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1 Aug 11 - IBM Data Management Magazine - IIUG user view: Happy 10th anniversary to IBM and Informix... Read
8 Jul 11 - Database Trends and Applications - Managing Time Series Data with Informix... Read
31 May 11 - Smart Grid - The meter data management pitfall utilities are overlooking... Read
27 May 11 - IBM Data Management Magazine - IIUG user view: Big data, big time ( Series data, warehouse acceleration, and 4GLs )... Read
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IDS Forum

Re: Use of ROWID in update statements

Posted By: Andreas Legner
Date: Tuesday, 14 February 2017, at 4:26 p.m.

In Response To: Re: Use of ROWID in update statements (Art Kagel)

There's one more case where a row's rowid can change, even within a=20
transaction and in a way that the row might even be found a second time by =

same statement: if an old version (in-place alter) page gets update to=20
latest version and some of its rows need to move out of this page - they'd =

do this in their entirety, without leaving a forward pointer on the old=20
So when relying on rowid =3D physical location for addressing a row, make=20
sure you don't have outstanding in-place alters.


From: "Art Kagel" <>
Date: 14.02.2017 22:12
Subject: Re: Use of ROWID in update statements [38632]
Sent by:


There are two different ROWIDs in Informix and a third ROWID condition=20
has to be handled:=20

1. ROWID for a non-fragmented table=20

This is the physical address of the row, it is relative page in the=20

table and shifted 8 bits plus the slot number on the page where the row=20

resides. This does not change. If a variable length row is updated and so=20

it outgrows the space available on its "home page" it is moved to another=20

page and leaves behind in its slot on the original home page a pointer to=20

its new location. So, its ROWID for all purposes, including indexing, id=20

permanent. This rowid is always 32 bits (the 8bit shift is why a single=20

partition table cannot exceed 2^24 pages).=20

2. ROWID for a fragmented table WITH ROWID=20

This is not really a ROWID but just a hidden SERIAL type column. This is=20

also a permanent value that never changes.=20

3. Fragmented tables without the WITH ROWID clause.=20

These rows have no ROWID at all. They do have a physical address that is=20

used in indexing, but there is no way that you can access that value.=20

So, yes, INT4 is sufficient to hold a ROWID. Never use a ROWID for=20
reference purposes in permanent structures because there are ways to=20
the physical location of a row of data and therefore its ROWID and that=20
would break such references. Example: export/import.=20


Art S. Kagel, President and Principal Consultant=20
ASK Database Management=20


Disclaimer: Please keep in mind that my own opinions are my own opinions=20
and do not reflect on the IIUG, nor any other organization with which I am =

associated either explicitly, implicitly, or by inference. Neither do=20
those opinions reflect those of other individuals affiliated with any=20
entity with which I am affiliated nor those of the entities themselves.=20

On Tue, Feb 14, 2017 at 3:41 PM, FLORIAN APOLLONER=20
> wrote:=20

> Hi,=20
> I am currently working on replacing some of our ESQL code with a 3rd=20
> library for easier consistency with Oracle. In the process I noticed=20
> this=20
> library doesn't really let me handle cursor the way I want, so something =

> like:=20
> UPDATE ... SET ... WHERE CURRENT OF <cursor=5Fname>=20
> is somewhat out of the question. I was thinking of switching the code to =

> fetch=20
> and use ROWID like we do in Oracle. Now I have two questions:=20
> * sqlca.sqlerrd in the ESQL sources seems to be an int4, is this enough? =

> * When does the ROWID change? Will it be stable inside a transaction or=20
> when=20
> modifying rows which have been selected with "SELECT FOR UPDATE" -- I'd=20
> assume=20
> yes, since it is a physical row id, but who knows ;)=20
> Thanks & best regards,=20
> Florian=20
> ************************************************************=20
> *******************=20
> Forum Note: Use "Reply" to post a response in the discussion forum.=20



Forum Note: Use "Reply" to post a response in the discussion forum.=20

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