From 8cbf9a0b440b6a60090b29001f67052fcaa4d16a Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Tue, 6 Feb 2024 10:19:51 +0300
Subject: [PATCH] [#957] treesvc: Use sorting when number of items is small

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 pkg/services/tree/bench_test.go |  2 +-
 pkg/services/tree/service.go    | 18 +++++++++++++-----
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/pkg/services/tree/bench_test.go b/pkg/services/tree/bench_test.go
index 1d2512d03..12325b99f 100644
--- a/pkg/services/tree/bench_test.go
+++ b/pkg/services/tree/bench_test.go
@@ -13,7 +13,7 @@ import (
 )
 
 func BenchmarkGetSubTree(b *testing.B) {
-	const count = 100_000
+	const count = simpleHeapFallbackThreshold
 
 	d := pilorama.CIDDescriptor{CID: cidtest.ID(), Size: 1}
 	treeID := "sometree"
diff --git a/pkg/services/tree/service.go b/pkg/services/tree/service.go
index 33ac3ef98..2f2479edc 100644
--- a/pkg/services/tree/service.go
+++ b/pkg/services/tree/service.go
@@ -446,11 +446,19 @@ type Heap interface {
 	ExtractMin() pilorama.NodeInfo
 }
 
-func makeHeap(ordered bool) Heap {
-	if ordered {
+// simpleHeapFallbackThreshold is the least number of nodes on a single level,
+// for which pairing heap implementation is used.
+const simpleHeapFallbackThreshold = 100_000
+
+func makeHeap(ordered bool, count int) Heap {
+	switch {
+	case ordered && simpleHeapFallbackThreshold <= count:
 		return heap.NewPairing()
+	case ordered:
+		return heap.NewOrderedSlice()
+	default:
+		return heap.NewUnorderedSlice()
 	}
-	return heap.NewUnorderedSlice()
 }
 
 func getSubTree(ctx context.Context, srv TreeService_GetSubTreeServer, cid cidSDK.ID, b *GetSubTreeRequest_Body, forest pilorama.Forest) error {
@@ -466,7 +474,7 @@ func getSubTree(ctx context.Context, srv TreeService_GetSubTreeServer, cid cidSD
 		return err
 	}
 
-	stack := []Heap{makeHeap(ordered)}
+	stack := []Heap{makeHeap(ordered, 1)}
 	stack[0].Insert(pilorama.NodeInfo{
 		ID:       b.GetRootId(),
 		Meta:     m,
@@ -501,7 +509,7 @@ func getSubTree(ctx context.Context, srv TreeService_GetSubTreeServer, cid cidSD
 				return err
 			}
 			if len(children) != 0 {
-				h := makeHeap(ordered)
+				h := makeHeap(ordered, len(children))
 				h.Insert(children...)
 				stack = append(stack, h)
 			}