class CopyAccountStats < ActiveRecord::Migration[5.2] disable_ddl_transaction! def up safety_assured do if supports_upsert? up_fast else up_slow end end end def down # Nothing end private def supports_upsert? version = select_one("SELECT current_setting('server_version_num') AS v")['v'].to_i version >= 90_500 end def up_fast say 'Upsert is available, importing counters using the fast method' Account.unscoped.select('id').find_in_batches(batch_size: 5_000) do |accounts| execute <<-SQL.squish INSERT INTO account_stats (account_id, statuses_count, following_count, followers_count, created_at, updated_at) SELECT id, statuses_count, following_count, followers_count, created_at, updated_at FROM accounts WHERE id IN (#{accounts.map(&:id).join(', ')}) ON CONFLICT (account_id) DO UPDATE SET statuses_count = EXCLUDED.statuses_count, following_count = EXCLUDED.following_count, followers_count = EXCLUDED.followers_count SQL end end def up_slow say 'Upsert is not available in PostgreSQL below 9.5, falling back to slow import of counters' # We cannot use bulk INSERT or overarching transactions here because of possible # uniqueness violations that we need to skip over Account.unscoped.select('id, statuses_count, following_count, followers_count, created_at, updated_at').find_each do |account| params = [[nil, account.id], [nil, account[:statuses_count]], [nil, account[:following_count]], [nil, account[:followers_count]], [nil, account.created_at], [nil, account.updated_at]] exec_insert('INSERT INTO account_stats (account_id, statuses_count, following_count, followers_count, created_at, updated_at) VALUES ($1, $2, $3, $4, $5, $6)', nil, params) rescue ActiveRecord::RecordNotUnique next end end end