Cron Connector

Overview

The Cron connector schedules data release based on cron expressions.

Connector Type: MeddleCron

Default Mode

Release all accumulated data at scheduled times:

{
  "type": "MeddleCron",
  "config": {
    "mode": "Default",
    "expression": "0 */5 * * * *",
    "maxRetained": 100,
    "timezone": "Europe/Rome"
  }
}

Unique Key Mode

Deduplicate data by key before release:

{
  "type": "MeddleCron",
  "config": {
    "mode": "UniqueKey",
    "expression": "0 0 * * * *",
    "uniqueKey": "sensor_id",
    "maxRetained": 1000
  }
}

Unique Key Keep Missing Mode

Deduplicate but keep records without the unique key:

{
  "type": "MeddleCron",
  "config": {
    "mode": "UniqueKeyKeepMissing",
    "expression": "0 30 * * * *",
    "uniqueKey": "device_id",
    "maxRetained": 500
  }
}

Cron Expression Format

Format: second minute hour day month weekday

Common Expressions

0 */5 * * * *      Every 5 minutes
0 0 * * * *        Every hour
0 0 0 * * *        Every day at midnight
0 30 9 * * 1-5     At 9:30 AM on weekdays
0 0 12 * * 0       At noon on Sundays
0 0 */6 * * *      Every 6 hours
0 15 10 * * *      At 10:15 AM every day

Field Values

Second: 0-59
Minute: 0-59
Hour: 0-23
Day: 1-31
Month: 1-12
Weekday: 0-6 (0 = Sunday)

Special Characters

* - Any value
*/n - Every n units
n-m - Range from n to m
n,m - Specific values

Configuration Parameters

mode: Default, UniqueKey, or UniqueKeyKeepMissing
expression: Cron expression
maxRetained: Maximum payloads to retain in memory
timezone: Timezone for scheduling (e.g., “Europe/Rome”, “America/New_York”)
uniqueKey: (UniqueKey modes) Field to use for deduplication

Use Cases

1. Hourly Reports

{
  "type": "MeddleCron",
  "config": {
    "mode": "Default",
    "expression": "0 0 * * * *",
    "maxRetained": 1000,
    "timezone": "UTC"
  }
}

2. Daily Batch Processing

{
  "type": "MeddleCron",
  "config": {
    "mode": "UniqueKey",
    "expression": "0 0 0 * * *",
    "uniqueKey": "machine_id",
    "maxRetained": 5000
  }
}

3. Business Hours Only

{
  "type": "MeddleCron",
  "config": {
    "mode": "Default",
    "expression": "0 0 9-17 * * 1-5",
    "maxRetained": 500,
    "timezone": "Europe/Rome"
  }
}

Best Practices

Set maxRetained to prevent memory issues
Use UniqueKey mode to avoid duplicate data
Choose appropriate timezone for your use case
Test expressions with online cron calculators

Merge - Time-based data combination
Filter - Filter before scheduling