Mysql connection limit how to#

While theoretically, a database like SQL Server allows you to open 32,767 connections, in practice, a system resource bottleneck will emerge at a much lower value.

Mysql connection limit how to#

How to increase the maximum number of database connections If the maximum number of connections is set too high, as it’s the case with many default settings, then you risk oversubscribing connection requests that starve DB resources, as explained in this very good video presentation. That value should be used then as the maximum number of connections that can be shared by all application nodes that connect to the database. Therefore, only a performance load test will provide you with the maximum number of connections that can deliver the best throughput on your particular system. So, in reality, the maximum number of connections a given database system provides is determined by the underlying hardware resources (e.g., CPU, IO, memory), optimizer capabilities, and the load that’s incurred by the SQL statements sent by clients.īy default, the maximum number of connection connections is set way too high, risking resource starvation on the database side. That’s why a much better formula is the Universal Scalability Law, which provides the relationship between throughput and the number of concurrent connections, which tells us that after reaching the maximum throughput, adding more connections will lower the throughput since the system will have to spend resources to coordinate all the concurrent connections. If you read the amazing Java Concurrency in Practice, then you are familiar with Amdahl’s law that gives the relationship between the maximum number of connections and the ability of the execution plans to parallelize, but this is just half the story.Īmdahl’s law only tells us that a system with limited resources can reach its maximum throughput, but it doesn’t take into consideration the cost of adding more connections.

In reality, even without setting a hard limit on the maximum number of connections, there will always be a maximum number of connections that provides the maximum throughput. What limits the maximum number of connections? MySQL also provides a max_connections setting to control the maximum number of concurrent connections, and the default value is 151. PostgreSQL provides a max_connections setting that has a default value of 100.īecause database connections in PostgreSQL run on individual OS processes, you don’t want to set the max_connections to a very high value, as that will hurt the throughput of your database system. Because user connections is a dynamic (self-configuring) option, SQL Server adjusts the maximum number of user connections automatically as needed, up to the maximum value allowable. SQL Server allows a maximum of 32,767 user connections. SQL ServerĪccording to the SQL Server documentation: However, as we will soon see, using 1500 concurrent connections on my current notebook would be a terrible idea since, in reality, the maximum connection count is relative to the underlying system resources, and such a high concurrency value would easily saturate the very limited resources of my notebook. The processes record shows that my current Oracle database has a hard limit of 1000 OS processes that can connect to it, and the sessions row tells us that this particular Oracle XE database supports a maximum number of 1528 concurrent connections. | RESOURCE_NAME | CURRENT_UTILIZATION | MAX_UTILIZATION | INITIAL_ALLOCATION | LIMIT_VALUE | In our case, we are interested in the processes and sessions resources, so we can use the following query to gather this info:Īnd when running this SQL query on my local Oracle XE database, I get the following result:

If you’re using Oracle, you can use the V$RESOURCE_LIMIT view to inspect the maximum limits for various system resources, as well as the current allocation numbers. In this article, we are going to see what limits the number of database connections, no matter if you’re using Oracle, SQL Server, PostgreSQL, or MySQL. Have you ever wondered what the maximum number of database connections provided by a given RDBMS is? So, enjoy spending your time on the things you love rather than fixing performance issues in your production system on a Saturday night! Well, Hypersistence Optimizer is that tool!Īnd it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, or Play Framework. Follow having a tool that can automatically detect JPA and Hibernate performance issues.