[fix](planner) query should be cancelled if limit reached (#44338) #45222
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Problem Summary:
When there is a `limit` cluse in SQL, if FE has obtained data with more
than the `limit` number of rows,
it should send a cancel command to BE to cancel the query to prevent BE
from reading more data.
However, this function has problems in the current code and does not
work.
Especially in external table query, this may result in lots of
unnecessary network io read.
1. `isBlockQuery`
In the old optimizer, if a query statement contains a `sort` or `agg`
node,
`isBlockQuery` will be marked as true, otherwise it will be false.
In the new optimizer, this value is always true.
Regardless of the old or new optimizer, this logic is wrong.
But only when `isBlockQuery = false` will the reach limit logic be
triggered.
2. Calling problem of reach limit logic
The reach limit logic judgment will only be performed when `eos = true`
in the rowBatch returned by BE.
This is wrong.
Because for `limit N` queries, each BE's own `limit` is N. But for FE,
as long as the total number of rows
returned by all BEs exceeds N, the reach limit logic can be triggered.
So it should not be processed only when `eos = true`.
The PR mainly changes:
1. Remove `isBlockQuery`
`isBlockQuery` is only used in the reach limit logic. And it is not
needed. Remove it completely.
2. Modify the judgment position of reach limit.
When the number of rows obtained by FE is greater than the limit,
it will check the reach limit logic.
3. fix wrong `limitRows` in `QueryProcessor`
the limitRows should be got from the first fragment, not last.
4. In scanner scheduler on BE side, if scanner has limit, ignore the
scan bytes threshold per round.
[fix](planner) query should be cancelled if limit reached
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Thank you for your contribution to Apache Doris. Please clearly describe your PR:
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run buildall |
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clang-tidy review says "All clean, LGTM! 👍" |
1 similar comment
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clang-tidy review says "All clean, LGTM! 👍" |
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TeamCity be ut coverage result: |
yiguolei
approved these changes
Dec 10, 2024
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PR approved by at least one committer and no changes requested. |
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PR approved by anyone and no changes requested. |
Closed
GoGoWen
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Sep 26, 2025
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cherry-pick #44338