Hive Digest, March 2011

Welcome to the first Hive digest!

Hive is a data warehouse built on Hadoop, initially developed by Facebook, it’s been under the Apache umbrella for about 2 years and has seen very active development. Last year there were 2 major releases which introduced loads of features and bug fixes. Now Hive 0.7.0 has just been released and is packed with goodness.

Hive 0.6.0

Hive 0.6.0 was released October last year. Some of its most interesting features included

Hive 0.7.0

Hive 0.7.0 has just been released! Some of the major features include:

  • Indexing has been implemented, index types are currently limited to compact indexes. This feature opens up lots of potential for future improvements, such as HIVE-1694 which aims to use indexes to accelerate query execution for GROUP BY, ORDER BY, JOINS and other misc cases and HIVE-1803 which will implement bitmap indexing.
  • Security features have been added with authorisation and authentication.
  • There is now an optional concurrency model which makes use of Zookeeper, so tables can now be locked during writes. It is disabled by default, but can be enabled using hive.support.concurrency=true in the config.

And many other small improvements including:

  • Making databases more useful, you can now select across a database.
  • The Hive command line interface has gotten some love and now supports auto-complete.
  • There’s now support for HAVING clauses, so users no longer have to do nested queries in order to apply a filter on group by expressions.

and much more.

You can download Hive 0.7.0 from here and you can follow @sematext on Twitter.

Wanted: Devops to run Search-Hadoop.com and Search-Lucene.com

If you are dreaming about working on search, big data, analytics, data mining, and machine learning, and are a positive, proactive, independent devops creature, inquire within!

We are a small and highly distributed team who likes to eat a little bit of everything: search for breakfast, mapreduce for lunch, and bigtable for dinner.  We are looking for a part-time-to-grow-into-full-time devops to work on the popular search-hadoop.com and search-lucene.com sites and take them to the next level. As such, you’ll need to be on top of Lucene, Solr, and Elastic Search.  Similarly, you must be completely at $HOME on the UNIX command line.  Working knowledge of Mahout or statistics/machine learning/data mining background would be a major plus, but is not required.  Experience with productive web frameworks and slick modern front-end frameworks is another plus, as is familiarity with EC2 and EBS.

More about the ideal you:

  • You are well organized, disciplined, and efficient
  • You don’t wait to be told what to do and don’t need hand-holding
  • You are reliable, friendly, have a positive attitude, and don’t act like a prima donna
  • You have an eye for detail – no sloppy code, no poor spelelling and typous
  • You are able to communicate complex ideas in a clear fashion in English (or pretty diagrams)
  • You have experience with (large scale) search or data analysis
  • You like to write about technologies relevant to what we do
  • You are an open-source software contributor

Not all of the above are required, of course – the closer the match, the higher the relevance score, that’s all.

Interested?  Please get in touch.

Sematext at Open Source Search Conference 2011

We are happy to report that we have been selected to present at the upcoming Open Source Search Conference 2011 in McLean, Virginia, this coming June.  We’ll be talking about Search Analytics.

Search Analytics: What? Why? How?

Search is increasingly the primary information access mechanism, so knowing how your search is doing often has direct business impact. You’ve indexed your data and people are searching it. But how do you know if they are happy with the results? How do you know if they are finding what they need?  Regardless of whether you are using Solr, Lucene, or some other search solution, you should be paying attention to what your users are searching for and clicking on – through those actions they are telling you what you can do to improve your search.

In this talk we’ll talk about search analytics and how it can be used to answer questions like:

  • Are too many users getting the dreaded “no matches” results?
  • How deep into search results do people dig?
  • Which hits are they clicking on, or what percentage of them don’t click on any hits?
  • How much do they use the “Did You Mean” or “Auto-Complete” suggestions?

We’ll explore what specific search analytics reports tell us and what specific actions you should take based on those reports.

You can browse through other presentations, too.  If you will be attending the conference, please do not hesitate the tap Otis‘ shoulder.  We’d also be happy to talk business if you think your organization may benefit from one of Sematext’s products or services or if you simply want to chat.  To keep up with us, follow @sematext on Twitter.

For more information on this topic read about Sematext Search Analytics service.

Google Summer of Code and Intern Sponsoring

Are you a student and looking to do some fun and rewarding coding this summer? Then join us for the 2011 Google Summer of Code!

The application deadline is in less than a month! Lucene has identified initial potential projects, but this doesn’t mean you can also pick your own.  If you need additional ideas, look at our Lucene / Solr for Academia: PhD Thesis Ideas (or just the spreadsheet if you don’t want to read the what and the why),  just be sure to discuss with the community first (send an email to dev@lucene.apache.org).

We should also add that, separately from GSoC, Sematext would be happy to sponsor good students and interns interested in work on projects involving search (Lucene, Solr), machine learning & analytics (Mahout), big data (Hadoop, HBase, Hive, Pig, Cassandra), and related areas. We are a virtual and geographically distributed organization whose members are spread over several countries and continents and we welcome students from all across the globe.  For more information please inquire within.

HBase Backup Options

If you are thinking about using HBase you will likely want to understand HBase backup options.  I know we did, so let us share what we found.  Please let us know what we missed and what you use for HBase backup!

Export

You could export your tables using the Export (org.apache.hadoop.hbase.mapreduce.Export) MapReduce job that will export the table data into a Sequence File on HDFS.  This was implemented in HBASE-1684 if you want to check out the patch or comments there.  This tool works on one table at a time, so if you need to backup multiple tables, run this on each table.  The exported data can then be imported back into HBase by the Import tool.

Copy Table

If you have another HBase cluster that you want to treat as a backup cluster, you can use the handy CopyTable tool to copy a table at a time.

Distcp

You could use Hadoop’s distcp command to copy the whole /hbase directory from one HDFS cluster to the other.  However, this can leave your data in an inconsistent state, so it should be avoided.  See http://search-hadoop.com/m/wkMgSjVLDb

At this point we should point out that all of the above backup methods are per-table.  Moreover, they don’t work or create a snapshot of the table.   Export and CopyTable are atomic only at the row level.  Furthermore, if you have multiple tables whose tables depend on each other, if they are being modified while you are exporting or copying them, you will end up with inconsistent data – the data in those tables will not be in sync.  See http://search-hadoop.com/m/Q4bU81G116p.

Backup from Mozilla

Because of the above mentioned issues with distcp when running it over a cluster whose data is being modified while distcp is running, developers at Mozilla came up with their own Backup tool.  They’ve described the tool and its use in the popular Migrating HBase in the Trenches post.

Cluster Replication

HBase has a relatively new and not yet widely used whole cluster replication mechanism.  The backup cluster does not have to be identical to the master cluster, which means that the backup cluster could be much less powerful and thus cheaper, while still having enough storage to serve as backup.

Table Snapshot

Ah, the infamous HBASE-50!  This issue saw some great work during GSoC 2010, but it looks like it was never integrated into HBase.  It is unclear whether the contributor simply ran out of steam or time or whether it became apparent that table snapshots are too difficult to implement or simply not doable because of highly distributed nature of HBase.  The JIRA issue does contain patches you can look at, and the author has a now inactive hbase-snapshot repository up on Github.

HDFS Replication

You could also simply crank up the replication factor to the level that makes you feel safe and call that a backup.  This may not guard against data corruption, but it does guard against certain partial hardware failures.

Since so many people seem to be asking about HBase backup options, I hope this serves as a good point-in-time snapshot, a summary of all HBase backup options that are currently on the table.  With time, this will be added to the HBase Book.

Are there other HBase backup options we should have included?

What you use for HBase backup?

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