Try to dump any cached state including fss on recovery to avoid memory bloat on restart.

Signed-off-by: Derek Collison <derek@nats.io>

server/filestore.go

@@ -750,6 +750,8 @@ func (fs *fileStore) recoverMsgBlock(fi os.FileInfo, index uint32) (*msgBlock, e
 		if (mb.rbytes == 0 && mb.msgs == 0) || bytes.Equal(lchk[:], mb.lchk[:]) {
 			if mb.msgs > 0 && !mb.noTrack && fs.psim != nil {
 				fs.populateGlobalPerSubjectInfo(mb)
+				// Try to dump any state we needed on recovery.
+				mb.tryForceExpireCacheLocked()
 			}
 			fs.addMsgBlock(mb)
 			return mb, nil
@@ -762,6 +764,8 @@ func (fs *fileStore) recoverMsgBlock(fi os.FileInfo, index uint32) (*msgBlock, e
 	}
 	if mb.msgs > 0 && !mb.noTrack && fs.psim != nil {
 		fs.populateGlobalPerSubjectInfo(mb)
+		// Try to dump any state we needed on recovery.
+		mb.tryForceExpireCacheLocked()
 	}
 
 	// Rewrite this to make sure we are sync'd.
@@ -2978,16 +2982,12 @@ func (mb *msgBlock) expireCacheLocked() {
 
 	// Check if we can clear out our fss and idx unless under force expire.
 	// We used to hold onto the idx longer but removes need buf now so no point.
-	if mb.llts > 0 {
-		mb.writePerSubjectInfo()
-		mb.fss = nil
-		if mb.indexNeedsUpdateLocked() {
-			mb.writeIndexInfoLocked()
-		}
-		mb.clearCache()
-	} else {
-		mb.resetCacheExpireTimer(mb.cexp)
+	mb.writePerSubjectInfo()
+	mb.fss = nil
+	if mb.indexNeedsUpdateLocked() {
+		mb.writeIndexInfoLocked()
 	}
+	mb.clearCache()
 }
 
 func (fs *fileStore) startAgeChk() {

server/filestore_test.go

@@ -4469,3 +4469,44 @@ func TestFileStoreNoFSSBugAfterRemoveFirst(t *testing.T) {
 		t.Fatalf("Expected no state for %q, but got %+v\n", "foo.bar.0", ss)
 	}
 }
+
+func TestFileStoreNoFSSAfterRecover(t *testing.T) {
+	storeDir := createDir(t, JetStreamStoreDir)
+	defer os.RemoveAll(storeDir)
+
+	fs, err := newFileStore(
+		FileStoreConfig{StoreDir: storeDir},
+		StreamConfig{Name: "zzz", Subjects: []string{"foo"}, Storage: FileStorage},
+	)
+	require_NoError(t, err)
+	defer fs.Stop()
+
+	n, msg := 100, []byte("no fss for you!")
+	for i := 0; i < n; i++ {
+		_, _, err := fs.StoreMsg(_EMPTY_, nil, msg)
+		require_NoError(t, err)
+	}
+
+	state := fs.State()
+	require_True(t, state.Msgs == uint64(n))
+
+	fs.Stop()
+	fs, err = newFileStore(
+		FileStoreConfig{StoreDir: storeDir},
+		StreamConfig{Name: "zzz", Subjects: []string{"foo"}, Storage: FileStorage},
+	)
+	require_NoError(t, err)
+	defer fs.Stop()
+
+	// Make sure we did not load the block trying to generate fss.
+	fs.mu.RLock()
+	mb := fs.blks[0]
+	fs.mu.RUnlock()
+
+	mb.mu.Lock()
+	defer mb.mu.Unlock()
+
+	if mb.fss != nil {
+		t.Fatalf("Expected no fss post recover")
+	}
+}