What is the MySQL version? OS and version? How much of your 4GB RAM is used by other processes?
Then please ...
(i) post the result of ...
select engine,data,indexes,total
from (
select
ifnull(engine,'TOTALS') as engine,
concat(data,' GB') as data,
concat(indexes,' GB') as indexes,
concat(tot,' GB') as total,
if(engine is null,-1,tot) as ord
from (
select
engine,
round( sum(data_length)/1024/1024/1024, 2 ) as data,
round( sum(index_length)/1024/1024/1024, 2 ) as indexes,
round( sum(data_length+index_length)/1024/1024/1024, 2 ) as tot
from information_schema.tables
where engine is not null and engine not in('information_schema','performance_schema')
group by engine with rollup
) sums
) list
order by list.ord desc;
(ii) post the results of running these queries in the mysql client program ...
show variables;
show global status;
if mysql 5.7 or later ...
select * from sys.memory_global_total;
select
substring_index(event_name,'/',2) as code_area,
sys.format_bytes( sum(current_alloc) ) as current_alloc
from sys.x$memory_global_by_current_bytes
group by substring_index(event_name,'/',2)
order by sum(current_alloc) desc;
select
concat(format(a.num * 100.0 / b.num,2),"%") bufferpoolfullpct
from
(select variable_value num from performance_schema.global_status
where variable_name = 'innodb_buffer_pool_pages_data') a,
(select variable_value num from performance_schema.global_status
where variable_name = 'innodb_buffer_pool_pages_total') b;
... and look for runaway mem use in the results of ...
select *
from performance_schema.memory_summary_global_by_event_name
where event_name like 'memory/performance_schema/%';
(iii) post the result of ...
free -m
or in Windows use systeminfo.
To get ready for optimising, turn on the slow query log if it's not already enabled.