Package com.atlassian.crowd.event

Class TimestampBasedEventStore

java.lang.Object
com.atlassian.crowd.event.TimestampBasedEventStore
All Implemented Interfaces:
EventStore
public class TimestampBasedEventStore extends Object implements EventStore
A cluster-safe implementation of EventStore that uses the entity creation and update timestamp, and the persisted tombstone information to create an event stream. The produced event streams may be different than the ones produced by @link com.atlassian.crowd.event.EventStoreGeneric, but should lead to creating the same state to the caller replaying the stream (i.e. doing an incremental sync), assuming all operations are idempotent (i.e. adding an entity that's added is not an error, but causes an update; deleting a missing entity is not an error).

Some caveats: - to alleviate for timestamp skew and operations that are not committed when fetching the events, the implementation produces a sync token that will cause events from a few minutes before the sync to be returned again during the next sync. As long as events are idempotent this shouldn't change the state of the caller. - some events make recreating the event stream impossible, and will throw EventTokenExpiredException as per contract because of the replaying this will make incremental sync impossible for the duration of the backoff - alias events are returned in a simplified form, that's different from EventStoreGeneric - as the only usage is to abort incremental sync when an aliasing event occurs, they're all transformed into alias tombstones, and returned a alias deletions - to limit the size of the list materialized in memory, there's a limit to how many events the implementation will return before throwing EventTokenExpiredException. The implementation MIGHT return larger lists if they are already materialized and there's no point in throwing them away.