UCP: support hint 'USE_CASCADES(ON|OFF)' to use/disuse cascades planner in a single query

[francis0407]

Description

Cascades planner is a new optimizer in TiDB. Currently, we uses a session variable tidb_enable_cascades_planner to determine whether uses the cascades planner or not. But sometimes, we only want to use cascades planner for a single query, without affecting other queris in the same session.
For example:

# This query should be forced to use cascades planner.
select /*+ USE_CASCADES(ON) */ * from t;

# This query should be forced to use core planner(the old one).
select /*+ USE_CASCADES(OFF) */ * from t;

Score

• 300

Mentor(s)

• @francis0407

Contact the mentors: #tidb-challenge-program channel in TiDB Community Slack Workspace

Recommended Skills

• Golang
• SQL

Learning Materials

• PR for tidb_enable_cascades_planner: *: add session variable "tidb_enable_cascades_planner" #7879
• Chinses blog for cascades planner: https://pingcap.com/blog-cn/tidb-cascades-planner/

[gauss1314]

/pick-up-challenge

[sre-bot]

"easy" issue is not available since you have got 200 score in this repo. Please pickup "medium" or "hard" directly. Or you can pick up "easy" Issue in other repos. Thank you.

[gauss1314]

Hi @francis0407 , there are other hints like USE_TOJA(true), ENABLE_PLAN_CACHE(false),
so for consistency, how about just change ON|OFF to true|false?

# This query should be forced to use cascades planner.
select /*+ USE_CASCADES(true) */ * from t;
# This query should be forced to use core planner(the old one).
select /*+ USE_CASCADES(false) */ * from t;

[francis0407]

@gauss1314 good catch! Use true|false then.

[gauss1314]

/pick-up-challenge

[sre-bot]

"easy" issue is not available since you have got 200 score in this repo. Please pickup "medium" or "hard" directly. Or you can pick up "easy" Issue in other repos. Thank you.

[you06]

@gauss1314 the pick problem is fixed and this task is in review stage now, you can pick up new issues.

[gauss1314]

/pick-up-challenge

[sre-bot]

@gauss1314 pick up issue success