Class LatestUpdateMergePolicy<K,V>

java.lang.Object

com.loomcache.server.wan.merge.LatestUpdateMergePolicy<K,V>

Type Parameters:

K - key type

V - value type

All Implemented Interfaces:

MergePolicy<K,V>

public final class LatestUpdateMergePolicy<K,V>
extends Object
implements MergePolicy<K,V>

Last-write-wins (LWW) merge policy with deterministic same-millisecond tie-break (BLK-2026-04-22-011).

Resolution order:

1. Higher timestampMs wins.
2. On timestamp tie, lexicographically greater writerNodeId wins. String.compareTo(String) is commutative across replicas, so two independently-resolving nodes converge to the same winner regardless of arrival order.
3. On full tie (same timestamp + same writerNodeId):
   • If both values are equal, this is an idempotent retry — return existing so no listener event fires.
   • If values differ, the inputs are inconsistent with the tie-break contract (two writes from the same writer on the same millisecond cannot legitimately produce different values). Return Optional.empty() to reject the incoming and log an error citing BLK-2026-04-22-011 so operators can investigate.

If existing is null, the incoming value is always accepted.

Since:

2.0

Nested Class Summary

Nested classes/interfaces inherited from interface MergePolicy

MergePolicy.MergeEntry<V>

Field Summary

Fields inherited from interface MergePolicy

NO_EXPIRATION_TIME_MILLIS

Constructor Summary

Constructors

Constructor	Description
LatestUpdateMergePolicy()

Method Summary

Modifier and Type	Method	Description
static <K,V> @NonNull LatestUpdateMergePolicy<K,V>	instance()	Return the shared instance of this stateless policy.
@NonNull Optional<V>	merge(@NonNull K key, @NonNull MergePolicy.MergeEntry<V> incoming, @Nullable MergePolicy.MergeEntry<V> existing)	Merge an incoming replication entry against the existing local entry.

Methods inherited from class Object

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

Constructor Details

LatestUpdateMergePolicy

public LatestUpdateMergePolicy()

Method Details

instance

public static <K,V>
@NonNull LatestUpdateMergePolicy<K,V> instance()

Return the shared instance of this stateless policy.

Type Parameters:

K - key type

V - value type

Returns:

a shared LatestUpdateMergePolicy instance

merge

public @NonNull Optional<V> merge(@NonNull K key,
 @NonNull MergePolicy.MergeEntry<V> incoming,
 @Nullable MergePolicy.MergeEntry<V> existing)

Description copied from interface: MergePolicy

Merge an incoming replication entry against the existing local entry.

Specified by:

merge in interface MergePolicy<K,V>

Parameters:

key - the key being replicated (non-null)

incoming - the incoming entry from the remote cluster (non-null)

existing - the current local entry, or null if the key has no local value

Returns:

the value to keep (non-empty to apply, empty to reject the incoming)