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Comment by ars | Hacker News Reader

So then when I'm on some kind of blocked WiFi and nothing resolves, and I switch to a properly working WiFi your code will continue to fail?

It's not so simple to cache misses - you don't know if it's a real miss or some kind of error.

For example if Facebook cached the miss, then even when they are back up nothing would connect.

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Yes. I handle around a million requests per minute. I exponentially increase the cache period after subsequent misses to avoid an outage ddos the whole system.

This tends to be beneficial regardless of the root cause.

edit this is especially useful for handling search/query misses as a query with no results is going to scan any relevant indexes etc. until it is clear no match exists meaning a no results query may take up more cycles than a hit.

It's remarkable the effect even short TTL caching can have given enough traffic. I recall once caching a value that was being accessed on every page load with a TTL of 1s resulting in a >99% reduction in query volume, and that's nowhere near Facebook/internet backbone scale.

yep, prepriming the cache rather than passively allowing it be rebuilt by request/queries can also result in some nice improvements and depending on replication delay across database servers avoid some unexpected query results reaching the end user.

In the past I was the architect of a top 2000 alexa ranked social networking site, data synchronization delays were insane under certain load patterns high single low double digit second write propagation delays.

I'm talking back-end not in app data caching. I would also cache misses there as well but with less aggressive ttl.

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