Introduction to apache_cassandra_for_develope

Introduction to Apache Cassandra (for Java developers!) Nate McCall [email_address] @zznate

Brief Intro NOT a "key/value store" Columns are dynamic inside a column family SSTables are immutable SSTables merged on reads All nodes share the same role (i.e. no single point of failure) Trading ACID compliance for scalability is a fundamental design decision

How does this impact development? Substantially. For operations affecting the same data, that data will become consistent eventually as determined by the timestamps. But you can trade availability for consistency. (More on this later) You can store whatever you want. It's all just bytes. You need to think about how you will query the data before you write it.

Neat. So Now What? Like any database, you need a client! Python: Telephus: http://github.com/driftx/Telephus (Twisted) Pycassa: http://github.com/pycassa/pycassa Java: Hector: http://github.com/rantav/hector (Examples https://github.com/zznate/hector-examples ) Pelops: http://github.com/s7/scale7-pelops Kundera http://code.google.com/p/kundera/ Datanucleus JDO: http://github.com/tnine/Datanucleus-Cassandra-Plugin Grails: grails-cassandra: https://github.com/wolpert/grails-cassandra .NET: FluentCassandra : http://github.com/managedfusion/fluentcassandra Aquiles: http://aquiles.codeplex.com/ Ruby: Cassandra: http://github.com/fauna/cassandra PHP: phpcassa: http://github.com/thobbs/phpcassa SimpleCassie : http://code.google.com/p/simpletools-php/wiki/SimpleCassie

Thrift Fast, efficient serialization and network IO. Lots of clients available (you can probably use it in other places as well) Why you don't want to work with the Thrift API directly: SuperColumn ColumnOrSuperColumn ColumnParent.super_column ColumnPath.super_column Map<ByteBuffer,Map<String,List<Mutation>>> mutationMap

Higher Level Client Hector JMX Counters Add/remove hosts: automatically programatically via JMX Plugable load balancing Complete encapsulation of Thrift API Type-safe approach to dealing with Apache Cassandra Lightweight ORM (supports JPA 1.0 annotations) Mavenized! http://repo2.maven.org/maven2/me/prettyprint/

"CQL" Currently in Apache Cassandra trunk Experimental Lots of possibilities from test/system/test_cql.py: UPDATE StandardLong1 SET 1L="1", 2L="2", 3L="3", 4L="4" WHERE KEY="aa" SELECT "cd1", "col" FROM Standard1 WHERE KEY = "kd" DELETE "cd1", "col" FROM Standard1 WHERE KEY = "kd"

Avro?? Gone. Added too much complexity after Thrift caught up. "None of the libraries distinguished themselves as being a particularly crappy choice for serialization." (See CASSANDRA-1765 )

Thrift API Methods Retrieving Writing/Removing Meta Information Schema Manipulation

Thrift API Methods - Retrieving get: retrieve a single column for a key get_slice: retrieve a "slice" of columns for a key multiget_slice: retrieve a "slice" of columns for a list of keys get_count: counts the columns of key (you have to deserialize the row to do it) get_range_slices: retrieve a slice for a range of keys get_indexed_slices (FTW!)

Thrift API Methods - Writing/Removing insert batch_mutate (batch insertion AND deletion) remove truncate**

Thrift API Methods - Meta Information describe_cluster_name describe_version describe_keyspace describe_keyspaces

Thrift API Methods - Schema system_add_keyspace system_update_keyspace system_drop_keyspace system_add_column_family system_update_column_family system_drop_column_family

vs. RDBMS - Consistency Level Consistency is tunable per request! Cassandra provides consistency when R + W > N (read replica count + write replica count > replication factor). *** CONSITENCY LEVEL FAILURE IS NOT A ROLLBACK*** Idempotent: an operation can be applied multiple times without changing the result

vs. RDBMS - Append Only Proper data modelling will minimizes seeks (Go to Tyler's presentation for more!)

On to the Code... https://github.com/zznate/cassandra-tutorial Uses Maven. Really basic. Modify/abuse/alter as needed. Descriptions of what is going on and how to run each example are in the Javadoc comments. Sample data is based on North American Numbering Plan http://en.wikipedia.org/wiki/North_American_Numbering_Plan

Data Shape 512 202 30.27 097.74 W TX Austin 512 203 30.27 097.74 L TX Austin 512 204 30.32 097.73 W TX Austin 512 205 30.32 097.73 W TX Austin 512 206 30.32 097.73 L TX Austin

Get a Single Column for a Key GetCityForNpanxx.java Retrieve a single column with: Name Value Timestamp TTL

Get the Contents of a Row GetSliceForNpanxx.java Retrieves a list of columns (Hector wraps these in a ColumnSlice) "SlicePredicate" can either be explicit set of columns OR a range (more on ranges soon) Another messy either/or choice encapsulated by Hector

Get the (sorted!) Columns of a Row GetSliceForStateCity.java Shows why the choice of comparator is important (this is the order in which the columns hit the disk - take advantage of it) Can be easily modified to return results in reverse order (but this is slightly slower)

Get the Same Slice from Several Rows MultigetSliceForNpanxx.java Very similar to get_slice examples, except we provide a list of keys

Get Slices From a Range of Rows GetRangeSlicesForStateCity.java Like multiget_slice, except we can specify a KeyRange (encapsulated by RangeSlicesQuery#setKeys(start, end) The results of this query will be significantly more meaningful with OrderPreservingPartitioner (try this at home!)

Get Slices From a Range of Rows - 2 GetSliceForAreaCodeCity.java Compound column name for controlling ranges Comparator at work on text field

Get Slices from Indexed Columns GetIndexedSlicesForCityState.java You only need to index a single column to apply clauses on other columns (BUT- the indexed column must be present with an EQUALS clause!) (It's just another ColumnFamily maintained automatically)

Insert, Update and Delete ... are effectively the same operation. InsertRowsForColumnFamilies.java DeleteRowsForColumnFamily.java Run each in succession (in whichever combination you like) and verify your results on the CLI Hint: watch the timestamps bin/cassandra-cli --host localhost use Tutorial; list AreaCode; list Npanxx; list StateCity;

Stuff I Punted on for the Sake of Brevity meta_* methods CassandraClusterTest.java: L43-81 @hector system_* methods SchemaManipulation.java @ hector-examples CassandraClusterTest.java: L84-157 @hector ORM (it works and is in production) ORM Documentation multiple nodes failure scenarios Data modelling (go see Tyler's presentation)

Things to Remember deletes and timestamp granularity "range ghosts" using the wrong column comparator and InvalidRequestException deletions actually write data use column-level TTL to automate deletion "how do I iterate over all the rows in a column family"? get_range_slices, but don't do that a good sign your data model is wrong

Dealing with *Lots* of Data (Briefly) Two biggest headaches have been addressed: Compaction pollutes os page cache ( CASSANDRA-1470 ) Greater than 143mil keys on a single SSTable means more BF false positives ( CASSANDRA-1555 ) Hadoop integration: Yes. (Go see Jeremy's presentation) Bulk loading: Yes. CASSANDRA-1278 For more information: http://wiki.apache.org/cassandra/LargeDataSetConsiderations

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