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Ron Johnson wrote:
> On 08/29/07 09:34, Decibel! wrote:
>> On Wed, Aug 29, 2007 at 08:37:26AM -0500, Ron Johnson wrote:
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>>> On 08/29/07 07:27, cluster wrote:
>>>> OK, thanks. But what with the second question in which the UPDATE is
>>>> based on a SELECT max(...) statement on another table? How can I ensure
>>>> that no other process inserts a row between my SELECT max() and UPDATE -
>>>> making my SELECT max() invalid?
>>>>
>>>> A table lock could be an option but I am only interested in blocking for
>>>> row insertions for this particular account_id. Insertions for other
>>>> account_ids will not make the SELECT max() invalid and should therefore
>>>> be allowed.
>>> Well, concurrency and transactional consistency *allows* other
>>> processes to update the table after you start your transaction. You
>>> just won't *see* their updates while you're inside of a transaction.
>> Just make sure and read up about transaction isolation... in the default
>> of READ COMMITTED mode, you can sometimes see changes made by other
>> transactions.
>
> Argh!!! The RDBMS that I typically use defaults to SERIALIZABLE.
SERIALIZABLE is really slow :). You should look into SERIALIZABLE only
for those transactions that need it. There is also SELECT FOR UPDATE.
Joshua D. Drake
>
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