Configuring Parallel Queries in Tableau Server

Published: 01 Mar 2017
Last Modified Date: 11 Apr 2018


How to configure parallel queries in Tableau Server.


Tableau Server 


You can set parallel query limits for Tableau Server either with tabadmin set 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

Setting Limits with tabadmin set Commands 

The format for setting parallel query limits using tabadmin set is:

tabadmin set native_api.connection.limit.<connection class> <n>

For example, to set a global limit:

tabadmin set native_api.connection.globallimit 8

Or to set a limit on a specific type of data source:

tabadmin set native_api.connection.limit.sqlserver 5

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

tabadmin set native_api.federated_evaluator_degree_of_parallelism 4

For a list of connection class strings, see “Class Strings,” below.

Setting Limits with a connection-configs.xml File 

A connection-configs.xml file is created by you and saved in the vizqlserver folder in the config directory (e.g. C:\ProgramData\Tableau\TableauServer\data\tabsvc\config\vizqlserver). You must copy this configuration file to all the vizqlserver configuration directories in all worker machines.

See the sample connection-configs.xml file at the end of this article.

Setting a global limit: 

A <connection> tag with no information about data source type, server, or database defines the maximum number of queries for all connections not covered by any other, more specific, connection specification. For example:

      <limit max='8'>

This value overrides the default parallel query limit. For the vizqlserver process, the default limit is 16; for the dataserver process, the default limit is 1,000,000.
Note: When connecting to Amazon Redshift, the default limit is 8 for both processes.

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:

classThe data source type. See the “Class Strings” table, below, for the strings to use for all data source types.
serverThe server computer.
dbnameThe database name.
schemaThis setting can be useful with Teradata data sources.

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'>

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 max='12'>

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 max='12' process='dataserver'>
This example will result in the same behavior as the previous example, but this time dataserver is explicitly specified. 

f 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.

Additional Information

Using tabadmin set commands is the simplest method for setting limits. When using tabadmin set commands, it is not necessary to copy the configuration file to all the worker computers. However,  you cannot set limits at the finer levels of granularity (for example, per server or per schema) that you can with a connection-configs.xml file. 

Example connection-configs.xml File

<?xml version='1.0' encoding='utf-8' ?>
   <connection class='sqlserver' dbname='SalesDB' server='SQLserver10'>
      <limit max='10'>
   <connection class='mysql' dbname='Inventory' server='MySQL_Public'>
      <limit max='10'>
   <connection class='teradata' schema='TravelData' server='TeradataProduction2'>
      <limit max='12'>
   <connection class='sqlserver'>
      <limit max='4'>
   <connection class='mysql'>
      <limit max='6'process='vizqlserver'>
      <limit max='10' process='dataserver'>
   <connection class='teradata'>
      <limit max='10'>
      <limit max='8'>

Class Strings

Use the following strings to identify data source types in connection-configs.xml.


Data SourceString
Actian Vectorwise"vectorwise"
Amazon EMR"awshadoophive"
Amazon Redshift“redshift”
Aster Database"asterncluster"
Cloudera Hadoop"hadoophive"
Extracts created from cube data sourcesNot configurable.
DataStax Enterprise"datastax"
Generic ODBC"genericodbc"
Google Analytics"google-analytics"
Google BigQuery"bigquery"
Hortonworks Hadooop Hive"hortonworkshadoophive"
HP Vertica“vertica”
IBM BigInsights“bigsql”
IBM DB2"db2"
JavaScript Connector"jsconnector"
MapR Hadoop Hive"maprhadoophive"
Microsoft Access"msaccess”
Microsoft Analysis Services"msolap"
Microsoft ExcelNot configurable.
Microsoft PowerPivot"powerpivot"
Microsoft SQL Server"sqlserver"
IBM Netezza"netezza"
Oracle Essbase“essbase”
Pivotal Greenplum"greenplum"
Progress OpenEdge"progressopenedge"
SAP HANA"saphana"
SAP Netweaver Business Warehouse"sapbw"
SAP Sybase ASE"sybasease"
SAP Sybase IQ"sybaseiq"
Spark SQL"spark"
Statistical FileNot configurable.
Tableau Data Extract"dataengine"
Text file“csv”
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