Package org.axonframework.eventsourcing.eventstore

Class ConflictDiagnosingEventStorageEngine

java.lang.Object

org.axonframework.eventsourcing.eventstore.ConflictDiagnosingEventStorageEngine

All Implemented Interfaces:

DescribableComponent, EventStorageEngine

@Internal
public class ConflictDiagnosingEventStorageEngine
extends Object
implements EventStorageEngine

Decorator for an EventStorageEngine that, upon an AppendEventsTransactionRejectedException, identifies an event that caused the rejection.

It does so by sourcing the same criteria used for the rejected append, starting from the violated consistency marker, and taking the first event returned. Any event returned by that lookup matches the criteria beyond the marker, which is exactly what an append rejection reports. The lookup always identifies a genuine conflicting event, regardless of how many criteria the condition combines, and without needing any storage-engine-specific knowledge of how the conflict was detected. Only the first match is fetched, closing the underlying read as soon as it is found, since a single example is enough to confirm and reproduce a conflict.

This lookup is an additional read against the wrapped delegate, performed only after a rejection has already occurred, so it does not add cost to the common, successful append path. It is not enabled by default; wrap an EventStorageEngine with this decorator to opt into it, for example while reproducing a specific issue.

All other operations are delegated to the wrapped engine unchanged.

Since:

5.3.2

Author:

John Hendrikx

Nested Class Summary

Nested classes/interfaces inherited from interface org.axonframework.eventsourcing.eventstore.EventStorageEngine

EventStorageEngine.AppendTransaction<R>

Constructor Summary

Constructors

Constructor	Description
ConflictDiagnosingEventStorageEngine(EventStorageEngine delegate)	Constructs a ConflictDiagnosingEventStorageEngine wrapping the given delegate.

Method Summary

Modifier and Type	Method	Description
CompletableFuture<EventStorageEngine.AppendTransaction<?>>	appendEvents(AppendCondition condition, @Nullable ProcessingContext context, List<TaggedEventMessage<?>> events)	Appends a List of events to the underlying storage solution.
void	describeTo(ComponentDescriptor descriptor)	Describe the properties of this DescribableComponent with the given descriptor.
CompletableFuture<TrackingToken>	firstToken()	Creates a TrackingToken that is at the first position of an event stream.
CompletableFuture<TrackingToken>	latestToken()	Creates a TrackingToken that is at the latest position of an event stream.
MessageStream<EventMessage>	source(SourcingCondition condition, @Nullable ProcessingContext context)	Creates a finite MessageStream of events matching the given condition, carrying along the active ProcessingContext.
MessageStream<EventMessage>	stream(StreamingCondition condition)	Creates an infinite MessageStream of events matching the given condition.
CompletableFuture<TrackingToken>	tokenAt(Instant at)	Creates a TrackingToken that tracks all events after the given at.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.axonframework.eventsourcing.eventstore.EventStorageEngine

appendEvents, source

Constructor Details

ConflictDiagnosingEventStorageEngine

public ConflictDiagnosingEventStorageEngine(EventStorageEngine delegate)

Constructs a ConflictDiagnosingEventStorageEngine wrapping the given delegate.

Parameters:

delegate - the EventStorageEngine to delegate to, and to source conflicting events from, cannot be null

Method Details

appendEvents

public CompletableFuture<EventStorageEngine.AppendTransaction<?>> appendEvents(AppendCondition condition,
 @Nullable ProcessingContext context,
 List<TaggedEventMessage<?>> events)

Description copied from interface: EventStorageEngine

Appends a List of events to the underlying storage solution.

Events will be appended in the order that they are offered in, validating the given condition before being stored. Note that all events should have a unique event identifier. Tags paired with the events will be stored as well.

Implementations may be able to detect conflicts during the append stage. In such case, the returned completable future will complete exceptionally, indicating such conflict. Other implementations may delay such checks until the EventStorageEngine.AppendTransaction.commit() is called.

Called during the

invalid reference

APPEND_EVENTS

phase, which follows PREPARE_COMMIT.

Specified by:

appendEvents in interface EventStorageEngine

Parameters:

condition - The condition describing the transactional requirements for the append transaction

context - The current ProcessingContext, if any.

events - The List of events to append to the underlying storage solution.

Returns:

A transaction instance that can be committed or rolled back.

source

public MessageStream<EventMessage> source(SourcingCondition condition,
 @Nullable ProcessingContext context)

Description copied from interface: EventStorageEngine

Creates a finite MessageStream of events matching the given condition, carrying along the active ProcessingContext.

Behaves identically to EventStorageEngine.source(SourcingCondition); the context is passed to decorators (for example snapshot-loading and tracing decorators) that need to correlate the sourcing operation with the surrounding unit of work.

Specified by:

source in interface EventStorageEngine

Parameters:

condition - the SourcingCondition dictating the stream of events to source

context - the ProcessingContext active while sourcing; may be null

Returns:

a finite MessageStream of events matching the given condition

stream

public MessageStream<EventMessage> stream(StreamingCondition condition)

Description copied from interface: EventStorageEngine

Creates an infinite MessageStream of events matching the given condition.

The condition may dictate the StreamingCondition.position() to start streaming from, as well as define filter criteria for the returned MessageStream.

Specified by:

stream in interface EventStorageEngine

Parameters:

condition - The StreamingCondition dictating the StreamingCondition.position() to start streaming from, as well as the filter criteria used for the returned MessageStream.

Returns:

An infinite MessageStream of events matching the given condition.

firstToken

public CompletableFuture<TrackingToken> firstToken()

Description copied from interface: EventStorageEngine

Creates a TrackingToken that is at the first position of an event stream.

In other words, a token that tracks events from the beginning of time.

Specified by:

firstToken in interface EventStorageEngine

Returns:

A CompletableFuture of a TrackingToken at the first position of an event stream.

latestToken

public CompletableFuture<TrackingToken> latestToken()

Description copied from interface: EventStorageEngine

Creates a TrackingToken that is at the latest position of an event stream.

In other words, a token that tracks all new events from this point forward.

Specified by:

latestToken in interface EventStorageEngine

Returns:

A CompletableFuture of a TrackingToken at the latest position of an event stream.

tokenAt

public CompletableFuture<TrackingToken> tokenAt(Instant at)

Description copied from interface: EventStorageEngine

Creates a TrackingToken that tracks all events after the given at.

If there is an event exactly at the given at, it will be tracked too.

Specified by:

tokenAt in interface EventStorageEngine

Parameters:

at - The Instant determining how the TrackingToken should be created. A tracking token should point to very first event before this Instant.

Returns:

A CompletableFuture of a TrackingToken at the given at, if there aren't events matching this criteria null is returned

describeTo

public void describeTo(ComponentDescriptor descriptor)

Description copied from interface: DescribableComponent

Describe the properties of this DescribableComponent with the given descriptor.

Components should call the appropriate describeProperty methods on the descriptor to register their properties. The descriptor is responsible for determining how these properties are formatted and structured in the final output.

Best Practices: As a general rule, all relevant fields of a DescribableComponent implementation should be described in this method. However, developers have discretion to include only the fields that make sense in the context. Not every field may be meaningful for description purposes, especially internal implementation details. Furthermore, components might want to expose different information based on their current state. The final decision on what properties to include lies with the person implementing the describeTo method, who should focus on providing information that is useful for understanding the component's configuration and state.

Example implementation:

 public void describeTo(ComponentDescriptor descriptor) {
     descriptor.describeProperty("name", this.name);
     descriptor.describeProperty("enabled", this.enabled);
     descriptor.describeProperty("configuration", this.configuration); // A nested component
     descriptor.describeProperty("handlers", this.eventHandlers);      // A collection
 }
 

Specified by:

describeTo in interface DescribableComponent

Parameters:

descriptor - The component descriptor to describe this DescribableComponentn its properties in.