The document describes the architecture of Cassandra, including its startup process, layers (API, Dynamo, database), services (StorageProxy, MessagingService, Gossip), and failure handling. It also details how nodes communicate via the Gossip protocol to exchange state information and maintain a consistent cluster view.

1. CASSANDRA SUMMIT SF 2014
CONTRIBUTOR BOOT
CAMP
Aaron Morton
@aaronmorton
Co-Founder & Principal Consultant
Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License

2. Architecture
Startup, Shutdown & Failure
StorageProxy
MessagingService
Gossip

3. Dynamo Cluster Architecture
Clients
API's
Dynamo
Database
Disk
API's
Dynamo
Database
Disk
Node 1 Node 2

4. API Layer
o.a.c.auth
o.a.c.cql3
o.a.c.metrics
o.a.c.thrift
o.a.c.transport

5. API Layer
Talks to Dynamo layer using
Commands via the
StorageProxy

6. Dynamo Layer
o.a.c.dht
o.a.c.gms
o.a.c.locator
o.a.c.net
o.a.c.repair
o.a.c.service
o.a.c.streaming

7. Dynamo Layer
Talks to Database layer by
sending messages to
IVerbHandler’s via the
MessagingService.

8. Database Layer
o.a.c.cache
o.a.c.concurrent
o.a.c.db
o.a.c.io
o.a.c.serializers

9. Global Services
o.a.c.config
o.a.c.trace
o.a.c.utils

10. Architecture
Startup, Shutdown & Failure
StorageProxy
MessagingService
Gossip

11. o.a.c.service.CassandraDaemon.main()
!
// Singleton
// Start MBean
setup() // here be magic

12. o.a.c.service.CassandraDaemon.setup()
// JNA
Thread.setDefaultUncaughtExceptionHandler()
// Check directories exist
SystemKeyspace.checkHealth();
DatabaseDescriptor.loadSchemas();
CFS.disableAutoCompaction();
!

13. o.a.c.service.CassandraDaemon.setup()
CommitLog.recover();
StorageService.registerDaemon();
StorageService.initServer();

14. Exception Hook
!
// Exception Metrics
!
FileUtils.handleFSError()
FileUtils.handleCorruptSSTable()

15. Shutdown and Drain Hook
!
// Shutdown client transports
// Shutdown thread pools
// Blocking flush to disk
// Shutdown commit log
!

16. Architecture
Startup, Shutdown & Failure
StorageProxy
MessagingService
Gossip

17. o.a.c.service.StorageProxy
!
// Cluster wide storage operations
// Select endpoints & check CL available
// Send messages to Stages
// Wait for response
// Store Hints

18. o.a.c.service.IResponseResolver
!
preprocess(MessageIn<T> message)
resolve() throws DigestMismatchException
!
RowDigestResolver
RowDataResolver
RangeSliceResponseResolver

19. Response Handlers / Callback
!
implements IAsyncCallback<T>
!
response(MessageIn<T> msg)
!

20. o.a.c.service.ReadCallback.get()
!
//Wait for blockfor & data
condition.await(timeout,
TimeUnit.MILLISECONDS)
!
// if condition not set
throw ReadTimeoutException()
!
resolver.resolve()

21. o.a.c.service.StorageProxy.fetchRows()
!
AbstractReadExecutor.getReadExecutor()
exec.executeAsync();
exec.maybeTryAdditionalReplicas();
---------------------------------------
AbstractReadExecutor.get() //handler.get
catch (DigestMismatchException ex)
catch (ReadTimeoutException ex)

22. AbstractReadExecutor.getReadExecutor()
!
StorageProxy.getLiveSortedEndpoints()
CFMetaData.newReadRepairDecision()
ConsistencyLevel.filterForQuery()
ConsistencyLevel.assureSufficientLiveNodes()
…

23. AbstractReadExecutor.getReadExecutor()
!
// no retry or blocking for all replicas
return new NeverSpeculatingReadExecutor()
!
// always retry or targeting all replicas
return new AlwaysSpeculatingReadExecutor()
!
// otherwise
return new SpeculatingReadExecutor()

24. AbstractReadExecutor()
!
resolver = new RowDigestResolver()
handler = new ReadCallback<>()

25. AbstractReadExecutor.executeAsync()
// makeDataRequests
MessagingService.sendRR(command.createMessage(), endpoint,
handler);
!
// makeDigestRequests
ReadCommand digestCommand = command.copy();
digestCommand.setDigestQuery(true);
MessageOut<?> message = digestCommand.createMessage();
MessagingService.instance().sendRR(message, endpoint,
handler);

26. StorageProxy.mutateAtomically()
!
wrapResponseHandler()
AbstractWriteResponseHandler.assureSufficientLiveNodes()
!
-----------------------------------------------------
getBatchlogEndpoints()
syncWriteToBatchlog() // all mutations
syncWriteBatchedMutations() // all wrappers
asyncRemoveFromBatchlog()
!
catch (UnavailableException e)
catch (WriteTimeoutException e)

27. StorageProxy.wrapResponseHandler()
!
StorageService.getNaturalEndpoints()
TokenMetadata.pendingEndpointsFor()
AbstractReplicationStrategy.getWriteResponseHandler()
-----------------------------------------
!
// AbstractWriteResponseHandler
WriteResponseHandler
DatacenterWriteResponseHandler
DatacenterSyncWriteResponseHandler
ReplayWriteResponseHandler

28. StorageProxy.syncWriteBatchedMutations()
!
// write to natural and pending endpoints
sendToHintedEndpoints()
!
---------------------------------------
!
AbstractWriteResponseHandler.get()

29. StorageProxy.sendToHintedEndpoints()
// loop all targets
MessagingService.sendRR() // for local
!
// group messages for remote DC’s
dcGroups.get(dc).add(destination)
!
// write hints for down nodes
submitHint()
---------------------------------------
!
sendMessagesToNonlocalDC()

30. Architecture
Startup, Shutdown & Failure
StorageProxy
MessagingService
Gossip

31. MessagingService Transport Layer
Custom Serialisation over TCP
Sockets.
Serialisers spread around
code.

32. o.a.c.net.MessagingService.verb<<enum>>
!
MUTATION
READ
REQUEST_RESPONSE
TREE_REQUEST
TREE_RESPONSE
(And more...)

33. o.a.c.net.MessagingService.verbHandlers
!
new EnumMap<Verb,
IVerbHandler>(Verb.class)

34. o.a.c.net.IVerbHandler<T>
!
doVerb(MessageIn<T> message, String id);
!

35. o.a.c.net.MessageIn<T>
public class MessageIn<T>
{
public final InetAddress from;
public final T payload;
public final Map<String, byte[]> parameters;
public final MessagingService.Verb verb;
public final int version;
…
}

36. o.a.c.net.MessageOut<T>
public class MessageOut<T>
{
public final InetAddress
public final MessagingService.Verb verb;
public final T payload;
public final IVersionedSerializer<T>
serializer;
public final Map<String, byte[]> parameters;
…
}

37. o.a.c.net.MessagingService.verbStages
!
new EnumMap<MessagingService.Verb,
Stage>(MessagingService.Verb.class)

38. o.a.c.net.MessagingService.verbStages
!
put(Verb.MUTATION, Stage.MUTATION);
put(Verb.READ, Stage.READ);
put(Verb.REQUEST_RESPONSE,
Stage.REQUEST_RESPONSE);

39. o.a.c.net.MessagingService.receive()
!
runnable = new MessageDeliveryTask(
message, id, timestamp);
!
StageManager.getStage(
message.getMessageType());
!
stage.execute(runnable);

40. o.a.c.net.MessageDeliveryTask.run()
!
// If dropable and rpc_timeout
MessagingService.incrementDroppedMessages(verb
);
!
MessagingService.getVerbHandler(verb)
verbHandler.doVerb(message, id)

41. Architecture
Startup, Shutdown & Failure
StorageProxy
MessagingService
Gossip

42. o.a.c.gms.ApplicationState
!
STATUS,
LOAD,
SCHEMA,
DC,
RACK,
RELEASE_VERSION,
REMOVAL_COORDINATOR,
INTERNAL_IP,
RPC_ADDRESS,
SEVERITY,
NET_VERSION …

43. o.a.c.gms.VersionedValue
!
public final int version;
public final String value;

44. o.a.c.gms.VersionGenerator
{
private static final AtomicInteger version = new
AtomicInteger(0);
!
public static int getNextVersion()
{
return version.incrementAndGet();
}
}

45. o.a.c.gms.EndpointState
{
private volatile HeartBeatState hbState;
final Map<ApplicationState, VersionedValue> applicationState = new
NonBlockingHashMap<ApplicationState, VersionedValue>();
!
}

46. o.a.c.gms.HeartBeatState
{
private int generation;
private int version;
…
}

47. o.a.c.db.SystemKeyspace.incrementAndGetGeneration()
SELECT gossip_generation FROM system.local WHERE key=‘local’;
!
// if none
generation = (int) (System.currentTimeMillis() / 1000);
!
// else
generation = (int) (System.currentTimeMillis() / 1000);
// and some other checks

48. nodetool gossipinfo
generation:1410220170
heartbeat:37
LOAD:1.57821104E8
STATUS:NORMAL,-1007384361686170050
RACK:rack1
NET_VERSION:8
SEVERITY:0.0
RELEASE_VERSION:2.1.0-rc5
SCHEMA:f3b70c8e-a904-3de9-ac5d-8ab30271441d
HOST_ID:4aac20b5-3c68-4a26-a415-2e2f2ff0ed46
RPC_ADDRESS:127.0.0.1

49. o.a.c.gms.Gossiper.GossipTask.run()
Gossip every second.
1 to 3 nodes.
!
Three step process.

50. Processed by IVerbHandlers
I Send SYN.
Remote replies with ACK.
I send ACK2.

51. o.a.c.gms.GossipDigestSyn
Exchange List<GossipDigest>
!
GossipDigest
{
final InetAddress endpoint;
final int generation;
final int maxVersion;
…
}

52. o.a.c.gms.Gossiper.examineGossiper()
// If empty SYN send all my info (shadow gossip)
!
if (remoteGeneration == localGeneration && maxRemoteVersion
== maxLocalVersion)
// do nothing
!
else if (remoteGeneration > localGeneration)
// we request everything from the gossiper
!
else if (remoteGeneration < localGeneration)
// send all data with generation = localgeneration and version >

53. o.a.c.gms.Gossiper.examineGossiper()
else if (remoteGeneration == localGeneration)
!
/*
If the max remote version is greater then we request the remote
endpoint send us all the data for this endpoint with version greater
than the max version number we have locally for this endpoint.
!
If the max remote version is lesser, then we send all the data we
have locally for this endpoint with version greater than the max
remote version.
*/

54. Thanks.
!

55. Aaron Morton
@aaronmorton
!
Co-Founder & Principal Consultant
www.thelastpickle.com
!
Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License