Bug with sequence

In article <92c0776e.0211180745.49911131@posting.google.com>,
Thomas Aichinger wrote:

Hi,

I recently installed pg 7.2.3 on my linux box and discovered that
there are some problems with datatype serial and sequence.

1.) If you create a table with a datatype serial, the corrsponding
sequence will be created, but if you drop the table the sequence is
not dropped.

I am pretty sure this has been fixed in version 7.3 (due to be
release real soon now.)

2.) If you create a sequence and grant it to public one cant use
currval() until one used setval() or nextval().
"ERROR: midnr.currval is not yet defined in this session"

This is actually the way sequences work (ie, it's a feature, not
a bug, heh heh)

currval() gives you the current value of the sequence
*as seen in this session* ... so until you do a setval()
or a nextval() there is no value seen by this session.

3.) Sometimes one gets 'not enogh privileges' error when using
nexval()

nextval()? hmm. well. If the user does not have privelege to
update the sequence, then the call will fail.

Am I the first one who discovered that?

Nah, and probably not the first one to avoid the FAQ either.
heh heh.

On Mon, 2002-11-18 at 15:45, Thomas Aichinger wrote:

Hi,

I recently installed pg 7.2.3 on my linux box and discovered that
there are some problems with datatype serial and sequence.

1.) If you create a table with a datatype serial, the corrsponding
sequence will be created, but if you drop the table the sequence is
not dropped.

This is fixed in 7.3

2.) If you create a sequence and grant it to public one cant use
currval() until one used setval() or nextval().
"ERROR: midnr.currval is not yet defined in this session"

This is how it is intended to work. Read the manual...
And it is nothing to do with its being granted to public; it is
fundamental to what currval() does, which is to provide the last value
given by nextval() *in*the*current*session*. If there has been no use
of nextval(), currval() cannot report anything.

If you want the last value given by anyone on the sequence, you could
use "select last_value from <sequence_name>", but that would not give
you anything done by uncompleted transactions. That's why currval()
exists.

3.) Sometimes one gets 'not enogh privileges' error when using
nexval()

When the sequence is created, you need to grant access rights on it to
other users who will need it.

--
Oliver Elphick Oliver.Elphick@lfix.co.uk
Isle of Wight, UK
http://www.lfix.co.uk/oliver
GPG: 1024D/3E1D0C1C: CA12 09E0 E8D5 8870 5839 932A 614D 4C34 3E1D 0C1C
========================================
"If my people, which are called by my name, shall
humble themselves, and pray, and seek my face, and
turn from their wicked ways; then will I hear from
heaven, and will forgive their sin, and will heal
their land." II Chronicles 7:14

On Wed, 2002-11-20 at 21:35, Robert Treat wrote:

On Wed, 2002-11-20 at 03:53, Oliver Elphick wrote:

On Mon, 2002-11-18 at 15:45, Thomas Aichinger wrote:

Hi,

I recently installed pg 7.2.3 on my linux box and discovered that
there are some problems with datatype serial and sequence.

1.) If you create a table with a datatype serial, the corrsponding
sequence will be created, but if you drop the table the sequence is
not dropped.

This is fixed in 7.3

out of curiosity, do you know the logic that implements this fix? I have
a couple of tables that use the same sequence; I'm wondering if dropping
one of the tables removes the sequence or if I have to drop all tables
before the sequence is removed

I just tried it.

I created a sequence using SERIAL when I created a table. I used the
same sequence for another table by setting a column default to
nextval(sequence).

I deleted the first table. The sequence was deleted too, leaving the
default of the second table referring to a non-existent sequence.

Could this be a TODO item in 7.4, to add a dependency check when a
sequence is set as the default without being created at the same time?

--
Oliver Elphick Oliver.Elphick@lfix.co.uk
Isle of Wight, UK
http://www.lfix.co.uk/oliver
GPG: 1024D/3E1D0C1C: CA12 09E0 E8D5 8870 5839 932A 614D 4C34 3E1D 0C1C
========================================
"If my people, which are called by my name, shall
humble themselves, and pray, and seek my face, and
turn from their wicked ways; then will I hear from
heaven, and will forgive their sin, and will heal
their land." II Chronicles 7:14

This requires changing the nextval() function to be an attribute of the
sequence.

ie. sequence.nextval and sequence.currval to deal with the sequence.

It should also be on the todo list.

On Wed, 2002-11-20 at 17:12, Oliver Elphick wrote:

On Wed, 2002-11-20 at 21:35, Robert Treat wrote:

On Wed, 2002-11-20 at 03:53, Oliver Elphick wrote:

On Mon, 2002-11-18 at 15:45, Thomas Aichinger wrote:

Hi,

I recently installed pg 7.2.3 on my linux box and discovered that
there are some problems with datatype serial and sequence.

1.) If you create a table with a datatype serial, the corrsponding
sequence will be created, but if you drop the table the sequence is
not dropped.

This is fixed in 7.3

out of curiosity, do you know the logic that implements this fix? I have
a couple of tables that use the same sequence; I'm wondering if dropping
one of the tables removes the sequence or if I have to drop all tables
before the sequence is removed

I just tried it.

I created a sequence using SERIAL when I created a table. I used the
same sequence for another table by setting a column default to
nextval(sequence).

I deleted the first table. The sequence was deleted too, leaving the
default of the second table referring to a non-existent sequence.

Could this be a TODO item in 7.4, to add a dependency check when a
sequence is set as the default without being created at the same time?

--
Rod Taylor <rbt@rbt.ca>

Oliver Elphick wrote:

On Wed, 2002-11-20 at 21:35, Robert Treat wrote:

On Wed, 2002-11-20 at 03:53, Oliver Elphick wrote:

On Mon, 2002-11-18 at 15:45, Thomas Aichinger wrote:

Hi,

I recently installed pg 7.2.3 on my linux box and discovered that
there are some problems with datatype serial and sequence.

1.) If you create a table with a datatype serial, the corrsponding
sequence will be created, but if you drop the table the sequence is
not dropped.

This is fixed in 7.3

out of curiosity, do you know the logic that implements this fix? I have
a couple of tables that use the same sequence; I'm wondering if dropping
one of the tables removes the sequence or if I have to drop all tables
before the sequence is removed

I just tried it.

I created a sequence using SERIAL when I created a table. I used the
same sequence for another table by setting a column default to
nextval(sequence).

I deleted the first table. The sequence was deleted too, leaving the
default of the second table referring to a non-existent sequence.

This sounds like a serious bug in our behaviour, and not something we'd
like to release.

Specifically in relation to people's existing scripts, and also to
people who are doing dump/restore of specific tables (it'll kill the
sequences that other tables depend on too!)

No real issue with the nicety for newbies, but am very concerned about
the lack of a dependancy check here.

:-/

Regards and best wishes,

Justin Clift

Could this be a TODO item in 7.4, to add a dependency check when a
sequence is set as the default without being created at the same time?

--
Oliver Elphick Oliver.Elphick@lfix.co.uk
Isle of Wight, UK
http://www.lfix.co.uk/oliver
GPG: 1024D/3E1D0C1C: CA12 09E0 E8D5 8870 5839 932A 614D 4C34 3E1D 0C1C
========================================
"If my people, which are called by my name, shall
humble themselves, and pray, and seek my face, and
turn from their wicked ways; then will I hear from
heaven, and will forgive their sin, and will heal
their land." II Chronicles 7:14

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--
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi

Justin Clift <justin@postgresql.org> writes:

This sounds like a serious bug in our behaviour, and not something
we'd like to release.

It's not ideal, I agree, but I *definately* don't think this is
grounds for changing the release schedule.

No real issue with the nicety for newbies, but am very concerned
about the lack of a dependancy check here.

Well, how would you suggest we fix this? ISTM this is partially a
result of the fact that we don't produce dependancy information for
function bodies. While it might be possible to do so (in 7.4) for
certain types of functions (e.g. for functions defined in SQL,
PL/PgSQL, etc.), I can't see a general solution (e.g. for functions
defined in C).

And adding random hacks to get specific functions (e.g. nextval()) to
work does not strike me as a very good idea.

Cheers,

Neil

--
Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC

Neil Conway wrote:

Justin Clift <justin@postgresql.org> writes:

This sounds like a serious bug in our behaviour, and not something
we'd like to release.

It's not ideal, I agree, but I *definately* don't think this is
grounds for changing the release schedule.

Hey, I'm no fan of slowing the release schedule either.

Bug this is definitely sounding like a bug.

No real issue with the nicety for newbies, but am very concerned
about the lack of a dependancy check here.

Well, how would you suggest we fix this? ISTM this is partially a
result of the fact that we don't produce dependancy information for
function bodies. While it might be possible to do so (in 7.4) for
certain types of functions (e.g. for functions defined in SQL,
PL/PgSQL, etc.), I can't see a general solution (e.g. for functions
defined in C).

Absolutely *no* idea.

And adding random hacks to get specific functions (e.g. nextval()) to
work does not strike me as a very good idea.

Agreed. Random hacks aren't always a good approach.

Regards and best wishes,

Justin Clift

Cheers,

Neil

--
Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC

--
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi

Justin Clift <justin@postgresql.org> writes:

Oliver Elphick wrote:

I created a sequence using SERIAL when I created a table. I used the
same sequence for another table by setting a column default to
nextval(sequence).

I deleted the first table. The sequence was deleted too, leaving the
default of the second table referring to a non-existent sequence.

This sounds like a serious bug in our behaviour, and not something we'd
like to release.

We will be releasing it whether we like it or not, because
nextval('foo') doesn't expose any visible dependency on sequence foo.

(If you think it should, how about nextval('fo' || 'o')? If you think
that's improbable, consider nextval('table' || '_' || 'col' || '_seq').)

The long-term answer is to do what Rod alluded to: support the
Oracle-style syntax foo.nextval, so that the sequence reference is
honestly part of the parsetree and not buried inside a string
expression.

In the meantime, I consider that Oliver was misusing the SERIAL
feature. If you want multiple tables fed by the same sequence object,
you should create the sequence as a separate object and then create
the tables using explicit "DEFAULT nextval('foo')" clauses. Doing what
he did amounts to sticking his fingers under the hood of the SERIAL
implementation; if he gets his fingers burnt, it's his problem.

Specifically in relation to people's existing scripts, and also to
people who are doing dump/restore of specific tables (it'll kill the
sequences that other tables depend on too!)

7.3 breaks no existing schemas, because older schemas will be dumped
as separate CREATE SEQUENCE and CREATE TABLE ... DEFAULT nextval()
commands.

regards, tom lane

Tom Lane wrote:

Justin Clift <justin@postgresql.org> writes:

Oliver Elphick wrote:

I created a sequence using SERIAL when I created a table. I used the
same sequence for another table by setting a column default to
nextval(sequence).

I deleted the first table. The sequence was deleted too, leaving the
default of the second table referring to a non-existent sequence.

This sounds like a serious bug in our behaviour, and not something we'd
like to release.

We will be releasing it whether we like it or not, because
nextval('foo') doesn't expose any visible dependency on sequence foo.

Awww rats.

<snip>

7.3 breaks no existing schemas, because older schemas will be dumped
as separate CREATE SEQUENCE and CREATE TABLE ... DEFAULT nextval()
commands.

Ok.

Thanks Tom. :)

Regards and best wishes,

Justin Clift

regards, tom lane

--
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi

It seems worth pointing out, too, that some SQL purists propose not
relying on product-specific methods of auto-incrementing.

I.e., it is possible to do something like:

insert into foo( col, ... )
values( coalesce( ( select max( col ) from foo ), 0 ) + 1, ... );

and this is easily placed in a trigger.

-tfo

In article <7017.1037851915@sss.pgh.pa.us>,
tgl@sss.pgh.pa.us (Tom Lane) wrote:

Of course, those would be SQL purists who _don't_ understand
concurrency issues. ;-)

---------------------------------------------------------------------------

Thomas O'Connell wrote:

It seems worth pointing out, too, that some SQL purists propose not
relying on product-specific methods of auto-incrementing.

I.e., it is possible to do something like:

insert into foo( col, ... )
values( coalesce( ( select max( col ) from foo ), 0 ) + 1, ... );

and this is easily placed in a trigger.

-tfo

In article <7017.1037851915@sss.pgh.pa.us>,
tgl@sss.pgh.pa.us (Tom Lane) wrote:

Justin Clift <justin@postgresql.org> writes:

Oliver Elphick wrote:

I created a sequence using SERIAL when I created a table. I used the
same sequence for another table by setting a column default to
nextval(sequence).

I deleted the first table. The sequence was deleted too, leaving the
default of the second table referring to a non-existent sequence.

This sounds like a serious bug in our behaviour, and not something we'd
like to release.

We will be releasing it whether we like it or not, because
nextval('foo') doesn't expose any visible dependency on sequence foo.

(If you think it should, how about nextval('fo' || 'o')? If you think
that's improbable, consider nextval('table' || '_' || 'col' || '_seq').)

The long-term answer is to do what Rod alluded to: support the
Oracle-style syntax foo.nextval, so that the sequence reference is
honestly part of the parsetree and not buried inside a string
expression.

In the meantime, I consider that Oliver was misusing the SERIAL
feature. If you want multiple tables fed by the same sequence object,
you should create the sequence as a separate object and then create
the tables using explicit "DEFAULT nextval('foo')" clauses. Doing what
he did amounts to sticking his fingers under the hood of the SERIAL
implementation; if he gets his fingers burnt, it's his problem.

Specifically in relation to people's existing scripts, and also to
people who are doing dump/restore of specific tables (it'll kill the
sequences that other tables depend on too!)

7.3 breaks no existing schemas, because older schemas will be dumped
as separate CREATE SEQUENCE and CREATE TABLE ... DEFAULT nextval()
commands.

regards, tom lane

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  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

Oliver Elphick wrote:

I deleted the first table. The sequence was deleted too, leaving the
default of the second table referring to a non-existent sequence.

Could this be a TODO item in 7.4, to add a dependency check when a
sequence is set as the default without being created at the same time?

Added to TODO:

* Have sequence dependency track use of DEFAULT sequences, seqname.nextval

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

On Thu, 2002-11-21 at 14:11, Bruce Momjian wrote:

Of course, those would be SQL purists who _don't_ understand
concurrency issues. ;-)

Or they're the kind that locks the entire table for any given insert.

--
Rod Taylor <rbt@rbt.ca>

"Thomas O'Connell" <tfo@monsterlabs.com> writes:

It seems worth pointing out, too, that some SQL purists propose not
relying on product-specific methods of auto-incrementing.
I.e., it is possible to do something like:
insert into foo( col, ... )
values( coalesce( ( select max( col ) from foo ), 0 ) + 1, ... );
and this is easily placed in a trigger.

... but that approach is entirely unworkable if you want any concurrency
of insert operations. (Triggers are a tad product-specific, too :-()

regards, tom lane

On 21 Nov 2002, Rod Taylor wrote:

On Thu, 2002-11-21 at 14:11, Bruce Momjian wrote:

Of course, those would be SQL purists who _don't_ understand
concurrency issues. ;-)

Or they're the kind that locks the entire table for any given insert.

Isn't that what Bruce just said? ;^)

On Thu, 2002-11-21 at 15:09, scott.marlowe wrote:

On 21 Nov 2002, Rod Taylor wrote:

On Thu, 2002-11-21 at 14:11, Bruce Momjian wrote:

Of course, those would be SQL purists who _don't_ understand
concurrency issues. ;-)

Or they're the kind that locks the entire table for any given insert.

Isn't that what Bruce just said? ;^)

I suppose so. I took what Bruce said to be that multiple users could
get the same ID.

I keep having developers want to make their own table for a sequence,
then use id = id + 1 -- so they hold a lock on it for the duration of
the transaction.

--
Rod Taylor <rbt@rbt.ca>

On 21 Nov 2002, Rod Taylor wrote:

On Thu, 2002-11-21 at 15:09, scott.marlowe wrote:

On 21 Nov 2002, Rod Taylor wrote:

On Thu, 2002-11-21 at 14:11, Bruce Momjian wrote:

Of course, those would be SQL purists who _don't_ understand
concurrency issues. ;-)

Or they're the kind that locks the entire table for any given insert.

Isn't that what Bruce just said? ;^)

I suppose so. I took what Bruce said to be that multiple users could
get the same ID.

I keep having developers want to make their own table for a sequence,
then use id = id + 1 -- so they hold a lock on it for the duration of
the transaction.

I was just funnin' with ya, but the point behind it was that either way
(with or without a lock) that using something other than a sequence is
probably a bad idea. Either way, under parallel load, you have data
consistency issues, or you have poor performance issues.

scott.marlowe@ihs.com ("scott.marlowe") wrote in message news:<Pine.LNX.4.33.0211211450100.23804-100000@css120.ihs.com>...

On 21 Nov 2002, Rod Taylor wrote:

On Thu, 2002-11-21 at 15:09, scott.marlowe wrote:

On 21 Nov 2002, Rod Taylor wrote:

On Thu, 2002-11-21 at 14:11, Bruce Momjian wrote:

Of course, those would be SQL purists who _don't_ understand
concurrency issues. ;-)

Or they're the kind that locks the entire table for any given insert.

Isn't that what Bruce just said? ;^)

I suppose so. I took what Bruce said to be that multiple users could
get the same ID.

I keep having developers want to make their own table for a sequence,
then use id = id + 1 -- so they hold a lock on it for the duration of
the transaction.

I was just funnin' with ya, but the point behind it was that either way
(with or without a lock) that using something other than a sequence is
probably a bad idea. Either way, under parallel load, you have data
consistency issues, or you have poor performance issues.

I'm not familiar with these "SQL purists" (perhaps the reference is to
J. Celko?) but the fact is that it's hard to call SEQUENCE
product-specific now that it's in Oracle, DB2, and SQL:2003. The
syntaxes do differ a little, usually due to choice of abbreviation,
but as far as I can tell the internals are similar across
implementations.

Peter Gulutzan
Author of "Sequences And Identity Columns"
(http://dbazine.com/gulutzan4.html)