基于模糊依赖的实时数据库的快速恢复

在实时数据库中，对数据的操作有硬实时要求。当数据被损坏时，传统的故障恢复技术（根据日记进行undo和redo操作）远远不能满足其需求。提出了一种基于模糊依赖的数据恢复方法用以满足实时应用的要求。该方法是利用数据挖掘技术生成的依赖信息快速的生成可接受的模糊值。     

Low-rank image completion with entropy features

In this paper, we propose a novel method to complete the images or textures with the property of low rank. Our method leverages saliency detection with two entropy features to estimate initial corrupted regions. Then an iterative optimization model for low-rank and sparse errors recovery is designed to complete the corrupted images. Our iterative model can improve the initial corrupted regions and generate accurate and continuous corrupted regions via fully connected CRFs. By introducing a F-norm term in our model to absorb small noise, we can generate completed images which are more precise and have lower rank. Experiments indicate that our method introduces less local distortions than example-based methods for images with regular structures. It is also superior to the previous low-rank image completion method especially when the images contain low-rank corrupted regions. Furthermore, we show that the entropy features benefit the existing saliency detection methods too.     

基于多级网络编码的多副本云数据存储

云数据存储的快速发展对数据的可用性提出了较高要求.目前,主要采用纠删码计算数据编码块进行分布式冗余数据存储来保证数据的可用性.虽然这种数据编码技术保证了存储数据的安全性并减少了额外的存储空间,但在损坏数据恢复时会产生较大的计算和通信开销.提出一种基于多级网络编码的多副本生成和损坏数据恢复算法.算法基于多级网络编码对纠删码的编码矩阵进行改进形成多级编码矩阵,利用其级联性生成多级编码(hierarchical coding,HC码)来构成多副本数据,使得各副本之间存在编码关系.在损坏数据恢复时,利用数据所有者提供的数据编码信息和云存储中保存的数据块直接计算进行恢复,从而避免从云存储中远程下载数据.理论分析和实验表明,所提算法在相同的存储空间下显著减少了损坏数据恢复时的通信开销并提高了数据的可用性.     

Detection and recovery techniques for database corruption

Increasingly, for extensibility and performance, special purpose application code is being integrated with database system code. Such application code has direct access to database system buffers, and as a result, the danger of data being corrupted due to inadvertent application writes is increased. Previously proposed hardware techniques to protect from corruption require system calls, and their performance depends on details of the hardware architecture. We investigate an alternative approach which uses codewords associated with regions of data to detect corruption and to prevent corrupted data from being used by subsequent transactions. We develop several such techniques which vary in the level of protection, space overhead, performance, and impact on concurrency. These techniques are implemented in the Dali main-memory storage manager, and the performance impact of each on normal processing is evaluated. Novel techniques are developed to recover when a transaction has read corrupted data caused by a bad write and gone on to write other data in the database. These techniques use limited and relatively low-cost logging of transaction reads to trace the corruption and may also prove useful when resolving problems caused by incorrect data entry and other logical errors.     

Header Detection to Improve Multimedia Quality Over Wireless Networks

Wireless multimedia studies have revealed that forward error correction (FEC) on corrupted packets yields better bandwidth utilization and lower delay than retransmissions. To facilitate FEC-based recovery, corrupted packets should not be dropped so that maximum number of packets is relayed to a wireless receiver's FEC decoder. Previous studies proposed to mitigate wireless packet drops by a partial checksum that ignored payload errors. Such schemes require modifications to both transmitters and receivers, and incur packet-losses due to header errors. In this paper, we introduce a receiver-based scheme which uses the history of active multimedia sessions to detect transmitted values of corrupted packet headers, thereby improving wireless multimedia throughput. Header detection is posed as the decision-theoretic problem of multihypothesis detection of known parameters in noise. Performance of the proposed scheme is evaluated using trace-driven video simulations on an 802.11b local area network. We show that header detection with application layer FEC provides significant throughput and video quality improvements over the conventional UDP/IP/802.11 protocol stack     

Analytical results for optimal choice of location update intervalfor mobility database failure restoration in PCS networks

When the location information for a mobile user in the Home Location Register (HLR) is corrupted or obsolete, the new arriving calls to the user may be lost. In order to minimize the effect of such HLR mobility database failure, a location update scheme called period location updating is proposed, and the cost analysis is performed. Analytical results for the failure recovery time distribution and the average number of call losses, which are crucial for cost analysis, are presented. The optimal location update period is given analytically as a function of other traffic parameters. This optimal choice of location update period lays the foundation for the adaptive adjustment of the location update period in failure restoration for PCS networks     

Oracle数据库日志文件损坏时修复方法的实验研究

Oracle数据库日志文件记录了对数据库进行的所有操作,而日志文件又分为重做日志文件和归档日志文件.重做日志可用于进行实例恢复,但如果数据文件意外丢失或损坏,则必须要用到归档日志.针对归档或非归档日志文件损坏或丢失时,数据库发生故障的情况,用模拟故障的方法研究了不同情况下的修复方法.     

Recovering Connected Error Region Based on Adaptive Error Concealment Order Determination

Parts of compressed video streams may be lost or corrupted when being transmitted over bandwidth limited networks and wireless communication networks with error-prone channels. Error concealment (EC) techniques are often adopted at the decoder side to improve the quality of the reconstructed video. Under the conditions of a high rate of data packets that arrives at the decoder corrupted, it is likely that the incorrectly decoded macro-blocks (MBs) are concentrated in a connected region, where important spatial reference information is lost. The conventional EC methods usually carry out the block concealment following a lexicographic scan (from top to bottom and from left to right of the image), which would make the methods ineffective for the case that the corrupted blocks are grouped in a connected region. In this paper, a temporal error concealment method, adaptive error concealment order determination (AECOD), is proposed to recover connected corrupted regions. The processing order of an MB in a connected corrupted region is adaptively determined by analyzing the external boundary patterns of the MBs in its neighborhood. The performances, on several video sequences, of the proposed EC scheme have been compared with those obtained by using other error concealment methods reported in the literature. Experimental results show that the AECOD algorithm can improve the recovery performance with respect to the other considered EC methods.      

一种有效的受损数据隔离方法

数据库可生存性要求在发现受损数据时采用受损限制技术,以尽快隔离受损数据从而防止由于数据共享造成受损范围进一步扩大带来的危害。在DBMS内部设计并实现了一种受损数据隔离策略语言,并提出了一种有效的受损数据隔离算法。该算法使用SQL语句动态替换技术最大限度保证隔离阶段用户请求数据的完整性,并通过子查询动态视图替换法保证数据隔离的有效性。基于TPC-W基准的吞吐率测试证明,提出的数据隔离算法具有较高的运行时效率。     

Oracle数据库块损坏的恢复——浅析BBED在数据库恢复中的应用

本文通过实例讲解利用ORACLE的BBED工具对损坏的Block进行恢复,以供遇到类似问题的ORACLE数据库管理员借鉴参考。     

Detecting corrupted pages in M replicated large files

A file in a distributed database system is replicated on M sites and may contain corrupted pages. Abdel-Ghafiar and El Abbadi gave a detection scheme assuming that the number of corrupted pages f相似文献   

Authenticating corrupted photo images based on noise parameter estimation

Photo image authentication is an interesting and demanding field in the computer vision and image processing community. This research is motivated by its wide range of applications, which include smart card authentication systems, biometric passport systems, etc. In this paper, we propose a method of authenticating corrupted photo images based on noise parameter estimation. The proposed method first generates corrupted images by adjusting the noise parameters in the initial training phase. This set of corrupted images and the noise parameters can be represented by a linear combination of the prototypes of the corrupted images and the noise parameters. In the testing phase, the noise parameters of the corrupted photo image can be estimated with a corrupted image and an original image. Finally, we can make a synthesized photo image from the original photo image using the estimated noise parameters and verify it with the corrupted photo image. The experimental results show that the proposed method can estimate the noise parameters accurately and improve the performance of photo image authentication.     

一种基于DCT系数恢复的错误隐藏技术

提出一种新的基于DCT系数恢复的错误隐藏技术.该技术的算法利用已解码的相邻块系数来重建丢失块的DCT系数.由于高频DCT系数对当前块的重建质量影响不大,为了减少计算量,在允许失真范围内,只计算关键的低频DCT系数.实验结果表明,算法不仅计算量小,而且可以获得与已有典型算法相当甚至更好的重建图像质量.     

面向服务的分布式数据库系统的容忍入侵方法

以分布式数据库系统提供的服务作为入侵检测的对象，采用了基于对可观测现象检测的原理，跟踪和定位被入侵的服务，借鉴了基于日志的破坏隔离围堵策略，准确定位了被破坏的数据，并对这些数据进行处理和恢复，不需要将整个系统进行“回退”，最大限度地保证数据库中其他服务的正常运行，保证了系统的可生存性。     

Adaptive Impulsive Noise Removal in TV Picture Transmission

This paper presents the capability and real-time processing features of an adaptive filter for the removal of impulse noise in TV picture transmission. The basic method, which has been extensively tested on data corrupted by randomly distributed impulses, is first enhanced to deal with real TV pictures suffering from impulse noise. In particular, the characteristics of the real impulses are incorporated in the noise identification stage. Then the suitability of the method in terms of real-time processing for images corrupted by randomly distributed impulse noise and those corrupted by real impulse strokes is analytically and numerically investigated. Impulse corrupted TV picture sequences are used to demonstrate that the proposed method potentially provides a real-time solution to quality TV picture transmission.     

RVLC decoding scheme for improved data recovery in MPEG-4 video coding standard

In this paper, we present a low-complexity ‘reversible variable length code’ (RVLC) decoding scheme for MPEG-4 video that recovers more blocks and sometimes more macroblocks (MBs) from error propagation region of corrupted video packets, as compared to the MPEG-4 scheme. The remaining blocks and MBs are concealed. Simulation studies have been carried out to show that the proposed scheme achieves better data recovery, both in terms of peak-signal-to-noise ratio (PSNR) and perceptual quality. In addition, we present more conditions for error detection than those suggested in MPEG-4, discuss properties of error propagation in corrupted video packets, and provide the RVLC codeword structure. The use of RVLC code structure will enable the decoding in both directions by using only one code table, instead of separate tables used for forward and backward decoding. Since the scheme is purely decoder based, the compliance with the standard is fully maintained. It is very simple for the decoder to keep track of the additional blocks/MBs recovered by the proposed scheme. Therefore, the data recovery scheme suggested in MPEG-4 can still be used as default scheme.     

结构化加权稀疏低秩恢复算法在人脸识别中的应用

针对训练样本或测试样本存在污损的情况，提出一种结构化加权稀疏低秩恢复算法（structured and weighted-sparse low rank representation，SWLRR）。SWLRR对低秩表示进行加权稀疏约束和结构化约束，使得低秩表示系数更加趋近于块对角结构，进而可获得具有判别性的低秩表示。SWLRR将训练样本恢复成干净训练样本后，再根据原始训练样本和恢复后的训练样本学习到低秩投影矩阵，把测试样本投影到相应的低秩子空间，即可有效地去除测试样本中的污损部分。在几个人脸数据库上的实验结果验证了SWLRR在不同情况下的有效性和鲁棒性。     

图像去噪混合滤波方法

传统均值滤波和中值滤波对高斯型噪声和椒盐型噪声有着不同的滤波特性。实际滤波时，由于图像往往会受到两种不同性质噪声的同时干扰，因此，单独采用中值滤波或均值滤波都不会达到最好的去噪效果，为了能同时对两种不同性质的噪声进行滤除，现提出了一种新的混合滤波算法，该算法首先利用局部阈值把受高斯型噪声污染的像素和受脉冲型噪声污染的像素区别开来，然后对受高斯噪声污染的像素采用均值滤波算法，而对受椒盐噪声污染的像素则采用中值滤波算法进行去噪。仿真结果证明，该方法更具有实用性和有效性。     

Reduction of residual noise based on eigencomponent filtering for speech enhancement

In this paper, residual noise of corrupted speech observations is further restrained based on eigencomponent (an eigenvalue and its corresponding eigenvector) filtering. Three relevant algorithms are proposed to obtain the core eigencomponents that deeply affect enhancement quality of speech fragments by joint diagonalization of clean speech and noise covariance matrix. In addition, the generalized inverse matrix transform is introduced to the recovery of enhanced speech signal for the issue of matrix irreversibility after eigencomponents are filtered. Experiment results show that the proposed methods work better than many other methods under various conditions on both noise reduction and speech distortion.     

Effects of update techniques on main memory database systemperformance

Update technique is an important issue related to database recovery. In a main memory database environment, transaction execution can be processed without any I/O, and all I/O operations involved are for recovery purposes. The efficiency of update techniques therefore has an important impact on the performance of main memory database systems. We compared the techniques of immediate and deferred update based on a database machine, MARS. The simulation results showed that immediate update outperforms deferred update unless system failure is a frequent occurrence