v.21.6Improvement

Measure Found Rate for Dictionaries in ClickHouse

Official CH changelog text
Measure found rate (the percentage for which the value was found) for dictionaries (see found_rate in system.dictionaries). #23916 (Azat Khuzhin).
Adds the ability to measure the found rate (the percentage of keys successfully found) for dictionaries in ClickHouse, accessible via the found_rate field in system.dictionaries.

Why it matters

This feature enables users to monitor and analyze the effectiveness of dictionary key lookups by providing a metric that shows what percentage of queried keys were found. It helps in identifying dictionary hit rates and can assist in troubleshooting and optimizing dictionary usage.

How to use it

Users can query the found_rate column in the system.dictionaries table to see the current found rate for each dictionary. For example, use: SELECT name, found_rate FROM system.dictionaries; to retrieve this information.

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