From: | "Dan Langille" <dan(at)langille(dot)org> |
---|---|
To: | Nicolas Nolst <nnolst(at)hotmail(dot)com> |
Cc: | pgsql-admin(at)postgresql(dot)org, pgsql-general(at)postgresql(dot)org |
Subject: | Re: [GENERAL] performance issue using DBI |
Date: | 2002-06-06 16:33:54 |
Message-ID: | 20020606163524.D685F3F28@bast.unixathome.org |
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Thread: | |
Lists: | pgsql-admin pgsql-general |
On 6 Jun 2002 at 17:14, Oliver Elphick wrote:
> On Thu, 2002-06-06 at 14:55, Joshua b. Jore wrote:u
> > Don't use currval since some other process might alter the
> > sequence between the time you call nextval and currval.
>
> This is wrong. currval() will always return the last serial assigned in
> *the*same*session*. It is not affected by other users at all.
Folks, here's a short test which might help. Note the BEGIN.
$ psql testing
testing=# create sequence test;
CREATE
testing=# select currval('test');
ERROR: test.currval is not yet defined in this session
testing=# select setval('test', 1);
setval
--------
1
(1 row)
testing=# select currval('test');
currval
---------
1
(1 row)
testing=# select currval('test');
currval
---------
1
(1 row)
testing=# select currval('test');
currval
---------
1
(1 row)
testing=# select currval('test');
currval
---------
1
(1 row)
testing=#
Then, in another window, I did this:
$ psql testing
# select nextval('test');
nextval
---------
2
(1 row)
testing=# select nextval('test');
nextval
---------
3
(1 row)
testing=# select nextval('test');
nextval
---------
4
(1 row)
testing=#
Then back to the other window:
testing=# select currval('test');
currval
---------
1
(1 row)
testing=# select nextval('test');
nextval
---------
5
(1 row)
testing=#
cheers
FWIW: I always use nextval when looking for a new ID.
--
Dan Langille
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