Consistency Scan

This document covers the concept and usage of the consistency scan feature.

Summary

The consistency scan reads all replicas of each shard to verify data consistency at a configured rate. It is useful for finding corrupt cold data by ensuring that all data is read periodically. Any errors found will be logged as TraceEvents with Severity = 40.

Configuration

You can configure the Consistency Scan via the FDB command line interface using the consistencyscan command.

Example commands

Enable consistency scan to scan the cluster once every 28 days with a maximum speed of 5MB/s: consistencyscan on maxRate 5000000 targetInterval 2419200.

Disable consistency scan on the cluster: consistencyscan off.

View the current stats for the consistency scan: consistencyscan stats.

Monitor

The consistency scan role publishes its configuration and metrics in Status JSON under the path .cluster.consistency_scan.

Trace Events

ConsistencyScanMetrics show the over-time stats of the consistency scan’s behavior, including bytes scanned, error counts, inconsistencies found, etc…