. It is hard to implement with the current interface design, especially when a sink is shared by multiple tables.

PRs：

• https://github.com/pingcap/ticdc/pull/3613
• https://github.com/pingcap/ticdc/pull/3621
• https://github.com/pingcap/ticdc/pull/3625
• https://github.com/pingcap/ticdc/pull/3638
• https://github.com/pingcap/ticdc/pull/3645
• https://github.com/pingcap/ticdc/pull/3746

[overvenus]

Change to severity/moderate, as most issues are fixed.

[asddongmen]

@overvenus I think we can close this issue as a result of all the fix PR have been merge.