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Fix account counters being overwritten by parallel writes (#12045)

tags/v3.0.0rc3
Eugen Rochko 2 months ago
parent
commit
62f60e86c2
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+ 22
- 0
app/models/account_stat.rb View File

@@ -11,6 +11,7 @@
# created_at :datetime not null
# updated_at :datetime not null
# last_status_at :datetime
# lock_version :integer default(0), not null
#

class AccountStat < ApplicationRecord
@@ -20,10 +21,26 @@ class AccountStat < ApplicationRecord

def increment_count!(key)
update(attributes_for_increment(key))
rescue ActiveRecord::StaleObjectError
begin
reload_with_id
rescue ActiveRecord::RecordNotFound
# Nothing to do
else
retry
end
end

def decrement_count!(key)
update(key => [public_send(key) - 1, 0].max)
rescue ActiveRecord::StaleObjectError
begin
reload_with_id
rescue ActiveRecord::RecordNotFound
# Nothing to do
else
retry
end
end

private
@@ -33,4 +50,9 @@ class AccountStat < ApplicationRecord
attrs[:last_status_at] = Time.now.utc if key == :statuses_count
attrs
end

def reload_with_id
self.id = find_by!(account: account).id if new_record?
reload
end
end

+ 15
- 0
db/migrate/20191001213028_add_lock_version_to_account_stats.rb View File

@@ -0,0 +1,15 @@
require Rails.root.join('lib', 'mastodon', 'migration_helpers')

class AddLockVersionToAccountStats < ActiveRecord::Migration[5.2]
include Mastodon::MigrationHelpers

disable_ddl_transaction!

def up
safety_assured { add_column_with_default :account_stats, :lock_version, :integer, allow_null: false, default: 0 }
end

def down
remove_column :account_stats, :lock_version
end
end

+ 2
- 1
db/schema.rb View File

@@ -10,7 +10,7 @@
#
# It's strongly recommended that you check this file into your version control system.

ActiveRecord::Schema.define(version: 2019_09_27_232842) do
ActiveRecord::Schema.define(version: 2019_10_01_213028) do

# These are extensions that must be enabled in order to support this database
enable_extension "plpgsql"
@@ -97,6 +97,7 @@ ActiveRecord::Schema.define(version: 2019_09_27_232842) do
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.datetime "last_status_at"
t.integer "lock_version", default: 0, null: false
t.index ["account_id"], name: "index_account_stats_on_account_id", unique: true
end


+ 53
- 0
spec/models/account_stat_spec.rb View File

@@ -1,4 +1,57 @@
require 'rails_helper'

RSpec.describe AccountStat, type: :model do
describe '#increment_count!' do
it 'increments the count' do
account_stat = AccountStat.create(account: Fabricate(:account))
expect(account_stat.followers_count).to eq 0
account_stat.increment_count!(:followers_count)
expect(account_stat.followers_count).to eq 1
end

it 'increments the count in multi-threaded an environment' do
account_stat = AccountStat.create(account: Fabricate(:account), statuses_count: 0)
increment_by = 15
wait_for_start = true

threads = Array.new(increment_by) do
Thread.new do
true while wait_for_start
AccountStat.find(account_stat.id).increment_count!(:statuses_count)
end
end

wait_for_start = false
threads.each(&:join)

expect(account_stat.reload.statuses_count).to eq increment_by
end
end

describe '#decrement_count!' do
it 'decrements the count' do
account_stat = AccountStat.create(account: Fabricate(:account), followers_count: 15)
expect(account_stat.followers_count).to eq 15
account_stat.decrement_count!(:followers_count)
expect(account_stat.followers_count).to eq 14
end

it 'decrements the count in multi-threaded an environment' do
account_stat = AccountStat.create(account: Fabricate(:account), statuses_count: 15)
decrement_by = 10
wait_for_start = true

threads = Array.new(decrement_by) do
Thread.new do
true while wait_for_start
AccountStat.find(account_stat.id).decrement_count!(:statuses_count)
end
end

wait_for_start = false
threads.each(&:join)

expect(account_stat.reload.statuses_count).to eq 5
end
end
end

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