CheckGCEnable is use to check whether GC is enable.

DisableGC will disable GC enable variable.

EnableGC will enable GC enable variable.

GetGCSafePoint loads GC safe point time from mysql.tidb.

ValidateSnapshot checks that the newly set snapshot time is after GC safe point time.

ValidateSnapshotWithGCSafePoint checks that the newly set snapshot time is after GC safe point time.