Re: TPC-A and -B Benchmarks

In <21h67kINNib@emory.mathcs.emory.edu> SNIEUWEN@nl.oracle.com ("Sandor (Mr. Oracle7)") writes: >In-Reply-To: NLUNIX:rmy.emory.edu!ilist@sun4nl.nl.oracle.com's message of 07-07-93 15:51 >What strikes me the most is that all messages about the subject of repeatable >reads, read consistency, cursor stability, isolation levels etc, all discuss >'how a database should implement a certain feature' instead 'whats the purpose >of a feature'. I don't see why you should use locks to implement repeatable >reads. Locking is just one way (and I don't think it is the best way) >Multiversioning, like Oracle implements is another way, which will not cause >any locks. The main reason why you use something like this is to retrieve the >correct data, not because you'd want to lock data. Superfluous locking of data >(even row locks) will cause serious performance degradation. >-- These opinions are just mine and not of Oracle Corporation --- >Sandor Nieuwenhuijs >Oracle Netherlands I was very careful *not* to say that Repeatable Read had to be implemented via locks. But Repeatable Read *does* require that the data selected is immutable for *the* *entire* *duration* *of* *the* *transaction*. Oracle Multiversioning Read Consistency provides *very* *good* read consistency (it is, IMHO, much better than Informix in this particular respect). It does *NOT* provide Repeatable Read, though, it only guarantees that you see consistent data (as it was at transaction start time), not consistent *and* *up-to-date* data. One of the more difficult requirements to implement (without table locking) is that new rows may not be inserted into the set defined by your cursor during your transaction. I have yet to see an implementation of Repeatable Read that did not use locking (and undesirably restrictive locking), but if Sandor can invent one, I'm sure the world will be grateful. graeme -- Disclaimer: The author's opinions are his own, and not necessarily those of Pyramid Technology Ltd. or Pyramid Technology Inc. --------------------------------------------------------------------------- -m------- Graeme Sargent Voice: +44 (0)252 373035 ---mmm----- Senior Database Consultant Fax : +44 (0)252 373135 -----mmmmm--- Pyramid Technology Ltd. Telex: Tell who??? -------mmmmmmm- Farnborough, Hants GU14 7PL Email: graeme@pyra.co.uk --------------------------------------------------------------------------- We have the technology. The tricky bit is learning how to use it.