io/socket/sql/client_connection - Amazon Aurora
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The io/socket/sql/client_connection event occurs when a thread is in the process of handling a new connection.

Supported engine versions

This wait event information is supported for the following engine versions:

  • Aurora MySQL versions 2 and 3


The event io/socket/sql/client_connection indicates that mysqld is busy creating threads to handle incoming new client connections. In this scenario, the processing of servicing new client connection requests slows down while connections wait for the thread to be assigned. For more information, see MySQL server (mysqld).

Likely causes of increased waits

When this event appears more than normal, possibly indicating a performance problem, typical causes include the following:

  • There is a sudden increase in new user connections from the application to your Amazon RDS instance.

  • Your DB instance can't process new connections because the network, CPU, or memory is being throttled.


If io/socket/sql/client_connection dominates database activity, it doesn't necessarily indicate a performance problem. In a database that isn't idle, a wait event is always on top. Act only when performance degrades. We recommend different actions depending on the causes of your wait event.

Identify the problematic sessions and queries

If your DB instance is experiencing a bottleneck, your first task is to find the sessions and queries that cause it. For a useful blog post, see Analyze Amazon Aurora MySQL Workloads with Performance Insights.

To identify sessions and queries causing a bottleneck
  1. Sign in to the Amazon Web Services Management Console and open the Amazon RDS console at

  2. In the navigation pane, choose Performance Insights.

  3. Choose your DB instance.

  4. In Database load, choose Slice by wait.

  5. At the bottom of the page, choose Top SQL.

    The queries at the top of the list are causing the highest load on the database.

Follow best practices for connection management

To manage your connections, consider the following strategies:

Scale up your instance if resources are being throttled

Look for examples of throttling in the following resources:

  • CPU

    Check your Amazon CloudWatch metrics for high CPU usage.

  • Network

    Check for an increase in the value of the CloudWatch metrics network receive throughput and network transmit throughput. If your instance has reached the network bandwidth limit for your instance class, consider scaling up your RDS instance to a higher instance class type. For more information, see Aurora DB instance classes.

  • Freeable memory

    Check for a drop in the CloudWatch metric FreeableMemory. Also, consider turning on Enhanced Monitoring. For more information, see Monitoring OS metrics with Enhanced Monitoring.

Check the top hosts and top users

Use Performance Insights to check the top hosts and top users. For more information, see Analyzing metrics with the Performance Insights dashboard.

Query the performance_schema tables

To get an accurate count of the current and total connections, query the performance_schema tables. With this technique, you identify the source user or host that is responsible for creating a high number of connections. For example, query the performance_schema tables as follows.

SELECT * FROM performance_schema.accounts; SELECT * FROM performance_schema.users; SELECT * FROM performance_schema.hosts;

Check the thread states of your queries

If your performance issue is ongoing, check the thread states of your queries. In the mysql client, issue the following command.

show processlist;

Audit your requests and queries

To check the nature of the requests and queries from user accounts, use AuroraAurora MySQL Advanced Auditing. To learn how to turn on auditing, see Using Advanced Auditing with an Amazon Aurora MySQL DB cluster.

Pool your database connections

Consider using Amazon RDS Proxy for connection management. By using RDS Proxy, you can allow your applications to pool and share database connections to improve their ability to scale. RDS Proxy makes applications more resilient to database failures by automatically connecting to a standby DB instance while preserving application connections. For more information, see Using Amazon RDS Proxy for Aurora.