@AYeschenko

Aleksey YeschenkoApache Cassandra Committer, Engineer @DataStax

What’s New in Cassandra 2.0

What’s new in Cassandra 2.0• Lightweight transactions (CAS)• Eager retries•Native protocol V2•Notable Internal improvements•New CQL3 features• Triggers (prototype!)

CAS

CAS: When

SELECT * FROM usersWHERE username = ’jbellis’

[empty resultset]

INSERT INTO users (...)VALUES (’jbellis’, ...)

Session 1SELECT * FROM usersWHERE username = ’jbellis’

[empty resultset]

INSERT INTO users (...)VALUES (’jbellis’, ...)

Session 2

When you absolutely require linearizable consistency (think - safely creating a user with a unique username)

CAS: How• Based on the Paxos consensus protocol• Paxos state is durable• All operations are quorum-based• Immediate consistency with no leader election or failover• Relatively expensive - requires 4 round trips vs. 1 for regular updates. Use only in the parts of your application where it’s really needed• ConsistencyLevel.SERIAL

CAS: CQL3// Insert a user with a unique username

INSERT INTO USERS (username, email, name)

VALUES ('jbellis', 'jbellis@datastax.com', 'Jonathan Ellis')

IF NOT EXISTS

// Reset user’s password transactionally

UPDATE usersSET reset_token = null AND password = ‘newpassword’IF reset_token = ‘some-generated-reset-token’

CAS: Further Reading• http://www.datastax.com/dev/blog/lightweight-transactions-in-cassandra-2-0• Paxos Made Simple: http://www.cs.utexas.edu/users/lorenzo/corsi/cs380d/past/03F/notes/paxos-simple.pdf• http://the-paper-trail.org/blog/consensus-protocols-paxos/

Eager Retries

Eager Retries•New per-table setting: speculative_retry (NONE|Xpercentile|Xms|ALWAYS)•Will issue extra read commands to other replicas behind the scenes if the current one(s) isn’t (aren’t) responding within the configured milliseconds/percentile•Minimizes read latencies, reduces the occurrence of read timeouts if one or several of the replicas crash or become overloaded• https://issues.apache.org/jira/browse/CASSANDRA-4705

Native Proto V2

Native Proto V2• Paging (cursors)• Batching prepared statements• Parametrized statements without the explicit prepare phase

Native Proto V2: PagingStatement stmt = new SimpleStatement("SELECT * FROM images");

stmt.setFetchSize(100);

ResultSet result = session.execute(stmt);

// Iterate over the ResultSet here (will transparently fetch new pages)

for (Row row : result) {

handleRow(row);

}

Native Proto V2: Paging

Native Proto V2: Paging• Paging state = last seen partition key + last seen cell name + remaining, opaque• https://issues.apache.org/jira/browse/CASSANDRA-4415

Native Proto V2: Batching PreparedPreparedStatement ps = session.prepare("INSERT INTO messages (user_id, msg_id, title, body) VALUES (?, ?, ?, ?)");

BatchStatement batch = new BatchStatement();

batch.add(ps.bind(uid, mid1, title1, body1));

batch.add(ps.bind(uid, mid2, title2, body2));

batch.add(ps.bind(uid, mid3, title3, body3));

session.execute(batch);

Native Proto V2: Batching Prepared• Variable statements count• Can mix prepared and non-prepared statements in a single batch• Fast• https://issues.apache.org/jira/browse/CASSANDRA-4693

Native Proto V2: Parametrized Queries// execute(String query, Object... values)

// executeAsync(String query, Object... values)

session.execute(

"INSERT INTO images (image_id, title, bytes) VALUES (?, ?, ?)",

imageId, imageTitle, imageBytes

);

Native Proto V2: Parametrized Queries•One-off prepare+execute w/out the explicit prepare phase•No need to escape the values•No need to serialize non-string data as strings• Esp. handy for blobs• https://issues.apache.org/jira/browse/CASSANDRA-5349

(Some) Notable Internal Improvements• Rewritten Streaming (CASSANDRA-5286)• Tracking max/min values on clustering columns for optimized reads (CASSANDRA-5514)• Single pass compaction roughly doubling compaction speed for large partitions (CASSANDRA-4180)• Size-tiered compaction for LCS L0 when it gets behind (CASSANDRA-5371)•Default LCS sstable size increased to 160MB (from 5MB) (CASSANDRA-5727)• http://www.datastax.com/dev/blog/whats-under-the-hood-in-cassandra-2-0

New CQL3 Features

New CQL3 Features• ALTER TABLE DROP• 2i on PRIMARY KEY columns• Preparing TIMESTAMP, TTL and LIMIT• Listing partition keys

CQL3: ALTER TABLE DROPALTER TABLE <table> DROP <column>;

// Immediately removes the column from table’s metadata

// Lazily gets rid of the data during compaction

CQL3: 2i on PRIMARY KEY columnsCREATE TABLE timeline (

event_id uuid,

week_in_year int,

created_at timeuuid,

content blob,

PRIMARY KEY ((event_id, week_in_year), created_at)

);

-- Invalid in C* 1.2, valid now in C* 2.0:

CREATE INDEX ON demo (event_id);

CREATE INDEX ON demo (week_in_year);

CREATE INDEX ON demo (created_at);

CQL3: Preparing Query Options// Preparing LIMIT

session.prepare("SELECT * FROM foo LIMIT ?");

// Preparing TIMESTAMP and TTL

session.prepare("UPDATE foo USING TIMESTAMP ? AND TTL ? SET bar = ? WHERE baz = ?");

CQL3: Listing Partition KeysSELECT event_id, week_in_year FROM timeline;

event_id | week_in_year

--------------------------------------+--------------

b27288fa-a4cd-4c1d-b0eb-55a8fe0f9ec0 | 1

b27288fa-a4cd-4c1d-b0eb-55a8fe0f9ec0 | 1

eb58d408-b264-41b9-928e-dd6c0e52888e | 1

eb58d408-b264-41b9-928e-dd6c0e52888e | 1

b27288fa-a4cd-4c1d-b0eb-55a8fe0f9ec0 | 2

b27288fa-a4cd-4c1d-b0eb-55a8fe0f9ec0 | 2

SELECT DISTINCT event_id, week_in_year FROM timeline;

event_id | week_in_year

--------------------------------------+--------------

b27288fa-a4cd-4c1d-b0eb-55a8fe0f9ec0 | 1

eb58d408-b264-41b9-928e-dd6c0e52888e | 1

b27288fa-a4cd-4c1d-b0eb-55a8fe0f9ec0 | 2

Triggers (Prototype!)

Triggers Interfacepublic interface ITrigger

{

/**

* Called exactly once per CF update, returned mutations are atomically updated.

*

* @param key - Row Key for the update.

* @param update - Update received for the CF

* @return modifications to be applied, null if no action to be performed.

*/

public Collection<RowMutation> augment(ByteBuffer key, ColumnFamily update);

}

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

DROP TRIGGER <name> ON <table>;

Triggers Summary• Prototype• Relies on logged batches• Exposes internal classes - RowMutation, ColumnFamily• Expect changes in 2.1• http://www.datastax.com/dev/blog/whats-new-in-cassandra-2-0-prototype-triggers-support

Questions?