Support Active Active Mode

[hongyunyan]

Design Doc #pingcap/tidb#64294
ref pingcap/tidb#64281

[Tema]

@hongyunyan will ticdc enable-transaction-atomic feature available without active-active feature (enable-active-active)? I'm interested to use it to replicate data to standby cluster where I can read data consistently without sync-point as the latter causes to much lag. What is expected impact ofenable-transaction-atomic on a checkpoint lag? Is it 1-2 seconds or in the territory 10s?

[hongyunyan]

Update:

1. enable-transaction-atomic will be adapted to scenarios where enable-active-active is false.

2. However, transaction atomicity only guarantees atomicity within a single transaction; it lacks the strict consistency guarantees of syncpoints.