Partition Pruning Failure
warninglatencyUpdated Jan 21, 2026
Queries fail to leverage partition pruning when filters use functions on partition columns, causing full table scans. This dramatically increases bytes read and query latency, especially on time-series data partitioned by date.
Technologies:
How to detect:
Use EXPLAIN ESTIMATE to check rows scanned vs expected. Monitor read_rows and read_bytes in system.query_log for queries with partition key filters. Alert when queries scan 10x+ more data than partition range suggests.
Recommended action:
Rewrite queries to use direct comparisons on partition columns instead of functions (e.g., 'event_time >= date AND event_time < date' instead of 'toYYYYMM(event_time) = value'). Use EXPLAIN indexes=1 to verify partition pruning works. Add skip indexes for non-partition filter columns.