TiFlash can not prevent data being removed after FLASHBACK DATABASE

[JaySon-Huang]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Found by manual check.

tidb support FLASHBACK DATABASE DBName [TO newDBName] since v6.4.0 https://docs.pingcap.com/tidb/stable/sql-statement-flashback-database
However, tiflash did not notice that. And if a database is recovered by FLASHBACK DATABASE, tiflash can not prevent the data from being removed after gc-safepoint passed the previous DROP DATABASE is executed.

tidb issue: pingcap/tidb#20463

2. What did you expect to see? (Required)

The data in TiFlash remain not removed after FLASHBACK DATABASE is executed even when gc-safepoint exceed

3. What did you see instead (Required)

The data in TiFlash is lost

4. What is your TiFlash version? (Required)

master, 7.5, 7.1, 6.5

[JaySon-Huang]

known issue on release-6.5/release-7.1:

FLASHBACK DATABASE after the fixed versions on release-6.5/release-7.1 can not handle some corner cases, for example:

mysql> alter table d1.t3 add column b int;
mysql> insert into d1.t3 values(2,2);
mysql> alter table d1.t4 add column b int;
-- drop immediately after adding new columns
mysql> drop database d1;
mysql> flashback database d1 to d1_new

after flashback, it maybe not able to read t3/t4 because the add column DDLs are not able to be handled on tiflash
fullstack-test2-logs.tar.gz

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The corner case can be handled properly on the release-7.5 and later