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The following commit(s) were added to refs/heads/master by this push:
new 21ea0055fc [improvement](scanner) use batch size of session instead of
limit to improve performance of reading (#22240)
21ea0055fc is described below
commit 21ea0055fc303896b39c8d57b755e7afeaec8817
Author: TengJianPing <[email protected]>
AuthorDate: Wed Jul 26 18:57:42 2023 +0800
[improvement](scanner) use batch size of session instead of limit to
improve performance of reading (#22240)
---
be/src/vec/exec/scan/new_olap_scanner.cpp | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/be/src/vec/exec/scan/new_olap_scanner.cpp
b/be/src/vec/exec/scan/new_olap_scanner.cpp
index decf12ee91..702d94c5f3 100644
--- a/be/src/vec/exec/scan/new_olap_scanner.cpp
+++ b/be/src/vec/exec/scan/new_olap_scanner.cpp
@@ -127,10 +127,11 @@ Status NewOlapScanner::init() {
// set limit to reduce end of rowset and segment mem use
_tablet_reader = std::make_unique<BlockReader>();
- _tablet_reader->set_batch_size(
- _parent->limit() == -1
- ? _state->batch_size()
- : std::min(static_cast<int64_t>(_state->batch_size()),
_parent->limit()));
+ // batch size is passed down to segment iterator, use _state->batch_size()
+ // instead of _parent->limit(), because if _parent->limit() is a very small
+ // value (e.g. select a from t where a .. and b ... limit 1),
+ // it will be very slow when reading data in segment iterator
+ _tablet_reader->set_batch_size(_state->batch_size());
// Get olap table
TTabletId tablet_id = _scan_range.tablet_id;
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