1. 美商優科無線 資深工程師
Boris Yen

2. 專家講座 B：
淺談 Apache Cassandra

3. Outline
• Cassandra vs SQL Server
• Overview
• Data in Cassandra
• Data Partitioning
• Data Replication
• Data Consistency
• Client Libraries

4. Cassandra vs SQL Server
• Cassandra
o More servers = More capacity.
o The concerns of scaling is transparent to application.
o No single point of failure.
o Horizontal scale.
• SQL Server
o More power machine = More capacity.
o Adding capacity requires manual labor from ops people
and substantial downtime.
o There would be limit on how big you could go.
o Vertical scale, Moore’s law scaling

5. Overview
• Features are coming from Dynamo and BigTable
• Distributed
o Data partitioned among all nodes
• Extremely Scalable
o Add new node = Add more capacity
o Easy to add new node
• Fault tolerant
o All nodes are the same
o Read/Write anywhere
o Automatic Data replication
• High Performance

6. Overview
http://www.datastax.com/dev/blog/whats-new-in-cassandra-1-0-
performance
http://www.cubrid.org/blog/dev-platform/nosql-
benchmarking/
http://techblog.netflix.com/2011/11/benchmarking-
cassandra-scalability-on.html

7. Data in Cassandra
• Keyspace ~ Database in RDBMS
• Column Family ~ Table in RDBMS
Keyspace
ColumnFamily
{
column: Phone,
ID Addr Phone value: 09...,
Key: Boris
timestamp: 1000
1 ... Taiwan 09..... }
timestamp is used
to resolve conflict.

8. Data in Cassandra
• Keyspace
o Where the replication strategy and replication factor
is defined.
CREATE KEYSPACE keyspace_name WITH
strategy_class = 'SimpleStrategy'
AND strategy_options:replication_factor=2;
• ColumnFamily
CREATE COLUMNFAMILY user (
id uuid PRIMARY KEY, address text, userName text ) WITH
comment='' AND comparator=text AND read_repair_chance=0.100000 AND
gc_grace_seconds=864000 AND default_validation=text AND
min_compaction_threshold=4 AND max_compaction_threshold=32 AND
replicate_on_write=True AND compaction_strategy_class='SizeTieredCompactionStrategy' AND
compression_parameters:sstable_compression='org.apache.cassandra.io.compress.SnappyCompres
sor';

9. Data in Cassandra
• Commit log
o Used to capture write activities. Data durability is
assured.
• Memtable
o Used to store most recent write activities.
• SSTable
o When a memtable got flushed to disk, it becomes a
sstable.

10. Data Read/Write
• Write
Data Commitlog Memtable
Flushed
SSTable
• Read
o Search Row cache, if the result is not empty, then return the
result. No further actions are needed.
o If no hit in the Row cache. Try to get data from Memtable(s)
and SSTable(s) that might contain requested key. Collate the
results and return.

11. Data Compaction
t2 > t1
Boris:{
name: boris (t1)
sstable1 phone: 092xxx (t1)
addr: tainan (t1)
}
Boris:{
addr: tainan (t1)
email: y@gmail (t2)
sstableX name: boris.yen (t2)
Boris:{ phone: 092xxx (t1)
name: boris.yen (t2) sex: male (t2)
sstable2 sex: male (t2)
email: y@gmail (t2) }
}
.
.
.
.

12. Data Partitioning
• The total data managed by the cluster is
represented as a circular space or ring.
• Before a node can join the ring, it must be assigned
a token.
• The token determines the node’s position on the
ring and the range of data it is responsible for.
• Partitioning strategy
o Random Partitioning
 Default and Recommended
o Order Partitioning
 Sequential writes can cause hot spots
 More administrative overhead to load balance the
cluster

13. Data Partitioning
Random
Partitioning
t1
hash(k2) hash(k1)
Data: k1 t5 t2 Data: k3
hash(k4)
hash(k3)
t4 t3

14. Data Replication
• To ensure fault tolerance and no single point
of failure.
• Replication is controlled by the parameters
replication factor and replication strategy
of a keyspace.
• Replication factor controls how many copies
of a row should be stored in the cluster
• Replication strategy controls how the data
being replicated.

15. Data Replication
Random Partitioning
t1
RF=3 hash(k1)
Data: k1 t5 t2
coordinator
t4 t3

16. Data Consistency
• Cassandra supports tunable data
consistency.
• Choose from strong and eventual
consistency depending on the need.
• Can be done on a per-operation basis, and
for both reads and writes.
• Handles multi-data center operations

17. Consistency Level
Write Read
Any
One One
Quorum Quorum
Local_Quorum Local_Quorum
Each_Quorum Each_Quorum
All All

18. Built-in Consistency Repair
Features
• Read Repair
• Hinted Handoff
• Anti-Entropy Node Repair
http://www.datastax.com/docs/0.8/dml/data_consistency#builtin-consistency

19. Client Library for Java
• Hector
o https://github.com/hector-client/hector.git
o https://github.com/hector-client/hector/wiki/User-
Guide
• Astyanax
o https://github.com/Netflix/astyanax.git
• CQL + JDBC
o http://code.google.com/a/apache-
extras.org/p/cassandra-jdbc/

20. Hector
• High level, simple object oriented
interface to cassandra
• Failover behavior on the client side
• Connection pooling for improved
performance and scalability
• Automatic retry of downed hosts
.
.
.

21. Hector
// slice query
SliceQuery<String, String> q = HFactory.createSliceQuery(ko, se, se, se);
q.setColumnFamily(cf).setKey("jsmith").setColumnNames("first", "last",
"middle");
Result<ColumnSlice<String, String>> r = q.execute();
// multi-get
MultigetSliceQuery<String, String, String> multigetSliceQuery =
HFactory.createMultigetSliceQuery(keyspace, stringSerializer, stringSerializer,
stringSerializer);
multigetSliceQuery.setColumnFamily("Standard1");
multigetSliceQuery.setKeys("fake_key_0", "fake_key_1",
"fake_key_2", "fake_key_3", "fake_key_4");
multigetSliceQuery.setRange("", "", false, 3);
Result<Rows<String, String, String>> result = multigetSliceQuery.execute();
// batch operation
Mutator<String> mutator = HFactory.createMutator(keyspace, stringSerializer);
mutator.addInsertion("jsmith", "Standard1",
HFactory.createStringColumn("first", "John")).addInsertion("jsmith",
"Standard1", HFactory.createStringColumn("last",
"Smith")).addInsertion("jsmith", "Standard1",
HFactory.createStringColumn("middle", "Q"));
mutator.execute();
https://github.com/hector-client/hector/wiki/User-Guide

22. CQL+JDBC
Class.forName("org.apache.cassandra.cql.jdbc.CassandraDriver");
String URL = String.format("jdbc:cassandra://%s:%d/%s",HOST,PORT,"system");
System.out.println("Connection URL = '"+URL +"'");
con = DriverManager.getConnection(URL);
Statement stmt = con.createStatement();
// Create KeySpace
String createKS = String.format("CREATE KEYSPACE %s WITH strategy_class =
SimpleStrategy AND strategy_options:replication_factor = 1;",KEYSPACE);
stmt.execute(createKS);
// Create the target Column family
String createCF = "CREATE COLUMNFAMILY RegressionTest (keyname text PRIMARY
KEY,” + "bValue boolean, “+ "iValue int “+ ") WITH comparator = ascii AND default_validation =
bigint;";
stmt.execute(createCF);
https://code.google.com/a/apache-extras.org/p/cassandra-
jdbc/source/browse/src/test/java/org/apache/cassandra/cql/jdbc/JdbcRegressionTest.java

23. CQL+JDBC
Statement statement = con.createStatement();
String truncate = "TRUNCATE RegressionTest;";
statement.execute(truncate);
String insert1 = "INSERT INTO RegressionTest (keyname,bValue,iValue) VALUES ('key0',true,
2000);";
statement.executeUpdate(insert1);
String insert2 = "INSERT INTO RegressionTest (keyname,bValue) VALUES( 'key1',false);";
statement.executeUpdate(insert2);
String select = "SELECT * from RegressionTest;";
ResultSet result = statement.executeQuery(select);
ResultSetMetaData metadata = result.getMetaData();
.
.
.
https://code.google.com/a/apache-extras.org/p/cassandra-
jdbc/source/browse/src/test/java/org/apache/cassandra/cql/jdbc/JdbcRegressionTest.java

24. Useful Tools
• cassandra-cli
o <cassandra-dir>/bin
o http://www.datastax.com/docs/1.0/dml/using_cli
• cqlsh
o <cassandra-dir>/bin
o http://www.datastax.com/docs/1.0/references/cql/index
• nodetool
o <cassandra-dir>/bin
o http://www.datastax.com/docs/1.0/references/nodetool
• stress
o <cassandra-dir>/tools/bin
o http://www.datastax.com/docs/1.0/references/stress_java

25. Useful Tools
• OpsCenter
o http://www.datastax.com/products/opscenter
• sstableloader
o <cassandra-dir>/bin
o http://www.datastax.com/dev/blog/bulk-loading
• More tools
http://en.wikipedia.org/wiki/Apache_Cassandra#Tools
_for_Cassandra

26. Questions?