Message-ID: <20040805065440.53274.qmail@web41808.mail.yahoo.com>
Date: Wed, 4 Aug 2004 23:54:40 -0700 (PDT)
From: Prabu Subroto <prabu_subroto@yahoo.com>
Subject: Re: Sequence Question
To: pgsql-general@postgresql.org
In-Reply-To: <20040805041942.0D6513953@sitemail.everyone.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii

kv=# create sequence sales_salesid_seq;
CREATE SEQUENCE
kv=# select setval('sales_salesid_seq', (select
max(salesid) from sales)+1);
 setval
--------
     16
(1 row)
kv=# alter table sales alter column salesid set
default nextval('sales_serialid_
seq');
ALTER TABLE

 Oscar Tuscon <obtuse@bmwe30.net> wrote:

> I'm looking at ways to get batches of sequence
> values s faster. I don't want to set cache or
> increment to a large number for a variety of
> reasons. I need to grab id's in batches of varying
> numbers at various times, from 1 to several thousand
> at once.
> Doing it 1 at a time works, but more time goes into
> it than I'd like. I tried setting cache_value high
> but the database roundtrips were eating more time
> that I wanted to see; I only saw a 25% improvement
> in average time.
> 
> SO... is the following approach safe? That is, will
> this be atomic, or is there a possibility that
> another connection could squeeze in a select
> nextval() between the select nextval() and the
> setval below?
> If it's safe I'd do this and take the sequences as
> the new currval - #I asked for (1500 or whatever).
> 
> mydb=# select setval('my_id_seq', (select
> nextval('my_id_seq')+1500));
> 
> Thanks
> Oscar
> 
> 
>
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