diff --git a/doc/install-guide/source/environment-sql-database.rst b/doc/install-guide/source/environment-sql-database.rst
index 6322ca5061..cbdfd5424e 100644
--- a/doc/install-guide/source/environment-sql-database.rst
+++ b/doc/install-guide/source/environment-sql-database.rst
@@ -7,6 +7,15 @@ guide use MariaDB or MySQL depending on the distribution. OpenStack
 services also support other SQL databases including
 `PostgreSQL <https://www.postgresql.org/>`__.
 
+.. note::
+
+   If you see ``Too many connections`` or ``Too many open files``
+   error log messages on OpenStack services, verify that maximum number of
+   connection settings are well applied to your environment.
+   In MariaDB, you may also need to change
+   `open_files_limit <https://mariadb.com/kb/en/library/server-system-variables/#open_files_limit>`__
+   configuration.
+
 .. toctree::
    :glob: