Kernel mechanisms for service differentiation in overloaded web servers

innovative new services such as e-commerce are placing new demands on Web servers. It is becoming essential for Web servers to provide performance isolation, have fast recovery times, and provide continuous service during overload at least to preferred customers. In this paper, we present the design and implementation of a kernel-based architecture that protects Web servers against overload by controlling the amount and rate of work entering the system. We present three mechanisms that provide admission control and service differentiation based on connection and application level information. Our basic admission control mechanism, TCP SYN policing, limits the acceptance rate of new requests based on the connection attributes. The second mechanism, prioritized listen queue, supports different service classes by reordering the listen queue of a server socket based on the priorities of the incoming connection requests. Third, we present URL-based connection control that uses application-level information such as URLs and cookies to define priorities and rate control policies. We have implemented these mechanisms in AIX 5.0. Through numerous experiments we demonstrate the effectiveness of these mechanisms in achieving the desired degree of service differentiation during overload. We also show that the kernel mechanisms are more efficient and scalable than application level controls implemented in the Web server. I

IN-KERNEL MECHANISMS FOR ADAPTIVE CONTROL OF OVERLOADED WEB SERVERS

ABSTRACT The increasing number of Internet users and innovative new services such as e-commerce are placing new demands on Internet servers, for example web servers. It is becoming essential for Internet servers to be highly available, have fast response times, and provide continuous service during overload at least to preferred customers. It is necessary, therefore, to protect Internet servers from overload since during server overload clients experience increased response times and service failures. In this paper we present a kernel-based architecture that protects Internet servers against overload by controlling the amount and rate of work entering the system. Our basic control algorithm limits the incoming TCP SYN requests based on connection attributes. By dropping non-compliant connection requests, the server can provide continuous service to preferred clients even under overload. We present a second mechanism that reorders the listen queue of a server socket based on the priorities of the incoming connection requests. Our experiments show that both mechanisms enable service differentiation during overload. We describe an adaptive architecture that uses these mechanisms to dynamically protect web servers from overload

Proceedings of the Sixth International Workshop on Web Caching and Content Distribution

OVERVIEW The International Web Content Caching and Distribution Workshop (WCW) is a premiere technical meeting for researchers and practitioners interested in all aspects of content caching, distribution and delivery on the Internet. The 2001 WCW meeting was held on the Boston University Campus. Building on the successes of the five previous WCW meetings, WCW01 featured a strong technical program and record participation from leading researchers and practitioners in the field. This report includes all the technical papers presented at WCW'01. Note: Proceedings of WCW'01 are published by Elsevier. Hardcopies of these proceedings can be purchased through the workshop organizers. As a service to the community, electronic copies of all WCW'01 papers are accessible through Technical Report BUCS‐TR‐2001‐017, available from the Boston University Computer Science Technical Report Archives at http://www.cs.bu.edu/techreps. [Ed.note: URL outdated. Use http://www.bu.edu/cs/research/technical-reports/ or http://hdl.handle.net/2144/1455 in this repository to access the reports.]Cisco Systems; InfoLibria; Measurement Factory Inc; Voler

Architectures and Algorithms for Scalable Wide-area Information Systems

viii Chapter 1 Introduction 1 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Information Systems: A Historical Perspective . . . . . . . . . . . . . . . . . . 4 1.3 Influence of Scale on Information System Design . . . . . . . . . . . . . . . . 6 1.3.1 What is Scalability? . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3.2 Magnitude of Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3.3 Design Principles for Scalability . . . . . . . . . . . . . . . . . . . . . 9 1.4 Summary of Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.4.1 Scalable Server Design . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.4.2 Scalable Information Delivery Architecture . . . . . . . . . . . . . . . 11 1.5 Outline of Dissertation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Chapter 2 Scalable Server Design 15 2.1 Data and Access Characteristics . . . . . . . . . . . . . . . . . . . ..

Design considerations for distributed caching on the Internet

In this paper, we describe the design and implementation of an integrated architecture for cache systems that scale to hundreds or thousands of caches with thousands to millions of users. Rather than simply try to maximize hit rates, we take an end-to-end approach to improving response time by also considering hit times and miss times. We begin by studying several Internet caches and workloads, and we derive three core design principles for large scale distributed caches: (1) minimize the number of hops to locate and access data on both hits and misses, (2) share data among many users and scale to many caches, and (3) cache data close to clients. Our strategies for addressing these issues are built around a scalable, high-performance data-location service that tracks where objects are replicated. We describe how to construct such a service and how to use this service to provide direct access to remote data and push-based data replication. We evaluate our system through trace-driven simulation and find that these strategies together provide response time speedups of 1.27 to 2.43 compared to a traditional three-level cache hierarchy for a range of trace workloads and simulated environments. 1

Taper: Tiered approach for eliminating redundancy in replica synchronization

We present TAPER, a scalable data replication protocol that synchronizes a large collection of data across multiple geographically distributed replica locations. TAPER can be applied to a broad range of systems, such as software distribution mirrors, content distribution networks, backup and recovery, and federated file systems. TA-PER is designed to be bandwidth efficient, scalable and content-based, and it does not require prior knowledge of the replica state. To achieve these properties, TA-PER provides: i) four pluggable redundancy elimination phases that balance the trade-off between bandwidth savings and computation overheads, ii) a hierarchical hash tree based directory pruning phase that quickly matches identical data from the granularity of directory trees to individual files, iii) a content-based similarity detection technique using Bloom filters to identify similar files, and iv) a combination of coarse-grained chunk matching with finer-grained block matches to achieve bandwidth efficiency. Through extensive experiments on various datasets, we observe that in comparison with rsync, a widely-used directory synchronization tool, TAPER reduces bandwidth by 15 % to 71%, performs faster matching, and scales to a larger number of replicas.