PREWHERE optimization
How
PREWHERE reduces I/O by filtering data before reading non-filter columns, and how to monitor its effectiveness.Allocation profiling
Profile memory allocations to diagnose memory pressure and tune resource usage in ClickHouse.
Caches
Query cache, query-condition cache, and userspace page cache for accelerating repeated workloads.
Skip indexes
Use secondary skip indexes to prune irrelevant data blocks and accelerate filtered queries.
Lazy materialization
Defer column reads until they are needed to reduce I/O for selective queries.
Troubleshooting
Sampling query profiler, hardware benchmarking, and debugging memory issues.