session lock problem

@makif,

It may be that something is configured wrong.  Have you checked your PHP ini file?  What version of PHP are you using(7.0.x or 7.1.x or 7.2.x or 7.3.x)? What are you database settings?  How long has this been an issue?

Php 7.1.18
mariadb version is 10.3.12
ci version is 3.1.8
it showed when data increased (exp: 20 million rows, 40 million rows)
i am using master-slave replication . Maybe it can be problem but i should use master-slave.
i will check my php.ini file, 
 
some settings on slave my.ini file

Code:

read_buffer_size = 2M
sort_buffer_size = 8M
join_buffer_size = 8M
query_cache_size = 1M
query_cache_limit = 1M
binlog_format=MIXED
long_query_time = 10
innodb_buffer_pool_size = 8G
[myisamchk]
key_buffer_size = 512M
sort_buffer_size = 512M
read_buffer = 8M
write_buffer = 8M

thank you for your attention