Chapter 5. Configuring Guacamole
A connection to Spark can be customized by setting the values of certain Spark properties. But that can be customized as shown in the example code below.
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Worker Node: A server that is part of the cluster and are available to run Spark jobs. Executor: A sort of virtual machine inside a node. One Node can have multiple Executors. Driver Node: The Node that initiates the Spark session. Typically, this will be the server where sparklyr is located. Spark configuration properties passed by R are just requests - In most cases, the cluster has the final say regarding the resources apportioned to a given Spark session.
Currently, there is no good way to manage user connections to the Spark service centrally. There are some caps and settings that can be applied, but in most cases there are configurations that the R user will need to customize. Cluster administrators and users can benefit from this document. See the Executor Memory Error.
This property is acknowledged by the cluster if spark. Disabling it provides more control over the number of the Executors that can be started, which in turn impact the amount of storage available for the session. For more information, please see the Dynamic Resource Allocation page in the official Spark website. Here is a sample connection:.
Notice that This is because the spark. This means that the server where R is running may not necessarily be the driver for that session. The server will need to have copies of at least two files: yarn-site. Requesting more memory or CPUs for Executors than allowed will return an error. It will return a message similar to this:. Otherwise, changes to those settings are done directly in the yarn-default. For more information visit this site: Apache - Authenticate with kinit. The default behavior in Standalone mode is to create one executor per worker.
So in a 3 worker node cluster, there will be 3 executors setup. If there are any connection errors, a PDOException object will be thrown. Example 2 Handling connection errors. If your application does not catch the exception thrown from the PDO constructor, the default action taken by the zend engine is to terminate the script and display a back trace. This back trace will likely reveal the full database connection details, including the username and password. Upon successful connection to the database, an instance of the PDO class is returned to your script.
The connection remains active for the lifetime of that PDO object. To close the connection, you need to destroy the object by ensuring that all remaining references to it are deleted—you do this by assigning NULL to the variable that holds the object. If you don't do this explicitly, PHP will automatically close the connection when your script ends.
Configuring Spark Connections
Example 3 Closing a connection. Many web applications will benefit from making persistent connections to database servers. Persistent connections are not closed at the end of the script, but are cached and re-used when another script requests a connection using the same credentials. The persistent connection cache allows you to avoid the overhead of establishing a new connection every time a script needs to talk to a database, resulting in a faster web application.
Example 4 Persistent connections. If setting this attribute with PDO::setAttribute after instantiation of the object, the driver will not use persistent connections. The ODBC Connection Pool is shared with other modules in the process; if PDO is told to cache the connection, then that connection would never be returned to the ODBC connection pool, resulting in additional connections being created to service those other modules.
Edit Report a Bug. Connections and Connection management Connections are established by creating instances of the PDO base class. Warning If your application does not catch the exception thrown from the PDO constructor, the default action taken by the zend engine is to terminate the script and display a back trace.
Using PHP 5. As usual PHP never explains some critical stuff in documentation.
And what a surprise! Your connection hangs for another 60 seconds.