filer: skip UpdateEntry when inline content is unchanged (#11580)

* filer: skip UpdateEntry when inline content is unchanged

SaveInsideFiler rewrites config files (IAM identities, filer.conf,
remote mappings, policies) unconditionally. Each no-op UpdateEntry is a
metadata event the local meta log persists to /topics/.system/log,
which appends a chunk to a volume. A client that rewrites identical
config on a timer, e.g. the seaweedfs-operator 5-minute resync calling
UpdateUser with unchanged actions, keeps .dat/.idx files growing on an
otherwise idle cluster and prevents HDD spindown
(seaweedfs/seaweedfs#11571).

Skip the UpdateEntry when the stored inline content is byte-identical,
so unchanged writes produce no metadata event and no volume writes.

* filer: test that identical SaveInsideFiler writes skip UpdateEntry

* filer: require stamped Md5 before skipping identical writes

An entry holding identical content but no Md5 (written before hashing,
or by a tool that cleared it) would never get the stamp that
IF_ETAG_MATCH conditional writes key off. Skip only when both the
stored content and its Md5 match, so one write still lands to repair
the stamp.

weed/filer/filer_conf_test.go

@@ -262,8 +262,9 @@ func TestClearReadOnly(t *testing.T) {
 type fakeFilerConfClient struct {
 	filer_pb.SeaweedFilerClient
 
-	mu      sync.Mutex
-	entries map[string]*filer_pb.Entry // key: dir+"/"+name
+	mu          sync.Mutex
+	entries     map[string]*filer_pb.Entry // key: dir+"/"+name
+	updateCalls int
 }
 
 func newFakeFilerConfClient() *fakeFilerConfClient {
@@ -310,6 +311,7 @@ func (c *fakeFilerConfClient) CreateEntry(_ context.Context, in *filer_pb.Create
 func (c *fakeFilerConfClient) UpdateEntry(_ context.Context, in *filer_pb.UpdateEntryRequest, _ ...grpc.CallOption) (*filer_pb.UpdateEntryResponse, error) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
+	c.updateCalls++
 	key := c.key(in.Directory, in.Entry.Name)
 	if !conditionHoldsLocked(in.Condition, c.entries[key]) {
 		return nil, errors.New("precondition failed")

weed/filer/read_write.go

@@ -75,6 +75,9 @@ func SaveInsideFiler(ctx context.Context, client filer_pb.SeaweedFilerClient, di
 		})
 	} else if err == nil {
 		entry := resp.Entry
+		if bytes.Equal(entry.Content, content) && bytes.Equal(entry.GetAttributes().GetMd5(), contentMd5[:]) {
+			return nil
+		}
 		entry.Content = content
 		entry.Attributes.Mtime = time.Now().Unix()
 		entry.Attributes.FileSize = uint64(len(content))

weed/filer/read_write_test.go

@@ -0,0 +1,51 @@
+package filer
+
+import (
+	"context"
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Rewriting identical inline content must not issue UpdateEntry: each one is a
+// metadata event the local meta log persists to /topics/.system/log, and a
+// client that rewrites the same config on a timer (e.g. the operator's 5-minute
+// resync) keeps the volumes growing on an otherwise idle cluster.
+func TestSaveInsideFilerSkipsIdenticalContent(t *testing.T) {
+	ctx := context.Background()
+	client := newFakeFilerConfClient()
+
+	require.NoError(t, SaveInsideFiler(ctx, client, DirectoryEtcSeaweedFS, "a.json", []byte("v1")))
+	require.Equal(t, 0, client.updateCalls)
+
+	require.NoError(t, SaveInsideFiler(ctx, client, DirectoryEtcSeaweedFS, "a.json", []byte("v1")))
+	assert.Equal(t, 0, client.updateCalls)
+
+	require.NoError(t, SaveInsideFiler(ctx, client, DirectoryEtcSeaweedFS, "a.json", []byte("v2")))
+	assert.Equal(t, 1, client.updateCalls)
+
+	content, err := ReadInsideFiler(ctx, client, DirectoryEtcSeaweedFS, "a.json")
+	require.NoError(t, err)
+	assert.Equal(t, []byte("v2"), content)
+}
+
+// A legacy entry holding identical bytes but no Md5 still gets one write to
+// stamp the hash that IF_ETAG_MATCH conditional writes key off; later
+// identical writes skip.
+func TestSaveInsideFilerStampsMd5OnLegacyEntry(t *testing.T) {
+	ctx := context.Background()
+	client := newFakeFilerConfClient()
+	client.entries[client.key(DirectoryEtcSeaweedFS, "b.json")] = &filer_pb.Entry{
+		Name:       "b.json",
+		Content:    []byte("v1"),
+		Attributes: &filer_pb.FuseAttributes{},
+	}
+
+	require.NoError(t, SaveInsideFiler(ctx, client, DirectoryEtcSeaweedFS, "b.json", []byte("v1")))
+	assert.Equal(t, 1, client.updateCalls)
+
+	require.NoError(t, SaveInsideFiler(ctx, client, DirectoryEtcSeaweedFS, "b.json", []byte("v1")))
+	assert.Equal(t, 1, client.updateCalls)
+}