Posted by Jerry Stuckle on 10/25/06 01:00

Daz wrote:
> Daz wrote:
>
>>Chung Leong wrote:
>>
>>>Then you end up with a race condition, I think even if a transaction is
>>>used. If there are two threads trying to insert the same data running
>>>simultaneously, a transaction would not block the second thread from
>>>fetching the same result set as the first. Thus both threads could
>>>think that a particular record doesn't exist and both would insert it.
>>>You would need to lock the table for the duration of the entire
>>>operation, which is pretty lousy.
>>
>>I am going to need to create a function that checks for duplicate
>>entries I think. However, the only time that there would be any chance
>>of a race condition, would be if the same user was logged on twice, and
>>carried out the same action symaltaniously. Baring in mind that there
>>is only an appromimately 0.1 second window (as this is how long the
>>transaction takes), I think it's very slim that it would happen. A user
>>shouldn't need to run the same thing twice symaltaniously, however, I
>>think I may start looking into methods that will log the user out of
>>one account if they login a second time with another.
>>
>>Basically, I acknowledge there is a very slim chance of having
>>duplicate entries, but how else could I get around this?
>>
>>All the best.
>>
>>Daz.
>
>
> Here is another possible idea. Why not have every script add a user ID
> to another database when a script is executed that will use the db.
> Once the script has finished, the user ID is removed. This can be
> indexed quite effectively, and will not allow the script to execute if
> their user ID is in that database. There could be a potential problem
> with any transaction that never finishes, but part of the table could
> be a timestamp. And whenever which will remove/update any rows that are
> more than say 30 seconds old, as this is the timeout limit for the
> server.
>
> The idea sounds a little rusty, but I personally feel it could work.
>

Because it's unnecessary overhead, that's why. Read Rik's comments.
You don't need it!

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Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
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