Database transaction schedule: Difference between revisions

Revision as of 03:24, 26 February 2024

Revision as of 03:43, 26 February 2024

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===Serial===

TheA transactionsschedule areis '''serial''' if the executed transactions are non-interleaved (i.e., a serial schedule is one in which no transaction starts until a running transaction has ended).

Schedule D is an example of a serial schedule:

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===Serializable===<!-- This section is linked from [[Concurrency control]] -->

A schedule thatis '''serializable''' if it is equivalent (in its outcome) to a serial schedule has the [[serializability]] property.

In schedule E, the order in which the actions of the transactions are executed is not the same as in D, but in the end, E gives the same result as D.

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====Conflict-serializable====

A schedule is said to be '''conflict-serializable''' when the schedule is conflict-equivalent to one or more serial schedules.

Equivalently, a schedule is conflict-serializable if and only if its [[precedence graph]] is acyclic when only committed transactions are considered. Note that if the graph is defined to also include uncommitted transactions, then cycles involving uncommitted transactions may occur without conflict serializability violation.

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A schedule is said to be commitment-ordered (commit-ordered), or commitment-order-serializable, if it obeys the [[Commitment ordering]] (CO; also commit-ordering or commit-order-serializability) schedule property. This means that the order in time of transactions' commitment events is compatible with the precedence (partial) order of the respective transactions, as induced by their schedule's acyclic precedence graph (serializability graph, conflict graph). This implies that it is also conflict-serializable. The CO property is especially effective for achieving [[Global serializability]] in distributed systems.

'''Comment:''' [[Commitment ordering]], which was discovered in 1990, is obviously not mentioned in ([[#Bern1987|Bernstein et al. 1987]]). Its correct definition appears in ([[#Weikum2001|Weikum and Vossen 2001]]), however the description thereof its related techniques and theory is partial, inaccurate, and misleading.{{According to whom|date=December 2011}} For an extensive coverage of commitment ordering and its sources see ''[[Commitment ordering]]'' and ''[[The History of Commitment Ordering]]''.

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