Configuring Parallel Queries in Tableau Server

You can set parallel query limits either with tabadmin/tsm commands or with a connection-configs.xml file. Once you configure Tableau Server for parallel queries, the feature is on automatically.

You can specify any and all of the following:

A global limit on the number of parallel queries for Tableau Server

Limits for a particular data source type, such as SQL Server

Limits for a particular data source type on a specific server

Limits for a particular data source type, on a specific server, when connecting to a specific database

Limits for how many data sources can be queried simultaneously in a cross-database join

• Set Limits in Tableau Server 2018.2 and later for Windows and Tableau Server for Linux (tsm)
• Setting Limits with a connection-configs.xml File 
• Setting a global Limit
• Set Additional Limits 

Set Limits in Tableau Server 2018.2 and later for Windows and Tableau Server for Linux (tsm)

The format for setting parallel query limits using tsm configuration set is:

tsm configuration set -k native_api.connection.limit.<connection class> -v <n>

For example, to set a global limit:

tsm configuration set -k native_api.connection.globallimit -v 8

To set a limit on a specific type of data source:

tsm configuration set -k native_api.connection.limit.sqlserver -v 5

To limit the parallel queries for a cross-database join:

tsm configuration set -k native_api.federated_evaluator_degree_of_parallelism -v 4

For a list of connection class strings, see “Class Strings", in Additional Information below.

Set Additional Limits 

Connection settings in connection-configs.xml can work at different levels of specificity. When establishing a connection, Tableau parses the file from top to bottom, so if there is more than one entry that would apply to a given connection, the entry nearest the top of the file is used.

For this reason, it is also appropriate to order connection specifications from most specific to least specific.

Additional (non-global) limits are set in a <connection-list> section at the top of the connection-configs.xml file.

The parameters you can use in a <connection> tag are:

You can specify parameters in any order and any combination—for example, you could specify a server and a dbname without specifying a class or schema.

Limits for Specific Server Processes 

You can also set limits on a per-connection basis for the vizql server and dataserver processes in Tableau Server, limiting how many simultaneous connections these processes can create. 

You specify process limits by adding a process attribute within the <limit> element. 

To set a connection limit for one of the processes, create a connection configuration like this:

<connection class='sqlserver'>

<limit max='6' process='vizqlserver'>

</limit>

</connection>

The above setting limits the vizqlserver process to six simultaneous connections. Because no limit is specified for the dataserver process, the connection limit is determined by the global limit.

Alternately, you could create a connection element like this:

 <connection class='sqlserver'>

<limit max='6' process='vizqlserver'>

</limit>

<limit max='12'>

</limit>

</connection>

As before, the vizqlserver process is limited to six simultaneous connections. But the dataserver process now uses the connection-specific limit for this connection class (12), rather than the global limit. When no process attribute is specified for a <limit> element, that limit applies to any server processes not specified above it within the connection element.

Finally, you can set separate specific limits for each process:

 <connection class='sqlserver'>

<limit max='6' process='vizqlserver'>

</limit>

<limit max='12' process='dataserver'>

</limit>

</connection>

The below example will result in the same behavior as the previous example, but this time dataserver is explicitly specified. 

If you want to set a limit for both server processes in a connection, you can either explicitly list them both (with a comma delimiter) in a single <limit> element, or just use a <limit> element with no processes specified. Thus, the following two limit elements are equivalent:

<limit max='10' process='dataserver, vizqlserver'>
<limit max='10'>
Note: These process limits are only relevant for configuring parallel queries on Tableau Server. If you use a connection-configs.xml file that contains process limits with Tableau Desktop, any <limit> element that specifies limits for either or both processes is ignored.