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Introductie van Micorosoft SQL Server 2016

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89 C H A P T E R 5 | Broader data access PolyBase services, but a server reboot is necessary before you can create PolyBase data objects, as we describe later in this chapter. If you are using Hadoop, you can optionally perform these additional steps: 1. Enable pushdown computations to your Hadoop cluster by copying the value of the yarn.application.classpath configuration key from the yarn-site.xml file in the Hadoop configuration directory and pasting it into the yarn.application.classpath property in the yarn_site.xml file in the \Program Files\Microsoft SQL Server\\Binn\Polybase\Hadoop\conf directory. 2. Configure Kerberos authentication to your Hadoop cluster by copying configuration key values from Hadoop configuration files into the value properties of the corresponding files in the \Program Files\Microsoft SQL Server\\Binn\Polybase\Hadoop\conf directory, as shown in the following table: Configuration file Configuration key Description core-site.xml polybase.kerberos.kdchost KDC host name polybase.kerberos.realm Kerberos realm Authentication configuration, such as kerberos hdfs-site.xml dfs.namenode.kerberos.principal Name node security principal, such as hdfs/_HOST@YOUR-REALM.COM mapred-site.xml mapreduce.jobhistory.address Job history server IPC host:port, such as mapreduce.jobhistory.principal Kerberos principal name for the job history server, such as mapred/_HOST@YOUR- REALM.COM yarn-site.xml yarn.resourcemanager.principal Yarn resource manager principal name, such as yarn/_HOST@YOUR-REALM.COM Scaling out with PolyBase Because data sets can become quite large in Hadoop or blob storage, you can create a PolyBase scale-out group, as shown in Figure 5-9, to improve performance. A PolyBase scale-out group has one head node and one or more compute nodes. The head node consists of the SQL Server database engine, the PolyBase engine service, and the PolyBase data movement service, whereas each compute node consists of a database engine and data movement service. The head node receives the PolyBase queries, distributes the work involving external tables to the data movement service on the available compute nodes, receives the results from each compute node, finalizes the results in the database engine, and then returns the results to the requesting client. The data movement service on the head node and compute nodes is responsible for transferring data between the external data sources and SQL Server and between the SQL Server instances on the head and compute nodes.

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