The CDC Log Latency Alert is triggered by default when SQL Server detects a delay between when changes are written to the transaction log and when they are processed by the CDC capture job. This may indicate:
- The CDC capture job is unable to keep up with the rate of incoming transactions.
- High transaction log activity is causing a processing backlog.
- I/O or disk performance issues are affecting log reading speed.
- Long-running or uncommitted transactions are delaying log truncation and CDC processing.
Detecting this latency promptly is critical because delays in processing the transaction log can create a growing backlog of unprocessed changes. This may result in outdated or incomplete data being delivered to downstream systems, increased storage usage in the transaction log, and potential performance degradation.
What can be done:
- Check CDC capture performance: Verify that the capture job is running continuously and not falling behind.
- Review transaction log activity: Identify spikes in write activity that may overwhelm CDC processing.
- Inspect disk performance: Ensure the log file and storage subsystem are not experiencing latency or bottlenecks.
- Monitor long transactions: Look for open or long-running transactions that delay log processing.
- Optimize workload if needed: Consider tuning queries or adjusting CDC job parameters to improve throughput.
In short, CDC relies on the timely processing of the transaction log to capture changes. Log latency disrupts this flow, so identifying and resolving it quickly ensures accurate data propagation and stable system performance.
About CDC
The Change Data Capture (CDC) in SQL Server is a feature that tracks changes (inserts, updates, deletes) in your tables and records them in separate change tables. It’s widely used for auditing, ETL processes, replication, and maintaining data warehouses. CDC allows you to capture data changes without modifying the application logic.
CDC ensures that any downstream systems (analytics, reporting, or replication) have accurate and up-to-date data. It reduces the risk of missing changes that could affect business decisions.
