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[enhancement](generic_iterator) fix num check and add some notes (#12434)

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Co-authored-by: yixiutt <yixiu@selectdb.com>
This commit is contained in:
yixiutt
2022-09-08 12:09:02 +08:00
committed by GitHub
parent a6880ca573
commit 2a64571bef
1 changed files with 9 additions and 2 deletions
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11
be/src/vec/olap/vgeneric_iterators.cpp
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@ -187,11 +187,18 @@ public:
return result;
}
// `advanced = false` when current block finished
// there is two situation in copy_rows:
// 1... `advanced = false` when current block finished, we should copy block before advance(iterator)
// If we iterator a block from start to end, _index_in_block=rows()-1, and _cur_batch_num=rows,
// so we should copy from (_index_in_block - _cur_batch_num + 1)
// 2... `advanced = true` when current block not finished and we advanced to next block, now
// cur_batch_num = (pre_block iteraotr num) + 1, but actually pre_block iterator num is cur_batch_num -1
// so we have a ` if (advanced) start -- `
void copy_rows(vectorized::Block* block, bool advanced = true) {
vectorized::Block& src = _block;
vectorized::Block& dst = *block;
if (_cur_batch_num == 0 || _index_in_block - _cur_batch_num < 0) {
if (_cur_batch_num == 0) {
return;
}