rcache: Allow disabling of rcache (#18)

* rcache: Allow disabling of rcache

* clean up

rsql/rcache.go

@@ -22,6 +22,14 @@ type rcache struct {
 	limit  int
 }
 
+// cacheDisabled is the source of truth whether the rcache is disabled or not.
+var cacheDisabled bool
+
+// DisableCache results in all loading going straight through to the underlying loader.
+func DisableCache() {
+	cacheDisabled = true
+}
+
 // newRCache returns a new read-through cache.
 func newRCache(loader loader, name string) *rcache {
 	return &rcache{
@@ -62,7 +70,8 @@ func (c *rcache) tailUnsafe() int64 {
 func (c *rcache) Load(ctx context.Context, dbc *sql.DB,
 	prev int64, lag time.Duration,
 ) ([]*reflex.Event, error) {
-	if res, ok := c.maybeHit(prev+1, lag); ok {
+	res, ok := c.maybeHit(prev+1, lag)
+	if !cacheDisabled && ok {
 		rcacheHitsCounter.WithLabelValues(c.name).Inc()
 		return res, nil
 	}
@@ -112,7 +121,8 @@ func (c *rcache) readThrough(ctx context.Context, dbc *sql.DB,
 	defer c.mu.Unlock()
 
 	// Recheck cache after waiting for lock
-	if res, ok := c.maybeHitUnsafe(prev+1, lag); ok {
+	res, ok := c.maybeHitUnsafe(prev+1, lag)
+	if !cacheDisabled && ok {
 		return res, nil
 	}
 

rsql/rcache_test.go

@@ -64,7 +64,9 @@ func TestGap(t *testing.T) {
 
 func TestRCache(t *testing.T) {
 	tests := []struct {
-		name    string
+		name     string
+		disabled bool
+
 		add1    int
 		q1      int64
 		len1    int
@@ -100,6 +102,20 @@ func TestRCache(t *testing.T) {
 			q2Count: 1,
 			cLen2:   2,
 		},
+		{
+			name:     "disabled-miss-hit",
+			disabled: true,
+			add1:     2,
+			len1:     2,
+			total1:   1,
+			q1Count:  1,
+			cLen1:    2,
+
+			len2:    2,
+			total2:  2,
+			q2Count: 2,
+			cLen2:   2,
+		},
 		{
 			name:    "miss-hit-offset",
 			add1:    3,
@@ -161,6 +177,12 @@ func TestRCache(t *testing.T) {
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
+			if test.disabled {
+				DisableCache()
+				t.Cleanup(func() {
+					cacheDisabled = false
+				})
+			}
 			q := newQ()
 			c := newRCache(q.Load, "test")
 			c.limit = rCacheLimit