Restart Recovery Research Articles

Multi-objective coordinated control of regeneratively-cooled scramjet engine with two-stage kerosene injection

Aimed at diversity of hypersonic flight mission, multi-objective coordinated control of regeneratively-cooled scramjet engine with two-stage kerosene injection is discussed for guaranteeing a safe, steady and high-efficient operation. Firstly, characteristics analyses and system identification are conducted under the situation of flight Mach number 5 using unsteady 1-D model for regeneratively-cooled scramjet engine. Based on transfer functions obtained from system identification, corresponding proportional integral (PI) controllers are designed for different control objectives such as thrust, steady margin and kerosene temperature at cooling channels outlet. Secondly, different control strategies where flow rates of two stage kerosene injections are adjusted are created in different single control loops, including thrust regulation, steady margin protection, restart recovery, temperature protection and overtemperature recovery control loop. Optimal control strategy is determined ultimately in respective single control loop by analyzing merits and demerits from the perspectives of response speed and engine performance. Lastly, multi-loop coordinated control system is designed on the basis of switch rules and algorithm. Simulation results indicate that rapid responses of control system, smooth and steady switch between different loops are realized. Engine can operate steadily with high performance and recover to a safe operation state rapidly during unstart and overtemperature.

A dynamic crash recovery scheme for distributed real-time database systems

Recovery performance in the event of failures is very important for distributed real-time database systems. This paper presents a time-cognizant logging-based crash recovery scheme (TCLCRS) that aims at distributed real-time databases, which adopts a main memory database as its ground support, hi our scheme, each site maintains a real-time log for local transactions and the sub-transactions, which execute at the site, and execute local checkpointing independently. Log records are stored in non-volatile high-speed store, which is divided into four different partitions based on transaction classes. During restart recovery after a site crash, partitioned crash recovery strategy is adopted to ensure that the site can be brought up before the entire local secondary database is reloaded in main memory. The partitioned crash recovery strategy not only guarantees the internal consistency to be recovered, but also guarantee the temporal consistency and recovery of the sates of physical world influenced by uncommitted transactions. Combined with two-phase commit protocol, TCLCRS can guarantee failure atomicity of distributed real-time transactions.

B-tree concurrency control and recovery in page-server database systems

We develop new algorithms for the management of transactions in a page-shipping client-server database system in which the physical database is organized as a sparse B-tree index. Our starvation-free fine-grained locking protocol combines adaptive callbacks with key-range locking and guarantees repeatable-read-level isolation (i.e., serializability) for transactions containing any number of record insertions, record deletions, and key-range scans. Partial and total rollbacks of client transactions are performed by the client. Each structure modification such as a page split or merge is defined as an atomic action that affects only two levels of the B-tree and is logged using a single redo-only log record, so that the modification never needs to be undone during transaction rollback or restart recovery. The steal-and-no-force buffering policy is applied by the server when flushing updated pages onto disk and by the clients when shipping updated data pages to the server, while pages involved in a structure modification are forced to the server when the modification is finished. The server performs the restart recovery from client and system failures using an ARIES/CSA-based recovery protocol. Our algorithms avoid accessing stale data but allow a data page to be updated by one client transaction and read by many other client transactions simultaneously, and updates may migrate from a data page to another in structure modifications caused by other transactions while the updating transaction is still active.

Concurrency control and recovery for balanced B-link trees

In this paper we present new concurrent and recoverable B-link-tree algorithms. Unlike previous algorithms, ours maintain the balance of the B-link tree at all times, so that a logarithmic time bound for a search or an update operation is guaranteed under arbitrary sequences of record insertions and deletions. A database transaction can contain any number of operations of the form “fetch the first (or next) matching record”, “insert a record”, or “delete a record”, where database records are identified by their primary keys. Repeatable-read-level isolation for transactions is guaranteed by key-range locking. The algorithms apply the write-ahead logging (WAL) protocol and the steal and no-force buffering policies for index and data pages. Record inserts and deletes on leaf pages of a B-link tree are logged using physiological redo-undo log records. Each structure modification such as a page split or merge is made an atomic action by keeping the pages involved in the modification latched for the (short) duration of the modification and the logging of that modification; at most two B-link-tree pages are kept X-latched at a time. Each structure modification brings the B-link tree into a structurally consistent and balanced state whenever the tree was structurally consistent and balanced initially. Each structure modification is logged using a single physiological redo-only log record. Thus, a structure modification will never be undone even if the transaction that gave rise to it eventually aborts. In restart recovery, the redo pass of our ARIES-based recovery protocol will always produce a structurally consistent and balanced B-link tree, on which the database updates by backward-rolling transactions can always be undone logically, when a physical (page-oriented) undo is no longer possible.

An efficient crash recovery technique for real-time main memory database

This paper presents an efficient recovery scheme suitable for real-time main memory database. In the recovery scheme, log records are stored in non-volatile RAM which is divided into four different partitions based on transaction types. Similarly, a main memory database is divided into four partitions based data types. When the using ratio of log store area exceeds the threshold value, checkpoint procedure is triggered. During executing checkpoint procedure, some useless log records are deleted. During restart recovery after a crash, partition reloading policy is adopted to assure that critical data are reloaded and restored in advance, so that the database system can be brought up before the entire database is reloaded into main memory. Therefore down time is obviously reduced. Simulation experiments show our recovery scheme obviously improves the system performance, and does a favor to meet the deadlines of real-time transactions.

ARIES/IM: an efficient and high concurrency index management method using write-ahead logging

This paper provides a comprehensive treatment of index management in transaction systems. We present a method, called ARIESIIM (Algorithm for Recovery and Isolation Exploiting Semantics for Index Management) , for concurrency control and recovery of B + -trees. ARIES/IM guarantees serializability and uses write-ahead logging for recovery. It supports very high concurrency and good performance by (1) treating as the lock of a key the same lock as the one on the corresponding record data in a data page (e.g., at the record level), (2) not acquiring, in the interest of permitting very high concurrency, commit duration locks on index pages even during index structure modification operations (SMOs) like page splits and page deletions, and (3) allowing retrievals, inserts, and deletes to go on concurrently with SMOs. During restart recovery, any necessary redos of index changes are always performed in a page-oriented fashion (i.e., without traversing the index tree) and, during normal processing and restart recovery, whenever possible undos are performed in a page-oriented fashion. ARIES/IM permits different granularities of locking to be supported in a flexible manner. A subset of ARIES/IM has been implemented in the OS/2 Extended Edition Database Manager. Since the locking ideas of ARIES/IM have general applicability, some of them have also been implemented in SQL/DS and the VM Shared File System, even though those systems use the shadow-page technique for recovery.

Communication primitives supporting the execution of atomic actions at remote sites

A request manager is described that provides a set of communication primitives supporting the cooperation between processes requesting service and processes providing service. These communication primitives allow the initiation and termination of atomic actions at remote sites. They also maintain recoverable action state tables, which can be used to recall uncompleted actions during restart recovery. The presented request manager is a good foundation on which to develop application oriented high-level primitives as well as language level primitives. Besides a detailed description of the services offered by the request manager, the paper develops a request management protocol that, no matter what happens, insures the atomic property of actions. Evaluation nets, which are a modified form of Petri nets, are applied to describe this protocol.