DXF: add a limitation that adding indexes to columns of TIMESTAMP data type via the DXF is not supported

mysql-schema.md

@@ -99,7 +99,6 @@ Currently, the `help_topic` is NULL.
 - `GLOBAL_VARIABLES`: global system variable table
 - `expr_pushdown_blacklist`: the blocklist for expression pushdown
 - `opt_rule_blacklist`: the blocklist for logical optimization rules
-- `table_cache_meta`: the metadata of cached tables
 - `tidb_import_jobs`: the job information of [`IMPORT INTO`](/sql-statements/sql-statement-import-into.md)
 - `tidb_timers`: the metadata of internal timers
 

tidb-distributed-execution-framework.md

@@ -69,7 +69,8 @@ Currently, for TiDB Self-Hosted, the DXF supports the distributed execution of t
 
 ## Limitation
 
-The DXF can only schedule the distributed execution of one `ADD INDEX` task at a time. If a new `ADD INDEX` task is submitted before the current `ADD INDEX` distributed task has finished, the new task is executed through a transaction.
+- The DXF can only schedule the distributed execution of one `ADD INDEX` task at a time. If a new `ADD INDEX` task is submitted before the current `ADD INDEX` distributed task has finished, the new task is executed through a transaction.
+- Creating indexes on columns with the TIMESTAMP data type through the DXF is not supported, because it might lead to inconsistency between the index and the data.
 
 ## Prerequisites