TAILIEUCHUNG - Apress bắt đầu ứng dụng với java google - p 4

Đây thực chất là những gì đang xảy ra với App Engine. Nếu bạn có một bước trở lại, bạn sẽ thấy những tác động lâu dài của phương pháp này. Là một nhà phát triển bây giờ bạn nhận được để bỏ qua vấn đề khả năng mở rộng như thời gian thực hiện trên các phương pháp sau khi đã tăng dữ liệu trong kho dữ liệu của bạn. Để đổi lại, bạn nhận được một thời gian cố định về thi hành bất kể quy mô của bạn trở nên. thời gian đáp ứng App Engine sẽ. | CHAPTER 2 INTRODUCTION TO APP ENGINE Breaking it down a bit more consider an apartment building App Engine with central air and heating controls. You are a tenant your App Engine application in this building. You can t directly adjust the temperature because that would affect the other tenants other App Engine applications . So you have to send a request to the building super to change the temperature on your behalf URLFetch Bigtable query Memcache mail XMPP any other Google App Engine service . This is essentially what is happening with App Engine. If you take a step back you ll see the long-term implications of this approach. As a developer you now get to ignore scalability concerns like execution time on methods after you have increased data in your datastore. In exchange you get a fixed duration on execution no matter what your scale becomes. App Engine s response times will be steady from your first request to your millionth request. GOOGLE APP ENGINE proiocol buffers Bigtable Datastore Figure 2-1. App Engine architecture Notice that no file system or components of the architecture represent the physical machine. With App Engine you have access only to the application layer. There are some open-source projects for example Google Virtual File System that allow you to 8 CHAPTER 2 INTRODUCTION TO APP ENGINE host an emulated virtual drive on App Engine but these are not part of the product offering at this time. Running all these services on behalf of your application isn t something App Engine handles without restrictions. Your application gets a daily limit on each type of request and each request is recorded and then subtracted from your daily allotment. Let s take a deeper look at these quotas. Being a Good Neighbor With Quotas As we mentioned in Chapter 1 App Engine is a multitenant platform. This is far different from hosting your application on a dedicated server or in your own data center. The fundamental difference is that you re not alone Thousands of .

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