add more docs in the fetchSize doc

Signed-off-by: Yang Keao <[email protected]>

Author: YangKeao

best-practices/java-app-best-practices.md

@@ -74,6 +74,10 @@ Usually, there are two kinds of processing methods in JDBC:
 
 TiDB supports both methods, but it is preferred that you use the first method, because it is a simpler implementation and has a better execution efficiency.
 
+For the second method, TiDB will load all data to the TiDB node at first and then return them to the client according to the fetch size. Therefore, it'll usually use more memory than the first choice and may spill the data to the temporary storage if [`tidb_enable_tmp_storage_on_oom`](/system-variables.md#tidb_enable_tmp_storage_on_oom) is `ON`.
+
+If the system variable [`tidb_enable_lazy_cursor_fetch`](/system-variables.md#tidb_enable_lazy_cursor_fetch) is `ON`, TiDB will try to only fetch the data when the client fetches it, and use less memory. For detail and limitations, read the description of the variable [`tidb_enable_lazy_cursor_fetch`](/system-variables.md#tidb_enable_lazy_cursor_fetch).
+
 ### MySQL JDBC parameters
 
 JDBC usually provides implementation-related configurations in the form of JDBC URL parameters. This section introduces [MySQL Connector/J's parameter configurations](https://dev.mysql.com/doc/connector-j/en/connector-j-reference-configuration-properties.html) (If you use MariaDB, see [MariaDB's parameter configurations](https://mariadb.com/kb/en/library/about-mariadb-connector-j/#optional-url-parameters)). Because this document cannot cover all configuration items, it mainly focuses on several parameters that might affect performance.

develop/dev-guide-connection-parameters.md

@@ -155,6 +155,10 @@ Usually, there are two kinds of processing methods in JDBC:
 
 TiDB supports both methods, but it is preferred that you use the first method, because it is a simpler implementation and has a better execution efficiency.
 
+For the second method, TiDB will load all data to the TiDB node at first and then return them to the client according to the fetch size. Therefore, it'll usually use more memory than the first choice and may spill the data to the temporary storage if [`tidb_enable_tmp_storage_on_oom`](/system-variables.md#tidb_enable_tmp_storage_on_oom) is `ON`.
+
+If the system variable [`tidb_enable_lazy_cursor_fetch`](/system-variables.md#tidb_enable_lazy_cursor_fetch) is `ON`, TiDB will try to only fetch the data when the client fetches it, and use less memory. For detail and limitations, read the description of the variable [`tidb_enable_lazy_cursor_fetch`](/system-variables.md#tidb_enable_lazy_cursor_fetch).
+
 ### MySQL JDBC parameters
 
 JDBC usually provides implementation-related configurations in the form of JDBC URL parameters. This section introduces [MySQL Connector/J's parameter configurations](https://dev.mysql.com/doc/connector-j/en/connector-j-reference-configuration-properties.html) (If you use MariaDB, see [MariaDB's parameter configurations](https://mariadb.com/kb/en/library/about-mariadb-connector-j/#optional-url-parameters)). Because this document cannot cover all configuration items, it mainly focuses on several parameters that might affect performance.

system-variables.md

@@ -2138,7 +2138,7 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
 - Possible values: `OFF`, `ON`
 - This variable controls whether to support creating `Global indexes` for partitioned tables. `Global index` is currently in the development stage. **It is not recommended to modify the value of this system variable**.
 
-### `tidb_enable_lazy_cursor_fetch` <span class="version-mark">New in v8.3.0</span>
+### tidb_enable_lazy_cursor_fetch <span class="version-mark">New in v8.3.0</span>
 
 > **Warning:**
 >