Re: IBM Debunks Oracle's MultiVersion Read Consistency ?

"Robert Allen" <rallen_at_NOSPAMOKhgi.com> wrote in message news:b_yoa.380076$HU.52078_at_news.easynews.com...
> http://www-
> 3.ibm.com/software/data/pubs/papers/readconsistency/readconsistency.pdf
>
> They raise some good points. Is it really as efficient as IBM suggests?
> What are the advantages that MVRC provide?

I agree with nearly all of it, especally the main point of the article. You should code your application to fit the characteristics of your RDBMS. To quote from the paper

" Similarly if you took a DB2 application and ported it directly to Oracle, you would find that it may have problems with ORA-1555 because of the frequent commits in the application. Each implementation does what it is designed to do and it's the application development that either
makes the best use of the technology or runs into issues." This is of course great advice, though it is vendor neutral.

--
Niall Litchfield
Oracle DBA
Audit Commission UK
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PS.
One thing I didn't like was the table (hope it doesn't wrap appallingly)
Transaction 1
Transaction 2
Begin transaction.

Begin transaction.
Select available seats on flight ABC111.
See seat 23F is the last seat available
Reserve this seat.

Select available seats on flight

ABC111. Also sees 23F as Oracle

will go to the rollback segment to

get the old version of that block.

That suggested select for update was a bad thing in this instance. Equally
If You had coded

Transaction 1
Transaction 2
Begin transaction.

Begin transaction.
update seats set status = reserved
where <customer criteria met>;
commit;

Error here when trying to reserve seat.

But my biggest bugbear of all of course was the idea that airline apps stop
reserving seats when the flight is full. Yeah right.