From 20f8dd034791d2e41572d65e9e27a4515db27b39 Mon Sep 17 00:00:00 2001
From: David Taylor <tinystatemachine@gmail.com>
Date: Sun, 16 Jan 2022 19:15:23 +0000
Subject: [PATCH] sstable: reuse index block iterator in Layout

---
 sstable/reader.go      |  6 +++++-
 sstable/reader_test.go | 10 ++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/sstable/reader.go b/sstable/reader.go
index 2c193ed802..ee9bb8c4bd 100644
--- a/sstable/reader.go
+++ b/sstable/reader.go
@@ -2478,6 +2478,7 @@ func (r *Reader) Layout() (*Layout, error) {
 	} else {
 		l.TopIndex = r.indexBH
 		topIter, _ := newBlockIter(r.Compare, indexH.Get())
+		iter := &blockIter{}
 		for key, value := topIter.First(); key != nil; key, value = topIter.Next() {
 			indexBH, err := decodeBlockHandleWithProperties(value)
 			if err != nil {
@@ -2490,7 +2491,9 @@ func (r *Reader) Layout() (*Layout, error) {
 			if err != nil {
 				return nil, err
 			}
-			iter, _ := newBlockIter(r.Compare, subIndex.Get())
+			if err := iter.init(r.Compare, subIndex.Get(), 0 /* globalSeqNum */); err != nil {
+				return nil, err
+			}
 			for key, value := iter.First(); key != nil; key, value = iter.Next() {
 				dataBH, err := decodeBlockHandleWithProperties(value)
 				if err != nil {
@@ -2499,6 +2502,7 @@ func (r *Reader) Layout() (*Layout, error) {
 				l.Data = append(l.Data, dataBH.BlockHandle)
 			}
 			subIndex.Release()
+			*iter = iter.resetForReuse()
 		}
 	}
 
diff --git a/sstable/reader_test.go b/sstable/reader_test.go
index 25a2c55fa9..1da780ffd4 100644
--- a/sstable/reader_test.go
+++ b/sstable/reader_test.go
@@ -1063,3 +1063,13 @@ func BenchmarkTableIterPrev(b *testing.B) {
 			})
 	}
 }
+
+func BenchmarkLayout(b *testing.B) {
+	r, _ := buildBenchmarkTable(b, WriterOptions{})
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		r.Layout()
+	}
+	b.StopTimer()
+	r.Close()
+}