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63 lines
2.5 KiB
63 lines
2.5 KiB
class FixReblogsInFeeds < ActiveRecord::Migration[5.1]
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def up
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redis = Redis.current
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fm = FeedManager.instance
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# find_each is batched on the database side.
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User.includes(:account).find_each do |user|
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account = user.account
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# Old scheme:
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# Each user's feed zset had a series of score:value entries,
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# where "regular" statuses had the same score and value (their
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# ID). Reblogs had a score of the reblogging status' ID, and a
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# value of the reblogged status' ID.
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# New scheme:
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# The feed contains only entries with the same score and value.
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# Reblogs result in the reblogging status being added to the
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# feed, with an entry in a reblog tracking zset (where the score
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# is once again set to the reblogging status' ID, and the value
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# is set to the reblogged status' ID). This is safe for Redis'
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# float coersion because in this reblog tracking zset, we only
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# need the rebloggging status' ID to be able to stop tracking
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# entries after they have gotten too far down the feed, which
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# does not require an exact value.
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# So, first, we iterate over the user's feed to find any reblogs.
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timeline_key = fm.key(:home, account.id)
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reblog_key = fm.key(:home, account.id, 'reblogs')
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redis.zrange(timeline_key, 0, -1, with_scores: true).each do |entry|
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next if entry[0] == entry[1]
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# The score and value don't match, so this is a reblog.
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# (note that we're transitioning from IDs < 53 bits so we
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# don't have to worry about the loss of precision)
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reblogged_id, reblogging_id = entry
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# Remove the old entry
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redis.zrem(timeline_key, reblogged_id)
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# Add a new one for the reblogging status
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redis.zadd(timeline_key, reblogging_id, reblogging_id)
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# Track the fact that this was a reblog
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redis.zadd(reblog_key, reblogging_id, reblogged_id)
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end
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end
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end
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def down
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# We *deliberately* do nothing here. This means that reverting
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# this and the associated changes to the FeedManager code could
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# allow one superfluous reblog of any given status, but in the case
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# where things have gone wrong and a revert is necessary, this
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# appears preferable to requiring a database hit for every status
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# in every users' feed simply to revert.
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# Note that this is operating under the assumption that entries
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# with >53-bit IDs have already been entered. Otherwise, we could
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# just use the data in Redis to reverse this transition.
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end
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end
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