Conventions

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, and user input are shown as follows: "A Map class to map lines into <key,value> pairs; for example, <"INFO",1>."

A block of code is set as follows:

LogLine    = load 'file.logs' as (level, message);
LevelGroup = group LogLine by level;
Result     = foreach LevelGroup generate group, COUNT(LogLine);
store Result into 'Results.txt';

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

import com.twitter.scalding._
 
class CalculateDailyAdPoints (args: Args) extends Job(args) {

  val logSchema = List ('datetime, 'user, 'activity, 'data,
   'session, 'location, 'response, 'device, 'error, 'server)

  val logs = Tsv("/log-files/2014/07/01", logSchema )
   .read
   .project('user,'datetime,'activity,'data)
   .groupBy('user) { group => group.sortBy('datetime) }
   .write(Tsv("/analysis/log-files-2014-07-01"))
}

Any command-line input or output is written as follows:

$ echo "This is a happy day. A day to remember" > input.txt
$ hadoop fs -mkdir -p hdfs:///data/input hdfs:///data/output
$ hadoop fs -put input.txt hdfs:///data/input/

New terms and important words are shown in bold.

Note

Warnings or important notes appear in a box like this.

Tip

Tips and tricks appear like this.