[Rails] Pessimistic locking locks the entire table?

Hi guys,

I must be missing something obvious with pessimistic locking. Here is
what I do (Rails 2.3, mySQL):

In my Foo model:

def test
Foo.transaction do
lock = UpdateLockForFoo.find_by_foo_id(self.id, :lock => true)
sleep 30
end
end

For each Foo model, I have an UpdateLockForFoo. This "lock" needs to
be acquired before doing any changes to Foo.

I believe it works, except that my entire UpdateLockForFoo table is
blocked during the sleep. If I open two terminals and do:

1st terminal:
f = Foo.find(1)
f.test

2nd termincal:
f = Foo.find(2)
f.test

The 2nd terminal waits 30s before doing what it has to do. My
understanding was that :lock => true only locks a specific record, but
it seems it is not the case and it locks the entire table.

Do you know?

Please note: it might not look like a good idea to have this separate
UpdateLockForFoo model but I am just simplifying the whole thing here
(I need this second model).

Thanks!

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