Refer to this post (Aug. 28, 2013) for state-of-the-art recommendations about hardware selection for new Hadoop clusters.
Apache Hadoop’s jobtracker, namenode, secondary namenode, datanode, and tasktracker all generate logs. That includes logs from each of the daemons under normal operation, as well as configuration logs, statistics, standard error, standard out, and internal diagnostic information. Many users aren’t entirely sure what the differences are among these logs, how to analyze them, or even how to handle simple administrative tasks like log rotation. This blog post describes each category of log, and then details where they can be found for each Hadoop component.
As Hadoop adoption increases among organizations, companies, and individuals, and as it makes its way into production, testing MapReduce (MR) jobs becomes more and more important. By regularly running tests on your MR jobs–either invoked by developers before they commit a change or by a continuous integration server such as hudson–an engineering organization can catch bugs early, strive for quality, and make developing and maintaining MR jobs easier and faster.
MR jobs are particularly difficult to test thoroughly because they run in a distributed environment.
As promised in my post about installing Scribe for log collection, I’m going to cover how to configure and use Scribe for the purpose of collecting Hadoop logs. In this post I’ll describe how to create the Scribe Thrift client for use in Java, add a new log4j Appender to Hadoop, configure Scribe, and collect logs from each node in a Hadoop cluster. At the end of the post, I will link to all source and configuration files mentioned in this guide.
Scribe is a newly released log collection tool that dumps log files from various nodes in a cluster to Scribe servers, where the logs are stored for further use. Facebook describes their usage of Scribe by saying, “[Scribe] runs on thousands of machines and reliably delivers tens of billions of messages a day.” It turns out that Scribe is rather difficult to install, so the hope of this post is to help those of you attempting to install Scribe.