Cassandra 0.7, Los Angeles High Scalability Group

Cassandra 0.7

Friday, December 10, 2010

Features
• Live schema modiﬁcation
• Secondary indexes
• Hadoop OutputFormat
• (Very) large rows
• up to 2 billion columns

• NetworkTopologyStrategy

Operations

• efﬁcient Streaming
• Per-ColumnFamily settings of memtable
thresholds
• Much more (optional) metadata about
columns


Operations backports
• HH disable (0.6.2)

• compaction priority (0.6.3)

• HH hourly scan (0.6.3)

• JMX metrics for row-level bloom ﬁlters (0.6.3)

• Flow control (0.6.4, 5)

• HH paging (0.6.5)

• Dynamic snitch (0.6.5)

• Tombstone removal in minor compaction (0.6.6)


Compatiblity

• Fully backwards-compatible with 0.6 data
• Some Thrift API changes
• String row keys become byte[]

• keyspace is set once per connection

• Requires drain + cluster restart


Features


Live schema changes

• Details: http://www.riptano.com/blog/live-
schema-updates-cassandra-07


Data model tradeoffs

• Twitter: “Fifteen months ago, it took two
weeks to perform ALTER TABLE on the
statuses [tweets] table.”


A static ColumnFamily


A dynamic ColumnFamily


SELECT * FROM tweets
WHERE user_id IN (SELECT follower FROM followers WHERE user_id = ?)

followers timeline
?

?

tweets

SuperColumns = full denormalization


A little deeper

• http://twissandra.com
• http://github.com/jhermes/twissjava


Secondary indexes


demo time

• Reading the slides after the talk? See http://
www.riptano.com/blog/whats-new-
cassandra-07-secondary-indexes


Hadoop OutputFormat
job.setOutputFormatClass(ColumnFamilyOutputFormat.class);
ConfigHelper.setOutputColumnFamily(job.getConfiguration(), KS, CF);
...
public void reduce(Text word, Iterable<IntWritable> values, Context
context)
{
int sum = 0;
for (IntWritable val : values)
sum += val.get();
context.write(outputKey, Collections.singletonList(getMutation
(word, sum)));
}


Large rows

• 0.6: smaller of {2GB, memory limit}
• 0.7: in_memory_compaction_limit_in_mb


NetworkTopologyStrategy

• RackAwareStrategy is tuned for 3 replicas
and 2 data centers
• renamed to OldNetworkTopologyStrategy

• NTS allows conﬁguring replicas per data
center, per Keyspace
• ignores replication_factor directive


Operations


Efﬁcient Streaming
• The following slides show how in 0.7, we
just send the data portion of the sstables
we are moving to a new node over to it
(which is contiguous on disk, no random i/
o), which rebuilds indexes etc
• This minimizes the impact on existing
nodes


W A

F
(A-L]

T

L


W A

F
(A-F]

(A-F]
T
(F-L]
L


W A

F

Data
T

L
Index
Filter

W A

F

T

L
Index
Filter

Per-CF memtable thresholds

• Easier tuning for large numbers of ColumnFamilies


Column Metadata

• 0.6: comparator, subcomparator
• 0.7: default_validation_class,
column_metadata


Native code

• JNA introduced in 0.6.5 for mlockall
• Extended to hard links in 0.6.6


Flow Control (0.6.4)
• Replica nodes drop hopeless requests on
the ﬂoor
• Coordinator node is unaffected

• TimedOutException signals client to back off

• Requires enough memory to buffer
RPCTimeout’s worth of requests

• (In the short term, you’re still screwed)

Flow control in 0.5

• Why backpressure doesn’t ﬁt Cassandra


Dynamic snitch

public void sortByProximity(List<InetAddress> addresses);


Everything else


0.7 performance
• Reads roughly 100% faster, thanks largely to
removing String creation
• Row-cached reads up to 8x faster after
optimizations by tjake and jbellis
• Optimizations for reads of large rows
• 0.7.1? ~15% improvement everywhere from
ByteBuffer optimizations


Thrift: the libpq of Cassandra

• OOMs on malformed packets
• Python Unicode string issues
• PHP support is buggy and maintainerless


Client support from Riptano

• Hector
• Building JPA/JDO layer on top

• pycassa
• phpcassa
• Soon: cassandra gem


After 0.7.0

• IndexOperator.GT
• Triggers / plugins
• Entity groups
• On-disk data format improvements
(Compression, compound keys?)


Summary


Cassandra 0.7, Los Angeles High Scalability Group

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