Supports `FLASHBACK TO TIMESTAMP` in TiDB

[Defined2014]

Background

Some users want to flash back the whole cluster to a determined timestamp when there is a problem with the database like delete some important values etc. In TiDB we use MVCC to store the key values in TiKV which means we could easy to flash back it before gc complete. This issue is the tracking issue for flashback cluster feature.

Task

Docs

• sql: add flashback cluster doc docs-cn#11443
• docs: add a proposal for flashback to timestamp #38367

TiDB

• Parser supports flash back cluster as of timestamp 'expression' #37229
• support flashback cluster pre-check #37262

• privilege check, a user with SUPER permission can run this stmts
• check TS
• check ddl history, can't have ddl jobs during flashback
• check tiflash node, can't do it with tiflash

• flushback cluster prepare & recover env #37376

• forbid & restart processing new ddl job in queue
• close & recover pd scheduling
• close & recover gc

• Execution
  • flashback cluster gets key ranges #37540
  • call client-go interface to send request #37665
• Support flashback table/databases
  • Parser supports flashback table and flashback database #38545
  • support execute flashback table/database with TiKV #38673
• Others

• show/get flashback cluster progress state from TiKV
• Refetch statistics from TiKV
• forbiden cancel flashback job in some states.
• Reset Auto ID (optional)
• Add flashback to telemetry #38896

• add gc_savepoint (optional)

• add a system table gc_savepoint
• support auto set savepoint by TiDB itself
• add a map according to natural physical time (Unix timestamp) -> TSO to avoid TSO drifts

• support flashback with ddl history #40026

Client-go

• Support 'flashback' request

• TiDB provide key range and tso to client-go, then client-go sending requests to all Region leaders in the key range (Could reuse some mechanism in client-go now, like backoff/coprocessor etc.)
• Forbid read/write request to specified region during flashback cluster
• Need an interface to get progress of flashback cluster

TiKV

• Tracking Issue for Flashback tikv/tikv#13303

PD

• Add an interface to add/delete gc_savepoint (optional)