You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
77 lines
3.0 KiB
77 lines
3.0 KiB
class FixReblogsInFeeds < ActiveRecord::Migration[5.1]
|
|
def up
|
|
redis = Redis.current
|
|
fm = FeedManager.instance
|
|
|
|
# Old scheme:
|
|
# Each user's feed zset had a series of score:value entries,
|
|
# where "regular" statuses had the same score and value (their
|
|
# ID). Reblogs had a score of the reblogging status' ID, and a
|
|
# value of the reblogged status' ID.
|
|
|
|
# New scheme:
|
|
# The feed contains only entries with the same score and value.
|
|
# Reblogs result in the reblogging status being added to the
|
|
# feed, with an entry in a reblog tracking zset (where the score
|
|
# is once again set to the reblogging status' ID, and the value
|
|
# is set to the reblogged status' ID). This is safe for Redis'
|
|
# float conversion because in this reblog tracking zset, we only
|
|
# need the reblogging status' ID to be able to stop tracking
|
|
# entries after they have gotten too far down the feed, which
|
|
# does not require an exact value.
|
|
|
|
# This process reads all feeds and writes 3 times for each reblogs.
|
|
# So we use Lua script to avoid overhead between Ruby and Redis.
|
|
script = <<-LUA
|
|
local timeline_key = KEYS[1]
|
|
local reblog_key = KEYS[2]
|
|
|
|
-- So, first, we iterate over the user's feed to find any reblogs.
|
|
local items = redis.call('zrange', timeline_key, 0, -1, 'withscores')
|
|
|
|
for i = 1, #items, 2 do
|
|
local reblogged_id = items[i]
|
|
local reblogging_id = items[i + 1]
|
|
if (reblogged_id ~= reblogging_id) then
|
|
|
|
-- The score and value don't match, so this is a reblog.
|
|
-- (note that we're transitioning from IDs < 53 bits so we
|
|
-- don't have to worry about the loss of precision)
|
|
|
|
-- Remove the old entry
|
|
redis.call('zrem', timeline_key, reblogged_id)
|
|
|
|
-- Add a new one for the reblogging status
|
|
redis.call('zadd', timeline_key, reblogging_id, reblogging_id)
|
|
|
|
-- Track the fact that this was a reblog
|
|
redis.call('zadd', reblog_key, reblogging_id, reblogged_id)
|
|
end
|
|
end
|
|
LUA
|
|
script_hash = redis.script(:load, script)
|
|
|
|
# find_each is batched on the database side.
|
|
User.includes(:account).find_each do |user|
|
|
account = user.account
|
|
|
|
timeline_key = fm.key(:home, account.id)
|
|
reblog_key = fm.key(:home, account.id, 'reblogs')
|
|
|
|
redis.evalsha(script_hash, [timeline_key, reblog_key])
|
|
end
|
|
end
|
|
|
|
def down
|
|
# We *deliberately* do nothing here. This means that reverting
|
|
# this and the associated changes to the FeedManager code could
|
|
# allow one superfluous reblog of any given status, but in the case
|
|
# where things have gone wrong and a revert is necessary, this
|
|
# appears preferable to requiring a database hit for every status
|
|
# in every users' feed simply to revert.
|
|
|
|
# Note that this is operating under the assumption that entries
|
|
# with >53-bit IDs have already been entered. Otherwise, we could
|
|
# just use the data in Redis to reverse this transition.
|
|
end
|
|
end
|