I do not claim it is trivial.<p>But .. fulltext index done right, including per hashtag, doubles the storage requirements at most. And the ability to call up any tweet from history does not need to be as instantaneous is recent tweets (It&#x27;s ok to wait 5 seconds for a tweet from 5 years ago).<p>&gt;  The fanout problem turns sharding into a lumpy problem because again, there is a power law distribution that can overwhelm any single machine.<p>Not really, in the case of twitter (where you only trace edges, not edges-of-edges and edges-of-edges-of-edges like Facebook and Linkedin do). In the simplified model I described, the web frontends all pull from the backend, but for the hot 10-million account followers -- of which there aren&#x27;t that many --, you can just push them to the webservers so they don&#x27;t even need to query)<p>&gt; Robustness at that scale is more than buying a pair of SSDs and setting up RAID.<p>I most definitely agree. But it is cheaply doable when everything is so perfectly shardable as it is in Twitter.<p>&gt; Then there&#x27;s the fun part that Twitter is so reliable these days that when something else on the internet breaks, we check Twitter for updates.<p>That&#x27;s possibly an illusion. Yes, Twitter is mostly reliable - but do you have any latency stats? e.g., would you know if, on a daily bases, 10% of tweets take 60 seconds until they appear on a viewer&#x27;s refresh? The &quot;hot&quot; accounts would be cached and immediately updated, but the long tail might have minutes delay and almost no one would notice.<p>&gt; But often, when you inquire, there is a solid non-obvious reason for non-trivial diversions from the simplest thing that could possibly work.<p>&gt; I always find it useful to give the benefit of the doubt.<p>I do not assume other engineers are morons. In my experience as a consultant, though, those solid non-obvious reasons for non-trivial diversions are much more often than not &quot;historical, do not apply any more&quot;, &quot;we didn&#x27;t have time or resources to do it the right way&quot;, &quot;the guy who did the initial design did it wrong for whatever reason, and now we are stuck with it&quot;, &quot;there&#x27;s a legal reason that&#x27;s not obvious why we can&#x27;t do it that way&quot;, and a few others.<p>Twitter had the resources to do it better from very early on, and they didn&#x27;t (I think it was 2012 or so before Twitter became reliable). For all I know, their system now could be the most efficient beast ever, and run on a ZX81 with 1K Ram with ultimate reliability, way better than I could ever hope to build.<p>I was just pointing out that the user facing side of twitter, technically speaking, is not very impressive. I&#x27;ve been doing it for a while on various technical forums - and not once did anyone offer a reason for why it&#x27;s much harder than it would seem -- most of the responses were along the lines of &quot;but mysql&#x2F;pgsql&#x2F;oracle can&#x27;t take the firehose load, I tried!&quot;. Which is correct, but irrelevant.