reference/configuration: add description about TiDB txn-total-size-li…

…mit (#2002) (#2181)

Co-authored-by: tiancaiamao <tiancaiamao@gmail.com>

reference/configuration/tidb-server/configuration-file.md

@@ -255,6 +255,12 @@ Configuration items related to performance.
 - Default value: `5000`
 - If a transaction does not roll back or commit after the number of statements exceeds `stmt-count-limit`, TiDB returns the `statement count 5001 exceeds the transaction limitation, autocommit = false` error. This configuration takes effect **only** in the retriable optimistic transaction. If you use the pessimistic transaction or have disabled the transaction retry, the number of statements in a transaction is not limited by this configuration.
 
+### `txn-total-size-limit`
+
+- The size limit of a transaction.
+- Default value: `104857600`
+- The total size of all key-value entries in bytes should be less than this value. Note that if the `binlog` is enabled, this value should be less than `104857600` (which means 100MB), because of the limitation of the binlog component. If `binlog` is not enabled, the maximum value of this configuration is `10737418240` (which means 10GB).
+
 ### `tcp-keep-alive`
 
 - Determines whether to enable `keepalive` in the TCP layer.