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When will DB2 get MVCC?

Hello,

In a rather large database, I face this problem:
Several tables are regularly updated through rather long-running DELETE
+INSERTs. Using uncommitted read as isolation level seems unsafe, as I'd
like consistent data (that's one of the main points of using a DBMS in
the first place, in my opinion).

Almost all other significant databases have gotten MultiVersion
Concurrency Control (MVCC)[1] by now, either by default, or optionally
(like in MSSQL2005: the DBA needs to activate it explicitly[2]).

The very nice and obvious advantage with MVCC is that readers don't block
writers, and vice versa: If I'm working read-only with a table, I simply
work with the latest committed data for that table at the time when my
query started. A concurrently running transaction with write activity
will continue working, but the reader doesn't see its actions unless
he starts a new query after the writing transaction has finished.
The obvious disadvantage -- more temporary data for the DBMS to keep
track of -- is a price which I'd gladly pay.

I've read a number of articles on how to mitigate DB2's locking problem,
but they either seem to suggest actions which don't really improve the
situation significantly, or they suggest actions which I find unsafe/ugly
(committing more often; but I _want_ consistency!).

What's keeping IBM?
Notes:
1) many different synonyms seem to exist for MVCC, such as
"row versioning", "snapshot isolation", ...
2) for reasons that I find strange -- turning it off should be the
optional setting if they were to ask me

--
Regards,
Troels Arvin <tr****@arvin.d k>
http://troels.arvin.dk/
Apr 19 '07
20 6192
You need a better newsreader (or provider).
Your post:
MeBuggyYouJane wrote:
IBM just has a different philosophy.

Beyond that, IBM's clients likely don't care. Here's why:

- according to the Gartner reports, going back to 2000, DB2 has majority
revenue and revenue growth on the MainFrame.
- said MainFrame clients mostly run decades olde COBOL code, running DB2
data through cursors and copybooks, just like they did for the VSAM data
for which the code was originally written. They have no use for MVCC
semantics.
- the remaining pool of convertible VSAM clients has got to be getting
as shallow as an Australian reservoir. There is a growing, albeit
slowly so, number of clients who have no use for MVCC semantics.
- DB2 on *nix is not growing much, if at all, where the non-COBOL view
of data prevails. There are a not so growing number of clients who
would benefit from MVCC semantics.
- IBM, in my opinion, made a big mistake in stuffing XML in v9; it
turned off the relationalists in the crowd (even, reading between the
lines, some IBM-ers who lurk here for our benefit), and there really
isn't much traffic here about things V9. The XML loonies wouldn't bother
with a real database anyway, much less pay for one. This year's Gartner,
due soon for subscribers (not I) and a bit later for the press release
condensed version, will be informative. I'd be willing to bet a nickel
that DB2 fares less well than the competition. Of most concern is how
the mix between MF and *nix comes up, and whether V9 has been a home
run. IBM could have added MVCC (called by some name) to V9, but chose
instead to add XML (must have caused Dr. Codd to soil his coffin, and
the IMS division to party). IBM thumbed their nose at those who would
benefit from MVCC semantics.
- the resource cavil is a strawman. If you want MVCC semantics, you pay
for them. G&R, and its references, which go back quite a ways further,
make that clear. TANSTAFL
--
My post:
Well, to each their opinions.
The market would be boring if everyone always came to the same
conclusion on what's right.
I too am looking forward to the Gartner numbers...
--
Don't recall me promising you a nickel..
Either way I'm still looking forward to the Gartner report (not the
press release)
The press release doesn't substantiate any of what you conclude.
For one XML wasn't shipped until mid last year. Way to late to have any
meaning in the 2006 market.
Are you into gardening? A green thumb requires patience.
I won't comment on the numbers themselves as the way how they are
arrived at is getting more and more dubious allowing anyone to claim
pretty much anything and, as you say, "free" offerings aren't included.

Cheers
Serge
--
Serge Rielau
DB2 Solutions Development
IBM Toronto Lab
Jun 19 '07 #11
It makes sense that a database that offers transactions would also
offer consistent read capabilities (transactions being there hust
because there is the notion of consistent real-world state), allowing
consistent real-world state reporting without halting the database
evolution (24/24 7/7 world).

Storage devices increase in capacity and throughput as do main
processor performances, so yes DB2 UDB should have this capability.

Bernard Dhooghe

Jun 19 '07 #12
Serge Rielau wrote:
You need a better newsreader (or provider).
Your post:
MeBuggyYouJane wrote:
IBM just has a different philosophy.

Beyond that, IBM's clients likely don't care. Here's why:

- according to the Gartner reports, going back to 2000, DB2 has majority
revenue and revenue growth on the MainFrame.
- said MainFrame clients mostly run decades olde COBOL code, running DB2
data through cursors and copybooks, just like they did for the VSAM data
for which the code was originally written. They have no use for MVCC
semantics.
- the remaining pool of convertible VSAM clients has got to be getting
as shallow as an Australian reservoir. There is a growing, albeit
slowly so, number of clients who have no use for MVCC semantics.
- DB2 on *nix is not growing much, if at all, where the non-COBOL view
of data prevails. There are a not so growing number of clients who
would benefit from MVCC semantics.
- IBM, in my opinion, made a big mistake in stuffing XML in v9; it
turned off the relationalists in the crowd (even, reading between the
lines, some IBM-ers who lurk here for our benefit), and there really
isn't much traffic here about things V9. The XML loonies wouldn't bother
with a real database anyway, much less pay for one. This year's Gartner,
due soon for subscribers (not I) and a bit later for the press release
condensed version, will be informative. I'd be willing to bet a nickel
that DB2 fares less well than the competition. Of most concern is how
the mix between MF and *nix comes up, and whether V9 has been a home
run. IBM could have added MVCC (called by some name) to V9, but chose
instead to add XML (must have caused Dr. Codd to soil his coffin, and
the IMS division to party). IBM thumbed their nose at those who would
benefit from MVCC semantics.
- the resource cavil is a strawman. If you want MVCC semantics, you pay
for them. G&R, and its references, which go back quite a ways further,
make that clear. TANSTAFL
--
My post:
Well, to each their opinions.
The market would be boring if everyone always came to the same
conclusion on what's right.
I too am looking forward to the Gartner numbers...
--
Don't recall me promising you a nickel..
Either way I'm still looking forward to the Gartner report (not the
press release)
The press release doesn't substantiate any of what you conclude.
For one XML wasn't shipped until mid last year. Way to late to have any
meaning in the 2006 market.
Are you into gardening? A green thumb requires patience.
I won't comment on the numbers themselves as the way how they are
arrived at is getting more and more dubious allowing anyone to claim
pretty much anything and, as you say, "free" offerings aren't included.

Cheers
Serge
This post is a keeper Serge: Thanks.
--
Daniel A. Morgan
University of Washington
da******@x.wash ington.edu (replace x with u to respond)
Jun 19 '07 #13
DA Morgan wrote:
This post is a keeper Serge: Thanks.
If I ever come to visit I hope to see it framed, on the wall and in the
living room

Cheers
Serge
--
Serge Rielau
DB2 Solutions Development
IBM Toronto Lab
Jun 19 '07 #14
Serge Rielau wrote:
You need a better newsreader (or provider).
Your post:
MeBuggyYouJane wrote:
IBM just has a different philosophy.

Beyond that, IBM's clients likely don't care. Here's why:

- according to the Gartner reports, going back to 2000, DB2 has majority
revenue and revenue growth on the MainFrame.
- said MainFrame clients mostly run decades olde COBOL code, running DB2
data through cursors and copybooks, just like they did for the VSAM data
for which the code was originally written. They have no use for MVCC
semantics.
- the remaining pool of convertible VSAM clients has got to be getting
as shallow as an Australian reservoir. There is a growing, albeit
slowly so, number of clients who have no use for MVCC semantics.
- DB2 on *nix is not growing much, if at all, where the non-COBOL view
of data prevails. There are a not so growing number of clients who
would benefit from MVCC semantics.
- IBM, in my opinion, made a big mistake in stuffing XML in v9; it
turned off the relationalists in the crowd (even, reading between the
lines, some IBM-ers who lurk here for our benefit), and there really
isn't much traffic here about things V9. The XML loonies wouldn't bother
with a real database anyway, much less pay for one. This year's Gartner,
due soon for subscribers (not I) and a bit later for the press release
condensed version, will be informative. I'd be willing to bet a nickel
that DB2 fares less well than the competition. Of most concern is how
the mix between MF and *nix comes up, and whether V9 has been a home
run. IBM could have added MVCC (called by some name) to V9, but chose
instead to add XML (must have caused Dr. Codd to soil his coffin, and
the IMS division to party). IBM thumbed their nose at those who would
benefit from MVCC semantics.
- the resource cavil is a strawman. If you want MVCC semantics, you pay
for them. G&R, and its references, which go back quite a ways further,
make that clear. TANSTAFL
--
My post:
Well, to each their opinions.
The market would be boring if everyone always came to the same
conclusion on what's right.
I too am looking forward to the Gartner numbers...
--
Don't recall me promising you a nickel..
Either way I'm still looking forward to the Gartner report (not the
press release)
The press release doesn't substantiate any of what you conclude.
Shall we examine?

What I said:
I'd be willing to bet a nickel that DB2 fares less well than the
competition.
What Gartner said:
Oracle and Microsoft experienced growth rates above the industry average
at 14.9 percent and 28 percent, respectively, while IBM trailed in terms
of growth with an 8.8 percent revenue increase in 2006.

My conclusion:
I was right.
What I said:
Of most concern is how the mix between MF and *nix comes up, and whether
V9 has been a home run.
What Gartner said:
Each of the major three vendors continue to dominate their particular
platform; Oracle on Unix and Linux, Microsoft on Windows, and IBM on the
zSeries.

My conclusion:
I was right. Not so clear cut as point 1, but a reasonable deduction.
V9 does not yet exist on MF, so that sector of growth can't be V9.
Since overall growth is behind the industry, it's reasonable to conclude
that IBM's off-MF share is not growing, by much anyway. Not much room
in that growth number for V9 being a Home Run.
Now, I bear no animus toward IBM or its staff (well, may be Chamberlin
on a professional level). My CubeLand has laid it's bed with DB2. It
is better for me if DB2 is a better RDBMS. The revenge of IMS tack is
foolish, and eventually will fail; along with SOA and other such
claptrap. And, what's up with Oracle syntax "compatibility" ?? Will
snapshot isolation be implemented, too? I didn't see that until this
morning. 1 April is long past, I think.
For one XML wasn't shipped until mid last year. Way to late to have any
meaning in the 2006 market.
Are you into gardening? A green thumb requires patience.
I won't comment on the numbers themselves as the way how they are
arrived at is getting more and more dubious allowing anyone to claim
pretty much anything and, as you say, "free" offerings aren't included.
Did you cavil when Gartner showed DB2 as doing well, circa 2002?
>
Cheers
Serge
Jun 19 '07 #15
Well, I suppose we both made our points.
One thing is disturbing to me though:
What the heck is your issue with Don? I learned SQL from Don :-)
--
Serge Rielau
DB2 Solutions Development
IBM Toronto Lab
Jun 20 '07 #16
Serge Rielau wrote:
Well, I suppose we both made our points.
One thing is disturbing to me though:
What the heck is your issue with Don? I learned SQL from Don :-)
Simple really. There is a body of thought that the perpetrator of sql
and xquery is no defender of the relational database. See, for example:

http://www.dbazine.com/ofinterest/oi-articles/pascal19
Contrast with:

http://www.research.ibm.com/resource...passaway.shtml

Part of which:

At a 1995 reunion of IBM's early relational database scientists,
Chamberlin recalled having an epiphany as he first heard Codd describe
his relational model at an internal seminar.

"Codd had a bunch of ...fairly complicated queries," Chamberlin said.
"And since I'd been studying CODASYL (the language used to query
navigational databases), I could imagine how those queries would have
been represented in CODASYL by programs that were five pages long that
would navigate through this labyrinth of pointers and stuff. Codd would
sort of write them down as one-liners. ... (T)hey weren't complicated at
all. I said, 'Wow.' This was kind of a conversion experience for me. I
understood what the relational thing was about after that."

Chamberlin seems to have overcome his conversion, preferring to lead the
revenge of IMS.

That's the issue. It's not personal.

Jun 21 '07 #17
Serge Rielau wrote:
Well, I suppose we both made our points.
One thing is disturbing to me though:
What the heck is your issue with Don? I learned SQL from Don :-)
Which, of course, got me motivated to review the history of IMS/CODASYL,
and to this quote from Stonebraker/Hellerstein:

Unfortunately, the main proposal in the current XML era bears a striking
resemblance to the CODASYL proposal from the early 1970’s, which failed
because of its complexity. Hence, the current era is replaying history,
and “what goes around comes around”. Hopefully the next era will be
smarter.

It comes up in a Google search as Chapter 1 from an MIT Press text.
This contradicts my recollection to the extent: 1) IMS post-dated
CODASYL, 2) IMS was created because IBM wanted out of a "standard"
database they couldn't lock in (call me paranoid, but that was widely
believed at the time), and 3) XML is IMS in drag, not CODASYL, aka
Network Database.

I feel much better now. The lithium is kicking in.
Jun 21 '07 #18
You you considered that the world is neither square nor hierarchical?
I see this as a pendulum. Is swings.
Relational sucks in certain areas. Especially when it comes to highly
fluctuating schemata.
When I was at University we worked on a KDBMS called Krisys
http://wwwdvs.informatik.uni-kl.de/a...ts/Krisys.html
It was all about evolving schemata on the fly. The mapping was done
(to Ingres) by mapping all data to one table with a composite key:
class.instance. attribute and payload was: value
I spent a significant amount of my time helping internal and external
ISVs cope with similar schemas they are using (such as Websphere
Commerce). Death by PIVOT.
Microsoft SQL Server 2005 has an SQL construct just for that purpose
which they are trying to put into the SQL Standard, so it's not such a
rare thing.

This class of applications is way better of with XML than with SQL.

Also you may want to keep in mind that it wasn't IBM that invented XML.
The whole DB2 pure XML thing is a response to the market. We are not
trying to create that market.

Cheers
Serge

--
Serge Rielau
DB2 Solutions Development
IBM Toronto Lab
Jun 21 '07 #19
Serge Rielau wrote:
You you considered that the world is neither square nor hierarchical?
I see this as a pendulum. Is swings.
Relational sucks in certain areas. Especially when it comes to highly
fluctuating schemata.
When I was at University we worked on a KDBMS called Krisys
http://wwwdvs.informatik.uni-kl.de/a...ts/Krisys.html
It was all about evolving schemata on the fly. The mapping was done
(to Ingres) by mapping all data to one table with a composite key:
class.instance. attribute and payload was: value
I spent a significant amount of my time helping internal and external
ISVs cope with similar schemas they are using (such as Websphere
Commerce). Death by PIVOT.
Microsoft SQL Server 2005 has an SQL construct just for that purpose
which they are trying to put into the SQL Standard, so it's not such a
rare thing.

This class of applications is way better of with XML than with SQL.

Also you may want to keep in mind that it wasn't IBM that invented XML.
The whole DB2 pure XML thing is a response to the market. We are not
trying to create that market.

Cheers
Serge
Celko and Date/Pascal/McGoveran don't agree on much. But, IIRC, this
non-schema schema they agree has nothing to do with Relational
Databases. And Migrations and Andromeda and MDA, et cetera can deal
with fluid design issues.

Jun 22 '07 #20

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