Just to recap, pessimistic detection thinks that conflicts are very likely to happen, so whenever there's a read or a write, it will check with another thread to see if there are conflicts with their actions.
Optimistic detection is the opposite, where you think "things are going to be just fine", so you do the entire transaction, then all the checks at the end. A benefit of this is if things really are fine, you didn't unnecessarily slow anything down by doing checks with every action.
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toastifer
Basically, pessimistic detection assumes that their going to cause a conflict and thus checks before doing the work. This undos less work, but does not guarantee something gets done and can cause more aborts. Optimistic detection assumes that their is not going to be a conflict and thus does all the work and checks afterwards. This can cause fairness problems, but guarantees that something gets done.
A real-world example is having a shared bank account with your family (with a low balance) and trying to buy groceries. Pessimistic detection would have you check your account balance before you start shopping and calling all of your family members to ensure that they are also not buying anything so that you don't get an overdraft fee. Optimistic detection would have you get all of the groceries, and then check the balance and call the family right before check out.
Just to recap, pessimistic detection thinks that conflicts are very likely to happen, so whenever there's a read or a write, it will check with another thread to see if there are conflicts with their actions.
Optimistic detection is the opposite, where you think "things are going to be just fine", so you do the entire transaction, then all the checks at the end. A benefit of this is if things really are fine, you didn't unnecessarily slow anything down by doing checks with every action.
This comment was marked helpful 1 times.
Basically, pessimistic detection assumes that their going to cause a conflict and thus checks before doing the work. This undos less work, but does not guarantee something gets done and can cause more aborts. Optimistic detection assumes that their is not going to be a conflict and thus does all the work and checks afterwards. This can cause fairness problems, but guarantees that something gets done.
A real-world example is having a shared bank account with your family (with a low balance) and trying to buy groceries. Pessimistic detection would have you check your account balance before you start shopping and calling all of your family members to ensure that they are also not buying anything so that you don't get an overdraft fee. Optimistic detection would have you get all of the groceries, and then check the balance and call the family right before check out.
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