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
· 阅读需 6 分钟
Knowledge Base
15 篇博文 包含标签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.
· 阅读需 3 分钟
Tips and tricks on optimizing basic data types in ClickHouse
Tips and tricks on optimizing basic data types in ClickHouse
· 阅读需 4 分钟
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.
· 阅读需 2 分钟
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.
· 阅读需 7 分钟
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.
· 阅读需 1 分钟
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.
· 阅读需 2 分钟
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.
· 阅读需 2 分钟
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.
· 阅读需 6 分钟
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.
· 阅读需 4 分钟