How to speed up mysql fetch?

Question

MySQL

Good day to all
, there is a mysql table with an id, value structure for ~ 3 million rows. id - primary, unique
query like "select id, value from table where id=1234567 limit 1" can be executed from 3 to 30 seconds
how to speed up query execution at least up to tenths of a second?
can you briefly tell about indes? like applied to the id field, but I don’t see the result,
will splitting the table into several, say, 10 thousand each help?
thanks in advance for the replies

Answer 1

There is an opinion that the index does not fit in memory. what is innodb_buffer_pool_size equal to?

Answer 2

do not use subselects, they are (de)optimized like depend subquery and slow down