From b57b3244f5864cb3af7f4d3e707c6f33445932ed Mon Sep 17 00:00:00 2001
From: Alexander Kuzmenkov <akuzm@yandex-team.ru>
Date: Wed, 10 Feb 2021 15:37:05 +0300
Subject: [PATCH] reuse sort order

---
 src/Interpreters/InterpreterSelectQuery.cpp | 135 +++++++++++++++-----
 1 file changed, 103 insertions(+), 32 deletions(-)

diff --git a/src/Interpreters/InterpreterSelectQuery.cpp b/src/Interpreters/InterpreterSelectQuery.cpp
index 2ee1b3956e4..f1a13e7afcb 100644
--- a/src/Interpreters/InterpreterSelectQuery.cpp
+++ b/src/Interpreters/InterpreterSelectQuery.cpp
@@ -1831,46 +1831,117 @@ void InterpreterSelectQuery::executeExpression(QueryPlan & query_plan, const Act
     query_plan.addStep(std::move(expression_step));
 }
 
+static bool windowDescriptionComparator(const WindowDescription * _left,
+    const WindowDescription * _right)
+{
+    const auto & left = _left->full_sort_description;
+    const auto & right = _right->full_sort_description;
+    if (left.size() != right.size())
+    {
+        return left.size() < right.size();
+    }
+
+    for (size_t i = 0; i < left.size(); ++i)
+    {
+        if (left[i].column_name < right[i].column_name)
+        {
+            return true;
+        }
+
+        if (left[i].column_number < right[i].column_number)
+        {
+            return true;
+        }
+
+        if (left[i].direction < right[i].direction)
+        {
+            return true;
+        }
+
+        if (left[i].nulls_direction < right[i].nulls_direction)
+        {
+            return true;
+        }
+
+        assert(left[i] == right[i]);
+    }
+
+    return false;
+}
+
+static bool sortIsPrefix(const WindowDescription & _prefix,
+    const WindowDescription & _full)
+{
+    const auto & prefix = _prefix.full_sort_description;
+    const auto & full = _full.full_sort_description;
+
+    if (prefix.size() > full.size())
+    {
+        return false;
+    }
+
+    for (size_t i = 0; i < prefix.size(); ++i)
+    {
+        if (full[i] != prefix[i])
+        {
+            return false;
+        }
+    }
+
+    return true;
+}
 
 void InterpreterSelectQuery::executeWindow(QueryPlan & query_plan)
 {
+    std::vector<const WindowDescription *> windows_sorted;
     for (const auto & [_, w] : query_analyzer->windowDescriptions())
     {
-        const Settings & settings = context->getSettingsRef();
+        windows_sorted.push_back(&w);
+    }
 
-        auto partial_sorting = std::make_unique<PartialSortingStep>(
-            query_plan.getCurrentDataStream(),
-            w.full_sort_description,
-            0 /* LIMIT */,
-            SizeLimits(settings.max_rows_to_sort, settings.max_bytes_to_sort,
-                settings.sort_overflow_mode));
-        partial_sorting->setStepDescription("Sort each block for window '"
-            + w.window_name + "'");
-        query_plan.addStep(std::move(partial_sorting));
+    std::sort(windows_sorted.begin(), windows_sorted.end(),
+        windowDescriptionComparator);
 
-        auto merge_sorting_step = std::make_unique<MergeSortingStep>(
-            query_plan.getCurrentDataStream(),
-            w.full_sort_description,
-            settings.max_block_size,
-            0 /* LIMIT */,
-            settings.max_bytes_before_remerge_sort,
-            settings.remerge_sort_lowered_memory_bytes_ratio,
-            settings.max_bytes_before_external_sort,
-            context->getTemporaryVolume(),
-            settings.min_free_disk_space_for_temporary_data);
-        merge_sorting_step->setStepDescription("Merge sorted blocks for window '"
-            + w.window_name + "'");
-        query_plan.addStep(std::move(merge_sorting_step));
+    const Settings & settings = context->getSettingsRef();
+    for (size_t i = 0; i < windows_sorted.size(); ++i)
+    {
+        const auto & w = *windows_sorted[i];
+        if (i == 0 || !sortIsPrefix(w, *windows_sorted[i - 1]))
+        {
+            auto partial_sorting = std::make_unique<PartialSortingStep>(
+                query_plan.getCurrentDataStream(),
+                w.full_sort_description,
+                0 /* LIMIT */,
+                SizeLimits(settings.max_rows_to_sort, settings.max_bytes_to_sort,
+                    settings.sort_overflow_mode));
+            partial_sorting->setStepDescription("Sort each block for window '"
+                + w.window_name + "'");
+            query_plan.addStep(std::move(partial_sorting));
 
-        // First MergeSorted, now MergingSorted.
-        auto merging_sorted = std::make_unique<MergingSortedStep>(
-            query_plan.getCurrentDataStream(),
-            w.full_sort_description,
-            settings.max_block_size,
-            0 /* LIMIT */);
-        merging_sorted->setStepDescription("Merge sorted streams for window '"
-            + w.window_name + "'");
-        query_plan.addStep(std::move(merging_sorted));
+            auto merge_sorting_step = std::make_unique<MergeSortingStep>(
+                query_plan.getCurrentDataStream(),
+                w.full_sort_description,
+                settings.max_block_size,
+                0 /* LIMIT */,
+                settings.max_bytes_before_remerge_sort,
+                settings.remerge_sort_lowered_memory_bytes_ratio,
+                settings.max_bytes_before_external_sort,
+                context->getTemporaryVolume(),
+                settings.min_free_disk_space_for_temporary_data);
+            merge_sorting_step->setStepDescription(
+                "Merge sorted blocks for window '" + w.window_name + "'");
+            query_plan.addStep(std::move(merge_sorting_step));
+
+            // First MergeSorted, now MergingSorted.
+            auto merging_sorted = std::make_unique<MergingSortedStep>(
+                query_plan.getCurrentDataStream(),
+                w.full_sort_description,
+                settings.max_block_size,
+                0 /* LIMIT */);
+            merging_sorted->setStepDescription(
+                "Merge sorted streams for window '" + w.window_name + "'");
+            query_plan.addStep(std::move(merging_sorted));
+        }
 
         auto window_step = std::make_unique<WindowStep>(
             query_plan.getCurrentDataStream(),