This section documents the additional database configuration changes necessary to correctly use Microsoft SQL Server or Microsoft Azure SQL databases with the Camunda Platform. It provides guides on:

• How to set the correct database transaction isolation level.
• How different Microsoft SQL Server versions are supported in Azure SQL.
• How Camunda supports Azure SQL.
• How to configure a database on Azure SQL to be supported by Camunda.

To use these guides, you should have a basic understanding of (Microsoft’s) T-SQL syntax. You should also have access to a database administration tool that can interact with your Microsoft database.

Transaction Isolation Levels

This section applies to the following database types:

• Microsoft SQL Server
• Microsoft Azure SQL

Microsoft SQL Server and Azure SQL implement the READ_COMMITTED isolation level different than most databases and do not interact well with the process engine’s optimistic locking scheme. As a result you may suffer deadlocks when putting the process engine under high load.

If you experience deadlocks in your MSSQL installation, you must execute the following statements in order to enable SNAPSHOT isolation:

ALTER DATABASE [process-engine]
SET ALLOW_SNAPSHOT_ISOLATION ON

ALTER DATABASE [process-engine]
SET READ_COMMITTED_SNAPSHOT ON

where [process-engine] contains the name of your database.

Camunda support for Azure SQL

This section applies only to the following Microsoft database products:

• Azure SQL Managed Instance
• Azure SQL Database

The SQL Server database engine has a Database Compatibility Level setting that provides backward compatibility with earlier versions of SQL Server. This backward compatibility covers Transact-SQL and query optimization behaviors, and can be applied per database.

Microsoft’s Azure SQL Managed Instance and Azure SQL Database products always use the latest stable version of the SQL Server database engine. In order to provide backward compatibility with earlier SQL Server versions, the Azure SQL products utilize the Database Compatibility Level setting.

Azure SQL compatibility levels supported by Camunda

Microsoft associates each SQL Server version with a Database Compatibility Level. You can find a table of the SQL Server versions, and their associated compatibility level values at the Microsoft Alter Compatibility Level page.

Camunda supports the Database Compatibility Level values of the currently supported Microsoft SQL Server versions documented in our Supported Database Products section.

Configuring a database on Azure SQL

It is advised to explicitly set the Database Compatibility Level setting for each database created on Azure SQL. The default value of the Database Compatibility Level setting is updated every time a new SQL Server version is released. If a Database Compatibility Level value isn’t explicitly set on a database, the default value will be used. Using the default value may lead to unexpected behavior, or behavior unsupported by Camunda.

To set the Database Compatibility Level to a specific value, execute the following code:

ALTER DATABASE [database_name]
SET COMPATIBILITY_LEVEL = [compatibility_level]

In the code above, [database_name] should be replaced with the name of your database, and [compatibility_level] should be replaced with the Database Compatibility Level value of the SQL Server version you would like to use. You can see a list of all the available values at the Microsoft Alter Compatibility Level page.