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Update MergeTreeReadPool.cpp

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Nikolai Kochetov 2020-10-29 10:04:23 +03:00 committed by GitHub
parent 10bad32fb4
commit 671d2b7f1b
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1 changed files with 4 additions and 4 deletions
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8
src/Storages/MergeTree/MergeTreeReadPool.cpp
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@ -272,8 +272,8 @@ void MergeTreeReadPool::fillPerThreadInfo(
std::queue<PartsInfo> parts_queue;
{
/// Group parts by volume name.
/// We try minimize the number of threads concurrently read from the same volume.
/// Group parts by disk name.
/// We try minimize the number of threads concurrently read from the same disk.
/// It improves the performance for JBOD architecture.
std::map<String, std::vector<PartInfo>> parts_per_disk;
@ -355,8 +355,8 @@ void MergeTreeReadPool::fillPerThreadInfo(
remaining_thread_tasks.insert(i);
}
/// Before processing next thread, change volume if possible.
/// Different threads will likely start reading from different volumes,
/// Before processing next thread, change disk if possible.
/// Different threads will likely start reading from different disk,
/// which may improve read parallelism for JBOD.
/// It also may be helpful in case we have backoff threads.
/// Backoff threads will likely to reduce load for different disks, not the same one.