Cloudera Blog · HBase Posts
The following guest post is provided by Aaron Kimball, CTO of WibiData.
The Kiji ecosystem has grown with the addition of a new module, KijiMR. The Kiji framework is a collection of components that offer developers a handle on building Big Data Applications. In addition to the first release, KijiSchema, we are now proud to announce the availability of a second component: KijiMR. KijiMR allows KijiSchema users to use MapReduce techniques including machine-learning algorithms and complex analytics to develop many kinds of applications using data in KijiSchema. Read on to learn more about the major features included in KijiMR and how you can use them.
KijiMR offers developers a set of new processing primitives explicitly designed for interacting with complex table-oriented data. The low-level batch interfaces available in MapReduce include basic InputFormat and OutputFormat implementations. The raw APIs are designed for processing key-value pairs stored in flat files in HDFS. Integrating MapReduce with HBase via InputFormat and OutputFormat APIs is hard to do from scratch in every algorithm. In KijiMR, we have extended the available MapReduce APIs to include:
There are various ways to access and interact with Apache HBase. The Java API provides the most functionality, but many people want to use HBase without Java.
There are two main approaches for doing that: One is the Thrift interface, which is the faster and more lightweight of the two options. The other way to access HBase is using the REST interface, which uses HTTP verbs to perform an action, giving developers a wide choice of languages and programs to use.
This series of how-to’s will discuss the REST interface and provide Python code samples for accessing it. The first post will cover HBase REST, some Python caveats, and table administration. The second post will explain how to insert multiple rows at a time using XML and JSON. The third post will show how to get multiples rows using XML and JSON. The full code samples can be found on my GitHub account.
HBase REST Basics
The current (4.2) release of CDH — Cloudera’s 100% open-source distribution of Apache Hadoop and related projects (including Apache HBase) — introduced a new HBase feature, recently landed in trunk, that allows an admin to take a snapshot of a specified table.
Prior to CDH 4.2, the only way to back-up or clone a table was to use Copy/Export Table, or after disabling the table, copy all the hfiles in HDFS. Copy/Export Table is a set of tools that uses MapReduce to scan and copy the table but with a direct impact on Region Server performance. Disabling the table stops all reads and writes, which will almost always be unacceptable.
In contrast, HBase snapshots allow an admin to clone a table without data copies and with minimal impact on Region Servers. Exporting the snapshot to another cluster does not directly affect any of the Region Servers; export is just a distcp with an extra bit of logic.
(Added Feb. 25 2013: Early Bird registration is now open – closes April 23, 2013!)
Cloudera University is the world leader in Apache Hadoop training and certification. Our full suite of live courses and online materials is the best resource to get started with your Hadoop cluster in development or advance it towards production. We offer deep industry insight into the skills and expertise required to establish yourself as a leading Developer or Administrator managing and processing Big Data in this fast-growing field.
But did you know Cloudera training can also help you plan for the advanced stages and progress of your Hadoop cluster? In addition to core training for Developers and Administrators, we also offer the best (and, in some cases, only) opportunity to get up to speed on lifecycle projects within the Hadoop ecosystem in a classroom setting. Cloudera University’s course offerings go beyond the basics to include Training for Apache HBase, Training for Apache Hive and Pig, and Introduction to Data Science: Building Recommender Systems. Depending on your Big Data agenda, Cloudera training can help you increase the accessibility and queryability of your data, push your data performance towards real-time, conduct business-critical analyses using familiar scripting languages, build new applications and customer-facing products, and conduct data experiments to improve your overall productivity and profitability.
For a limited time, Cloudera University is offering a 15% discount when you register for two or more Hadoop training courses to help you build out and realize your Big Data plan. Cover the basics with Developer or Administrator training, move beyond the HDFS and MapReduce core by pairing Developer and HBase training, work towards machine learning with Hive and Pig training and Introduction to Data Science, or customize your own learning path. Just use discount code 15off2 when you register for multiple public training classes from Cloudera University. This offer is only available for new enrollments and is only valid for classes delivered by Cloudera and scheduled to begin before March 1, 2013.
This following post was originally published via blog.apache.org; we republish it here for your convenience.
NOTE: This blog post describes how Apache HBase does concurrency control. This assumes knowledge of the HBase write path, which you can read more about in this other blog post.
Apache HBase provides a consistent and understandable data model to the user while still offering high performance. In this blog, we’ll first discuss the guarantees of the HBase data model and how they differ from those of a traditional database. Next, we’ll motivate the need for concurrency control by studying concurrent writes and then introduce a simple concurrency control solution. Finally, we’ll study read/write concurrency control and discuss an efficient solution called Multiversion Concurrency Control.
Why Concurrency Control?
For several good reasons, 2013 is a Happy New Year for Apache Hadoop enthusiasts.
In 2012, we saw continued progress on developing the next generation of the MapReduce processing framework (MRv2), work that will bear fruit this year. HDFS experienced major progress toward becoming a lights-out, fully enterprise-ready distributed filesystem with the addition of high availability features and increased performance. And a hint of the future of the Hadoop platform was provided with the Beta release of Cloudera Impala, a real-time query engine for analytics across HDFS and Apache HBase data.
Let’s look at the highlights of the 2012 developments around projects supported by Cloudera.
Apache Hadoop Releases
Our hearty congratulations to the Cloudera engineers who have been accepted as ApacheCon NA 2013 (Feb. 26-28 in Portland, OR) speakers for these talks:
At Cloudera, we put great pride into drinking our own champagne. That pride extends to our support team, in particular.
Cloudera Manager, our end-to-end management platform for CDH (Cloudera’s open-source, enterprise-ready distribution of Apache Hadoop and related projects), has a feature that allows subscription customers to send a snapshot of their cluster to us. When these cluster snapshots come to us from customers, they end up in a CDH cluster at Cloudera where various forms of data processing and aggregation can be performed.
Today, the system provides real-time support via an application we call CSI. When a support employee looks at a ticket, they can use CSI to examine the customer’s latest snapshot and see cluster stats such as version information, number of nodes in service, which services are used, and so on. CSI also visualizes different aggregations and groupings, such as versions, which allows us to detect misconfigured clusters, or issues caused during upgrade or installation.
AssignmentManager is a module in the Apache HBase Master that manages regions to RegionServers assignment. (See HBase architecture for more information.) It ensures that all regions are assigned and each region is assigned to just one RegionServer.
Although the AssignmentManager generally does a good job, the existing implementation does not handle assignments as well as it could. For example, if a region was assigned to two or more RegionServers, some regions were stuck in transition and never got assigned, or unknown region exceptions were thrown in moving a region from one RegionServer to another.
In the past we tried to fix these bugs without changing the underlying design. Consequently, the AssignmentManager ended up having many band-aids, and the code base became hard to understand/maintain. Furthermore, the underlying issues had not been completely fixed.