Prometheus’s TSDB failed to write data because it received a chunk of data that was shorter than the minimum required size, indicating a problem with data ingestion or storage.
The most common culprit is a network partition or a slow network connection between Prometheus scraping targets and the Prometheus server, causing incomplete data to be sent.
Diagnosis: Check Prometheus’s remote write metrics for remote_write_failed_operations and remote_write_pending_batches.
Fix: Ensure network stability and sufficient bandwidth between scrape targets and the Prometheus server. If using remote write, verify the target endpoint is healthy and responsive.
Example: promtool tsdb check can sometimes reveal issues with corrupted or malformed chunks in the TSDB.
Another frequent cause is a bug in a custom exporter or an application generating metrics that produces malformed or truncated data points.
Diagnosis: Inspect the output of your Prometheus exporters or the metrics endpoints of your applications directly using curl. Look for incomplete data points or unexpected formatting.
Fix: Update or fix the buggy exporter/application. Ensure it adheres to the Prometheus exposition format. For example, a line might look like metric_name{label="value"} 123.45 1678886400. If any part is missing or malformed, it can cause this error.
A less common, but still possible, reason is an issue with the underlying storage where Prometheus writes its TSDB data. Disk I/O errors or filesystem corruption can lead to incomplete data writes.
Diagnosis: Check system logs for disk-related errors (e.g., dmesg on Linux). Run fsck on the filesystem where Prometheus stores its data.
Fix: Resolve any underlying disk or filesystem issues. If the storage is unreliable, migrate Prometheus data to a more stable storage solution.
A race condition within Prometheus itself, particularly in older versions or under extremely high load, could theoretically lead to data corruption during the write process. Diagnosis: Review Prometheus logs for any unusual errors or panics during periods of high scrape or ingestion load. Fix: Upgrade Prometheus to the latest stable version. If the issue persists, consider reducing the scrape interval or the number of targets if your hardware is at its limit.
Corrupted WAL (Write-Ahead Log) files can also contribute to this error if Prometheus attempts to replay them during startup or recovery and finds incomplete data segments.
Diagnosis: Navigate to Prometheus’s data directory and inspect the wal subdirectory. Look for unusually small or incomplete segment files.
Fix: In a severe case, you might need to remove the WAL directory (ensure Prometheus is stopped first) and let it rebuild from the TSDB blocks. This will result in a short period of data loss for metrics scraped since the last successful block write.
If you are using remote write to an external TSDB (like Cortex, Thanos, or VictoriaMetrics), the issue might originate on the receiving end, which incorrectly signals successful writes or corrupts data before it’s persisted. Diagnosis: Check the health and logs of your remote write endpoint. Look for errors related to ingestion or data validation. Fix: Ensure your remote write receiver is healthy, has sufficient resources, and is correctly configured. Update its agents or components if necessary.
The next error you’ll encounter is likely a out of memory error or a TSDB metadata corruption error if the underlying storage or ingestion problem isn’t fully resolved.