Implement Dead Letter Queues for Failed Items That Need Manual Review

Some failures cannot be automatically retried or recovered. For these, route failed items to a dead letter queue (DLQ) -- a Google Sheet, database table, or dedicated queue where failed items wait for manual review and reprocessing. This prevents data loss and gives your team a clear remediation process.

Real-world example: A data migration workflow processes 10,000 records. 47 fail due to data quality issues (missing required fields, invalid formats). Rather than losing these records, route them to a DLQ sheet for the data team to fix and reprocess.

// Code node: "Prepare DLQ Entry"
// This runs on the failure branch after the "Split Successes/Failures" node

const failedItems = $input.all();

return failedItems.map(item => ({
  json: {
    // Identification
    dlq_id: `DLQ-${Date.now()}-${Math.random().toString(36).substr(2, 6)}`,
    created_at: new Date().toISOString(),

    // Source information
    workflow_name: $workflow.name,
    execution_id: $execution.id,
    source_node: 'Enrich Company Data',

    // Original data (for reprocessing)
    original_payload: JSON.stringify(item.json),

    // Error details
    error_message: item.json.error?.message || 'Unknown error',
    error_code: item.json.error?.statusCode || null,

    // Triage fields
    status: 'pending',         // pending | investigating | resolved | ignored
    retryable: item.json.retryable || false,
    assigned_to: null,
    resolution_notes: null
  }
}));
```text
Write to a Google Sheet (Dead Letter Queue):

```yaml
Google Sheets node configuration:
  Operation: Append
  Sheet: "Dead Letter Queue"
  Columns:
    A: dlq_id
    B: created_at
    C: workflow_name
    D: execution_id
    E: source_node
    F: original_payload
    G: error_message
    H: error_code
    I: status
    J: retryable
    K: assigned_to
    L: resolution_notes
```text
Build a reprocessing workflow:

```yaml

# Separate workflow: "DLQ Reprocessor"

# Triggered manually or on a schedule

[Manual Trigger or Schedule]
  --> [Google Sheets: Read rows where status = 'pending' AND retryable = true]
  --> [Code: Parse original_payload back to JSON]
  --> [Original processing logic (copied or via Execute Workflow)]
  --> [IF: Success?]
      True:  [Google Sheets: Update status to 'resolved']
      False: [Google Sheets: Update status to 'investigating', increment retry_count]
```text
```sql
-- Postgres DLQ alternative (better for high volume)
CREATE TABLE dead_letter_queue (
  id SERIAL PRIMARY KEY,
  dlq_id TEXT UNIQUE NOT NULL,
  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
  workflow_name TEXT NOT NULL,
  execution_id TEXT,
  source_node TEXT,
  original_payload JSONB NOT NULL,
  error_message TEXT,
  error_code INTEGER,
  status TEXT DEFAULT 'pending' CHECK (status IN ('pending', 'investigating', 'resolved', 'ignored')),
  retryable BOOLEAN DEFAULT false,
  retry_count INTEGER DEFAULT 0,
  assigned_to TEXT,
  resolved_at TIMESTAMPTZ,
  resolution_notes TEXT
);

CREATE INDEX idx_dlq_status ON dead_letter_queue(status);
CREATE INDEX idx_dlq_created ON dead_letter_queue(created_at);
```text
No data is lost. Every failed item is accounted for and has a clear path to resolution, whether automatic retry or manual intervention.

**Related:** [Use "Pin Data" to Freeze Node Output](../testing-and-debugging/01-use-pin-data-to-freeze-node-output.md) | [Break Large Workflows into Sub-Workflows](../workflow-architecture/01-break-large-workflows-into-sub-workflows.md)