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Reddit has 8 million unique visitors, but only 300k subscribers to /r/pics, the top auto-subscribed subreddit. Generously assuming half of people manually unsu

by teej 16y ago

Reddit has 8 million unique visitors, but only 300k subscribers to /r/pics, the top auto-subscribed subreddit. Generously assuming half of people manually unsubscribe, that's at most 7% of their user base that are logged in. I know full well about cache churn with logged in users, but that's a lot of lurkers. I'm also not sure what makes a Facebook game's domain more "widely cachable". 100% of users are logged in. The vast majority of actions taken are changing state. Any app touchpoint is writing to the database. Page caching is nearly impossible. It's a lot less different than you think.

cheald 16y ago
I can't claim to know the specifics of your application, but consider that a single upvote invalidates however many thousand copies of a given page. An action in a Facebook game might invalidate a page for 10 or 20 or 50 users. An upvote, (or a comment, or an edit, or an upvote on a comment) invalidates that page for upwards of 300k+ users. Combine that with the rate at which reddit's pages change, and you're talking an obscene amount of CPU time spent building fragments/pages to stick into your cache. Scope of visibility of a change means a lot. You obviously know how to scale an app if you were pulling 16 million pageviews a day, and I don't intend to discount that at all. I just mean to point out that while fundamentally the same problem, reddit has to deal with a version of that particular problem that most applications don't begin to approach.
- parfe 16y ago
  >a single upvote invalidates however many thousand copies of a given page I never understood this. Does reddit really need to spend the capital making sure I see a stranger's upvote the moment it occurs? A 60 second delay to refresh pages in batches seems perfectly reasonable. Perhaps with a client side script to mark my own upvotes so the system doesn't look like is losing my selections.

by teej 16y ago

cheald 16y ago

I can't claim to know the specifics of your application, but consider that a single upvote invalidates however many thousand copies of a given page. An action in a Facebook game might invalidate a page for 10 or 20 or 50 users. An upvote, (or a comment, or an edit, or an upvote on a comment) invalidates that page for upwards of 300k+ users. Combine that with the rate at which reddit's pages change, and you're talking an obscene amount of CPU time spent building fragments/pages to stick into your cache. Scope of visibility of a change means a lot. You obviously know how to scale an app if you were pulling 16 million pageviews a day, and I don't intend to discount that at all. I just mean to point out that while fundamentally the same problem, reddit has to deal with a version of that particular problem that most applications don't begin to approach.

parfe 16y ago
>a single upvote invalidates however many thousand copies of a given page I never understood this. Does reddit really need to spend the capital making sure I see a stranger's upvote the moment it occurs? A 60 second delay to refresh pages in batches seems perfectly reasonable. Perhaps with a client side script to mark my own upvotes so the system doesn't look like is losing my selections.