update description about SPM and SQL Bind (pingcap#5541)

Author: Liuxiaozhen12

sql-plan-management.md

@@ -230,7 +230,7 @@ The default value of `tidb_evolve_plan_baselines` is `off`.
 >
 > The feature baseline evolution is not generally available for now. It is **NOT RECOMMENDED** to use it in the production environment.
 
-After the automatic binding evolution feature is enabled, if the optimal execution plan selected by the optimizer is not among the binding execution plans, the optimizer marks the plan as an execution plan that waits for verification. At every `bind-info-lease` (the default value is `3s`) interval, an execution plan to be verified is selected and compared with the binding execution plan that has the least cost in terms of the actual execution time. If the plan to be verified has shorter execution time, this plan is marked as a usable binding. The following example describes the process above.
+After the automatic binding evolution feature is enabled, if the optimal execution plan selected by the optimizer is not among the binding execution plans, the optimizer marks the plan as an execution plan that waits for verification. At every `bind-info-lease` (the default value is `3s`) interval, an execution plan to be verified is selected and compared with the binding execution plan that has the least cost in terms of the actual execution time. If the plan to be verified has shorter execution time (the current criterion for the comparison is that the execution time of the plan to be verified is no longer than 2/3 that of the binding execution plan), this plan is marked as a usable binding. The following example describes the process above.
 
 Assume that table `t` is defined as follows:
 
@@ -264,7 +264,7 @@ The binding evolution can address this kind of issues. When the optimizer recogn
 
 To reduce the impact that the automatic evolution has on clusters, use the following configurations:
 
-- Set `tidb_evolve_plan_task_max_time` to limit the maximum execution time of each execution plan. The default value is `600s`.
+- Set `tidb_evolve_plan_task_max_time` to limit the maximum execution time of each execution plan. The default value is `600s`. In the actual verification process, the maximum execution time is also limited to no more than twice the time of the verified execution plan.
 - Set `tidb_evolve_plan_task_start_time` (`00:00 +0000` by default) and `tidb_evolve_plan_task_end_time` (`23:59 +0000` by default) to limit the time window.
 
 ### Notes

sql-statements/sql-statement-create-binding.md

@@ -16,13 +16,13 @@ The bound SQL statement is parameterized and stored in the system table. When a
 
 ```ebnf+diagram
 CreateBindingStmt ::=
-    'CREATE' GlobalScope 'BINDING' 'FOR' SelectStmt 'USING' SelectStmt
+    'CREATE' GlobalScope 'BINDING' 'FOR' BindableStmt 'USING' BindableStmt
 
 GlobalScope ::=
     ( 'GLOBAL' | 'SESSION' )?
 
-SelectStmt ::=
-    ( SelectStmtBasic | SelectStmtFromDualTable | SelectStmtFromTable ) OrderByOptional SelectStmtLimit SelectLockOpt SelectStmtIntoOption
+BindableStmt ::=
+    ( SelectStmt | UpdateStmt | InsertIntoStmt | ReplaceIntoStmt | DeleteStmt )
 ```
 
 ****

sql-statements/sql-statement-drop-binding.md

@@ -14,13 +14,13 @@ A `BINDING` can be on either a `GLOBAL` or `SESSION` basis. The default is `SESS
 
 ```ebnf+diagram
 DropBindingStmt ::=
-    'DROP' GlobalScope 'BINDING' 'FOR' SelectStmt ( 'USING' SelectStmt )?
+    'DROP' GlobalScope 'BINDING' 'FOR' BindableStmt ( 'USING' BindableStmt )?
 
 GlobalScope ::=
     ( 'GLOBAL' | 'SESSION' )?
 
-SelectStmt ::=
-    ( SelectStmtBasic | SelectStmtFromDualTable | SelectStmtFromTable ) OrderByOptional SelectStmtLimit SelectLockOpt SelectStmtIntoOption
+BindableStmt ::=
+    ( SelectStmt | UpdateStmt | InsertIntoStmt | ReplaceIntoStmt | DeleteStmt )
 ```
 
 ## Syntax description
@@ -140,4 +140,4 @@ This statement is a TiDB extension to MySQL syntax.
 * [SHOW [GLOBAL|SESSION] BINDINGS](/sql-statements/sql-statement-show-bindings.md)
 * [ANALYZE TABLE](/sql-statements/sql-statement-analyze-table.md)
 * [Optimizer Hints](/optimizer-hints.md)
-* [SQL Plan Management](/sql-plan-management.md)
+* [SQL Plan Management](/sql-plan-management.md)