[Reply]
Stephen,
I think that from what you say, gaps are not a problem, it is uniqueness that you are
looking for. Am I right?
Assuming I am (for once this year), then all you need to do is to generate the unqiue
ID outside the transaction that will use it.
eg
Process 1: Start TransactionA - Generate ID (=11)- Commit TransactionA - Start
TransactionB - start doing whatever .....
Process 2: Start TransactionC - Generate ID (=12)- Commit TransactionC - Start
TransactionD - start doing whatever .....
.
.
Process 1: Aborts Rollback TransactionB
Process 3: Start TransactionE - Generate ID (=13) - Commit TransactionE - Start
TransactionF - start doing whatever .....
To do this, you will need to use a method to generate ID's (Interbase is so easy in
this sense because generators are produced outside
any transactions) . One way is to have a table which you keep the last value in. Look
to your database documentation for details on
how to do this. It is so basic to any database activity.
Kind Regards
Gary
At 17:21 on 11/01/2001 you wrote
>To :
>CC :
>From: Stephen Bertram, [EMAIL PROTECTED]
>The problem is :
>
>Process 1 generates 11
>Process 2 generates 12
>Process 3 generates 13
>Process 1 issues a rollback - ID 11 is now unused
>Process 4 generates 11 - based on rolledback seed value.
>Process 5 generates 12 !! Duplicate
>Process 6 generates 13 !! Duplicate
>
>Or am I missing something here? I can't see how to hold a value that is the
>basis for the next value (sequential or random) that isn't reset by a
>rollback.
>
>The other option of holding a table of all used values works well and is
>safe, but we end up with a table of X million rows with an associated index
>that does nothing useful. If this was the selected option I suspect the
>best functionality would be to create a random number and then check for
>existance. This at least would avoid the index problems that exist with
>sequential keys in some environments.
>
>Stephen
>
>
>-----Original Message-----
>From: Nic Wise [mailto:[EMAIL PROTECTED]]
>Sent: Thursday, 11 January 2001 4:52 p.m.
>To: Multiple recipients of list delphi
>Subject: Re: [DUG]: [DUG-DB]: Unique IDs
>
>
>> The suggestion that Gary has put forward is exactly what I was thinking
>of,
>> but I still don't see how to "remember" rolled back ID's.
>
>
>do you really need to? does 1 2 3 6 7 8 9 10 14 16 17 make a difference, as
>long as they are all in order???? whats it for?
>
>N
>
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