That transaction talk is really good, thank you. I can now finally name the effect that I had noticed but had trouble explaining and referring to, write skews.
It's interesting that he doesn't mention phantom reads as the difference between repeatable read/snapshot isolation, and serializable, which is what other sources tend to do.
Snapshot isolation always seemed to me like cheating the intended meaning of repeatable read, insofar as some databases refer to their snapshot isolation level as repeatable read.
That is, in the strictest sense, if you read a row twice, you get the same value with snapshot isolation, but you don't actually know that the value will be the same when you commit, which as I understand is a case of a write skew.
In fact, if one thinks of the definition of these levels in terms of locking semantics, one would expect a repeatable read to have the same meaning as obtaining a read lock on the row you read, which I understand would prevent at least some types of write skew, since no modification would be possible on that row, because it would need a write lock. There could still be hazards related to phantom reads (and possibly other effects), such as making a decision based on a computed aggregate that can change if new rows are inserted. Still, this meaning of repeatable reads would already provide a useful isolation level for various cases, except that it doesn't work with snapshot isolation.
I have a suspicion that applications out there made incorrect assumptions as to the actual isolation provided by the DB they use.
Thief controls are still great, they feel "crisp". I think System Shock is fine too, I even like using a mouse pointer to aim and interact with the world. Ultima Underworld I find a bit harder to play.
Does 2 have huge walls of text like the first one?
When I tried the first one, I was very impressed by the combat system as shown on the starting tutorial, but as soon as you get to the first city there is too much dialog. I realize that dialog is part of cRPGs, but when the ratio of gameplay to dialog is too low, I'd rather read a book.
I had enjoyed Sundiver and Startide Rising from the same series quite a bit, but I have to be honest, this one is trying my patience. I like the whole uplift concept, but I'm finding the writing in this one a bit clumsy.
It's interesting that he doesn't mention phantom reads as the difference between repeatable read/snapshot isolation, and serializable, which is what other sources tend to do.
Snapshot isolation always seemed to me like cheating the intended meaning of repeatable read, insofar as some databases refer to their snapshot isolation level as repeatable read.
That is, in the strictest sense, if you read a row twice, you get the same value with snapshot isolation, but you don't actually know that the value will be the same when you commit, which as I understand is a case of a write skew.
In fact, if one thinks of the definition of these levels in terms of locking semantics, one would expect a repeatable read to have the same meaning as obtaining a read lock on the row you read, which I understand would prevent at least some types of write skew, since no modification would be possible on that row, because it would need a write lock. There could still be hazards related to phantom reads (and possibly other effects), such as making a decision based on a computed aggregate that can change if new rows are inserted. Still, this meaning of repeatable reads would already provide a useful isolation level for various cases, except that it doesn't work with snapshot isolation.
I have a suspicion that applications out there made incorrect assumptions as to the actual isolation provided by the DB they use.