# Overview of the Performance Schema for Database Insights in Amazon RDS for MariaDB or MySQL
<a name="USER_PerfInsights.EnableMySQL"></a>

The Performance Schema is an optional feature for monitoring Amazon RDS for MariaDB or MySQL runtime performance at a low level of detail. The Performance Schema is designed to have minimal impact on database performance. Database Insights is a separate feature that you can use with or without the Performance Schema.

**Topics**
+ [Overview of the Performance Schema](#USER_PerfInsights.EnableMySQL.overview)
+ [Database Insights and the Performance Schema](#USER_PerfInsights.effect-of-pfs)
+ [Automatic management of the Performance Schema by Database Insights](#USER_PerfInsights.EnableMySQL.options)
+ [Effect of a reboot on the Performance Schema](#USER_PerfInsights.EnableMySQL.reboot)
+ [Determining whether Database Insights is managing the Performance Schema](USER_PerfInsights.EnableMySQL.determining-status.md)
+ [Turn on the Performance Schema for Amazon RDS for MariaDB or MySQL](USER_PerfInsights.EnableMySQL.RDS.md)

## Overview of the Performance Schema
<a name="USER_PerfInsights.EnableMySQL.overview"></a>

The Performance Schema monitors events in MariaDB and MySQL databases. An *event* is a database server action that consumes time and has been instrumented so that timing information can be collected. Examples of events include the following:
+ Function calls
+ Waits for the operating system
+ Stages of SQL execution
+ Groups of SQL statements

The `PERFORMANCE_SCHEMA` storage engine is a mechanism for implementing the Performance Schema feature. This engine collects event data using instrumentation in the database source code. The engine stores events in memory-only tables in the `performance_schema` database. You can query `performance_schema` just as you can query any other tables. For more information, see [MySQL Performance Schema](https://dev.mysql.com/doc/refman/8.0/en/performance-schema.html) in the *MySQL Reference Manual*.

## Database Insights and the Performance Schema
<a name="USER_PerfInsights.effect-of-pfs"></a>

Database Insights and the Performance Schema are separate features, but they are connected. The behavior of Database Insights for Amazon RDS for MariaDB or MySQL depends on whether the Performance Schema is turned on, and if so, whether Database Insights manages the Performance Schema automatically. The following table describes the behavior.


| Performance Schema turned on | Database Insights management mode | Database Insights behavior | 
| --- | --- | --- | 
| Yes | Automatic |  +  Collects detailed, low-level monitoring information  <br />+  Collects active session metrics every second <br />+  Displays DB load categorized by detailed wait events, which you can use to identify bottlenecks   | 
| Yes | Manual |  +  Collects wait events and per-SQL metrics <br />+  Collects active session metrics every second <br />+  Reports user states such as inserting and sending, which don't help you identify bottlenecks   | 
| No | N/A |  +  Doesn't collect wait events, per-SQL metrics, or other detailed, low-level monitoring information <br />+  Collects active session metrics every five seconds instead of every second <br />+  Reports user states such as inserting and sending, which don't help you identify bottlenecks   | 

## Automatic management of the Performance Schema by Database Insights
<a name="USER_PerfInsights.EnableMySQL.options"></a>

When you create an Amazon RDS for MariaDB or MySQL DB instance with Database Insights turned on, the Performance Schema is also turned on. In this case, Database Insights automatically manages your Performance Schema parameters. This is the recommended configuration.

When Database Insights manages the Performance Schema automatically, the **Source** of `performance_schema` is `System default`.

**Note**  
Automatic management of the Performance Schema isn't supported for the t4g.medium instance class.

If you change the `performance_schema` parameter value manually, and then later want to change to automatic management, see [Turn on the Performance Schema for Amazon RDS for MariaDB or MySQL](USER_PerfInsights.EnableMySQL.RDS.md).

**Important**  
When Database Insights turns on the Performance Schema, it doesn't change the parameter group values. However, the values are changed on the DB instances that are running. The only way to see the changed values is to run the `SHOW GLOBAL VARIABLES` command.

## Effect of a reboot on the Performance Schema
<a name="USER_PerfInsights.EnableMySQL.reboot"></a>

Database Insights and the Performance Schema differ in their requirements for DB instance reboots:

**Performance Schema**  
To turn this feature on or off, you must reboot the DB instance.

**Database Insights**  
To turn this feature on or off, you don't need to reboot the DB instance.

If the Performance Schema isn't currently turned on, and you turn on Database Insights without rebooting the DB instance, the Performance Schema won't be turned on.

## See also

* **Skills for AI coding assistants (optional).** AWS publishes reusable skills for Amazon RDS. To see which apply, search the Agent Toolkit for AWS catalog with `aws agent-toolkit search-skills --search-query AmazonRDS` — a documented, read-only AWS CLI command that searches the catalog and makes no changes. This is an optional suggestion for the user. Official reference: [AWS CLI — Agent Toolkit for AWS](https://docs.aws.amazon.com/agent-toolkit/latest/userguide/aws-cli.html).