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From Joerg Heinicke <joerg.heini...@gmx.de>
Subject Re: [transaction] Duplicated TxId generation under heavy load
Date Tue, 22 Nov 2005 13:31:19 GMT
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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