In this paper we present a simple and efficient method, called ARIES ( Algorithm for Recouery and Isolation Exploiting Semantics), which supports partial rollbacks of transactions, finegranularity (e.g., record) locking and recovery using write-ahead logging (WAL). We introduce the paradigm of repeating history to redo all missing updates before performing the rollbacks of the loser transactions during restart after a system failure. ARIES uses a log sequence number in each page to correlate the state of a page with respect to logged updates of that page. All updates of a transaction are logged, including those performed during rollbacks. By appropriate chaining of the log records written during rollbacks to those written during forward progress, a bounded amount of logging is ensured during rollbacks even in the face of repeated failures during restart or of nested rollbacks We deal with a variety of features that are very Important in building and operating an industrial-strength transaction processing system ARIES supports fuzzy checkpoints, selective and deferred restart, fuzzy image copies, media recovery, and high concurrency lock modes (e. g., increment /decrement) which exploit the semantics of the operations and require the ability to perform operation logging. ARIES is flexible with respect to the kinds of buffer management policies that can be implemented. It supports objects of

Several alternatives to manage large XML document collections exist, ranging from file systems over relational or other database systems to specifically tailored XML repositories. In this paper we give a tour of Natix, a database management system designed from scratch for storing and processing XML data. Contrary

Standard locking (two-phase locking with on-demand lock requests and blocking upon lock conflict) is the primary concurrency control (CC) method for centralized databases. The main source of performance degradation with standard locking is blocking, whereas transaction (txn) restarts to resolve deadlocks have a secondary effect on performance. We provide a performance analysis of standard locking that accurately estimates its performance degradation leading to thrashing. We next introduce two sets of methods to cope with its performance limitations. Restartoriented locking methods selectively abort txns to increase the level of concurrency for active txns with respect to standard locking in high-contention environments. For example, the running-priority method aborts blocked txns based on the essential blocking principle, which only allows blocking by active txns. The waitdepth-limited (WDL) method further minimizes wasted processing by basing abort decisions on the progress made by a txn. Restart waiting serves as a load-control mechanism by deferring the restart of an aborted txn until conflicting txns have left the system. These two methods have performance superior to other restartoriented

This paper describes Cricket, a new database storage system that is intended to be used as a platform for design environments and persistent programming languages. Cricket uses the memory management primitives of the Mach operating system to provide the abstraction of a shared, transactional single-level store that can be directly accessed by user applications. In this paper, we present the design and motivation for Cricket. We also present some initial performance results which show that, for its intended applications, Cricket can provide better performance than a general-purpose database storage system.

To achieve high concurrency in a database system has meant building a system that copes well with important special cases. Recent work on multilevel systems suggests a systematic way of providing high concurrency. A multi-level system using locks permits restrictive low level locks of a subtransaction to be replaced with less restrictive high level locks when a subtransaction commits, hence enhancing concurrency. This is possible because sub-transactions can be undone by executing high level compensation actions rather than by restoring a prior lower level state. We describe a recovery scheme, called Multi-Level Recovery (MLR) that logs this high level undo operation with the commit record for the subtransaction that it compensates, posting log records to only a single log. A variant of the method copes with nested transactions, and both nested and multi-level transactions can be treated in a unified fashion. Keywords: multi-level transactions, logging, recovery, hierarchical systems c...

In this paper we present a solution to the problem of concurrent operations in the R-tree, a dynamic access structure capable of storing multidimensional and spatial data. We describe the R-link tree, a variant of the R-tree that adds sibling pointers to nodes, a technique first deployed in B-link trees, to compensatefor concurrent structure modifications. The main obstacle to the use of sibling pointers is the lack of linear ordering among the keys in an R-tree; we overcome this by assigning sequence numbers to nodes that let us reconstruct the "lineage" of a node at any point in time. The search, insert and delete algorithms for R-link trees are designed to completely avoid holding locks during I/O operations and to allow concurrent modifications of the tree structure. In addition, we further describe how to achieve degree 3 consistency with an inexpensive predicate locking mechanism and demonstrate how to make R-link trees recoverable in a write-ahead logging environment. Experiment...

In this paper, three techniques to implement logical OIDs are thoroughly evaluated: hashing, B-trees and a technique called direct mapping. Among these three techniques, direct mapping is the most robust; it induces at most one page fault to map an OID, and it scales very well to large, rapidly growing databases. Furthermore, the clustering of handles that are used to map logical OIDs is studied. In particular, the performance of B-trees and direct mapping can improve significantly if the handles of objects that are frequently accessed by the same methods are clustered. For direct mapping, two placement policies are compared: linear and matrix clustering. 1 Introduction The full support of object identity is one of the most important features of object-oriented database systems [KM94]. To improve referential integrity, an object base system allocates an object identifier (OID) to every object at the time the object is created. The OID is used to identify the object uniquely and to im...

We describe a distributed index structure, in which data is distributed among multiple sites and indexes to the data are replicated over multiple sites. This permits good scalability as storage and accessing load are distributed over the sites and each site with an index replica has fast local access to the index structure, making remote requests at most for data at the leaves of the index tree. We call our method the dPi-tree because it is based on the Pi-tree. We replicate the index without the need for coherence messages. This works whether the index replica is persistent or a transient cached copy. We generalize a technique first used to provide recovery for Pi-tree indexes to independently and lazily maintain the index replicas. A further result is that each index replica is fully recoverable, an area not treated previously in replication schemes. We also show how the data in the leaves of the index can be distributed and re-distributed at very low cost. 1 Introduction 1.1 Scala...

This paper presents general algorithms for concurrency control in tree-based access methods as well as a recovery protocol and a mechanism for ensuring repeatable read. The algorithms are developed in the context of the Generalized Search Tree (GiST) data structure, an index structure supporting an extensible set of queries and data types. Although developed in a GiST context, the algorithms are generally applicable to many tree-based access methods. The concurrency control protocol is based on an extension of the link technique originally developed for B-trees, and completely avoids holding node locks during I/Os. Repeatable read isolation is achieved with a novel combination of predicate locks andtwo-phase locking of data records. To our knowledge, this is the first time that isolation issues have been addressed outside the context of B-trees. A discussion of the fundamental structural differences between Btrees and more general tree structures like GiSTs explains why the algorithms ...

ion Dal's architecture, illustrated in Figure 2, is organized in multiple layers of abstraction to support the toolkit approach discussed earlier. At the highest level, users can interact with Dal's relational manager. Below that level is what we call the heap-file/indexing layer, which provides support for fixed-length and variable-length collections, as well as template-based Locks Logs System database Database file 1 Database file 2 Database file N Process 1 user code Dal library Virtual memory of process 1 Virtual memory of process 2 System physical memory Process 2 user code Dal library Log of updates to database Checkpoint images of database Figure 1. Architecture of the Dal system. Bell LabsTechnical Journal uWinter 1997 39 indexing abstractions. In general, at this level, a user does not need to interact with individual locks or latches. (A latchis a short-term lock implemented by a high-speed mutual exclusion mechanism.) Instead, the user specifi...