Re: creating a table with a serial column sets currval

From: Kris Jurka <books(at)ejurka(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: creating a table with a serial column sets currval
Date: 2007-10-18 23:24:57
Message-ID: Pine.BSO.4.64.0710181919160.5403@leary.csoft.net
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On Thu, 18 Oct 2007, Tom Lane wrote:

>> Looks like any alter sequence command will do this. The serial case uses
>> alter sequence owned by under the hood which exposes this. The problem is
>> that altering the sequence puts it into the SeqTable cache list when it
>> really shouldn't be.
>
> It's not that it gets put in the cache, it's that read_info gets called
> (setting elm->increment). I think we probably should clean this up by
> creating a separate flag in that struct that explicitly says "currval is
> valid", which would be set by nextval(), setval() (because historically
> it's acted that way), and I guess ALTER SEQUENCE RESTART WITH (for
> consistency with setval()).

Personally I think setval should only set validCurrval and the last_value
if iscalled = true. If is_called = false I think it should retain the
previous last_value if any until the next nextval call.

jurka=# create sequence s;
CREATE SEQUENCE
jurka=# select nextval('s');
nextval
---------
1
(1 row)

jurka=# select setval('s',5, false);
setval
--------
5
(1 row)

jurka=# select currval('s');
currval
---------
5
(1 row)

Should return 1 instead of 5.

Kris Jurka

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