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Why AO3 Was Down

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153 points danso | 2 comments | 05 Jul 25 02:23 UTC | HN request time: 0.403s | source
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RainyDayTmrw ◴[05 Jul 25 05:19 UTC] No.44470247[source]▶
It's kinda impressive that they got to 2 billion rows - with indexes, no less - without falling over.
replies(1): >>44471169 #
jiggawatts ◴[05 Jul 25 08:47 UTC] No.44471169[source]▶
Point queries — typical of this kind of app - scales as log(n) in the number of rows. (Assuming a typical b-tree database index.)

This kind of workload cheerfully “scales” to your disk capacity.

replies(1): >>44477412 #
1. RainyDayTmrw ◴[06 Jul 25 02:47 UTC] No.44477412[source]▶
Locking would make that more complex, I believe?
replies(1): >>44478691 #
2. jiggawatts ◴[06 Jul 25 07:50 UTC] No.44478691[source]▶
Not necessarily. Typically a b-tree single-row modification updates only one leaf page. Higher levels change only 1/N times where N is the number of items per page, typically in the hundreds. So three levels up the chance of a lock conflict is only 1/N^3 or about one in a million. Four levels it is one in a hundred million, etc...