Why is my primary key not used? How can I check?
Covers a common reason why a primary key is not used in ordering and how we can confirm
· 6 min read
Knowledge Base
15 posts tagged with "Performance and Optimizations"
Profiling ClickHouse with LLVM's XRay
Learn how to profile ClickHouse using LLVM's XRay instrumentation profiler, visualize traces, and analyze performance.
· 3 min read
Tips and tricks on optimizing basic data types in ClickHouse
Tips and tricks on optimizing basic data types in ClickHouse
· 4 min read
How to achieve data read consistency in ClickHouse?
Learn how to ensure data consistency when reading from ClickHouse, whether you're connected to the same node or a random node.
· 2 min read
How to Verify Query Cache Usage in ClickHouse
Learn how to check if query cache is being utilized in ClickHouse using `clickhouse-client` trace logs or SQL commands.
· 7 min read
How to Measure Query Processing Time Without Returning Rows
Learn how to use the `FORMAT Null` option in ClickHouse to measure query processing time without returning any rows to the client.
· One min read
Identifying Expensive Queries by Memory Usage in ClickHouse
Learn how to use the `system.query_log` table to find the most memory-intensive queries in ClickHouse, with examples for clustered and standalone setups.
· 2 min read
How to calculate the ratio of empty/zero values in every column in a table
Learn how to calculate the ratio of empty or zero values in every column of a ClickHouse table to optimize sparse column serialization.
· 2 min read
How to Identify the Most Expensive Queries in ClickHouse
Learn how to use the `query_log` table in ClickHouse to identify the most memory and CPU-intensive queries across distributed nodes.
· 6 min read
Synchronous data reading
The new setting `allow_asynchronous_read_from_io_pool_for_merge_tree` allows the number of reading threads (streams) to be higher than the number of threads in the rest of the query execution pipeline.
· 4 min read