Package org.opensearch.cluster.coordination

Class FollowersChecker

java.lang.Object

org.opensearch.cluster.coordination.FollowersChecker

public class FollowersChecker
extends Object

The FollowersChecker is responsible for allowing a leader to check that its followers are still connected and healthy. On deciding that a follower has failed the leader will remove it from the cluster. We are fairly lenient, possibly allowing multiple checks to fail before considering a follower to be faulty, to allow for a brief network partition or a long GC cycle to occur without triggering the removal of a node and the consequent shard reallocation.

Opensearch.internal:

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	FollowersChecker.FollowerCheckRequest	Request to check follower.

Field Summary

Fields

Modifier and Type	Field	Description
static final String	FOLLOWER_CHECK_ACTION_NAME
static final Setting<org.opensearch.common.unit.TimeValue>	FOLLOWER_CHECK_INTERVAL_SETTING
static final Setting<Integer>	FOLLOWER_CHECK_RETRY_COUNT_SETTING
static final Setting<org.opensearch.common.unit.TimeValue>	FOLLOWER_CHECK_TIMEOUT_SETTING

Constructor Summary

Constructors

Constructor	Description
FollowersChecker(Settings settings, ClusterSettings clusterSettings, TransportService transportService, Consumer<FollowersChecker.FollowerCheckRequest> handleRequestAndUpdateState, BiConsumer<DiscoveryNode,String> onNodeFailure, NodeHealthService nodeHealthService, ClusterManagerMetrics clusterManagerMetrics)

Method Summary

Modifier and Type	Method	Description
void	clearCurrentNodes()	Clear the set of known nodes, stopping all checks.
Set<DiscoveryNode>	getFaultyNodes()
void	setCurrentNodes(DiscoveryNodes discoveryNodes)	Update the set of known nodes, starting to check any new ones and stopping checking any previously-known-but-now-unknown ones.
String	toString()
void	updateFastResponseState(long term, Coordinator.Mode mode)	The system is normally in a state in which every follower remains a follower of a stable leader in a single term for an extended period of time, and therefore our response to every follower check is the same.

Methods inherited from class java.lang.Object

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

Field Details

FOLLOWER_CHECK_ACTION_NAME

public static final String FOLLOWER_CHECK_ACTION_NAME

See Also:

• Constant Field Values

FOLLOWER_CHECK_INTERVAL_SETTING

public static final Setting<org.opensearch.common.unit.TimeValue> FOLLOWER_CHECK_INTERVAL_SETTING

FOLLOWER_CHECK_TIMEOUT_SETTING

public static final Setting<org.opensearch.common.unit.TimeValue> FOLLOWER_CHECK_TIMEOUT_SETTING

FOLLOWER_CHECK_RETRY_COUNT_SETTING

public static final Setting<Integer> FOLLOWER_CHECK_RETRY_COUNT_SETTING

Constructor Details

FollowersChecker

public FollowersChecker(Settings settings,
 ClusterSettings clusterSettings,
 TransportService transportService,
 Consumer<FollowersChecker.FollowerCheckRequest> handleRequestAndUpdateState,
 BiConsumer<DiscoveryNode,String> onNodeFailure,
 NodeHealthService nodeHealthService,
 ClusterManagerMetrics clusterManagerMetrics)

Method Details

setCurrentNodes

public void setCurrentNodes(DiscoveryNodes discoveryNodes)

Update the set of known nodes, starting to check any new ones and stopping checking any previously-known-but-now-unknown ones.

clearCurrentNodes

public void clearCurrentNodes()

Clear the set of known nodes, stopping all checks.

updateFastResponseState

public void updateFastResponseState(long term,
 Coordinator.Mode mode)

The system is normally in a state in which every follower remains a follower of a stable leader in a single term for an extended period of time, and therefore our response to every follower check is the same. We handle this case with a single volatile read entirely on the network thread, and only if the fast path fails do we perform some work in the background, by notifying the FollowersChecker whenever our term or mode changes here.

getFaultyNodes

public Set<DiscoveryNode> getFaultyNodes()

Returns:

nodes in the current cluster state which have failed their follower checks.

toString

public String toString()

Overrides:

toString in class Object