Re: Queries on MyISAM

[Rick James]

One core per connection. This is totally true for MyISAM, and mostly true for InnoDB. PARTITION does not use multiple cores.

Two connections use one thread each. However, they _may_ slow each other down. (MyISAM comments here)
* A write (such as via replication from the Master) will block SELECTs on that table(s).
* A SELECT will block replication writes.
* Two SELECTs (same table or different tables) will fight for the key_buffer, but usually the contention is unnoticeable.

There are many other possible explanations for what you are seeing; please provide
* SHOW CREATE TABLE tbl\G -- engine, indexes
* SHOW TABLE STATUS LIKE 'tbl'\G -- sizes
* EXPLAIN SELECT ...\G -- clues of inefficiencies
* SHOW VARIABLES LIKE '%buffer%'; -- cache size
and surround them with [ code ] and [ / code ]
How much RAM do you have?