Revert "Storages: Update the length of Block queue and the number of …

…read threads (#8702)" (#8732)
pingcap · Jan 25, 2024 · bcc9e7f · bcc9e7f
1 parent ddea3a4
commit bcc9e7f
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Showing 2 changed files with 4 additions and 5 deletions.
diff --git a/dbms/src/Interpreters/Settings.h b/dbms/src/Interpreters/Settings.h
@@ -320,7 +320,7 @@ struct Settings
                                                                                                                                                                                                                                         \
     M(SettingDouble, dt_page_gc_threshold, 0.5, "Max valid rate of deciding to do a GC in PageStorage")                                                                                                                                 \
     M(SettingBool, dt_enable_read_thread, true, "Enable storage read thread or not")                                                                                                                                                    \
-    M(SettingDouble, dt_read_thread_count_scale, 2.0, "Number of read thread = number of logical cpu cores * dt_read_thread_count_scale.  Only has meaning at server startup.")                                                         \
+    M(SettingDouble, dt_read_thread_count_scale, 1.0, "Number of read thread = number of logical cpu cores * dt_read_thread_count_scale.  Only has meaning at server startup.")                                                         \
     M(SettingUInt64, dt_max_sharing_column_bytes_for_all, 2048 * Constant::MB, "Memory limitation for data sharing of all requests. 0 means disable data sharing")                                                                      \
     M(SettingUInt64, dt_max_sharing_column_count, 5, "ColumnPtr object limitation for data sharing of each DMFileReader::Stream. 0 means disable data sharing")                                                                         \
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diff --git a/dbms/src/Storages/DeltaMerge/SegmentReadTaskPool.h b/dbms/src/Storages/DeltaMerge/SegmentReadTaskPool.h
@@ -185,10 +185,9 @@ class SegmentReadTaskPool : private boost::noncopyable
         , exception_happened(false)
         , mem_tracker(current_memory_tracker == nullptr ? nullptr : current_memory_tracker->shared_from_this())
         // If the queue is too short, only 1 in the extreme case, it may cause the computation thread
-        // to encounter empty queues frequently, resulting in too much waiting and thread context switching.
-        // We limit the length of block queue to be 1.5 times of `num_streams_`, and in the extreme case,
-        // when `num_streams_` is 1, `block_slot_limit` is at least 2.
-        , block_slot_limit(std::ceil(num_streams_ * 1.5))
+        // to encounter empty queues frequently, resulting in too much waiting and thread context
+        // switching, so we limit the lower limit to 3, which provides two blocks of buffer space.
+        , block_slot_limit(std::max(num_streams_, 3))
         // Limiting the minimum number of reading segments to 2 is to avoid, as much as possible,
         // situations where the computation may be faster and the storage layer may not be able to keep up.
         , active_segment_limit(std::max(num_streams_, 2))