Hashtags aren't like user accounts, no - they're strings that are part of a tweet. In theory, a separate data structure shouldn't be needed since you can just s

Hashtags aren't like user accounts, no - they're strings that are part of a tweet. In theory, a separate data structure shouldn't be needed since you can just search the full text of tweets, but in practice, I don't know how that scales for the number of all-time tweets.