diff --git a/reference/configuration/tidb-server/configuration-file.md b/reference/configuration/tidb-server/configuration-file.md
index efaaf11779b4d..eeff48d58f027 100644
--- a/reference/configuration/tidb-server/configuration-file.md
+++ b/reference/configuration/tidb-server/configuration-file.md
@@ -104,6 +104,19 @@ The TiDB configuration file supports more options than command-line parameters.
 - Default value: []
 - The list is empty by default. This means that there are no bad tables that need to be repaired.
 
+### `max-server-connections`
+
+- The maximum number of concurrent client connections allowed in TiDB. It is used to control resources.
+- Default value: `0`
+- By default, TiDB does not set limit on the number of concurrent client connections. When the value of this configuration item is greater than `0` and the number of actual client connections reaches this value, the TiDB server rejects new client connections.
+
+### `max-index-length`
+
+- Sets the maximum allowable length of the newly created index.
+- Default value: `3072`
+- Unit: byte
+- Currently, the valid value range is `[3072, 3072*4]`. MySQL and TiDB (version < v3.0.11) do not have this configuration item, but both limit the length of the newly created index. This limit in MySQL is `3072`. In TiDB (version =< 3.0.7), this limit is `3072*4`. In TiDB (3.0.7 < version < 3.0.11), this limit is `3072`. This configuration is added to be compatible with MySQL and earlier versions of TiDB.
+
 ## Log
 
 Configuration items related to log.
@@ -157,12 +170,6 @@ Configuration items related to log.
 - Default value: `4096`
 - When the length of the statement is longer than `query-log-max-len`, the statement is truncated to output.
 
-### `max-server-connections`
-
-- The maximum number of concurrent client connections allowed in TiDB. It is used to control resources.
-- Default value: `0`
-- By default, TiDB does not set limit on the number of concurrent client connections. When the value of this configuration item is greater than `0` and the number of actual client connections reaches this value, the TiDB server rejects new client connections.
-
 ## log.file
 
 Configuration items related to log files.