i Analysis of Caching Algorithms for Distributed File Systems
操作系统课程电子教案
a. 100x50
b. 50
10-cont.
10.11 Consider the following page reference string: 1, 2, 3, 4, 2, 1, 5,
6, 2, 1, 2, 3, 7, 6, 3, 2, 1, 2, 3, 6.
How many page faults would occur for the following replacement
algorithms, assuming one, two, three, four, five, six, or seven frames?
Remember all frames are initially empty, so your first unique pages will
all cost one fault each.
when a page fault occurs.
A page fault occurs when an access to a page that
has not been brought into main memory takes place.
The operating system verifies the memory access,
the effective memory reference time? (Assume that finding a
page-table entry in the associative registers takes zero time, if
e table)+200(access word)
schemes could be used successfully with this hardware?
Algorithm Analysis (Big O)
1
Complexity
In examining algorithm efficiency we must understand the idea of complexity
▪ Space complexity ▪ Time Complexity
F.C. n+1 n2+n n2 n2 ____ 3n2+2n+1
Big O = O(n2)
clearing coefficients : n2+n
picking the most significant term: n2
10
What is Big O
Big O
▪ rate at which algorithm performance degrades as a function of the amount of data it is asked to handle
f(n)=O(g(n)), iff there exist constants c and n0
such that:
f(n) <= c g(n) for all n>=n0
Thus, g(n) is an upper bound on f(n)
Note: f(n) = O(g(n)) is NOT the same as O(g(n)) = f(n)
n+1
1
{ cout << i;
n
2
p = p + i;
n
3
}
____
3n+1
totaling the counts produces the F.C. (frequency count)
关于算法利与弊的作文800字
关于算法利与弊的作文800字英文回答：Advantages and Disadvantages of Algorithms.Algorithms are step-by-step procedures or instructions used to solve a problem or complete a task. They are widely used in various fields, including computer science, mathematics, and engineering. While algorithms have many advantages, they also come with some disadvantages.One of the major advantages of algorithms is their ability to provide efficient solutions. By breaking down complex problems into smaller, manageable steps, algorithms help save time and resources. They enable us to solve problems systematically and ensure accuracy in the results. For example, in computer programming, algorithms are used to develop efficient code that can perform complex tasks quickly and accurately.Furthermore, algorithms are essential for automation and optimization. They enable machines and systems to perform tasks without human intervention, leading to increased productivity and efficiency. For instance, algorithms are used in self-driving cars to analyze data from sensors and make decisions in real-time, ensuring safe and efficient navigation.On the other hand, algorithms also have some disadvantages. One of the main concerns is the potentialfor bias and discrimination. Algorithms are created by humans, and they can inadvertently reflect the biases and prejudices of their creators. For example, algorithms used in hiring processes may inadvertently discriminate against certain groups of people based on factors such as gender or race.Additionally, algorithms can be complex and difficult to understand. This can lead to a lack of transparency and accountability. When algorithms are used to make important decisions, such as in the criminal justice system or credit scoring, it becomes crucial to ensure that they are fairand unbiased. However, the complexity of algorithms can make it challenging to identify and address any potential flaws or biases.中文回答：算法的优缺点。
Analysis of Tree Algorithms for RFID Arbitration
1. The distance between the interrogator and the tags is relatively short (generally several meters), so the total packet transmission time is dominated by the packet size and the baud rate. Propagation delays are negligible.
The two most important measures of system performance in RFID arbitration are the total time required to arbitrate a complete set of tags, and the total power consumed by the tags during the process. This is in contrast to the measures of throughput and packet delay for typical multiaccess systems.
3. A tag never communicates without being prompted by the interrogator. This type of master/slave relationship is somewhat unique to RFID. Furthermore, contention for the communication medium is short{lived, since once the tags have been identi ed, the interrogator can communicate with them in a point{ to{point fashion. This is in contrast to a typical multiaccess system where the transmitting units operate more independently and contention is an ongoing problem. Thus, RFID arbitration is a transient process as opposed to the steady{state process more commonly encountered in multiaccess systems.
an introduction to the analysis of algorithms
An introduction to the analysis of algorithms"An Introduction to the Analysis of Algorithms" is a book or course title that suggests a focus on understanding and evaluating algorithms. Here is a brief overview of what such a study might involve:Overview:1.Algorithm Basics:* Introduction to the concept of algorithms.* Understanding algorithm design principles.* Basic algorithmic paradigms (e.g., divide and conquer, greedy algorithms, dynamic programming).2.Algorithm Analysis:* Time complexity analysis: Big-O notation, time complexity classes.* Space complexity analysis: Memory usage analysis.* Worst-case, average-case, and best-case analysis.3.Asymptotic Notation:* Big-O, Big-Theta, and Big-Omega notation.* Analyzing the efficiency of algorithms as the input size approaches infinity.4.Recursion:* Understanding recursive algorithms.* Analyzing time and space complexity of recursive algorithms.5.Sorting and Searching:* Analysis of sorting algorithms (e.g., bubble sort, merge sort, quicksort).* Analysis of searching algorithms (e.g., binary search).6.Dynamic Programming:* Introduction to dynamic programming principles.* Analyzing algorithms using dynamic programming.7.Greedy Algorithms:* Understanding the greedy algorithmic paradigm.* Analyzing algorithms using greedy strategies.8.Graph Algorithms:* Analyzing algorithms related to graphs (e.g., Dijkstra's algorithm, breadth-first search, depth-first search).9.Case Studies:* Analyzing real-world applications of algorithms.* Case studies on how algorithm analysis influences practical implementations.10.Advanced Topics:* Introduction to advanced algorithmic concepts.* Optional topics such as randomized algorithms, approximation algorithms, and more.Conclusion:"An Introduction to the Analysis of Algorithms" provides a foundation for students or readers to understand the efficiency and performance of algorithms. It equips them with the tools to choose the right algorithms for specific tasks and to evaluate their impact on system resources.。
Convergence Analysis of Canonical Genetic Algorithm
in Section 11, some basic definitions and results from finite Markov chain theory are introduced in Section 111. Section IV is devoted to the Markov chain analysis of CGA’s and their variants, and contains the essential results. Finally, the results are discussed with respect to the schema theorem [l].
Manuscript received March 10, 1993; revised June 28, 1993. The author is with the Department of Computer Science, LS XI, University of Dortmund, D-44221 Dortmund, Germany. This work was supported under project no. 107 004 91 by the Research Initiative Parallel Computing of the Ministry of Science and Research of Northrhine-Westfalia, Germany. IEEE Log Number 9213550.
Mutation operates independently on each individual by probabilistically perturbing each bit string. The event that the jth bit of the ith individual is flipped is stochastically independent and occurs with probability p , E ( 0 , l ) . For example, the ’ probability that string = OOOOo transitions to string b = 10110 by mutation is p , . (1 - p,) . p , p , . (1 - p,) = p i ( l - p,)‘-‘ with IC = 3 and 1 = 5 . Clearly, IC is just the Hamming distance H ( b , b’) between strings b and b’. Therefore the probability that string b; resembles string b’; after mutation
系统辨识综述
Contents lists available at ScienceDirect
Journal of Process Control
journal homepage: /locate/jprocont
b
a r t i c l e
i n f o
a b s t r a c t
Step and relay feedback tests have been widely used for model identification in the process industry. The corresponding identification methods developed in the past three decades are surveyed in this paper. Firstly, the process models with time delay mainly adopted for identification in the literature are presented with a classification on different response types. By categorizing the major technical routes developed in the existing references for parameter estimation relating to different applications, the identification methods are subsequently clustered into groups for overview, along with two specific categories for robust identification against load disturbance and the identification of multivariable or nonlinear processes. The rationales of each category are briefly explained, while a typical or state-of-the-art identification algorithm of each category is elucidated along with application to benchmark examples from the literature to illustrate the achievable accuracy and robustness, for the purpose of facilitating the readers to have a general knowledge of the research development. Finally, an outlook on the open issues regarding step or relay identification is provided to call attention to future exploration. © 2013 Elsevier Ltd. All rights reserved.
计算机操作系统课后习题答案 第四版
计算机操作系统课后习题答案第四版1. Describe the concept of a process and its typical attributes.A process is an entity that represents the execution of a program on a computer system. It consists of the program code, data, and execution context. The typical attributes of a process include a unique process identifier (PID), a program counter that keeps track of the next instruction to be executed, a stack that holds temporary data, a heap for dynamically allocated memory, and a set of resources such as open files and I/O devices.2. Explain the difference between process control block (PCB) and thread control block (TCB).A process control block (PCB) is a data structure used by the operating system to manage a process. It contains information about the process, such as its current state, scheduling information, memory allocation, and I/O status. On the other hand, a thread control block (TCB) is a data structure used to manage a thread within a process. It contains information specific to the thread, such as its program counter, stack pointer, and register values. Multiple threads can exist within a single process, sharing the same resources.3. Discuss the advantages and disadvantages of using threads instead of processes.One advantage of using threads instead of processes is that they are more lightweight in terms of resource consumption. Since threads share the same memory space, inter-thread communication is faster and uses less memory compared to inter-process communication. Threads also enable betterutilization of multi-core processors, as multiple threads can run in parallel on different cores.However, there are also disadvantages to using threads. The main disadvantage is that threads within the same process can interfere with each other if not properly synchronized. This can lead to issues such as race conditions, deadlocks, and data corruption. Additionally, debugging and testing multi-threaded applications can be more complex and time-consuming compared to single-threaded applications.4. Explain the concepts of mutual exclusion, deadlock, and starvation in the context of operating systems.Mutual exclusion refers to the concept of ensuring that only one process or thread can access a shared resource at a time. This is typically achieved using synchronization mechanisms such as locks or semaphores. Mutual exclusion is important to prevent data corruption or inconsistent results due to concurrent access.Deadlock occurs when two or more processes are waiting indefinitely for each other to release resources, resulting in a situation where none of the processes can proceed. It can happen when processes acquire resources in a different order or when they fail to release resources properly. Deadlocks can lead to system failures and require careful resource allocation and scheduling algorithms to avoid.Starvation refers to a situation where a process is unable to acquire the necessary resources to progress, despite its requests. It can occur when resource allocation policies favor certain processes over others, leading to along waiting time for some processes. Starvation can negatively impact the performance and fairness of the system.5. Discuss the purpose and functionality of memory management units (MMUs) in operating systems.Memory management units (MMUs) are hardware components responsible for translating virtual memory addresses used by processes into physical memory addresses. They provide address translation and memory protection mechanisms. MMUs use page tables or translation lookaside buffers (TLBs) to map virtual addresses to physical addresses, allowing processes to utilize more memory than physically available.MMUs also enforce memory protection by assigning memory access permissions to different regions of the process's address space. This prevents processes from accessing memory that they should not be able to, ensuring data integrity and security. Additionally, MMUs help optimize memory access by caching frequently used memory pages in the TLB, reducing the number of costly memory accesses.Overall, MMUs play a crucial role in memory management, allowing processes to have their own virtual address spaces and ensuring efficient and secure memory access.(Note: The above answers are just sample content for the given topic. Please modify and expand them according to your needs, as the word limit has been exceeded.)。
软件工程专业英语-Main Memory Database
Concept Check
• What is a Main Memory database? • Describe the Differences between Main Memory database and disk resident
database. • How many features do MMDBs have?
• In MMDBMSs the situation is different: Since data is guaranteed to stay present in main memory, index structures and all the other parts of the database do not need to consider disk access and can be tuned for low computational cost.
软件我工们程毕专业业啦英语
SOFTWARE E其N实是G答IN辩的E标E题R地I方NG ESSENTIALS
CHPTER 3 MAIN MEMORY DATABASES
3.1 An Overview of Main Memory Databases 3.2 The Evolution of Main Memory Databases 3.3 The Key Technology of Main Memory Database SUMMARY
3.1.3 Features of Main Memory Databases
The main memory database has many excellent features, and some important ones are listed as follows: • High throughput rate and low access delay • Excellent parallel processing power • High hardware dependencies
DistributedSystemsPrinciplesandParadigms中文版书名分布
Marcus,Sten : Blueprints for High Availablity
Birman, Reliable Distributed Systems
Byzantine Failure问题：
Pease,M., “Reaching Agreement in the Presence of Faults” J.ACM,1980
Lamport,L.: “Byzantine Generals Problem. ” ACM T ng.syst. 1982
Shooman,M.L: Reliability of Computer Systems and Networks :Fault Tolerance, Analysis, and Design. 2002
Tanisch,P., “Atomic Commit in Concurrent Computing. ” IEEE Concurrency,2000
集中式体系结构：C/S
分布式体系结构：
点对点系统(peer-peer system):DHT(distributed hash table),例如Chord
随机图(random map)
混合体系结构：
协作分布式系统BitTorrent、Globule
自适应软件技术：
①要点分离
②计算映像
③基于组件的设计
Henning,M., “A New Approach to Object-Oriented Middleware”
第11章分布式文件系统
NFS (Network File System):远程访问模型
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2 Related Research
This study was constructed similar to a study done previously by Bunt et al. [1]. They traced calls to the getblk system call on a single NFS client using various workloads, and then ran the trace through a simulator that simulated various sizes of client and server caches. Their results show the frequency-based policies performed significantly better than LRU as the client cache increases.
1 Introduction
Caching has proven to be a very effective way to reduce the penalty of accessing data on disks. UNIX file access patterns tend to exhibit temporal locality which makes LRU an effective cache replacement policy. When the files reside on an NFS server, the server cache only receives requests that can't be serviced by the client cache. It would seem that LRU performance would go down dramatically if the temporal locality of the requests get filtered out by the client cache. This study seeks to determine whether LRU is a good replacement policy to use in a server.
i
Hale Waihona Puke AbstractWhen picking a cache replacement policy for file systems, LRU (Least Recently Used) has always been the obvious choice, because of the temporal locality found in programs and data. However, in the case of Sun NFS servers much of the locality is filtered out by the client cache. It has been conjectured that this filtering of locality by the client caches render LRU ineffective as a server cache replacement policy. This study disproves the conjecture by simulating a NFS server cache with real worm traces. Traces were taken of NFS read and write requests sent to an NFS server. These traces were then run through a cache simulator using six different cache replacement policies: Least Recently Used (LRU), Least Frequently Used (LFU), Frequency Based Replacement (FBR), First In First Out (FIFO), Random (RAND), and Optimal (OPT). RAND and OPT were used to provide lower and upper bounds on performance. Results show that LRU is an effective NFS server cache replacement policy and frequency based tend to exhibit erratic behavior in the presence of temporal locality and sequentially accessed files.
12
We decided to redo the experiment, but to avoid modifying the kernel we traced NFS requests as they went across the ethernet. By tracing the network instead of the kernel we were able to trace normal workloads from multiple NFS clients. We chose to simulate the same cache replacement policies as the previous study and to have the cache simulate a Berkeley fast file system
Analysis of Caching Algorithms for Distributed File Systems
Benjamin Reed and Darrell D. E. Long Department of Computer Scier~ce University of California Santa Cruz, CA 95064
[3].
3 Data Collection
One of the advantages to simulating an NFS server cache is that traces are easy to get since the requests are passed over the network. NFS uses the Sun RPC [5] (Remote Procedure Call) protocol to send requests from the NFS client to the server. RPC is implemented on top of UDP [8] (User Datagram Protocol). NFS has reserved UDP port 2049 for exclusive use. The client sends call requests to the server and the server replies with data and/or return codes. Traces were collected by listening to all the call requests being sent to the NFS file server. This was done by putting the ethernet interface on the same network as the server in promiscuous mode. In promiscuous mode, the ethernet interface will read every packet that goes by on the network. If the computer is on the same network as the file server, it will be able to gather information about all the requests sent to the server. A major advantage of this approach is that it doesn't interfere with the performance of the client or the server, thus eliminating any anomalies that can arise from the monitoring tool affecting the performance of the system. In order to cut down the number of packets processed, the NIT_PF packet filter was used. NIT_PF is a STREAMS packet filter in SunOS that only lets through packets that meet a certain criteria. The filter was set up to let through only those packets destined for UDP port 2049 of the server and only those that are call requests. The information needed for the simulator is extracted by parsing the packet headers and body. The information recorded in the trace is the current time, the source and destination of the request, the request type, and the information that corresponds to the request type. For a write request, a file handle and an offset is recorded. For a read request, a file handle, offset, and count are recorded.