fix GC desc

Signed-off-by: y_static_y@sina.com <y_static_y@sina.com>

docs/design/2022-12-06-Keyspace.md

@@ -74,7 +74,11 @@ If "keyspace-name" is set when executing the Lightning command, it will encode k
    - Indicates that the keyspace will advance its own GC safe point.
    - Keyspace GC-related data: min start ts, GC safe point, service safe point, stored in own etcd path of each keyspace in PD.
 
-Previously there was only one GCWorker leader for GC in the whole PD & TiKV cluster. After supporting keyspace level GC, for keyspace, the default GC management type is global GC. Or you can specify the GC management type as `global_gc` or `keyspace_level_gc` via keyspace meta's config `gc_management_type`. In keyspace level GC each keyspace has its own GCWorker leader that can separately advance its own GC safe point, safe point information stored in PD, It is also isolated by keyspace prefix, and only cleans the data below its keyspace range, without affecting each other.
+Previously there was only one GCWorker leader for GC in the whole PD & TiKV cluster. After supporting keyspace level GC, for keyspace, the default GC management type is global GC. Or you can specify the GC management type as `global_gc` or `keyspace_level_gc` via keyspace meta's config `gc_management_type`. 
+
+When a specified keyspace uses the global gc: This keyspace will have its own GCworker leader, but this GCworker leader is not responsible for calculating GC safe point and resolve locks. This keyspace will rely on the GC safe point produced by the GCworker leader of TiDB with no keyspace set in the cluster for GC, and use its own GCworker leader for delete range.
+
+When a specified keyspace uses the keyspace level GC: This keyspace will have its own GCworker leader and compute its own GC safe point, resolve locks, and delete ranges. The keyspace level safe point information stored in PD, It is also isolated by keyspace prefix, and only GC the data below its keyspace range, without affecting other keyspaces.
 
 ### TiKV