Re: [Postgres-xc-developers] bug：sequence problem

[xiong w. <wan...@gm...>]

Hi,

About the sequence, we tried to realize the executing by change the
statement. For example,
create table t(a int, b int default nextval('seq1'));

If we insert a tuple like insert into t values(1), we replace the
statement with insert into t values(1,2) (here, we assume
nextval('seq1') is 2).

But we met a problem that we couldn't process when we add a column
with default nextval('seq1')  into a table which has multiple tuples.
Because the column needs increase automatically, we couldn't use a
proper sequence value to replace the default value.

For example:
create table t1(a int);
insert into t1 values(1),(1),(1);

select * from t1;
TEST=# select * from t1;
 A
---
 1
 1
 1
(3 行)

alter table t1 add column b int default nextval('seq1');
select * from t1;
TEST=# select * from t1;
 A | B
---+----
 1 | 1
 1 | 2
 1 | 3
(3 行)

Regards,
Benny
在 2010年12月9日 上午9:15，Koichi Suzuki <ko...@in...> 写道：
> This should be put into the track.
>
> I discussed with Michael and found that the issue is not that simple
> because we should consider the case of the replicated table.   It is not
> correct to get sequence value directly from GTM to Datanode in this
> case.   Coordinator should handle this.
>
> Regards;
> ---
> Koichi
>
> (2010年12月09日 10:11), xiong wang wrote:
>> Hi Koichi,
>>
>> Yes, I consider sequence should be created on datanodes but not only
>> on coordinators. But all the sequence value should be from GTM.
>>
>> Regards,
>> Benny
>>
>> 2010/12/9 Koichi Suzuki<ko...@in...>:
>>> In the current implementation, sequence value is supplied by GTM, as you
>>> know.   It is assumed that this value is supplied to the datanode through
>>> the coordinator.   In the case of your case, default value must be handled
>>> by the datanode and the datanode has to inquire GTM for the nextval of the
>>> sequence.
>>>
>>> I'm afraid this is missing in the current code.
>>> ---
>>> Koichi
>>>
>>> (2010年12月08日 19:33), xiong wang wrote:
>>>>
>>>> Dears,
>>>>
>>>> steps:
>>>> postgres=# create sequence seq start with 1;
>>>> CREATE SEQUENCE
>>>> postgres=# create table t(a int default nextval('seq'), b int);
>>>> ERROR:  Could not commit (or autocommit) data node connection
>>>>
>>>> datanode log as follows:
>>>> LOG:  statement: create table t(a int default nextval('seq'), b int);
>>>> ERROR:  relation "seq" does not exist
>>>>
>>>> When I checked the source code, I found sequence can't be created on
>>>> datanodes. Could you explain why?
>>>>
>>>> Regards,
>>>> Benny
>>>>
>>>>
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>
>