From 378ad6b51784cfaef2977be8087cc2e27f8b880d Mon Sep 17 00:00:00 2001
From: Chao Chen <chaochn@amazon.com>
Date: Fri, 22 Oct 2021 16:36:37 -0700
Subject: [PATCH] [3.5] Backport: non mutating requests pass through
 quotaKVServer when NOSPACE

Signed-off-by: Vaibhav Mehta <mehvaibh@amazon.com>
---
 server/etcdserver/quota.go         |  7 ++++++-
 tests/integration/v3_alarm_test.go | 24 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/server/etcdserver/quota.go b/server/etcdserver/quota.go
index 33c06e619..c5fadc4b1 100644
--- a/server/etcdserver/quota.go
+++ b/server/etcdserver/quota.go
@@ -125,8 +125,13 @@ func NewBackendQuota(s *EtcdServer, name string) Quota {
 }
 
 func (b *backendQuota) Available(v interface{}) bool {
+	cost := b.Cost(v)
+	// if there are no mutating requests, it's safe to pass through
+	if cost == 0 {
+		return true
+	}
 	// TODO: maybe optimize backend.Size()
-	return b.s.Backend().Size()+int64(b.Cost(v)) < b.maxBackendBytes
+	return b.s.Backend().Size()+int64(cost) < b.maxBackendBytes
 }
 
 func (b *backendQuota) Cost(v interface{}) int {
diff --git a/tests/integration/v3_alarm_test.go b/tests/integration/v3_alarm_test.go
index d51fb53bb..576fb0591 100644
--- a/tests/integration/v3_alarm_test.go
+++ b/tests/integration/v3_alarm_test.go
@@ -89,6 +89,30 @@ func TestV3StorageQuotaApply(t *testing.T) {
 		case <-time.After(10 * time.Millisecond):
 		}
 	}
+	
+	// txn with non-mutating Ops should go through when NOSPACE alarm is raised
+	_, err = kvc0.Txn(context.TODO(), &pb.TxnRequest{
+		Compare: []*pb.Compare{
+			{
+				Key:         key,
+				Result:      pb.Compare_EQUAL,
+				Target:      pb.Compare_CREATE,
+				TargetUnion: &pb.Compare_CreateRevision{CreateRevision: 0},
+			},
+		},
+		Success: []*pb.RequestOp{
+			{
+				Request: &pb.RequestOp_RequestDeleteRange{
+					RequestDeleteRange: &pb.DeleteRangeRequest{
+						Key: key,
+					},
+				},
+			},
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	ctx, cancel := context.WithTimeout(context.TODO(), RequestWaitTimeout)
 	defer cancel()