Optimize FixReblogsInFeeds migration (#5538)
We have changed how we store reblogs in the redis for bigint IDs. This process is done by 1) scan all entries in users feed, and 2) re-store reblogs by 3 write commands. However, this operation is really slow for large instances. e.g. 1hrs on friends.nico (w/ 50k users). So I have tried below tweaks. * It checked non-reblogs by `entry[0] == entry[1]`, but this condition won't work because `entry[0]` is String while `entry[1]` is Float. Changing `entry[0].to_i == entry[1]` seems work. -> about 4-20x faster (feed with less reblogs will be faster) * Write operations can be batched by pipeline -> about 6x faster * Wrap operation by Lua script and execute by EVALSHA command. This really reduces packets between Ruby and Redis. -> about 3x faster I've taken Lua script way, though doing other optimizations may be enough.main
parent
22da775a85
commit
0129f5eada
|
@ -3,48 +3,62 @@ class FixReblogsInFeeds < ActiveRecord::Migration[5.1]
|
|||
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 coersion because in this reblog tracking zset, we only
|
||||
# need the rebloggging 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
|
||||
|
||||
# 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 coersion because in this reblog tracking zset, we only
|
||||
# need the rebloggging 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.
|
||||
|
||||
# So, first, we iterate over the user's feed to find any reblogs.
|
||||
timeline_key = fm.key(:home, account.id)
|
||||
reblog_key = fm.key(:home, account.id, 'reblogs')
|
||||
redis.zrange(timeline_key, 0, -1, with_scores: true).each do |entry|
|
||||
next if entry[0] == entry[1]
|
||||
|
||||
# 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)
|
||||
|
||||
reblogged_id, reblogging_id = entry
|
||||
|
||||
# Remove the old entry
|
||||
redis.zrem(timeline_key, reblogged_id)
|
||||
|
||||
# Add a new one for the reblogging status
|
||||
redis.zadd(timeline_key, reblogging_id, reblogging_id)
|
||||
|
||||
# Track the fact that this was a reblog
|
||||
redis.zadd(reblog_key, reblogging_id, reblogged_id)
|
||||
end
|
||||
redis.evalsha(script_hash, [timeline_key, reblog_key])
|
||||
end
|
||||
end
|
||||
|
||||
|
|
Loading…
Reference in New Issue