org.tools4j.elara.application

Interface DuplicateHandler

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface DuplicateHandler

Duplicate commands and events are detected and skipped by the engine. This handler allows applications to log react in such situations for instance to log an information or warning message.

Field Summary

Fields

Modifier and Type	Field and Description
static DuplicateHandler	DEFAULT Default handler printing only dropped commands to system output
static DuplicateHandler	NOOP No-op handler silently ignoring all duplicates.

Method Summary

Modifier and Type	Method and Description
void	dropCommandReceived(Command command) A command is dropped and not appended to the command log because it is already stored there.
default void	skipCommandProcessing(Command command) Command processing is skipped as all events for this command ID have already been applied.
default void	skipEventApplying(Event event) Event applying is skipped because it has already been applied.

Field Detail

DEFAULT

static final DuplicateHandler DEFAULT

Default handler printing only dropped commands to system output

NOOP

static final DuplicateHandler NOOP

No-op handler silently ignoring all duplicates.

Method Detail

skipCommandProcessing

default void skipCommandProcessing(Command command)

Command processing is skipped as all events for this command ID have already been applied.

This usually happens when

1. events from the event log are reapplied to reconstruct the application state
2. subsequently commands for the same events are processed for instance by replaying the command log

Parameters:

command - the skipped command

skipEventApplying

default void skipEventApplying(Event event)

Event applying is skipped because it has already been applied.

This usually happens when

1. events are directly applied in the same run when commands are processed
2. subsequently the same events are polled from the event log and attempted to reapply

Parameters:

event - the skipped event

dropCommandReceived

void dropCommandReceived(Command command)

A command is dropped and not appended to the command log because it is already stored there.

This can happen when upstream applications re-send messages and those messages are identified as duplicates by the sequencer. Duplicates are identified via unique (input-id/sequence) pair of the command. Duplicate detection utilises the constraint that sequences must be monotonically increasing per input.

Parameters:

command - the dropped command