At 9:10 PM -0800 1999-12-12, Joshua Chamas wrote:
>Andy wrote:
>>
>> Hi,
>>
>> I read in the manual that I can use get_lock to simulate row-level locking.
>> But I don't see how that would work. I thought mysql automatically lock the
>> whole table on selects & updates, so even if I do a get_lock("row_id", 10)
>> for every select & update, mysql will still acquire table lock and that
>> would defeat the whole purpose.
>>
>
>If you need to lock a row across more than one query, get_lock()
>does simulate row level locking. It doesn't do anything for you
>if you are just looking for the row level locking performance
>for a single select statement.
>
>> Also, what type of lock does get_lock() acquire? shared or exclusive?
>>
>
>Exclusive.
It's exclusive only for applications that cooperate in its use.
In other words, it doesn't lock anything, if another application
decides to simply not check for the lock.
GET_LOCK() implements advisory, cooperative locks.
>
>> Can someoone help me out? Anyone has used get_lock for this purpose? I'd
>> love to learn about your eperience.
>>
>
>Yes I have used it, and it works well. If I want to do a set of SQL
>operations based on a row, then I acquire a get_lock() on a key
>built of that rows'd unique id & maybe table name or some other
>identifier.
--
Paul DuBois, paul@stripped
