[request setFetchBatchSize:500];//从数据库里每次加载500条数据来筛选数据
[request setFetchOffset:sizeCount];//读取数据库的游标偏移量，从游标开始读取数据
sizeCount += 10;
[request setFetchLimit:10];//每次要取多少条数据，10就是每次从数据库读取10条数据

国外讲解：

If you have many records in your table (entity) and your fetch is set up to retrieve many records from this table, faulting is a method by which your app can preserve memory. Rather than retrieving all of these records and loading them into memory all at the same time, your fetchBatchSize will limit the number of records retrieved to that limit, and will fault the remaining records – they will only be fetched when they are needed. If you set the fetchBatchSize this faulting will be handled for you automatically.

Hope this clarifies things a bit.