C. H. Papadimitriou. The Theory of Database Concurrency Control. Computer Science Press, 1986. 14  Home/Search   Document Not in Database   Summary   Related Articles   Check

....IS IX S SIX IS IX S SIX X X Table 6.1: Lock mode compatibility matrix for granular locks. The purpose of the various lock modes are shown alongside. Serializability Concepts and the Phantom Problem Transactions, locking and serializability concepts are well documented in the literature [112, 113, 55]. The phantom problem is defined as follows (from the ANSI ISO SQL 92 specifications [93, 7] Transaction T1 reads a set of data items satisfying some search condition . Transaction T2 then creates data items that satisfy T1 s search condition and commits. If T1 then repeats its scan with the ....

C. Papadimitriou. The theory of database concurrency control. Computer Science Press, 1986.

....the key concepts here is the notion of serializability, i.e. that the outcome of concurrently executed transactions is equivalent to a strictly serial execution of the transactions. Most of the protocols that guarantee serializability already found their way into textbooks more than a decade ago [2, 10, 14]. During the last decade some researchers have concentrated on defining notions weaker than serializability and developed protocols that allow a more liberal cooperation between users. For a survey on cooperating transactions and synchronization in general see [15] However, we believe that ....

....therefore talk about nodes only. 3 Protocols In this section we introduce the core protocols for synchronizing structure traversals and modifications of XML documents. We also give some more details necessary for the explanations. Generally speaking, our protocols are based on two phase locking [2, 14]. It is important to note that all core protocols require that document access starts at the root node and traverses documents top down. This requirement is relaxed in Section 5. 3.1 Lock Modes In standard two phase locking protocols for synchronizing read and write operations, we have two kinds ....

C. H. Papadimitriou. The Theory of Database Concurrency Control. Computer Science Press, 1986. 14

....Figure 1: Two seemingly correct scenarios, updating fuel amounts the executions are partially ordered and we infer distributed implementations. 2 Sample MSC Inference We motivate inference of missing scenarios using an example related to serializability in database transactions (see, e.g. [23]) Consider the following standard example, described in the setting of a nuclear power plant. Two clients, P 1 and P 2 , seek to perform remote updates on data used in the control of a nuclear power plant. In this database the variable UR controls the amount of Uranium fuel in the daily supply at ....

C. Papadimitriou. The Theory of Database Concurrency Control. Computer Science Press, 1986.

....for ordered time and not for the generalized metrics of [4] leaving this as a loose end. In between [4] and [1] we introduced the notion of higher dimensional automaton (HDA) 6] as an algebraic topological form of automata theory supporting Papadimitriou s geometric view of concurrency control [7] in terms of higherdimensional state spaces, in which mutual exclusion takes the form of a hole. At that time we were unable to answer Boris Trakhtenbrot s question after our POPL talk as to how HDAs were related to event spaces, leaving another loose end which we only recently tied up using ....

Papadimitriou, C.: The Theory of Database Concurrency Control. Computer Science Press (1986)

....of XML document collections. The development of synchronization protocols to isolate different applications has a long standing and successful history in the database community. Most of the protocols that guarantee serializability already found their way into textbooks more than a decade ago [2, 9, 14]. During the last decade some researchers concentrated on defining notions weaker than serializability and developed protocols that allow cooperation between users. For a recent survey on cooperating transactions and synchronization in general see [15] Although cooperation will play a major role ....

....to synchronize structure traversals and modifications of XML documents. We start by introducing several protocols based on two phase locking. Next, we introduce a core protocol based on timestamp ordering. Both protocols are well known and already found their way into several textbooks, e.g. [2, 14]. A novel feature of our variant of the timestamp ordering protocol is that 4 T M T M (a) TL TR TA TZ ML MR MA MZ TL TR TA TZ ML MR MA MZ (b) ....

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C. H. Papadimitriou. The Theory of Database Concurrency Control. Computer Science Press, 1986.

....global database is in a correct (consistent) state, if and only if all its component databases are in correct (consistent) states. 2.2 Effects of Local Autonomies and Indirect Conflicts In the literature of concurrency control, serializability is usually used as the correctness criterion. [2, 3] The aim is to keep the execution serializable. However, the goal is difficult to achieve in a multidatabase environment. For example, let G 11 , G 12 be two subtransactions of a global transaction G 1 , and G 21 , G 22 be two subtransactions of another global transaction G 2 , where G ij (i; j = ....

C. Papadimitriou, The Theory of Database Concurrency Control, Computer Science Press, 1986.

....with W i [x i ] When T i reads an item, it reads the value of a version written by some transaction T j , notated like: R i [x j ] Each element from I is read or written once by a given transaction. All read actions are executed before the write actions. This often justified simplification [9] renders the algorithms and their accompanying proofs much simpler. An example of the execution of transaction T i is: T i = R i [x j ]R i [y k ]W i [x i ]W i [z i ] The values of j and k depend on the history of the data items. A transaction T i has a read set RS i and a write set WS i defined ....

Papadimitriou, C.H. The theory of Database Concurrency Control. Computer Science Press, 1986.

....paradigm [6; 12] is inherently solved by this approach. 2 The formal model This section develops the schedule based formal model for dynamic actions. For a complete description, the reader is referred to [7] The notion of schedules is the basis for the well developed theory of concurrency [11]. Hadzilacos [4; 5] introduces a Herbrand semantics [3] for schedules, that allows to analyse reliability properties of schedules. However, the achievement of [5] is to formalise conditions how to commit concurrent, isolated computations. In the following, the approach of [5] is extended to ....

C. H. Papadimitriou. The Theory of Database Concurrency Control. Rockville, Computer Science Press, 1986

....performance, the e ect must be the same as if transactions were executed sequentially. Transaction throughput is a crucial issue for all databases. The common approach in practice considers con ict serializable schedules, where con icts correspond to read and write operations on database objects [8, 20]. No matter which granularity is taken for these objects pages, records or even relations occur in practice this approach rules out acceptable, but formally not serializable schedules. In order to increase the rate of concurrency multi level transactions (as a special form of nested ....

....of a global level, a local logical object level, a local level of physical objects and a page level. This is the view adopted in the DOMOCC project currently under investigation at Clausthal. The general approach to concurrency control is the use of locking protocols, especially two phase locking [20]. It will be shown how to generalize lock protocols to multi level transactions. This will ll Section 3. The major problems with this approach are transaction throughput and the possibility of deadlocks due to transactions waiting for each other to release locks. There are several algorithms for ....

C. Papadimitriou. The Theory of Database Concurrency Control . Computer Science Press, 1986.

.... reserve(A) modify(p1) write(A) reserve(A) modify(p2) write(A) reserve(B) modify(p3) write(B) reserve(B) modify(p4) write(B) Time Figure 2: Serializable schedule or concurrently with other transactions in a multi programmed system [Bernstein et al. 87; Papadimitriou 86] Let us follow up on our previous example to demonstrate the transaction concept. John and Mary are now assigned the task of fixing two bugs that were suspected to be in modules A and B. The first bug is caused by an error in procedure p1 in module A, which is called by procedure p3 in module ....

Papadimitriou, C. The Theory of Database Concurrency Control. Computer Science Press, Rochville, MD, 1986. 77

....at one extreme, to application dependent, special purpose compensating transactions, at the other extreme. We return to study the characteristics of compensating transactions in more depth after we introduce the model in the next section. 3 A Transaction Model In the classical transaction model [Pap86, BHG87] transactions are viewed as sequences of read and write operations that map consistent database states to consistent states when executed in isolation. The correctness criterion of this model is called serializability. A concurrent execution of a set of transactions is represented as 4 an ....

....not commute. Part of the orderings implied by the total order in which operations are composed to form a history are arbitrary, since only conflicting operations must be totally ordered. In essence, our equivalence notion (when restricted to database state) is similar to final state equivalence [Pap86] However, in what follows, we shall need to equate histories that are not necessarily over the same set of transactions, which is in contrast to final state equivalence (and actually to all familiar equivalence notions) A projection of a history X on an entity e is is a subsequence of X, that ....

C. Papadimitriou. The Theory of Database Concurrency Control. Computer Science Press, Rockville, Maryland, 1986.

....to a version as an alternative. Thus, the alternatives are expected to be managed by the applications themselves. When not specified 3 explicitly, the last written alternative will be regarded as being the one to which a reference is being made. Note that in the standard models (e.g. see [BHG87, Pap86] only one alternative of an entity (i.e. the standard alternative see [KS88, Pap86] is accessible. Each entity is permitted to have a set of application dependent attributes. For example, an attribute timestamp(d) for an entity d may be regarded as a temporal attribute for the entity d. ....

....themselves. When not specified 3 explicitly, the last written alternative will be regarded as being the one to which a reference is being made. Note that in the standard models (e.g. see [BHG87, Pap86] only one alternative of an entity (i.e. the standard alternative see [KS88, Pap86] is accessible. Each entity is permitted to have a set of application dependent attributes. For example, an attribute timestamp(d) for an entity d may be regarded as a temporal attribute for the entity d. Note that the semantics associated with timestamp(d) are entirely application dependent in ....

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C. Papadimitriou. The Theory of Database Concurrency Control. Computer Science Press, Rockville, Maryland, 1986.

....executing transactions in a serial order. Since these protocols and implementations, in general, yield poor performance, a significant amount of research has been done to devise methods to obtain better performance. The two most common techniques for achieving this are pipelining and concurrency [1, 2, 6, 7, 8, 9, 10, 11]. Pipelining is a method for overlapping the execution of multiple operations of a process, whereas concurrency is a method for overlapping the execution of multiple operations of different processes (a process is an execution of a sequential program, namely, an execution of a sequential operation ....

....operation R(object) We assume that the system stalls before issuing a write operation until all reads that write is dependent are performed. Hence, for any write operation a that is dependent on a read operation b, b p a. 15 3. 6 Interpretation We borrow the notion of interpretation from [7]. The interpretation of a schedule (IB i ) is specified by the program of process P i from which the schedule is originated. An interpretation of a schedule is a pair I i = D; F ) where D = fD x ; D y ; g is a set of domains, one for each entity in E; each domain is a set of values for the ....

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C. Papadimitriou, The Theory of Database Concurrency Control, Computer Science Press, 1986.

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C. H. Papadimitriou. The Theory of Database Concurrency Control. Computer Science Press, 1986. 14

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C. H. Papadimitriou. The Theory of Database Concurrency Control. Computer Science Press, 1986.

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C. Papadimitriou, "The Theory of Database Concurrency Control, Computer Science Press, 1986.

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C. Papadimitriou. The Theory of Database Concurrency Control. Computer Science Press, Rockville, Maryland, 1986.

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C. Papadimitriou. The theory of database concurrency control. Computer Science Press, 1986.

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C. Papadimitriou. The theory of database concurrency control. Computer Science Press, 1986.

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C. H. Papadimitriou. The Theory of Database Concurrency Control. Computer Science Press, 1986.

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C. Papadimitriou. The theory of database concurrency control. Computer Science Press, 1986.

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C. Papadimitriou. The Theory of Database Concurrency Control. Principles of Computer Science. Computer Science Press, Rockville, Maryland, 1986.

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C. Papadimitriou, The Theory of Database Concurrency Control, Computer Science Press, 1986.

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C.H. Papadimitriou, The theory of database concurrency control. Computer Science Press, Rockville, 1986.

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Papadimitriou, C. The Theory of Database Concurrency Control, Computer Science Press, 1986.

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