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I'm trying to compare Cached and Hashed Clickhouse Dictionaries. What are some of the use cases for both, and where they overlap in strengths what are some queries I could launch to compare them?

John Miller
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  • official docs https://clickhouse.tech/docs/en/sql-reference/dictionaries/external-dictionaries/external-dicts-dict-layout/ ? – vladimir Apr 05 '21 at 14:23
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    @vladimir Yep I've been through that several times although there's and if you had read it there's a section on achieving 99% hit rate for cache dictionaries to be effective and playing around with the parameters to fine tune the dictionary. What are the parameters I should be changing and how should I entry and achieve a 99% hit rate, and if I do get such a hit rate how should I then compare the results to hashed dictionaries. – John Miller Apr 05 '21 at 17:20
  • hashed dictionary may require hundreds gigabytes of memory. Instead you can use cached and adjust memory usage / hit-rate using size_in_cells `1000000000` – Denny Crane Apr 06 '21 at 20:42

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