From c96d043f16662312f6f01623056d6d42f9e27205 Mon Sep 17 00:00:00 2001
From: Bilal Akhtar <bilal@cockroachlabs.com>
Date: Fri, 18 Oct 2019 15:44:33 -0400
Subject: [PATCH] cache: Update cache targetSize to always return a positive
 int

Noticed when ingesting SSTables as part of a cockroach snapshot apply.
reservedSize would exceed maxSize, leading to an infinite loop in
evict().
---
 internal/cache/clockpro.go      |  9 ++++++++-
 internal/cache/clockpro_test.go | 10 ++++++----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/internal/cache/clockpro.go b/internal/cache/clockpro.go
index b5fa8270f2..1e47d22dfb 100644
--- a/internal/cache/clockpro.go
+++ b/internal/cache/clockpro.go
@@ -372,7 +372,14 @@ func (c *shard) Size() int64 {
 }
 
 func (c *shard) targetSize() int64 {
-	return c.maxSize - c.reservedSize
+	target := c.maxSize - c.reservedSize
+	// Always return a positive integer for targetSize. This is so that we don't
+	// end up in an infinite loop in evict(), in cases where reservedSize is
+	// greater than or equal to maxSize.
+	if target < 1 {
+		return 1
+	}
+	return target
 }
 
 // Add the entry to the cache, returning true if the entry was added and false
diff --git a/internal/cache/clockpro_test.go b/internal/cache/clockpro_test.go
index 963b8bbf71..5c535092dd 100644
--- a/internal/cache/clockpro_test.go
+++ b/internal/cache/clockpro_test.go
@@ -154,7 +154,7 @@ func TestZeroSize(t *testing.T) {
 }
 
 func TestReserve(t *testing.T) {
-	cache := newShards(2, 2)
+	cache := newShards(4, 2)
 	cache.Set(1, 0, 0, []byte("a"))
 	cache.Set(2, 0, 0, []byte("a"))
 	require.EqualValues(t, 2, cache.Size())
@@ -162,12 +162,14 @@ func TestReserve(t *testing.T) {
 	require.EqualValues(t, 0, cache.Size())
 	cache.Set(1, 0, 0, []byte("a"))
 	cache.Set(2, 0, 0, []byte("a"))
-	require.EqualValues(t, 0, cache.Size())
+	cache.Set(3, 0, 0, []byte("a"))
+	cache.Set(4, 0, 0, []byte("a"))
+	require.EqualValues(t, 2, cache.Size())
 	r()
-	require.EqualValues(t, 0, cache.Size())
+	require.EqualValues(t, 2, cache.Size())
 	cache.Set(1, 0, 0, []byte("a"))
 	cache.Set(2, 0, 0, []byte("a"))
-	require.EqualValues(t, 2, cache.Size())
+	require.EqualValues(t, 4, cache.Size())
 }
 
 func TestReserveDoubleRelease(t *testing.T) {