Re: TPC-A and -B Benchmarks

In-Reply-To: NLUNIX:rmy.emory.edu!ilist@sun4nl.nl.oracle.com's message of 07-06-93 21:11 Just for your information: Oracle (v6 and Oracle7) *DO* support repeatable reads, *WITHOUT* locking whatsoever. By default (so without setting any parameters or changing any settings), Oracle implements statement level multi-version read-consistency. This advanced technique will always return correct data for a query, making sure there are no inconsistencies because of changes made by other users during the query. Changes made by other users *ARE* allowed however, you won't see them as the result of the query when they are commited AFTER the start of executing of the query. Multiple versions of rows can be reconstructed very easy, as this information is contained in the rollback data. This works out very efficiently for multi-user systems, but, which is also quite interesting, it also has effect within one statement. Consider the following update statement: UPDATE employees e1 SET salary = ( SELECT avg(e2.salary) FROM employees e2 WHERE e1.department = e2.department ) The purpose of this statement is to set each employee's salary to the average of all salaries in his/her department. When read-comsistency is not correctly implemented, you might get the wrong result, i.e. changing averages, or at least an unpredictable result. After using 'SET TRANSACTION READONLY' in a session, Oracle will also enforced read-consistency over multiple statements, allowing constructions like: SELECT region, sum(salary) FROM employees GROUP BY region; SELECT department, sum(salary) FROM employess GROUP BY department; both statements will have to return the same total when run consecutively, even if some salaries are changed in between. Session level read consistency will do the job, again *WITHOUT* locking (in Oracle) One note: I'm pretty sure Oracle will come up with TPC-C results some time. I am not aware of any time scale, but I think TPC-A is still the most accepted at this time. One of the purposed of benchmarks is that you can compare (allthough very carefully) figures. If almost nobody is running TPC-C's (at this moment only IBM as far as I know, both on AS/400 and RS/6000 with Informix), what can customers do with these figures, as long as there is nothing to compare it with. That's why I think a lot of DB vendors are a bit hesitant to immediately start doing TPC-C's. ** These opinions are just mine and not of Oracle Corporation ** Sandor Nieuwenhuijs Oracle Netherlands