London + Dublin Cassandra 2.0

©2013 DataStax Confidential. Do not distribute without consent.
@spyced
Jonathan Ellis
CTO, DataStax / Project Chair, Apache Cassandra
Cassandra 2.0

Five Years of Cassandra
Jul-09 May-10 Feb-11 Dec-11 Oct-12 Jul-13
0.1 0.3 0.6 0.7 1.0 1.2
...
2.0
DSE
Jul-08

Core values
0
20000
40000
60000
80000
0 2 4 6 8 10 12
Cassandra HBase Redis MySQL
• Massive scalablility
• High performance
• Reliability/Availability

CREATE TABLE users (
id uuid PRIMARY KEY,
name text,
state text,
birth_date int
);
CREATE INDEX ON users(state);
SELECT * FROM users
WHERE state=‘Texas’
AND birth_date > 1950;
New Core Value
• Massive scalablility
• High performance
• Reliability/Availability
• Ease of use

*Key concepts?
*Data Modeling section of documentation: http://www.datastax.com/
documentation/cassandra/1.2/index.html#cassandra/ddl/
ddl_anatomy_table_c.html
CQL delivers
"Coming from a relational database background we found
the transition to Cassandra to be very straightforward. There are a
few simple key concepts one must grasp at first but ever since it's
been smooth sailing for us."
Boris Wolf, Comcast

1.2 for Developers
• CQL3
• Thrift compatibility
• Collections
• Data dictionary
• Auth support
• Hadoop support
• Native drivers
• Tracing
• Atomic batches

[cassandra.yaml]
authenticator: PasswordAuthenticator
# DSE offers KerberosAuthenticator as well
CREATE USER robin WITH PASSWORD 'manager' SUPERUSER;
ALTER USER cassandra WITH PASSWORD 'newpassword';
LIST USERS;
DROP USER cassandra;
Authentication

[cassandra.yaml]
authorizer: CassandraAuthorizer
GRANT select ON audit TO jonathan;
GRANT modify ON users TO robin;
GRANT all ON ALL KEYSPACES TO lara;
Authorization

Native drivers
• CQL native protocol: efficient, lightweight, asynchronous
• Java (GA): https://github.com/datastax/java-driver
• .NET (Beta): https://github.com/datastax/csharp-driver
• Python (Beta): https://github.com/datastax/python-driver
• Coming soon: PHP, Ruby, others

1.2 for Operators
• Virtual nodes
• “Dense node” support (5-10TB/machine)
• JBOD improvements
• Off-heap bloom filters, compression metadata
• Parallel leveled compaction

1.2.5+
• ~1/2 memory usage in partition summary

1.2.5+
• Improved compaction throttle

1.2.5+

1.2.5+
• Removed cell-name bloom filters

1.2.5+
• Thread-local allocation

1.2.5+
• LZ4 compression (default in 2.0)

1.2.5+
• (1.2.7) CQL Input/Output for Hadoop

1.2.5+
• (1.2.7) Range tombstone performance

1.2.5+
• (1.2.7) Range tombstone performance
• (1.2.9) Larger default LCS filesize (160MB > 5MB)

2.0
• Lightweight transactions
• Triggers (experimental)
• Improved compaction
• CQL cursors

SELECT * FROM users
WHERE username = ’jbellis’
[empty resultset]
INSERT INTO users (...)
VALUES (’jbellis’, ...)
Session 1
SELECT * FROM users
[empty resultset]
INSERT INTO users (...)
VALUES (’jbellis’, ...)
Session 2
Lightweight transactions: the problem

Paxos
• All operations are quorum-based
• Each replica sends information about unfinished operations to the leader
during prepare
• Paxos made Simple

LWT: details
• 4 round trips vs 1 for normal updates
• Paxos state is durable
• Immediate consistency with no leader election or failover
• ConsistencyLevel.SERIAL
• http://www.datastax.com/dev/blog/lightweight-transactions-in-
cassandra-2-0

LWT: Use with caution
• Great for 1% of your application
• Eventual consistency is your friend
• http://www.slideshare.net/planetcassandra/c-summit-2013-eventual-consistency-
hopeful-consistency-by-christos-kalantzis

UPDATE USERS
SET email = ’jonathan@datastax.com’, ...
IF email = ’jbellis@datastax.com’;
INSERT INTO USERS (username, email, ...)
VALUES (‘jbellis’, ‘jbellis@datastax.com’, ... )
IF NOT EXISTS;
Using LWT

Triggers
CREATE TRIGGER <name> ON <table> USING <classname>;

Trigger implementation
class MyTrigger implements ITrigger
{
public Collection<RowMutation> augment(ByteBuffer key, ColumnFamily update)
{
...
}
}

Experimental!
• Relies on internal RowMutation, ColumnFamily classes
• [partition] key is a ByteBuffer
• Expect changes in 2.1

Compaction
• Single-pass, always
• LCS performs STCS in L0

Cursors (before)
SELECT *
FROM timeline
WHERE (user_id = :last_key
AND tweet_id > :last_tweet)
OR token(user_id) > token(:last_key)
LIMIT 100
CREATE TABLE timeline (
  user_id uuid,
  tweet_id timeuuid,
  tweet_author uuid,
tweet_body text,
  PRIMARY KEY (user_id, tweet_id)
);

Cursors (after)
SELECT *
FROM timeline

Misc. performance improvements

• Tracking statistics on clustered columns allows eliminating unnecessary
sstables from the read path

• New half-synchronous, half-asynchronous Thrift server based on LMAX
Disruptor

Disruptor
• Faster partition index lookups and cache reads by improving performance
of off-heap memory

Disruptor
of off-heap memory
• Faster reads of compressed data by switching from CRC32 to Adler
checksums

Disruptor
of off-heap memory
• Faster reads of compressed data by switching from CRC32 to Adler
checksums
• JEMalloc support for off-heap allocation

Spring cleaning
• Removed compatibility with pre-1.2.5 sstables and pre-1.2.9 schema

Spring cleaning
• The potentially dangerous countPendingHints JMX call has been replaced
by a Hints Created metric

Spring cleaning
• The on-heap partition cache (“row cache”) has been removed

Spring cleaning
• Vnodes are on by default

Spring cleaning
• the old token range bisection code for non-vnode clusters is gone

Spring cleaning
• the old token range bisection code for non-vnode clusters is gone
• Removed emergency memory pressure valve logic

Operational concerns
• Java7 is now required!

• Leveled compaction level information has been moved into sstable
metadata

metadata
• Kernel page cache skipping has been removed in favor of optional row
preheating (preheat_kernel_page_cache)

metadata
• Streaming has been rewritten to be more transparent and robust.

metadata
• Streaming has been rewritten to be more transparent and robust.
• Streaming support for old-version sstables

London + Dublin Cassandra 2.0

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