CONTINUE Command Overview

Purpose

The primary purpose of the CONTINUE command is to:

1. Resume event delivery for a specific event type that was previously paused

2. Allow clients to manage their event processing capacity by controlling when they receive events

3. Provide a mechanism to handle temporary processing backlogs without losing events

When to Use

Use the CONTINUE command when:

• Your client has caught up with processing its backlog and is ready to receive new events

• A temporary processing issue has been resolved

• You want to resume normal event flow after a maintenance period

• You need to selectively resume specific event types while keeping others paused

How It Works

1. Validation: The system verifies that:

   • The client exists and is authenticated

   • The client has an active subscription to the specified event type

   • The subscription is currently in a paused state

2. Resumption: When a subscription is continued:

   • The subscription's state is changed from "paused" to "active"

   • Any events that were queued during the pause period are delivered

   • New events begin flowing to the client immediately

3. Position Preservation: The client's position in the event stream is maintained:

   • Events are delivered from the point where the client last acknowledged

   • No events are skipped or lost during the pause/continue cycle

Relationship to Other Commands

• PAUSE: The counterpart to CONTINUE, used to temporarily stop event delivery

• SUB: Establishes the initial subscription that can later be paused or continued

• UNSUB: Permanently removes a subscription (unlike PAUSE which is temporary)

• ACK: Still required to acknowledge events after continuing a subscription

Best Practices

1. Selective Continuation: Only continue subscriptions when your client is ready to process events

2. Monitoring: Track the number of queued events during pause periods to anticipate processing load

3. Backpressure Management: Use pause/continue cycles strategically to implement backpressure

4. Error Handling: Implement proper error handling for the case where a subscription cannot be continued

5. Domain-Level Control: Use wildcards to continue multiple related event types at once

Implementation Details

The CONTINUE command is implemented in the EnSyncMaster system using:

• A state management system that tracks subscription status

• Event queuing mechanisms that buffer events during pause periods

• Client position tracking to ensure event delivery continuity

• Permission checks to ensure only authorized clients can continue subscriptions

Security Considerations

• Only the client that owns a subscription can continue it

• Clients can only continue subscriptions to event types they have permission to receive

• The system validates client authentication before processing continue requests