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From Cservenak Tamas <cserve...@is-micro.hu>
Subject Re: [transaction] Duplicated TxId generation under heavy load
Date Tue, 22 Nov 2005 14:07:46 GMT
Yes, youre right.

Anyway, in my case it would be more appropriate to generate Tx ID's by
myself to avoid generatedUniqueTxId() problem. As first step i will
probably copy this patched method into my code and use it instead of
calling frm.generated....

Thanks for help. And sorry for bothering, this should go to the users
maillist, not dev, right?

~t~


Joerg Heinicke wrote:
> Cservenak Tamas <cservenak <at> is-micro.hu> writes:
>
>   
>> The generatedUniqueTxId() method in FileResourceManager uses
>> System.currentTimeMillis() to generate txId's.
>>
>> On my system it causes duplicate txId generation and FRM failure. I have
>> 4 threads accessing one FRM instance.
>>
>> This simple patch adds "salt" to it, with a little overhead to solve
>> this problem.
>>     
>
> Unfortunately this does not help much, it only solves your problem "under heavy
> load". But if there is already another txId equal to this one (e.g. generated
> externally) FRM will again fail. It can only work if inside the synchronized
> block the generated txId is "preserved", e.g. by putting a final static object
> PRESERVED into the map and testing for it in the startTransaction(Object) method.
>
> This will solve almost all problems except one:
> 1. Thread 1: generateUniqueTxId()
> 2. Thread 2: startTransaction(txId) with an externally generated txId -
> coincidentally equal to the above generated one
> 3. Thread 1: startTransaction(txId) with the generated txId
>
> But is again a magnitude more unlikely.
>
> Jörg
>
>
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