Cache Stratejileri - Cache Stampede

Giriş

Açıklamalar çoğunlukla buradan.

1. No protection

Every caller discovers the miss and independently loads the value.

This is the classic cache stampede / thundering herd.

The dangerous part is that the application may be completely correct. The database is simply receiving an unexpected burst.

2. Local singleflight

Here, each application instance says:

"If another thread on this same machine is already loading this key, I'll wait for its result."

Burada halen pod sayısı kadar hit gelebilir.

3. Fleet refresh lease

Only the pod that acquires the lease is allowed to refresh. Burada A uyandı ancak işi bitiremedi, sonra B uyandı işi bitirdi ve daha sonra A uyandı o da işi bitirdi ancak eski veriyi yazdı problemi var. Yani optimistic lock koymak lazım

4. Stale-while-revalidate

you distinguish:

- fresh

- stale-but-usable

- too-old / unavailable

Stale iken de veriyi sunar

The TTL jitter

Hepsi için kullanılabilir. Açıklaması şöyle

Bad jitter

If you do:

TTL = maxTTL + random()

then everything is already guaranteed to live at least maxTTL.

You're spreading the expiration times, but you're also violating the intended freshness boundary.

Subtractive jitter

Instead:

TTL = maxTTL - random()

gives:

maxTTL-0

maxTTL-3

maxTTL-17

maxTTL-42

...

So everything expires at or before the maximum freshness deadline.

The important concept isn't really the exact formula.

It's:

Randomize expiration without extending the maximum allowed lifetime.