[#963] added note about MySQL performance tweak

diff --git a/doc/sphinx/arm/admin.rst b/doc/sphinx/arm/admin.rst
index f584381b373660de4fc5178edb83948c84b1be46..8957d69f211312d343bb53a19a7d794afe8d3b5f 100644 (file)
--- a/doc/sphinx/arm/admin.rst
+++ b/doc/sphinx/arm/admin.rst
@@ -340,6 +340,27 @@ earlier version. To perform an upgrade, issue the following command:
     According to the naming of collations when the name finishes by ``_ci``
     the collation is case-insensitive.
 
+.. _mysql-performance:
+
+Simple MySQL tweak to gain performance
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Changing MySQL internal value ``innodb_flush_log_at_trx_commit`` from default value
+``1`` to ``2`` can result with huge gain in Kea performance. It can be set per session for testing:
+
+.. code-block:: mysql
+    mysql> SET GLOBAL innodb_flush_log_at_trx_commit=2;
+    mysql> SHOW SESSION VARIABLES LIKE 'innodb_flush_log%';
+
+or permanently in ``/etc/mysql/my.cnf``:
+
+.. code-block:: mysql
+    [mysqld]
+    innodb_flush_log_at_trx_commit=2
+
+Be aware that changing this value can result with problems during data recovery
+after crash, we strongly recommend to check `MySQL documentation <https://dev.mysql.com/doc/refman/8.0/en/innodb-parameters.html#sysvar_innodb_flush_log_at_trx_commit>`__.
+
 .. _pgsql-database:
 
 PostgreSQL