diff --git a/README.md b/README.md
index 5eb32ae..8801d58 100644
--- a/README.md
+++ b/README.md
@@ -358,3 +358,21 @@ token, so that it is removed automatically.
 
 It'd better to inject the dependency of Redis connection into the `Authn`
 middleware so that it's simpler to test.
+
+### 2024/10/15
+
+Redis is integrated to keep a blacklist of logged out users. BTW `memcached`
+is also interesting. In case later I want to switch to another key-value
+storage, I have made an interface. It also helps for the test. I can even
+just drop the redis and use a bare-hand native hashmap.
+
+Quite a lot benefits. And then I realised that I have done "wrong" about
+`sqlc`. I shouldn't have used the pgx driver, instead the `database/sql`
+driver is more universal, if I want to switch to sqlite or mysql later.
+
+Well it's not about changing the technical solution every 3 days, but a
+system than can survive those changes elegantly must be a robust system, with
+functionalities well decoupled and interfaces well defined.
+
+I will add some tests for existing code and then it's time to move on to
+my core business logic.