possible to lock a single row in table?

Hello!
i have a lots of threads that work on a table, making insertions,
updates removes.....

now i certain cases its important to keep data integrity, so i looked
into locks....


all i found was a lock function that locks the entire table....

now even in shared mode, if i understand it well this means that as long
as the locking procedure isn't finished, no other thread can update or
delete data, right? Thats really harsh, since there are really an awful
lot of threads....

isn't it possible to lock only a specific row?

and what happens to other insert queries whilst the lock is operational?
Are they postponed and the valling thread waits, or does the call return
with an error?

-- 
ciao bboett
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