yaooqinn opened a new pull request, #37355:
URL: https://github.com/apache/spark/pull/37355
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### What changes were proposed in this pull request?
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This ticket intends to add query hints for cache behaviors, users can
perform actions like the use/skip/cache/uncache, etc on the cached results by
the following hints.
- RESULT_CACHE: spark will use cache by default, this hint keeps this
behavior but will cache the child plan if uncached yet.
- NO_RESULT_CACHE:with this hint, we can skip the default behavior to bypass
the cached data if it is cached
- RESULT_UNCACHE: with this hint, we can remove the cached data.
RESULT_CACHE and NO_RESULT_CACHE are borrowed from oracle,
FYI,[https://docs.oracle.com/database/121/TGDBA/tune_result_cache.htm#TGDBA647.](https://docs.oracle.com/database/121/TGDBA/tune_result_cache.htm#TGDBA647),
while RESULT_UNCACHE's added accordingly via the naming rule.
Similar ideas can also be found in MySQL, FYI
https://dev.mysql.com/doc/refman/5.7/en/query-cache-in-select.html
Maybe we can add more cache hints like RESULT_RECACHE to refresh the cached
data, or maybe some cache behaviors that relate to metadata.
### Why are the changes needed?
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As a supplement for CACHE/UNCACHE commands, pure SQL users can operate the
cache in their queries directly without extra definitions. Also, cache skipping
is supported by hints.
### Does this PR introduce _any_ user-facing change?
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yes, this PR brings some new hints
### How was this patch tested?
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- new tests for ut
- test dist by hand
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