From 0e62143fcf44e551508154803fcac4af46a5f56c Mon Sep 17 00:00:00 2001
From: sumeerbhola <sumeer@cockroachlabs.com>
Date: Tue, 9 May 2023 23:08:38 -0400
Subject: [PATCH] db: intialize memTable.reserve when creating memTable

Informs https://github.com/cockroachdb/cockroach/issues/102945

Fixes #2516
---
 mem_table.go      |  1 +
 mem_table_test.go | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/mem_table.go b/mem_table.go
index 13f4329076..acc0b90b72 100644
--- a/mem_table.go
+++ b/mem_table.go
@@ -143,6 +143,7 @@ func newMemTable(opts memTableOptions) *memTable {
 	m.skl.Reset(arena, m.cmp)
 	m.rangeDelSkl.Reset(arena, m.cmp)
 	m.rangeKeySkl.Reset(arena, m.cmp)
+	m.reserved = arena.Size()
 	return m
 }
 
diff --git a/mem_table_test.go b/mem_table_test.go
index 5380c7cfa8..1c7fddd233 100644
--- a/mem_table_test.go
+++ b/mem_table_test.go
@@ -389,6 +389,21 @@ func TestMemTableConcurrentDeleteRange(t *testing.T) {
 	}
 }
 
+func TestMemTableReserved(t *testing.T) {
+	m := newMemTable(memTableOptions{size: 5000})
+	// Increase to 2 references.
+	m.writerRef()
+	// The initial reservation accounts for the already allocated bytes from the
+	// arena.
+	require.Equal(t, m.reserved, m.skl.Arena().Size())
+	b := newBatch(nil)
+	b.Set([]byte("blueberry"), []byte("pie"), nil)
+	require.NotEqual(t, 0, int(b.memTableSize))
+	prevReserved := m.reserved
+	m.prepare(b)
+	require.Equal(t, int(m.reserved), int(b.memTableSize)+int(prevReserved))
+}
+
 func buildMemTable(b *testing.B) (*memTable, [][]byte) {
 	m := newMemTable(memTableOptions{})
 	var keys [][]byte