Re: Numbering Rows (SEQUENCE, OID) questions

> 
> On Sunday, December 16, 2001, at 11:42 AM, Stephan Szabo wrote:
> 
> > On Sun, 16 Dec 2001, Terrence Brannon wrote:
> >
> >> The Momjian book is excellent (in spite of some of the bonehead
> >> reviews on amazon.com). I just finished the "Numbering Rows"
> >> section and have a few questions. None of these were in the FAQ,
> >> BTW.
> >>
> >> 1 - are OIDs ever re-used if rows are deleted?
> >
> > OIDs wraparound, but they don't just fill holes, so uniqueness
> > isn't guaranteed unless you have something like a unique index
> > on oid.
> 
> Where do you get this information? If I am reading the Momjian 
> book correctly, it disagrees with you:
> 
> Every row in POSTGRESQL is assigned a unique, normally invisible 
> number called an object identification number (OID). When the 
> software is initialized with initdb?, 12.1 a counter is created 
> and set to approximately seventeen-thousand. 12.2 The counter is 
> used to uniquely number every row. Although databases may be 
> created and destroyed, the counter continues to increase. It is 
> used by all databases, so identification numbers are always 
> unique. No two rows in any table or in any database will ever 
> have the same object ID.

The book asssume you are not going to roll over the counter.  Very large
installations have been concerned about such rollover after inserting >4
billion rows.  We have not gotten any actual report of it happening, but
it could theoretically happen.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026