[FIXED] Filestore cache is expired too early with recent write

Signed-off-by: Maurice van Veen <github@mauricevanveen.com>

Author: MauriceVanVeen

server/filestore.go

@@ -6576,10 +6576,10 @@ func (mb *msgBlock) tryForceExpireCache() {
 
 // We will attempt to force expire this by temporarily clearing the last load time.
 func (mb *msgBlock) tryForceExpireCacheLocked() {
-	llts, lwts := mb.llts, mb.lwts
-	mb.llts, mb.lwts = 0, 0
+	llts := mb.llts
+	mb.llts = 0
 	mb.expireCacheLocked()
-	mb.llts, mb.lwts = llts, lwts
+	mb.llts = llts
 }
 
 // This is for expiration of the write cache, which will be partial with fip.

server/filestore_test.go

@@ -13538,6 +13538,44 @@ func TestFileStoreSyncBlocksNoErrorOnConcurrentRemovedBlock(t *testing.T) {
 	require_True(t, fs.werr == nil)
 }
 
+func TestFileStoreDontExpireCacheWithRecentWrite(t *testing.T) {
+	fcfg := FileStoreConfig{StoreDir: t.TempDir()}
+	cfg := StreamConfig{Name: "zzz", Storage: FileStorage, Subjects: []string{">"}}
+	fs, err := newFileStore(fcfg, cfg)
+	require_NoError(t, err)
+	defer fs.Stop()
+
+	_, _, err = fs.StoreMsg("foo", nil, nil, 0)
+	require_NoError(t, err)
+
+	// Cache should still exist after above write.
+	fmb := fs.getFirstBlock()
+	fmb.mu.Lock()
+	cacheLoaded := fmb.cacheAlreadyLoaded()
+	fmb.llseq = 0
+	fmb.mu.Unlock()
+	require_True(t, cacheLoaded)
+
+	// The load will try to expire the cache, but shouldn't due to the recent write.
+	_, _, err = fs.LoadNextMsg(fwcs, true, 0, nil)
+	require_NoError(t, err)
+
+	fmb.mu.Lock()
+	fmb.llseq = 0
+	cacheLoaded = fmb.cacheAlreadyLoaded()
+	// We update the last write timestamp to be very old, so the next load can expire the cache.
+	fmb.lwts = 0
+	fmb.mu.Unlock()
+	require_True(t, cacheLoaded)
+	_, _, err = fs.LoadNextMsg(fwcs, true, 0, nil)
+	require_NoError(t, err)
+
+	fmb.mu.Lock()
+	cacheLoaded = fmb.cacheAlreadyLoaded()
+	fmb.mu.Unlock()
+	require_False(t, cacheLoaded)
+}
+
 func TestFileStoreNoDirectoryNotEmptyError(t *testing.T) {
 	fcfg := FileStoreConfig{StoreDir: t.TempDir()}
 	mconfig := StreamConfig{Name: "TEST_DELETE", Storage: FileStorage, Subjects: []string{"foo"}, Replicas: 1}