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