binlog旋转时，mysql查询变得非常慢

Mysql版本是5.7.13。
每次binlog文件旋转时，所有查询和dml都会变得非常慢。
服务器“冻结”约40秒。
在慢速查询日志中，我只看到提交和系统/会话变量查询（如select@@session.tx_read_only；）大约需要20秒

==================主服务器我的.cnf===================== [mysqld]

# Remove leading # and set to the amount of RAM for the most important data 
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%. 
# innodb_buffer_pool_size = 128M 
innodb_buffer_pool_size = 2048M 
innodb_log_file_size = 360M 
innodb_log_buffer_size = 8M 
innodb_flush_log_at_trx_commit = 2 
innodb_max_dirty_pages_pct = 50 


# Remove leading # to turn on a very important data integrity option: logging 
# changes to the binary log between backups. 
# log_bin 

log-bin=/alidata1/binlog/mysql-bin 
expire_logs_days=7 
binlog-do-db=mydb 
sync_binlog=6 
server_id=10 

slow_query_log=on 
slow_query_log_file=/data/slow_query/slow_query.log 
log_queries_not_using_indexes=off 
long_query_time=1 
wait_timeout=10800 
max_connections=800 

sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES 
#character_set_server=utf8 
character-set-client-handshake=FALSE 
character-set-server=utf8mb4 
collation-server=utf8mb4_unicode_ci 
init_connect='SET NAMES utf8mb4' 

[client] 
default-character-set=utf8mb4 

[mysql] 
default-character-set=utf8mb4 

===========================binlog文件=========================

# User@Host: user[user] @ [10.24.165.8] Id: 130132 
# Query_time: 14.186255 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0 
SET timestamp=1499749959; 
select @@session.tx_read_only; 

# User@Host: user[user] @ [10.25.208.208] Id: 130317 
# Query_time: 13.943930 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0 
SET timestamp=1499749959; 
select @@session.tx_read_only; 

# User@Host: user[user] @ [10.24.165.8] Id: 130204 
# Query_time: 13.848498 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0 
SET timestamp=1499749959; 
select @@session.tx_read_only; 

# User@Host: user[user] @ [10.24.165.8] Id: 130197 
# Query_time: 12.988434 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0 
SET timestamp=1499749959; 
select @@session.tx_read_only;

===================mysql慢速日志==========================

# User@Host: user[user] @ [10.24.165.8] Id: 130132 
# Query_time: 14.186255 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0 
SET timestamp=1499749959; 
select @@session.tx_read_only; 

# User@Host: user[user] @ [10.25.208.208] Id: 130317 
# Query_time: 13.943930 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0 
SET timestamp=1499749959; 
select @@session.tx_read_only; 

# User@Host: user[user] @ [10.24.165.8] Id: 130204 
# Query_time: 13.848498 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0 
SET timestamp=1499749959; 
select @@session.tx_read_only; 

# User@Host: user[user] @ [10.24.165.8] Id: 130197 
# Query_time: 12.988434 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0 
SET timestamp=1499749959; 
select @@session.tx_read_only;