Failed Partitions

Chronicle partitions the events an observer (a reactor, reducer, or projection) processes — typically by event source id — so many partitions can make progress independently. When a handler keeps failing for a partition, Chronicle stops retrying it and marks it failed, without blocking any other partition; events already applied to other partitions keep flowing. Use eventStore.failedPartitions to inspect the partitions an observer has given up on.

API

eventStore.failedPartitions exposes:

• getAllFailedPartitions() — every failed partition, across every observer.
• getFailedPartitionsFor(observerId) — failed partitions for one specific observer (reactor/reducer) identifier.

Both return a FailedPartition[]:

Property	Description
id	Unique identifier of the failed partition registration.
observerId	The identifier of the observer (reactor/reducer) the partition failed for.
partition	The partition key that failed (typically an event source id).
attempts	Every attempt Chronicle made at processing the partition, oldest first.

Each FailedPartitionAttempt carries:

Property	Description
occurred	When the attempt happened.
sequenceNumber	The sequence number being processed at the time of failure.
messages	Error message(s) captured for the attempt.
stackTrace	The associated stack trace, if any.

Example

import { ChronicleClient, ChronicleOptions } from '@cratis/chronicle';

const client = new ChronicleClient(ChronicleOptions.development());
const eventStore = await client.getEventStore('MyStore');

const failedPartitions = await eventStore.failedPartitions.getAllFailedPartitions();
for (const failedPartition of failedPartitions) {
    console.log(`Observer ${failedPartition.observerId} failed partition ${failedPartition.partition}`);
    for (const attempt of failedPartition.attempts) {
        console.log(`  [seq ${attempt.sequenceNumber.value}] ${attempt.messages.join('; ')}`);
    }
}

client.dispose();

Get failed partitions for a specific observer

const reactorFailures = await eventStore.failedPartitions.getFailedPartitionsFor('HrNotificationReactor');

Waiting for completion instead of polling

Rather than polling failedPartitions after an append, AppendResult.waitForCompletion() waits (5 second default timeout) for every observer affected by that specific append to either catch up or fail, and reports any failed partitions directly:

const result = await eventStore.eventLog.append('order-123', new OrderShipped());
const completion = await result.waitForCompletion();
if (!completion.isSuccess) {
    for (const failedPartition of completion.failedPartitions) {
        console.log(`Observer ${failedPartition.observerId} failed partition ${failedPartition.partition}`);
    }
}

See Event Log for more on waitForCompletion.