Advanced search and Top-K queries in Cassandra
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Introduction to Cassandra Cassandra query methods Stratio Lucene based 2i implementation Integrating Lucene 2i with Apache Spark
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Advanced search and Top-K queries in Cassandra
- 1. Advanced search and Top-K queries in Cassandra 1 Andrés de la Peña andres@stratio.com @a_de_la_pena Apache Cassandra Meetup 2015
- 2. • Stratio is a Big Data Company • Founded in 2013 • Commercially launched in 2014 • 70+ employees in Madrid • Office in San Francisco • Certified Spark distribution Apache Cassandra Meetup 2015 Who are we?
- 3. Introduction to Cassandra Cassandra query methods Stratio Lucene based 2i implementation Integrating Lucene 2i with Apache Spark 1 2 3 CONTENTS Apache Cassandra Meetup 2015 4
- 4. Tunable consistency Tradeoffs between consistency and latency are tunable. C* values a high availability and partitioning against consistency; strong consistency can be achieved but there is no row locking. Incremental scalability Nodes added to a cluster increase throughput in a predictable & linear fashion. The best of Dynamo & Big Table Combines the partitioning and replication of Amazon’s Dynamo with the log- structured data model of Google’s Bigtable. Decentralized P2P architecture without master node or single point of failure. Apache Cassandra overview 4Apache Cassandra Meetup 2015
- 5. Apache Cassandra operators 5Apache Cassandra Meetup 2015
- 6. primary key secondary indexes token ranges Throughput Expressiveness Cassandra query methods 6Apache Cassandra Meetup 2015
- 7. • O(1) node lookup for partition key • Range slices for clustering key • Usually requires denormalization Primary key queries Node 3 Node 1 Node 2 Partition key Clustering key range CLIENT apena 2014-04-10:body When you.. aagea dhiguero apena 2014-04-06:body 2014-04-07:body 2014-04-08:body To study and… To think and... If you see what.. 2014-04-06:body The cautious… 2014-04-10:body When you.. 2014-04-11:body When you do… 7Apache Cassandra Meetup 2015
- 8. primary key secondary indexes token ranges Throughput Expressiveness Cassandra query methods 8Apache Cassandra Meetup 2015
- 9. CLIENT C* node C* node 2i local column family C* node 2i local column family 2i local column family Secondary indexes queries • Inverted index • Mitigates denormalization • Queries may involve all C* nodes • Queries limited to a single column 9Apache Cassandra Meetup 2015
- 10. primary key secondary indexes token ranges Throughput Expressiveness Cassandra query methods 10Apache Cassandra Meetup 2015
- 11. C* node C* node C* node Spark master Token range queries • Used by MapReduce frameworks as Hadoop or Spark • All kinds of queries are possible • Low throughput • Ad-hoc queries • Batch processing • Materialized views CLIENT query= function (all data) 11Apache Cassandra Meetup 2015
- 12. C* node C* node C* node Combining 2i with MapReduce • Expressiveness avoiding full scans • Still limited by one indexed column per query Spark masterCLIENT Secondary index Secondary index Secondary index 12Apache Cassandra Meetup 2015
- 13. MORE EXPRESIVENESS What do we miss from 2i indexes? • Range queries • Multivariable search • Full text search • Sorting by fields • Top-k queries 13Apache Cassandra Meetup 2015
- 14. IT’S ARCHITECTURE What do we like from the existing 2i? • Each node indexes its own data • The index implementations do not need to be distributed • Can be created after design and ingestion • Natural extension point 14Apache Cassandra Meetup 2015
- 15. Thinking in a custom secondary index implementation… WHY NOT USE ? 15Apache Cassandra Meetup 2015
- 16. Why we like Lucene • Proven stable and fast indexing solution • Expressive queries - Multivariable, ranges, full text, sorting, top-k, etc. • Mature distributed search solutions built on top of it - Solr, ElasticSearch • Can be fully embedded in application code • Published under the Apache License 16Apache Cassandra Meetup 2015
- 17. HOW IT WORKS Apache Cassandra Meetup 2015
- 18. ALTER TABLE tweets ADD lucene TEXT; CREATE TABLE tweets ( id bigint, createdAt timestamp, message text, userid bigint, username text, PRIMARY KEY (userid, createdAt, id) ); Create index • Built in the background in any moment • Real time updates • Mapping eases ETL • Language aware 18 CREATE CUSTOM INDEX tweets_idx ON twitter.tweets (lucene) USING 'com.stratio.index.RowIndex' WITH OPTIONS = { 'refresh_seconds' : '60', 'schema' : '{ default_analyzer : "EnglishAnalyzer”, fields : { createdat : {type : "date", pattern : "yyyy-MM-dd"}, message : {type : "text", analyzer : ”EnglishAnalyzer"}, userid : {type : "string"}, username : {type : "string”} } }' }; Apache Cassandra Meetup 2015
- 19. SELECT * FROM tweets WHERE lucene = ‘{ filter : {type : "match", field : "text", value : "cassandra"} }’ LIMIT 10; search 10 found 6 found 4 We are done ! Filtering query CLIENT C* node C* node C* node Lucene index Lucene index Lucene index 19Apache Cassandra Meetup 2015
- 20. Found 5 Found 4 Found 5 Top-k query SELECT * FROM tweets WHERE lucene = ‘{ query: {type : "match", field : "text", value : "cassandra"} }’ LIMIT 5; Search top-5 CLIENT Search top-5 C* node C* node C* node Lucene index Lucene index Lucene index Merge 14 to best 5 20Apache Cassandra Meetup 2015
- 21. SELECT * FROM tweets WHERE lucene = ‘{ filter : { type : "boolean", must : [ {type : "range", field : "time" lower : "2014/04/25”}, {type : "boolean", should : [ {type : "prefix", field : "user", value : "a"} , {type : "wildcard", field : "user", value : "*b*"} , {type : "match", field : "user", value : "fast"} ] } ] }, sort : { fields: [ {field :"time", reverse : true}, {field : "user", reverse : false} ] } }’ LIMIT 10000; Queries can be as complex as you want 21Apache Cassandra Meetup 2015
- 22. NO MAINTENANCE REQUIRED Some implementation details • A Lucene document per CQL row, and a Lucene field per indexed column • SortingMergePolicy keeps index sorted in the same way that C* does • Index commits synchronized with column family flushes • Segments merge synchronized with column family compactions 22Apache Cassandra Meetup 2015
- 24. Split friendly. It supports searches within a token range SELECT * FROM tweets WHERE lucene = ‘{ filter : {type:"match", field:"text", value:"cassandra"} }’ AND TOKEN(userid, createdAt, id) > 253653456456 AND TOKEN(userid, createdAt, id) <= 3456467456756 LIMIT 10000; Integrating Lucene & Spark 24Apache Cassandra Meetup 2015
- 25. SELECT * FROM tweets WHERE lucene = ‘{ filter : {type:"match", field:"text", value:"cassandra"} }’ AND userid = 3543534 AND createdAt > 2011-02-03 04:05+0000 LIMIT 5000; Paging friendly: It supports starting queries in a certain point Integrating Lucene & Spark 25Apache Cassandra Meetup 2015
- 26. Integrating Lucene & Spark CLIENT Spark master C* node C* node C* node Lucene Lucene Lucene • Compute large amounts of data • Avoid systematic full scan • Reduces the amount of data to be processed • Filtering push-down 26Apache Cassandra Meetup 2015
- 27. WHEN TO USE INDEXES AND WHEN TO USE FULL SCAN Apache Cassandra Meetup 2015
- 28. Index performance in Spark Time Records returned Full scan Lucene 2i 28Apache Cassandra Meetup 2015
- 29. DEMOLucene indexes in C* Apache Cassandra Meetup 2015
- 30. Conclusions • Added new query methods - Multivariable queries (AND, OR, NOT) - Range queries (>, >=, <, <=) and regular expressions - Full text queries (match, phrase, fuzzy...) • Top-k query support - Lucene scoring formula - Sort by field values • Compatible with MapReduce frameworks • Preserves Cassandra’s functionality 30Apache Cassandra Meetup 2015
- 31. Its open source 31 github.com/stratio/stratio-cassandra • Published as fork of Apache Cassandra • Apache License Version 2.0 stratio.github.io/crossdata • Apache License Version 2.0 github.com/stratio/deep-spark • Apache License Version 2.0 Apache Cassandra Meetup 2015
- 32. Advanced search and Top-K queries in Cassandra 32 Andrés de la Peña andres@stratio.com @a_de_la_pena Apache Cassandra Meetup 2015