Date of publication: 2017-07-08 16:26
Amazon’s e-commerce platform is composed of hundreds of services that work in concert to deliver functionality ranging from recommendations to order fulfillment to fraud detection. Each service is exposed through a well defined interface and is accessible over the network. These services are hosted in an infrastructure that consists of tens of thousands of servers located across many data centers world-wide. Some of these services are stateless (., services which aggregate responses from other services) and some are stateful (., a service that generates its response by executing business logic on its state stored in persistent store).
Efficiency : The system needs to function on a commodity hardware infrastructure. In Amazon’s platform, services have stringent latency requirements which are in general measured at the percentile of the distribution. Given that state access plays a crucial role in service operation the storage system must be capable of meeting such stringent SLAs (see Section below). Services must be able to configure Dynamo such that they consistently achieve their latency and throughput requirements. The tradeoffs are in performance, cost efficiency, availability, and durability guarantees.
Other Assumptions: Dynamo is used only by Amazon’s internal services. Its operation environment is assumed to be non-hostile and there are no security related requirements such as authentication and authorization. Moreover, since each service uses its distinct instance of Dynamo, its initial design targets a scale of up to hundreds of storage hosts. We will discuss the scalability limitations of Dynamo and possible scalability related extensions in later sections.
Dynamo uses consistent hashing to partition its key space across its replicas and to ensure uniform load distribution. A uniform key distribution can help us achieve uniform load distribution assuming the access distribution of keys is not highly skewed. In particular, Dynamo’s design assumes that even where there is a significant skew in the access distribution there are enough keys in the popular end of the distribution so that the load of handling popular keys can be spread across the nodes uniformly through partitioning. This section discusses the load imbalance seen in Dynamo and the impact of different partitioning strategies on load distribution.
Advances in storage devices such as NVMe SSD have led to vast researches on storage stack optimization of operating systems to exploit full performance of these state-of-the-art devices.
When a node becomes available again, or a new node is added to the system, the newly available node accepts a roughly equivalent amount of load from each of the other available nodes.
Now, emptying the Recycle Bin is much easier than gathering your recyclables out of the kitchen and taking to the curb or recycle center. Go to the Recycle Bin, right-click on it and choose Empty Recycle Bin (left-click). 'Are you sure you want to permanently delete?' and it will tell you how many. I'm going to say Yes, and cha-ching, it's gone.
MSDOS, PC-DOS, and its clones, DR-DOS and FreeDOS, were operating systems widely used on PCs in the 6985s and early 6995s. The last I checked, the open source equivalent, FreeDOS, is still under development and runs fine on modern hardware.