org.eclipse.jgit.internal.ketch

Class KetchSystem

java.lang.Object

org.eclipse.jgit.internal.ketch.KetchSystem

public class KetchSystem
extends Object

Ketch system-wide configuration.

This class provides useful defaults for testing and small proof of concepts. Full scale installations are expected to subclass and override methods to provide consistent configuration across all managed repositories.

Servers should configure their own ScheduledExecutorService.

Constructor Summary

Constructors

Constructor and Description
KetchSystem() Create a default system with a thread pool of 1 thread per CPU.
KetchSystem(ScheduledExecutorService executor, MonotonicClock clock, String txnNamespace) Create a Ketch system with the provided executor service.

Method Summary

Modifier and Type	Method and Description
KetchLeader	createLeader(Repository repo) Construct the KetchLeader instance of a repository.
protected List<KetchReplica>	createReplicas(KetchLeader leader, Repository repo) Get the collection of replicas for a repository.
static ScheduledExecutorService	defaultExecutor() Get default executor, one thread per available processor.
MonotonicClock	getClock() Get clock to obtain timestamps from.
ScheduledExecutorService	getExecutor() Get executor to perform background operations.
Duration	getMaxWaitForMonotonicClock() Get how long the leader will wait for the getClock()'s ProposedTimestamp used in commits proposed to the RefTree graph (getTxnAccepted())
String	getTxnAccepted() Get name of the accepted RefTree graph.
String	getTxnCommitted() Get name of the committed RefTree graph.
String	getTxnNamespace() Get the namespace used for the RefTree graph and transaction management.
String	getTxnStage() Get prefix for staged objects, e.g.
PersonIdent	newCommitter(ProposedTimestamp time) Create new committer PersonIdent for ketch system
String	newLeaderTag() Construct a random tag to identify a candidate during leader election.
boolean	requireMonotonicLeaderElections() Whether elections should require monotonically increasing commit timestamps

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

KetchSystem

public KetchSystem()

Create a default system with a thread pool of 1 thread per CPU.

KetchSystem

public KetchSystem(ScheduledExecutorService executor,
                   MonotonicClock clock,
                   String txnNamespace)

Create a Ketch system with the provided executor service.

Parameters:

executor - thread pool to run background operations.

clock - clock to create timestamps.

txnNamespace - reference namespace for the RefTree graph and associated transaction state. Must begin with "refs/" and end with '/', for example "refs/txn/".

Method Detail

defaultExecutor

public static ScheduledExecutorService defaultExecutor()

Get default executor, one thread per available processor.

Returns:

default executor, one thread per available processor.

getExecutor

public ScheduledExecutorService getExecutor()

Get executor to perform background operations.

Returns:

executor to perform background operations.

getClock

public MonotonicClock getClock()

Get clock to obtain timestamps from.

Returns:

clock to obtain timestamps from.

getMaxWaitForMonotonicClock

public Duration getMaxWaitForMonotonicClock()

Get how long the leader will wait for the getClock()'s ProposedTimestamp used in commits proposed to the RefTree graph (getTxnAccepted())

Returns:

how long the leader will wait for the getClock()'s ProposedTimestamp used in commits proposed to the RefTree graph (getTxnAccepted()). Defaults to 5 seconds.

requireMonotonicLeaderElections

public boolean requireMonotonicLeaderElections()

Whether elections should require monotonically increasing commit timestamps

Returns:

true if elections should require monotonically increasing commit timestamps. This requires a very good MonotonicClock.

getTxnNamespace

public String getTxnNamespace()

Get the namespace used for the RefTree graph and transaction management.

Returns:

reference namespace such as "refs/txn/".

getTxnAccepted

public String getTxnAccepted()

Get name of the accepted RefTree graph.

Returns:

name of the accepted RefTree graph.

getTxnCommitted

public String getTxnCommitted()

Get name of the committed RefTree graph.

Returns:

name of the committed RefTree graph.

getTxnStage

public String getTxnStage()

Get prefix for staged objects, e.g. "refs/txn/stage/".

Returns:

prefix for staged objects, e.g. "refs/txn/stage/".

newCommitter

public PersonIdent newCommitter(ProposedTimestamp time)

Create new committer PersonIdent for ketch system

Parameters:

time - timestamp for the committer.

Returns:

identity line for the committer header of a RefTreeGraph.

newLeaderTag

@Nullable
public String newLeaderTag()

Construct a random tag to identify a candidate during leader election.

Multiple processes trying to elect themselves leaders at exactly the same time (rounded to seconds) using the same newCommitter(ProposedTimestamp) identity strings, for the same term, may generate the same ObjectId for the election commit and falsely assume they have both won.

Candidates add this tag to their election ballot commit to disambiguate the election. The tag only needs to be unique for a given triplet of newCommitter(ProposedTimestamp), system time (rounded to seconds), and term. If every replica in the system uses a unique newCommitter (such as including the host name after the "@" in the email address) the tag could be the empty string.

The default implementation generates a few bytes of random data.

Returns:

unique tag; null or empty string if newCommitter() is sufficiently unique to identify the leader.

createLeader

public KetchLeader createLeader(Repository repo)
                         throws URISyntaxException

Construct the KetchLeader instance of a repository.

Parameters:

repo - local repository stored by the leader.

Returns:

leader instance.

Throws:

URISyntaxException - a follower configuration contains an unsupported URI.

createReplicas

protected List<KetchReplica> createReplicas(KetchLeader leader,
                                            Repository repo)
                                     throws URISyntaxException

Get the collection of replicas for a repository.

The collection of replicas must include the local repository.

Parameters:

leader - the leader driving these replicas.

repo - repository to get the replicas of.

Returns:

collection of replicas for the specified repository.

Throws:

URISyntaxException - a configured URI is invalid.