I mean, was that 20,000 transactions that are likely to have lock contention related to foreign key constraints? Because otherwise you are measuring the wrong thing.
What kind of lock contention is that? (In Oracle) you'd have to be (a) manipulating the values of a primary key and (b) choosing not to index the child FK column.
Even without (b) I'd be asking "Why are you altering primary keys?" because it pretty much aint a primary key anymore if you're doing that :-)
Even without (b) I'd be asking "Why are you altering primary keys?" because it pretty much aint a primary key anymore if you're doing that :-)