How To Change The Floppy Image Of Qemu?

Question

I am wondering whether I really do need transactions/locks in the following scenario. I can carry out 3 operations which might be concurrent in any number of them (i.e. I could have two Task 1 running and three Task 2 running):

Task 1:

select distinct count(some_id) as my_counter from table_1;
update table_2 set counter = my_counter;

Task 2:

insert into table_1 ...;
update table_2 set counter = counter + 1;

Task 3:

delete from table_1 where id = ...;
update table_2 set counter = counter - 1;

How should I implement the above being sure that I will never corrupt table_2's field counter?

Thank you very much!

Solution

You can open qemu's console by pressing Ctrl-Alt-2 then type:

(qemu) change floppy0 os.img

Ctrl-Alt-1 to switch back to the VM's display.

If you start qemu from a terminal, an easier way of doing this is to run qemu with the -monitor stdio option, which will give the same qemu console in the terminal window.

Comments

[usr]

I would not say that a trigger does any locking by itself at all. I don't think this answer is correct.