Comment by layer8

I agree about the practical difficulties of implementing WSI. However, what’s not clear to me is how to reason about SI as an application programmer. Whenever you write data within a transaction that depends on data read within that transaction, you can’t exclude the possibility that the data you read is stale and hence that what you write will create inconsistencies. In principle, you have to read everything with SELECT FOR UPDATE in a read-write transaction. But if you do that, isn’t the performance impact similar as it would be for WSI, in that all rows that are read have to be tagged until the transaction completes?