Transactional support for adaptive indexing

Adaptive indexing initializes and optimizes indexes incrementally, as a side effect of query processing. The goal is to achieve the benefits of indexes while hiding or minimizing the costs of index creation. However, index-optimizing side effects seem to turn read-only queries into update transactions that might, for example, create lock contention. This paper studies concurrency contr

A Personal Virtual Computer Recorder

Continuing advances in hardware technology have enabled the proliferation of faster, cheaper, and more capable personal computers. Users of all backgrounds rely on their computers to handle ever-expanding information, communication, and computation needs. As users spend more time interacting with their computers, it is becoming increasingly important to archive and later search the knowledge, ideas and information that they have viewed through their computers. However, existing state-of-the-art web and desktop search tools fail to provide a suitable solution, as they focus on static, accessible documents in isolation. Thus, finding the information one has viewed among the ever-increasing and chaotic sea of data available from a computer remains a challenge. This dissertation introduces DejaView, a personal virtual computer recorder that enhances personal computers with the ability to process display-centric content to help users with all the information they see through their computers. DejaView continuously records a user's session to provide a complete WYSIWYS (What You Search Is What You've Seen) record of a desktop computing experience, enabling users to playback, browse, search, and revive records, making it easier to retrieve and interact with information they have seen before. DejaView records visual output, checkpoints corresponding application and file system states, and captures onscreen text with contextual information to index the record. A user can then browse and search the record for any visual information that has been previously displayed on the desktop, and revive and interact with the desktop computing state corresponding to any point in the record. DejaView introduces new, transparent operating system, display and file system virtualization techniques and novel semantic display-centric information recording, and combines them to provide its functionality without any modifications to applications, window systems, or operating system kernels. Our results demonstrate that DejaView can provide continuous low-overhead recording without any user-noticeable performance degradation, and allows users to playback, browse, search, and time-travel back to records fast enough for interactive use. This dissertation also demonstrates how DejaView's execution virtualization and recording extend beyond the desktop recorder context. We introduce a coordinated, parallel checkpoint-restart mechanism for distributed applications that minimizes synchronization overhead and uniquely supports complete checkpoint and restart of network state in a transport protocol independent manner, for both reliable and unreliable protocols. We introduce a scalable system that enables significant energy saving by migrating network state and applications off of idle hosts allowing the hosts to enter low-power suspend state, while preserving their network presence. Finally, we show how our techniques can be integrated into a commodity operating system, mainline Linux, thereby allowing the entire operating systems community to benefit from mature checkpoint-restart that is transparent, secure, reliable, efficient, and integral to the Linux kernel

Database recovery

Recovery techniques are an important aspect of database systems. They are essential to ensure that data integrity is maintained after any type of failure occurs. The recovery mechanism must be designed so that the availability and performance of the system are not unacceptably impacted by the recovery algorithms running during normal execution. On the other hand, enough information must be stored so that the database can be restored or transactions backed out in a reasonable amount of time. Concepts, techniques, and problems associated with database recovery will be presented in this thesis. The recovery issues for both centralized and distributed systems will be discussed, along with the tradeoffs of different recovery tools. The database recovery schemes in IMS/VS, DB2 and SDD-1 will be described to show approaches in existing systems

Accessing multiversion data in database transactions

Many important database applications need to access previous versions of the data set, thus requiring that the data are stored in a multiversion database and indexed with a multiversion index, such as the multiversion B+-tree (MVBT) of Becker et al. The MVBT is optimal, so that any version of the database can be accessed as efficiently as with a single-version B+-tree that is used to index only the data items of that version, but it cannot be used in a full-fledged database system because it follows a single-update model, and the update cannot be rolled back. We have redesigned the MVBT index so that a single multi-action updating transaction can operate on the index structure concurrently with multiple concurrent read-only transactions. Data items created by the transaction become part of the same version, and the transaction can roll back. We call this structure the transactional MVBT (TMVBT). The TMVBT index remains optimal even in the presence of logical key deletions. Even though deletions in a multiversion index must not physically delete the history of the data items, queries and range scans can become more efficient, if the leaf pages of the index structure are merged to retain optimality. For the general transactional setting with multiple updating transactions, we propose a multiversion database structure called the concurrent MVBT (CMVBT), which stores the updates of active transactions in a separate main-memory-resident versioned B+-tree index. A system maintenance transaction is periodically run to apply the updates of committed transactions into the TMVBT index. We show how multiple updating transactions can operate on the CMVBT index concurrently, and our recovery algorithm is based on the standard ARIES recovery algorithm. We prove that the TMVBT index is asymptotically optimal, and show that the performance of the CMVBT index in general transaction processing is on par with the performance of the time-split B+-tree (TSB-tree) of Lomet and Salzberg. The TSB-tree does not merge leaf pages and is therefore not optimal if logical data-item deletions are allowed. Our experiments show that the CMVBT outperforms the TSB-tree with range queries in the presence of deletions

Database and System Design for Emerging Storage Technologies

Emerging storage technologies offer an alternative to disk that is durable and allows faster data access. Flash memory, made popular by mobile devices, provides block access with low latency random reads. New nonvolatile memories (NVRAM) are expected in upcoming years, presenting DRAM-like performance alongside persistent storage. Whereas both technologies accelerate data accesses due to increased raw speed, used merely as disk replacements they may fail to achieve their full potentials. Flash’s asymmetric read/write access (i.e., reads execute faster than writes opens new opportunities to optimize Flash-specific access. Similarly, NVRAM’s low latency persistent accesses allow new designs for high performance failure-resistant applications. This dissertation addresses software and hardware system design for such storage technologies. First, I investigate analytics query optimization for Flash, expecting Flash’s fast random access to require new query planning. While intuition suggests scan and join selection should shift between disk and Flash, I find that query plans chosen assuming disk are already near-optimal for Flash. Second, I examine new opportunities for durable, recoverable transaction processing with NVRAM. Existing disk-based recovery mechanisms impose large software overheads, yet updating data in-place requires frequent device synchronization that limits throughput. I introduce a new design, NVRAM Group Commit, to amortize synchronization delays over many transactions, increasing throughput at some cost to transaction latency. Finally, I propose a new framework for persistent programming and memory systems to enable high performance recoverable data structures with NVRAM, extending memory consistency with persistent semantics to introduce memory persistency.PhDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107114/1/spelley_1.pd