Bringing Web Time Travel to MediaWiki: An Assessment of the Memento MediaWiki Extension

We have implemented the Memento MediaWiki Extension Version 2.0, which brings the Memento Protocol to MediaWiki, used by Wikipedia and the Wikimedia Foundation. Test results show that the extension has a negligible impact on performance. Two 302 status code datetime negotiation patterns, as defined by Memento, have been examined for the extension: Pattern 1.1, which requires 2 requests, versus Pattern 2.1, which requires 3 requests. Our test results and mathematical review find that, contrary to intuition, Pattern 2.1 performs better than Pattern 1.1 due to idiosyncrasies in MediaWiki. In addition to implementing Memento, Version 2.0 allows administrators to choose the optional 200-style datetime negotiation Pattern 1.2 instead of Pattern 2.1. It also permits administrators the ability to have the Memento MediaWiki Extension return full HTTP 400 and 500 status codes rather than using standard MediaWiki error pages. Finally, version 2.0 permits administrators to turn off recommended Memento headers if desired. Seeing as much of our work focuses on producing the correct revision of a wiki page in response to a user's datetime input, we also examine the problem of finding the correct revisions of the embedded resources, including images, stylesheets, and JavaScript; identifying the issues and discussing whether or not MediaWiki must be changed to support this functionality.Comment: 23 pages, 18 figures, 9 tables, 17 listing

Optimizing Replacement Policies for Content Delivery Network Caching: Beyond Belady to Attain A Seemingly Unattainable Byte Miss Ratio

When facing objects/files of differing sizes in content delivery networks (CDNs) caches, pursuing an optimal object miss ratio (OMR) by approximating Belady no longer ensures an optimal byte miss ratio (BMR), creating confusion about how to achieve a superior BMR in CDNs. To address this issue, we experimentally observe that there exists a time window to delay the eviction of the object with the longest reuse distance to improve BMR without increasing OMR. As a result, we introduce a deep reinforcement learning (RL) model to capture this time window by dynamically monitoring the changes in OMR and BMR, and implementing a BMR-friendly policy in the time window. Based on this policy, we propose a Belady and Size Eviction (LRU-BaSE) algorithm, reducing BMR while maintaining OMR. To make LRU-BaSE efficient and practical, we address the feedback delay problem of RL with a two-pronged approach. On the one hand, our observation of a rear section of the LRU cache queue containing most of the eviction candidates allows LRU-BaSE to shorten the decision region. On the other hand, the request distribution on CDNs makes it feasible to divide the learning region into multiple sub-regions that are each learned with reduced time and increased accuracy. In real CDN systems, compared to LRU, LRU-BaSE can reduce "backing to OS" traffic and access latency by 30.05\% and 17.07\%, respectively, on average. The results on the simulator confirm that LRU-BaSE outperforms the state-of-the-art cache replacement policies, where LRU-BaSE's BMR is 0.63\% and 0.33\% less than that of Belady and Practical Flow-based Offline Optimal (PFOO), respectively, on average. In addition, compared to Learning Relaxed Belady (LRB), LRU-BaSE can yield relatively stable performance when facing workload drift

Measuring and Managing Answer Quality for Online Data-Intensive Services

Online data-intensive services parallelize query execution across distributed software components. Interactive response time is a priority, so online query executions return answers without waiting for slow running components to finish. However, data from these slow components could lead to better answers. We propose Ubora, an approach to measure the effect of slow running components on the quality of answers. Ubora randomly samples online queries and executes them twice. The first execution elides data from slow components and provides fast online answers; the second execution waits for all components to complete. Ubora uses memoization to speed up mature executions by replaying network messages exchanged between components. Our systems-level implementation works for a wide range of platforms, including Hadoop/Yarn, Apache Lucene, the EasyRec Recommendation Engine, and the OpenEphyra question answering system. Ubora computes answer quality much faster than competing approaches that do not use memoization. With Ubora, we show that answer quality can and should be used to guide online admission control. Our adaptive controller processed 37% more queries than a competing controller guided by the rate of timeouts.Comment: Technical Repor

CHORUS Deliverable 2.1: State of the Art on Multimedia Search Engines

Based on the information provided by European projects and national initiatives related to multimedia search as well as domains experts that participated in the CHORUS Think-thanks and workshops, this document reports on the state of the art related to multimedia content search from, a technical, and socio-economic perspective. The technical perspective includes an up to date view on content based indexing and retrieval technologies, multimedia search in the context of mobile devices and peer-to-peer networks, and an overview of current evaluation and benchmark inititiatives to measure the performance of multimedia search engines. From a socio-economic perspective we inventorize the impact and legal consequences of these technical advances and point out future directions of research

A Vertical PRF Architecture for Microblog Search

In microblog retrieval, query expansion can be essential to obtain good search results due to the short size of queries and posts. Since information in microblogs is highly dynamic, an up-to-date index coupled with pseudo-relevance feedback (PRF) with an external corpus has a higher chance of retrieving more relevant documents and improving ranking. In this paper, we focus on the research question:how can we reduce the query expansion computational cost while maintaining the same retrieval precision as standard PRF? Therefore, we propose to accelerate the query expansion step of pseudo-relevance feedback. The hypothesis is that using an expansion corpus organized into verticals for expanding the query, will lead to a more efficient query expansion process and improved retrieval effectiveness. Thus, the proposed query expansion method uses a distributed search architecture and resource selection algorithms to provide an efficient query expansion process. Experiments on the TREC Microblog datasets show that the proposed approach can match or outperform standard PRF in MAP and NDCG@30, with a computational cost that is three orders of magnitude lower.Comment: To appear in ICTIR 201

A Framework for Verifying Scalability and Performance of Cloud Based Web Applications

Antud magistritöö uurib võimalusi, kuidas kasutada veebirakendust MediaWiki, mida kasutatakse Wikipedia rakendamiseks, ja kuidas kasutada antud teenust mitme serveri peal nii, et see oleks kõige optimaalsem ja samas kõik veebikülastajad saaks teenusele ligi mõistliku ajaga. Amazon küsib raha pilves toimivate masinate ajalise kasutamise eest, ümardades pooleldi kasutatud tunnid täistundideks. Antud töö sisaldab vahendeid kuidas mõõta pilves olevate serverite jõudlust ning võimekust ja skaleerida antud veebirakendust. Amazon EC2 pilvesüsteemis on võimalik kasutajatel koostada virtuaalseid tõmmiseid operatsiooni süsteemidest, mida saab pilves rakendada XEN virtualiseerimise keskkonnas, kui eraldiseisvat serverit. Antud virtuaalse tõmmise peale sai paigaldatud tööks vaja minev keskkond, et koguda andmeid serverite kasutuse kohta ja võimaldada platvormi, mis lubab dünaamiliselt ajas lisada servereid ja eemaldada neid. Magistritöö uurib Amazon EC2 pilvesüsteemi kasutusvõimalusi, mille hulka kuulub Auto Scale, mis aitab skaleerida pilves kasutatavaid rakendusi horisontaalselt. Amazon pilve kasutatakse antud töös MediaWiki seadistamiseks ja suuremahuliste eksperimentide rakendamiseks. Vajalik on teha palju optimiseerimisi ja seadistamisi, et suurendada teenuse läbilaske võimsust. Antud töö raames loodud raamistik aitab mõõta serverite kasutust, kogudes andmeid protsessori, mälu ja võrgu kasutamise kohta. See aitab leida süsteemis olevaid kitsaskohti, mis võivad põhjustada süsteemi olulist aeglustumist. Antud töö raames sai tehtud erinevaid teste, et selgitada välja parim võimalik paigutus ja seadistus. Saavutatud seadistust kontrolliti hiljem 2 suuremahulise eksperimentiga, mis kestis üks päev ja mille käigus tekitati 22 miljonit päringut, leidmaks kuidas raamistik võimaldab teenust pilves skaleerida ülesse päringute arvu tõusmisel ja vähendada servereid, kui päringute arv väheneb. Ühes eksperimendis kasutati optimaalset heuristikat, et selgitada välja optimaalne serverite arv, mida on vaja pilves rakendada. Teine eksperimentidest kasutas Amazon Auto Scale teenust, mis kasutas serverite keskmist protsessori kasutamist, et selgitada välja, kas pilves on vaja servereid lisada või eemaldada. Antud eksperimendid näitavad selgelt, et kasutades dünaamilist arvu servereid, olenevalt päringute arvust, on võimalik teenuse üleval hoidmiseks säästa raha.Network usage and bandwidth speeds have increased massively and vast majority of people are using Internet on daily bases. This has increased CPU utilization on servers meaning that sites with large visits are using hundreds of computers to accommodate increasing traffic rates to the services. Making plans for hardware ordering to upgrade old servers or to add new servers is not a straightforward process and has to be carefully considered. There is a need to predict traffic rate for future usage. Buying too many servers can mean revenue loss and buying too few servers can result in losing clients. To overcome this problem, it is wise to consider moving services into virtual cloud and make server provisioning as an automatic step. One of the popular cloud service providers, Amazon is giving possibility to use large amounts of computing power for running servers in virtual environment with single click. They are providing services to provision as many servers as needed to run, depending how loaded the servers are and whatever we need to do, to add new servers or to remove existing ones. This will eliminate problems associated with ordering new hardware. Adding new servers is an automatic process and will follow the demand, like adding more servers for peak hours and removing unnecessary servers at night or when the traffic is low. Customer pays only for the used resources on the cloud. This thesis focuses on setting up a testbed for the cloud that will run web application, which will be scaled horizontally (by replicating already running servers) and will use the benchmark tool for stressing out the web application, by simulating huge number of concurrent requests and proper load-balancing mechanisms. This study gives us a proper picture how servers in the cloud are scaled and whole process remains transparent for the end user, as it sees the web application as one server. In conclusion, the framework is helpful in analyzing the performance of cloud based applications, in several of our research activities

Scalable cooperative caching algorithm based on bloom filters

This thesis presents the design, implementation and evaluation of a novel cooperative caching algorithm based on the bloom filter data structure. The new algorithm uses a decentralized approach to resolve the problems that prevent the existing solutions from being scalable. The problems consist of an overloaded manager, a communication overhead among clients, and a memory overhead on the global cache. The new solution reduces the manager load and the communication overhead by distributing the global cache information among cooperating clients. Thus, the manager no longer maintains the global cache. Furthermore, the memory overhead is decreased due to a bloom filter data structure. The bloom filter saves memory space in the global cache and makes the new algorithm scalable. The correctness of the research hypothesis is verified by running experiments on the caching algorithms. The experiment results demonstrate that the new caching algorithm maintains a low block access time as existing algorithms. In addition, the new algorithm decreases the manager load by the factor of nine. Moreover, the communication overhead is reduced by nearly a factor of six as a result of distributing the global cache to clients. Finally, the results show a significant reduction in the memory overhead which also contributes to the scalability of the new algorithm

A Holistic Approach to Lowering Latency in Geo-distributed Web Applications

User perceived end-to-end latency of web applications have a huge impact on the revenue for many businesses. The end-to-end latency of web applications is impacted by: (i) User to Application server (front-end) latency which includes downloading and parsing web pages, retrieving further objects requested by javascript executions; and (ii) Application and storage server(back-end) latency which includes retrieving meta-data required for an initial rendering, and subsequent content based on user actions. Improving the user-perceived performance of web applications is challenging, given their complex operating environments involving user-facing web servers, content distribution network (CDN) servers, multi-tiered application servers, and storage servers. Further, the application and storage servers are often deployed on multi-tenant cloud platforms that show high performance variability. While many novel approaches like SPDY and geo-replicated datastores have been developed to improve their performance, many of these solutions are specific to certain layers, and may have different impact on user-perceived performance. The primary goal of this thesis is to address the above challenges in a holistic manner, focusing specifically on improving the end-to-end latency of geo-distributed multi-tiered web applications. This thesis makes the following contributions: (i) First, it reduces user-facing latency by helping CDNs identify and map objects that are more critical for page-load latency to the faster CDN cache layers. Through controlled experiments on real-world web pages, we show the potential of our approach to reduce hundreds of milliseconds in latency without affecting overall CDN miss rates. (ii) Next, it reduces back-end latency by optimally adapting the datastore replication policies (including number and location of replicas) to the heterogeneity in workloads. We show the benefits of our replication models using real-world traces of Twitter, Wikipedia and Gowalla on a 8 datacenter Cassandra cluster deployed on EC2. (iii) Finally, it makes multi-tier applications resilient to the inherent performance variability in the cloud through fine-grained request redirection. We highlight the benefits of our approach by deploying three real-world applications on commercial cloud platforms