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Fix comment.

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This commit is contained in:
Nikolai Kochetov 2022-12-09 15:44:59 +00:00
parent f75250eaf4
commit 9e04473e8c
1 changed files with 3 additions and 5 deletions
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8
src/Storages/MergeTree/MergeTreeBaseSelectProcessor.h
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@ -169,16 +169,14 @@ protected:
std::deque<MergeTreeReadTaskPtr> delayed_tasks;
std::deque<MarkRanges> buffered_ranges;
/// This setting is used in base algorithm only an an additionally limit the number of granules to read.
/// This setting is used in base algorithm only to additionally limit the number of granules to read.
/// It is changed in ctor of MergeTreeThreadSelectAlgorithm.
///
/// The reason why we have it here is because MergeTreeReadPool takes the full task
/// ignoring min_marks_to_read setting in case of remote disk (see MergeTreeReadPool::getTask).
/// Which makes a logic of adaptive granulatity
/// (merge_tree_min_rows_for_concurrent_read_for_remote_filesystem and
/// merge_tree_min_bytes_for_concurrent_read_for_remote_filesystem settings) a bit useless.
/// In this case, we won't limit the number of rows to read based on adaptive granularity settings.
///
/// On the other hand, big tasks are better for remote disk and prefetches.
/// Big reading tasks are better for remote disk and prefetches.
/// So, for now it's easier to limit max_rows_to_read.
/// Somebody need to refactor this later.
size_t min_marks_to_read = 0;