![]() This command is often included in a boot script. The command mount -a Ĭauses all filesystems mentioned in fstab (of the proper type and/or having or not having the proper options) to be mounted as indicated, except for those whose line contains the noauto keyword. The file /etc/fstab may contain lines describing what devices are usually mounted where, using which options. The Files /etc/fstab, /etc/mtab And /proc/mounts The customary choice none is less fortunate: the error message " none busy" from umount can be confusing since something is indeed busy. The proc filesystem is not associated with a special device, and when mounting it, an arbitrary keyword such as proc can be used instead of a device specification. The string representation of the UUID should be based on lowercase characters. ![]() The UUIDs from command line or fstab are not converted to internal binary representation. Internally, mount command uses udev symlinks, so using symlinks in /etc/fstab has no advantage over " LABEL=/UUID=". The tags are more readable, robust and portable. ] device| dir mount device| dir umount syntax umount umount -a umount " udev symlinks in the /etc/fstab file. Verify the contents of the relation Upper_case as shown below.Syntax mount mount -a mount. Grunt> Upper_case = FOREACH emp_data GENERATE sample_eval(name) Let us now convert the names of the employees in to upper case using the UDF sample_eval. Grunt> emp_data = LOAD 'hdfs://localhost:9000/pig_data/emp1.txt' USING PigStorage(',')Īs (id:int, name:chararray, age:int, city:chararray) Suppose there is a file named emp_data in the HDFS /Pig_Data/ directory with the following content.Īnd assume we have loaded this file into Pig as shown below. Public class Sample_Eval extends EvalFunc ĭefine the alias for sample_eval as shown below.Īfter defining the alias you can use the UDF same as the built-in functions. In the Maven Dependencies section, you can find the downloaded jar files.Ĭreate a new class file with name Sample_Eval and copy the following content in it. This file contains the Maven dependencies for Apache Pig and Hadoop-core jar files. Open Eclipse and create a new project (say myproject).Ĭonvert the newly created project into a Maven project.Ĭopy the following content in the pom.xml. Before proceeding further, make sure you have installed Eclipse and Maven in your system.įollow the steps given below to write a UDF function − In this section, we discuss how to write a sample UDF using Eclipse. To write a UDF using Java, we have to integrate the jar file Pig-0.15.0.jar. ![]() These functions are used to perform full MapReduce operations on an inner bag. These functions accept a Pig value as input and return a Pig result.Īlgebraic Functions − The Algebraic functions act on inner bags in a FOREACHGENERATE statement. These functions accept a Pig value as input and return a Boolean value.Įval Functions − The Eval functions are used in FOREACH-GENERATE statements. While writing UDF’s using Java, we can create and use the following three types of functions −įilter Functions − The filter functions are used as conditions in filter statements. Using Piggybank, we can access Java UDF’s written by other users, and contribute our own UDF’s. In Apache Pig, we also have a Java repository for UDF’s named Piggybank. Since Apache Pig has been written in Java, the UDF’s written using Java language work efficiently compared to other languages. Using Java, you can write UDF’s involving all parts of the processing like data load/store, column transformation, and aggregation. The UDF support is provided in six programming languages, namely, Java, Jython, Python, JavaScript, Ruby and Groovy.įor writing UDF’s, complete support is provided in Java and limited support is provided in all the remaining languages. Using these UDF’s, we can define our own functions and use them. In addition to the built-in functions, Apache Pig provides extensive support for User Defined Functions (UDF’s).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |