Dugga 1 Distributed Computing Tittis slides + chapter 1 i boken

Vad är grid computing systems?

Applications Collective layer Connectivity layer, Resource layer fabric layer

What is concurrency transparency?

two independent users may each have stored their files on the same file server or may be accessing the same tables in a shared database. In such cases, it is important that each user does not notice that the other is making use of the same resource.

vad är Distributed pervasive systems?

Embrace contextual changes. Encourage ad hoc competition. Recognize sharing as the default.

Definition av ett distributed system?

En kollektion av självständiga computing elements som framstås som ett enhetligt system för användare

Describe the 5 core requirements for a ubiquitous computing system

1. (Distribution) Devices are networked, distributed, and accessible in a transparent manner 2. (Interaction) Interaction between users and devices is highly unobtrusive 3. (Context awareness) The system is aware of a user's context in order to optimize interaction 4. (Autonomy) Devices operate autonomously without human intervention, and are thus highly self-managed 5. (Intelligence) The system as a whole can handle a wide range of dynamic actions and interactions

8 Pitfalls when developing distributed systems?

1. Network is reliable. 2. Network is secure. 3. Network is homogeneous. 4. Topology does not change. 5. Latency is zero. 6. Bandwidth is infinite. 7. Transport cost is zero. 8. There is only one administrator.

Nämn fyra decentralized algorithms!

1. No machine has complete information about the system state. 2. Machines make decisions based only on local information. 3. Failure on one machine doesn't ruin the algorithm. 4. There is no implicit assumption that a global clock exists.

Beskriv en nested transaction!

A nested transaction is used to provide a transactional guarantee for a subset of operations performed within the scope of a larger transaction. Doing this allows you to commit and abort the subset of operations independently of the larger transaction.

Nämn 7 termar av ett transparant distributed system.

Access: Hide differences in data representation and how a resource is accessed. Location: Hide where a resource is located. Migration: Hide a resource that may move location. Relocation: Hide a resource that may move location while in use. Replication: Hide that a resource is replicated. Concurrency: Hide that a resource may be shared by several competitive users. Failure: Hide failure and recovery of a resource.

Vad är transaction processing systems ACID?

Atomic: To the outside world, the transaction happens indivisibly Consistent: Transaction doesn't violate system variants. Isolated: Samverkande transactions don't interfere with each other. Durable: Once a transaction commits, the changes are permanent

Vad är transaction processing systems?

Begin transaction End_transaction = terminate transaction/commit Abort_transaction = Kill transaction/restore old values read Write

Nämn tre scalability problems!

Centralized service: A single server for all users, can become a bottleneck when numbers of users and data grows. Centralized data: A single on-line telephone book, saturation of datalines in and out of a single server. Centralized algorithms: Doing routing based on complete information, overloading of network.

Nämn 4 exempel på vanliga middleware services (sid. 6 i boken).

Communication Transactions Service composition Reliability

Vad är Cluster computing systems? (sid. 27)

In virtually all cases, cluster computing is used for parallel programming in which a single (compute intensive) program is run in parallel on multiple machines.

Name examples of pervasive systems!

Mobile computing systems Sensor networks

Describe pervasive computing!

Pervasive computing, also called ubiquitous computing, is the growing trend of embedding computational capability (generally in the form of microprocessors) into everyday objects to make them effectively communicate and perform useful tasks in a way that minimizes the end user's need to interact with computers as computers. Pervasive computing devices are network-connected and constantly available.

Nämn tre scacable dimensions! (sid. 15-20)

Size scalability: A system can be scalable with respect to its size, meaning that we can easily add more users and resources to the system without any noticeable loss of performance. Geographical scalability: A geographically scalable system is one in which the users and resources may lie far apart, but the fact that communication delays may be significant is hardly noticed. Administrative scalability: An administratively scalable system is one that can still be easily managed even if it spans many independent administrative organizations.

Why is a Distributed system a middleware?

The middleware layer extends over multiple machines, and offers each application the same interface.

What is failure transparency?

This means that a user or application does not notice that some piece of the system fails to work properly, and that the system subsequently (and automatically) recovers from that failure.