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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Sequences CYCLEing -- was RE: How do you genrate primary
I created such a beast a few years ago.
The 'customer' gave me no choice. The unique ID for a record had to be the current date+Id, and the idea had to start over every day at midnight. That was an interesting bit of code. It certainly wouldn't scale, but this was very low volume OLTP, so we could live with it.
And I certainly didn't use this value as the PK.
Jared
Hemant K Chitale <hkchital_at_singnet.com.sg>
Sent by: ml-errors_at_fatcity.com
11/09/2003 07:04 AM
Please respond to ORACLE-L
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
cc:
Subject: Re: Sequences CYCLEing -- was RE: How do you genrate primary
So, let's start another thread.
How many of you have actually seen Sequences implemented in the manner I
described
and Mladen demonstrated below ?
Hemant
At 08:24 AM 08-11-03 -0800, you wrote:
>Being sort of DBA Doubting Tom, I have a bad habit of trying and testing
>stuff. Here is what happens with sequences:
>
>SQL> create sequence test1 start with 1 maxvalue 4 cycle nocache;
>
>Sequence created.
>
>SQL> select test1.nextval from dual
> 2 /
>
> NEXTVAL
>----------
> 1
>
>SQL> /
>
> NEXTVAL
>----------
> 2
>
>SQL> /
>
> NEXTVAL
>----------
> 3
>
>SQL> /
>
> NEXTVAL
>----------
> 4
>
>SQL> /
>
> NEXTVAL
>----------
> 1
>
>SQL> /
>
> NEXTVAL
>----------
> 2
>
>SQL>
>
>On 2003.11.08 10:54, Hemant K Chitale wrote:
>>Ah yes. The exception case when sequence numbers are not unique.
>>Believe me, I've seen Sequences with low MAXVALUE [the guy decided that
the
>>the number would never exceed 4 digits and didn't want to "waste
resources
>>and space"].
>>And I do vaguely remember that I HAVE seen a Sequence CYCLE over and
>>restart. Can't remember the details, though .... this was many years
ago.
>>It takes all kinds of developers and database designers to make Oracle
>>interesting.
>>Hemant
>>At 03:29 PM 05-11-03 -0800, you wrote:
>>>In theory I suppose it's possible to have overlaps, but this has
nothing to
>>>do with OPS/RAC. If you create the sequence to CYCLE (not the default)
AND
>>>set MAXVALUE to something less than reasonable (the default is
NOMAXVALUE
>>>which IIRC means 10 to the power 27) AND don't create a unique index on
the
>>>column storing the sequence, then maybe you can end up with multiple
rows
>>>having the same value? Never heard of anyone doing that, of course,
but in
>>>theory ...
>>>Pete
>>>"Controlling developers is like herding cats."
>>>Kevin Loney, Oracle DBA Handbook
>>>"Oh no, it's not. It's much harder than that!"
>>>Bruce Pihlamae, long-term Oracle DBA
>>>
>>>-----Original Message-----
>>>Millsap
>>>Sent: Thursday, November 06, 2003 7:34 AM
>>>To: Multiple recipients of list ORACLE-L
>>>
>>>I've never heard of an Oracle sequence not generating unique id's,
OPS/RAC
>>>or not. Gaps, yes. Overlaps, never.
>>>
>>>Cary Millsap
>>>Hotsos Enterprises, Ltd.
>>>http://www.hotsos.com
>>>Upcoming events:
>>>- Performance Diagnosis 101: 11/19 Sydney
>>>- SQL Optimization 101: 12/8-12 Dallas
>>>- Hotsos Symposium 2004: March 7-10 Dallas
>>>- Visit www.hotsos.com for schedule details...
>>>
>>>-----Original Message-----
>>>Todd Boss
>>>Sent: Wednesday, November 05, 2003 1:09 PM
>>>To: Multiple recipients of list ORACLE-L
>>>There's six very good reasons listed below to NOT use SSN as your
unique
>>>PK,
>>>and honestly I can't believe this is STILL an issue for any dba
>>>who deals w/ SSNs. These arguments are YEARS old. Isn't this Data
>>>Modelling 101? I know for sure this exact case is in every text i've
read.
>>>How to deal with Natural keys:
>>>- Create a surrogate PK that the user never sees but guarantees
uniqueness.
>>>- Create a separate (unique if you can) index on your "natural key."
>>>- Go on with life.
>>>I'm a bit more concerned about what i'm hearing about Sequences. Is it
true
>>>that sequences are NOT guaranteed to be unique?? After all
>>>this time listening to Oracle people scoff at the Sybase/Ms Sql
identity
>>>feature and its inadequacies as compared to Sequences for generating
>>>sequential surrogate keys .... they're NOT guaranteed to be unique if
>>>you're
>>>working in a parallel processing environment??
>>>Is this really true? Do Oracle developers have to depend on
>>>circa 1990 techniques to generate something as BASIC as a surrogate key
by
>>>designing their own little lookup table systems? Or am I just reading
this
>>>thread incorrectly?
>>>Todd
>>>
>>> >
>>> > I'm fully convinced. SSN should not be used as a PK.
>>> >
>>> > Can we also conclude that natural keys in general are only good if
you
>>>sit in
>>> > an ivory tower and do unrealistic lab test?
>>> >
>>> > Yong Huang
>>> >
>>> > --- "Bellow, Bambi" <bbellow_at_chi.navtech.com> wrote:
>>> > > Having worked for the government in a situation where we were
>>>actually
>>> > > tracking information BY Social Security Number, let me tell you
the
>>>problems
>>> > > with it.
>>> > >
>>> > > 1) Social Security Numbers ARE NOT GUARANTEED TO BE UNIQUE
>>> > > 2) Individuals ARE NOT GUARANTEED TO HAVE ONE AND ONLY ONE Social
>>>Security
>>> > > Number
>>> > > 3) Not all Social Security Numbers are numeric
>>> > > 4) Not all Social Security Numbers which ARE numeric are 9
>>>characters in
>>> > > length
>>> > > 5) Social Security Numbers can be changed by the holder
>>> > > 6) It is illegal to use the Social Security Number for any
purpose
>>>other
>>> > > than that which the government specifically uses Social Security
>>>Numbers for
>>> > > (ie., the distribution of benefits). I'll bet *that* one is
>>>strictly
>>> > > enforced.
>>> > >
>>> > > HTH,
>>> > > Bambi.
>>> > >
>>> > > -----Original Message-----
>>> > > Sent: Wednesday, November 05, 2003 8:00 AM
>>> > > To: Multiple recipients of list ORACLE-L
>>> > >
>>> > >
>>> > > Tom,
>>> > >
>>> > > I think using a natural key such as Soc. Sec. # as the primary key
>>>is a good
>>> > > idea. You don't need to maintain the sequence so there's no
>>>performance
>>> > > issue
>>> > > associated with sequences. There's no issue of gaps. No index root
>>>block
>>> > > contention. It doesn't seem to be industry common practice though.
>>> > >
>>> > > In your college student case, changing primary keys is rare so
it's
>>>not a
>>> > > big
>>> > > problem.
>>> > >
>>> > > Yong Huang
>>> > >
>>> > > --- "Mercadante, Thomas F" <NDATFM_at_labor.state.ny.us> wrote:
>>> > > > Jonathan,
>>> > > >
>>> > > > I think your idea of a paper is a good one. But I think we need
>>>to back
>>> > > th
>>> > > > question up to what the requirements are.
>>> > > >
>>> > > > First, to me, a primary key should not be something that a user
>>>would ever
>>> > > > see or use. So the Soc. Sec. # is out. (A side issue - I used
to
>>>work at
>>> > > a
>>> > > > college. Want to know how many times we had to change the Soc.
>>>for an
>>> > > > individual student because the parent filled the form out and
used
>>>their
>>> > > > soc, or the kid used the wrong one?). Any id entered by a user
is
>>>subject
>>> > > > to mistakes and changes. So the PK value must be protected from
>>>these
>>> > > types
>>> > > > of errors.
>>> > > >
>>> > > > The next requirement that may be needed is sequentiallity (is
this
>>>a
>>> > > word?).
>>> > > > Does the application require that every sequence number be used.
>>> > > Sometimes
>>> > > > the answer is yes, and sometimes it just doesn't matter.
>>> > > >
>>> > > > These are the only two requirements I can think of. Based on
the
>>>answers,
>>> > > > we then have options. Right now, Oracle sequences are working
>>>well for
>>> > > me.
>>> > > > I like the idea of SYS_GUID, just not sure where I would need
it.
>>> > > >
>>> > > > Good idea and good luck!
>>> > > >
>>> > > > Tom Mercadante
>>> > > > Oracle Certified Professional
>>> > > >
>>> > > >
>>> > > > -----Original Message-----
>>> > > > Sent: Wednesday, November 05, 2003 8:19 AM
>>> > > > To: Multiple recipients of list ORACLE-L
>>> > > >
>>> > > >
>>> > > > The recent article that mentioned sequences got me to thinking.
I
>>> > > > might pitch a more detailed article on sequences to Builder.com.
>>> > > > But a more interesting article might be one that explored
various
>>> > > > ways to automatically generate primary keys. So, in the name of
>>> > > > research, let me throw out the following questions:
>>> > > >
>>> > > > What mechanisms have you used to generate primary keys? Which
ones
>>> > > > worked well, and why? Which mechanisms worked poorly?
>>> > > >
>>> > > > I've run up against the following approaches:
>>> > > >
>>> > > > * Hit a table that keeps a counter. This is the "roll your own
>>> > > > sequence method". The one time I recall encountering this
>>> > > > approach, I helped convert it over to using stored sequences.
This
>>> > > > was because of concurrency problems: with careful timing, two
>>> > > > users could end up with the same ID number for different
records.
>>> > > > Is there ever a case when this roll-your-own approach makes
sense,
>>> > > > and is workable?
>>> > > >
>>> > > > * Stored sequences. I worked on one app that used a separate
>>> > > > sequence for each automatically generated primary key. I worked
on
>>> > > > another app, a smaller one, that used the same sequence for more
>>> > > > than one table. The only issue that I recall is that sometimes
>>> > > > numbers would be skipped. But end users really didn't care, or
>>> > > > even notice.
>>> > > >
>>> > > > * The SYS_GUID approach. I've never used SYS_GUID as a primary
key
>>> > > > generator. I wonder, was that Oracle's motivation for creating
the
>>> > > > function? Has anyone used it for primary keys in a production
app?
>>> > > > What's the real reason Oracle created this function?
>>> > > >
>>> > > > * Similar to SYS_GUID, I once worked on an obituary-tracking
>>> > > > application that built up a primary key from, as best I can
recall
>>> > > > now: date of death, part of surname, part of first name, and a
>>> > > > sequence number used only to resolve collisions, of which there
>>> > > > were few. The approached worked well, actually, because whatever
>>> > > > fields we munged together to generate a primary key gave us a
>>> > > > unique key the vast majority of the time.
>>> > > >
>>> > > > The SYS_GUID approach is interesting, but if you need an ID
number
>>> > > > that users will see, and that users might type in themselves
(e.g.
>>> > > > social security number), is SYS_GUID really all that viable?
>>> > > >
>>> > > > Best regards,
>>> > > >
>>> > > > Jonathan Gennick --- Brighten the corner where you are
>>> > > > http://Gennick.com * 906.387.1698 * mailto:jonathan@gennick.com
>>> > > >
>>> > > > Join the Oracle-article list and receive one
>>> > > > article on Oracle technologies per month by
>>> > > > email. To join, visit
>>> > > > http://four.pairlist.net/mailman/listinfo/oracle-article,
>>> > > > or send email to Oracle-article-request_at_gennick.com and
>>> > > > include the word "subscribe" in either the subject or body.
>>> > > >
>>> > > > --
>>> > > > Please see the official ORACLE-L FAQ: http://www.orafaq.net
>>> > > > --
>>> > > > Author: Jonathan Gennick
>>> > > > INET: jonathan_at_gennick.com
>>> > > >
>>> > > > Fat City Network Services -- 858-538-5051
>>>http://www.fatcity.com
>>> > > > San Diego, California -- Mailing list and web hosting
>>>services
>>> > > >
>>>---------------------------------------------------------------------
>>> > > > To REMOVE yourself from this mailing list, send an E-Mail
message
>>> > > > to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and
>>>in
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>>> > > > --
>>> > > > Please see the official ORACLE-L FAQ: http://www.orafaq.net
>>> > > > --
>>> > > > Author: Mercadante, Thomas F
>>> > > > INET: NDATFM_at_labor.state.ny.us
>>> >
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>>> >
Hemant K Chitale
Oracle 9i Database Administrator Certified Professional
My personal web site is : http://hkchital.tripod.com
-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Hemant K Chitale INET: hkchital_at_singnet.com.sg Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: INET: Jared.Still_at_radisys.com Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Mon Nov 10 2003 - 14:19:42 CST
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