Mysql – How to artificially create a slow query in thesql

You have a server with 256M, but you can't use all of that -- remember there's some OS overhead. Add to that with the fact you're over committing as other folks have mentioned and you'll definitely thrash here. 256M is only enough for a small DB, 20 connections is a lot with what you've got configured.

1) reduce your max connections to 4 (you're using 3 out of 20)

2) optimize your query cache better; 8M is really large, and 64M total is a lot based on your hits/prunes; try a 4/32 combo and see how it goes. Really I think a 2/24 combo would work for you.

3) you have no sorts requiring temp tables, why is that max_heap_table_size verb in there? Comment that out, use the defaults

4) do you actually have 128 tables? Try cutting that table_cache in half to 64 or 48

5) reduce thread_cache_size to 4

6) optimize those tables to reduce fragmenting

Those are some things to start with. It looks like you threw a bunch of numbers in a config without any actual profiling to know what you needed and have created a mess; if all else fails go back to the defaults and get rid of your custom settings and start over using some performance tuning guides you can find on Google. Get the output of SHOW VARIABLES and SHOW STATUS, find any one of a bajillion tuning guides and plug in your actual, real numbers into their equations and that'll tell you the exact-ish numbers you need to put in your config file.

Some nice pictures, but there's a lot of info missing from your post.

What's the max connections? How big is the database? What engine? What's the key buffer size? How much free memory does the DBMS have?

full table scans, could this maybe be the problem?

Could be - not enough information to say. If the query needs to read more than approx a tenth of the data, the a full table scan will be faster than an index lookup.

queries, one for a menu that outputs around 1000 rows

You have menus on your web pages with 1000 entries? Then most of your problems are not in the database. Your application is fetching FAR TOO MUCH DATA from the database. If it's then sending this information across internet then performance will be appalling. If it's not sending out all the data it's fetching then why aren't you doing the filtering on the DBMS.

Every table has a primary index and thats it

Maybe you should think about aligning your schema with your queries (i.e. add relevant indexes) however think the biggest problem you've got is that you're fetching data from the DBMS which just isn't getting used.

OTOH do you mean that when you analyse the queries using the same tool as in your screenshot it tells you it's processing thousands of rows? In that case fixing the indexing will have a huge impact.