HBase at Mendeley

HBase at Mendeley Dan Harvey Data Mining Engineer dan.harvey@mendeley.com

Overview ➔ What is Mendeley ➔ Why we chose HBase ➔ How we're using HBase ➔ Challenges

Mendeley helps researchers work smarter

Mendeley helps researchers work smarter Install Mendeley Desktop Mendeley extracts research data..

Mendeley helps researchers work smarter ..and aggregates research data in the cloud Mendeley extracts research data..

Mendeley in numbers ➔ 600,000+ users ➔ 50+ million user documents ➔ Since January 2009 ➔ 30 million unique documents ➔ De-duplicated from user and other imports ➔ 5TB of papers

Data Mining Team ➔ Catalogue ➔ Importing ➔ Web Crawling ➔ De-duplication ➔ Statistics ➔ Related and recommended research ➔ Search

Starting off ➔ Users data in MySQL ➔ Normalised document tables ➔ Quite a few joins.. ➔ Stuck with MySQL for data mining ➔ Clustering and de-duplication ➔ Got us to launch the article pages

But.. ➔ Re-process everything often ➔ Algorithms with global counts ➔ Modifying algorithms affect everything ➔ Iterating over tables was slow ➔ Could not easily scale processing ➔ Needed to shard for more documents ➔ Daily stats took > 24h to process...

What we needed ➔ Scale to 100s of millions of documents ➔ ~80 million papers ➔ ~120 million books ➔ ~2-3 billion references ➔ More projects using data and processing ➔ Update the data more often ➔ Rapidly prototype and develop ➔ Cost effective

So much choice.. And many more... But they mostly miss out good scalable processing.

HBase and Hadoop ➔ Scalable storage ➔ Scalable processing ➔ Designed to work with map reduce ➔ Fast scans ➔ Incremental updates ➔ Flexible schema

Where HBase fits in

How we store data ➔ Mostly documents ➔ Column Families for different data ➔ Metadata / raw pdf files ➔ More efficient scans ➔ Protocol Buffers for metadata ➔ Easy to manage 100+ fields ➔ Faster serialisation

Example Schema ● All data for documents in one table Row Column family Qualifier sha1_hash metadata document date_added date_modified source content pdf full_text entity_extraction canonical_id version_live

How we process data ➔ Java Map Reduce ➔ More control over data flows ➔ Allows us to do more complex work ➔ Pig ➔ Don't have to think in map reduce ➔ Twitter's Elephant Bird decodes protocol buffers ➔ Enables rapid prototyping ➔ Less efficient than using java map reduce ➔ Quick example...

Example ➔ Trending keywords over time ➔ For a give keyword, how many documents per year? ➔ Multiple map/reduce tasks ➔ 100s of line of java...

Pig Example -- Load the document bag rawDocs = LOAD 'hbase://canonical_documents' USING HbaseLoader('metadata:document') AS (protodoc); -- De-serialise protocol buffer docs = FOREACH rawDocs GENERATE DocumentProtobufBytesToTuple(protodoc)AS doc; -- Get keyword, year tuples tagYear = FOREACH docs GENERATE FLATTEN (doc.(year, keywords_bag)) AS keyword, doc::year AS year;

-- Group unique (keyword, year) tuples yearTag = GROUP tagYear BY (keyword, year); -- Create (keyword, year, count) tuples yearTagCount = FOREACH yearTag GENERATE FLATTEN(group) AS (keyword, year), COUNT(tagYear) AS count; -- Group the counts by keyword tagYearCounts = GROUP yearTagCount BY keyword; -- Group the counts by keyword tagYearCounts = FOREACH tagYearCounts GENERATE group AS keyword, yearTagCount.(year, count) AS years; STORE tagYearCounts INTO 'tag_year_counts';

Challenges ➔ MySQL hard to export from ➔ Many joins slow things down ➔ Don't normalise if you don't have to! ➔ HBase needs memory ➔ Stability issues if you give it too little

Challenges: Hardware ➔ Knowing where to start is hard... ➔ 2x quad core Intel cpu ➔ 4x 1TB disks ➔ Memory ➔ Started with 8GB, then 16GB ➔ Upgrading to 24GB soon ➔ Currently 15 nodes

www.mendeley.com

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HBase at Mendeley

by Dan Harvey

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