Re: Issue with sequence and transactions

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От Bruno Wolff III
Тема Re: Issue with sequence and transactions
Дата
Msg-id 20041109034429.GA16284@wolff.to
обсуждение исходный текст
Ответ на Issue with sequence and transactions  (Ian Meyer <misc@crewcial.org>)
Список pgsql-novice
On Mon, Nov 08, 2004 at 22:27:39 -0500,
  Ian Meyer <misc@crewcial.org> wrote:
>
> Why does the sequence not get rolled back? I have looked in
> documentation, read endlessly in a PostgreSQL book and can't figure out
> if that is the expected behavior.. and if so, why?

By not having the value of a sequence rolled back on transaction failure,
applications using sequences run faster under load.

>
> What I want to happen (at least, the way I see it happening) is if
> someone creates a username, but the query fails, or the username is
> taken already, then the transaction is rolled back, and the id that
> would have been taken, is still free.

Then you probably don't want to use a sequence. Sequences should be used
to obtain unique values, not to generate a list of id numbers without
gaps.

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