commit: 0129f5eada3d146c4e3550c7c82b94520a18d2ba
parent: 22da775a8546a0496b4f501f7cb6e321b0168f40
Author: unarist <m.unarist@gmail.com>
Date: Fri, 27 Oct 2017 23:10:22 +0900
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.
Diffstat:
1 file changed, 49 insertions(+), 35 deletions(-)
diff --git a/db/migrate/20170920032311_fix_reblogs_in_feeds.rb b/db/migrate/20170920032311_fix_reblogs_in_feeds.rb
@@ -3,48 +3,62 @@ class FixReblogsInFeeds < ActiveRecord::Migration[5.1]
redis = Redis.current
fm = FeedManager.instance
- # 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.
- # 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]
+ # 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]
- # 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)
+ -- 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
- reblogged_id, reblogging_id = entry
+ -- 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.zrem(timeline_key, reblogged_id)
+ -- Remove the old entry
+ redis.call('zrem', timeline_key, reblogged_id)
- # Add a new one for the reblogging status
- redis.zadd(timeline_key, reblogging_id, reblogging_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.zadd(reblog_key, reblogging_id, reblogged_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
