rfc: query result cache.

[RinChanNOWWW]

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Summary

RFC of query result cache.

Closes #10011

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Name	Status	Preview	Comments	Updated
databend	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Feb 14, 2023 at 1:28AM (UTC)

[mergify]

This pull request's title is not fulfill the requirements. @RinChanNOWWW please update it 🙏.

Valid format:

fix(query): fix group by string bug
  ^         ^---------------------^
  |         |
  |         +-> Summary in present tense.
  |
  +-------> Type: rfc, feat, fix, refactor, ci, docs, chore

Valid types:

• rfc: this PR proposes a new RFC
• feat: this PR introduces a new feature to the codebase
• fix: this PR patches a bug in codebase
• refactor: this PR changes the code base without new features or bugfix
• ci: this PR changes build/testing/ci steps
• docs: this PR changes the documents or websites
• chore: this PR only has small changes that no need to record

[rschu1ze]

Hi! There seems to be a significant overlap in terms of design, integration and naming of this RFC and the recently introduced query cache in ClickHouse (which I am the author of). Perhaps allow me to post the original blog post and docs for reference, thanks.

[RinChanNOWWW]

Hi @rschu1ze, thanks for your comments and concerns.

For some namings and functionalities, we did refer other databases like ClickHouse and snowflake, we will add references in this RFC later.

For the detail design and implementation, Databend is totally different from ClickHouse. For example, ClickHouse use a hash table (has limit) to store cache information and tolerate inconsistent. However, Databend use its meta service (doesn't have limit) to store cache information and doesn't allow inconsistent by default.

You can find the implementation of the first version of query result cache in #10010, and we didn't refer any codes of ClickHouse.