Towards Flash Disk Use in Databases - Keeping Performance While Saving Energy?
Green computing or energy saving when processing information is primarily considered a task of processor development. We, however, advocate that a holistic approach is necessary to reduce power consumption to a minimum. We explore the potential of NAND flash memory in comparison to magnetic disks for DBMS-based architectures. For this reason, we attempt to identify the IO performance of both storage types at the device level and file system interface, before we approach the most important question how DBMS applications can take advantage of the flash performance characteristics. Furthermore, based on an analysis of storage structures and related benchmark runs in our XTC system, we discuss how IO-intensive DBMS algorithms have to be adjusted to take most out of the flash technology which is entering the server area with dramatic pace. The ultimate goal is to substantially improve energy efficiency while comparable performance as in disk-based DB servers is maintained.

title: Tailor-Made Native XML Storage Structures
abstract: Automatically choosing suitable native storage structures for XML doc- uments arriving at the XML DBMS is a challenging task for its storage manager. While some of the critical parameters require pre-specification, others can be deter- mined by pre-analysis or sampling of the incoming document or by just making ex- perience-driven "educated guesses". In this paper, we discuss approaches to achieve an adaptive behavior of the storage manager to provide tailor-made native XML stor- age structures to the extent possible. 1I ntroduction The XML data model allows for a great deal of modeling flexibility with which order, op- tional and multi-valued concepts, as well as deeply nested relationships can be captured. Therefore, the resulting tree structures of natively represented XML documents exhibit large variations in breadth and depth. Furthermore, XML documents may be data-centric having relatively little 'content' stored as short text values or they may be document-cen- tric where a single content node may contain huge portions of text, e.g., an entire book in a digital library. For these reasons, it is highly advisable to equip the storage manager with the ability to select reasonable or even optimal storage structures for documents. Furthermore, two cas- es have to be considered: a document sent by a client arrives at a time—the so-called block mode, i.e., the document can be pre-parsed and analyzed before a storage structure is cho- sen—or it arrives at the DBMS interface in stream mode where fragments present, due to their size, have to be allocated in a suitable storage structure on disk before the entire "streamed" document is available for the DBMS. In the latter case, the storage manager must decide—based on imprecise structural information—on the storage structure to be chosen and, at best, can make some educated guesses based on context or sampling infor- mation.

title: An Adaptive Storage Manager for XML Documents
abstract: Effective and efficient management and manipulation of XML documents requires stable decisions at the time a document enters the XML DBMS to provide for storage structures which are adjusted to the document characteristics and which reflect the future processing needs. While some of the critical parameters require a kind of pre-specification, others can be determined by pre-analysis or sampling of the incoming document or by just making experience-driven “educated guesses”. Important parameters are related to node labeling, path synopsis, document container layout, and indexing. In this paper, we discuss approaches to achieve an adaptive behavior of the storage manager to provide tailor-made native XML storage structures to the extent possible.

title: Usage-driven storage structures for native XML databases
abstract: There are numerous and influential parameters associated with the selection of suitable native storage structures for XML documents within an XML DBMS. The most important parameters are related to node labeling, path synopsis, document container layout, indexing, and text compression. While node labeling and the presence of a path synopsis greatly determine flexibility and efficiency of the entire DBMS-internal XML processing, the remaining issues primarily address I/O demand and space consumption. In particular, text compression---considered orthogonal to the design choices affected by the other parameters---implies additional algorithmic costs for encoding/decoding during document processing. Having the vision in mind that future storage managers can autonomously figure out optimal choices for all of these parameters, we discuss how various storage options favor different usage patterns and how they can be specified beforehand to influence native XML storage options by the anticipated usages.

title: Adaptive Resource Management in a Native XDBMS
abstract: A graphite reinforced glass composite is described comprising discontinuous graphite fibers in substantially planar orientation in a glass matrix with strength and fracture toughness greater than the unreinforced glass matrix. The resulting composite has superior strength, fluid impermeability, wear resistance, failure strain and fracture toughness. In fact, the stress-strain, curve for composites of the invention resembles that of metal making it particularly suitable for a variety of moldable shapes and machinable designs.

title: Autonomous Management of Soft Indexes
abstract: In recent years the support for index tuning as pan of physical database design has gained focus in research and product development, which resulted in index and design advisors. Nevertheless, these tools provide a one-off solution for a continuous task and are not deeply integrated with the DBMS functionality by only applying the query optimizer for index recommendation and profit estimation and decoupling the decision about and execution of index configuration changes from the core system functionality. In this paper we propose an approach that continuously collects statistics for recommended indexes and based on this, repetitively solves the Index Selection Problem (lSP).A key novelty is the on-the-fly index generation during query processing implemented by new query plan operators In-dexBuildScan and SwitchPlan. Finally, we present the implementation and evaluation of the introduced concepts as part of the PostgreSQL system.

title: Integrating Low Level Symmetries into Reachability Analysis
abstract: We present three methods for the integration of symmetries into reachability analysis. Two of them lead to maximal reduction but their runtime depends on the symmetry structure. The third one works always fast but does not always yield maximal reduction.

title: Using Petri net invariants in state space construction
abstract: The linear algebraic invariant calculus is a powerful technique for the verification of Petri nets. Traditionally it is used for structural verification, i.e. for avoiding the explicit construction of a state space. In this paper, we study the use of Petri net invariants for reducing the memory resources required during state space construction. While place invariants help to reduce the amount of memory needed for each single state (without reducing the number of states as such), transition invariants can be used to reduce the number of states to be stored. Interestingly, our approach does not require computing invariants in full, let alone storing them permanently. All information we need can be deduced from an upper triangular form of the Petri net's incidence matrix. Experiments prove that the place invariant technique leads to improvements in both memory and run time costs while transition invariants lead to a space/time tradeoff that can be controlled heuristically.

title: Automated Generation of a Progress Measure for the Sweep-Line Method
abstract: In the context of Petri nets, we propose an automated construction of a progress measure which is an important pre-requisite for a state space reduction technique called the sweep-line method. Our construction is based on linear-algebraic considerations concerning the transition vectors of the Petri net under consideration.

title: LoLA: a low level analyser
abstract: With LoLA, we put recently developed state space oriented algorithms to other tool developers disposal. Providing a simple interface was a major design goal such that it is as easy as possible to integrate LoLA into tools of different application domains. LoLA supports place/transition nets. Implemented verification techniques cover standard properties (liveness, reversibility, boundedness, reachability, dead transitions, deadlocks, home states) as well as satisfiability of state predicates and CTL model checking. For satisfiability, both exhaustive search and heuristically goal oriented system execution are supported. For state space reduction, LoLA features symmetries, stubborn sets, and coverability graphs.

title: Narrowing Petri Net State Spaces Using the State Equation
abstract: Given a (possibly partially defined) state, all count vectors of transition sequences reaching that state are solutions to a corresponding Petri net state equation. We propose a search strategy where sequences corresponding to a minimal solution of the state equation are explored first. Then step by step the search space is relaxed to arbitrary count vectors. This heuristics relies on the observation that in many (though provably not in all) cases, minimal solutions of the state equation can be realized as a firing sequence. If no target state is reachable, either the state equation does not have solutions, or our search method would yield the full state space. We study the impact of the state equation on reachability, present an algorithm that exploits information from the state equation and discuss its application in stateless search as well as its combination with stubborn set reduction.