A query is slow while CPU is free or one query takes all CPU
Tune ClickHouse query parallelism to improve performance and balance CPU usage under high concurrency.
November 2, 202612 min read
Tag: query optimization
Posts tagged "query optimization"
ClickHouse Not Using the Primary Key? How to Fix It
A ClickHouse® query reads all granules and ignores the primary key. Learn how to confirm it with EXPLAIN, fix the filter, and use force_primary_key.
November 2, 202610 min read
EXPLAIN PRETTY and COMPACT in ClickHouse® 26.3
Learn how to visualize ClickHouse® query plans using EXPLAIN pretty=1 and compact=1 in version 26.3 to better understand query execution and optimization.
July 17, 202611 min read
ClickHouse® Internals: How the Query Analyzer Works
Learn how the Query Analyzer works in ClickHouse®. Explore how SQL queries are transformed from an Abstract Syntax Tree (AST) into a Query Tree.
July 11, 20268 min read
ClickHouse® Data Sampling: Querying Billions of Rows Fast
Learn how ClickHouse® Data Sampling speeds up analytical queries using the SAMPLE clause, when to use it, its limitations, and best practices.
July 1, 20267 min read
ClickHouse® Memory Management and Tuning
Learn how ClickHouse® manages memory during query execution, practical tuning strategies to optimize performance and prevent out-of-memory errors in production.
June 27, 20268 min read
Dealing with Duplicates in ClickHouse®: Deduplication Strategies
Learn practical ClickHouse® deduplication strategies using ReplacingMergeTree, FINAL, and ingestion best practices
June 26, 20265 min read
Best Practices for Choosing a Primary Key in ClickHouse®
Learn how to choose the right primary key in ClickHouse® to improve filtering, data skipping, and query performance.
June 24, 20265 min read
When ClickHouse® Queries Are Slow: A Practical Debugging Guide
Struggling with slow ClickHouse® Learn the real reasons behind poor performance and 7 practical fixes to reduce scans and speed up queries.
April 8, 20265 min read
Optimizing ClickHouse® Queries: Adding and Benchmarking Projections
Learn how to optimize ClickHouse® queries by adding and benchmarking projections with before-and-after performance comparisons.
March 10, 20265 min read