Re: [GENERAL] Postgres concurrency : urgent

On Fri, 12 Nov 1999, Chairudin Sentosa Harjo wrote:

> How do I lock a sequence?
> I must be able to rollback to previous sequence curr.value, if the
> transaction fails to work.
> I have been looking this for ages, it seems I haven't found the answer
> yet.
>

I use it like this:

BEGIN;
LOCK any_seq IN ACCESS EXCLUSIVE MODE;

SELECT any_seq.last_value+1...
INSERT into ... values(any_seq.last_value+1,....)
UPDATE ... set ...=any_seq.last_value+1...
...
SELECT nextval(any_seq);
END;

now I am sure that all SELECT, INSERT , ...
use exactly the same value of any_seq.last_value+1 and when any operation
fails my any_seq remains unchanged. I am also sure that only one
transaction that modify any_seq is running.


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    Marcin Inkielman

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