Database replication techniques: a three parameter classification

Abstract

Data replication is an increasingly important topic as

Managing Multiple Isolation Levels in Middleware Database Replication Protocols

“…Thus, in [21] three parameters of this kind were identified: server architecture, server interaction and transaction termination. Each one of these parameters can take two different values, generating eight different classes of protocols.…”

“…As a result of this, only two of the original eight classes identified in [21] should be surveyed as general replication protocols in this paper: those based on an update everywhere server architecture, with constant server interaction and with either voting or non-voting transaction termination.…”

“…Additionally, two schemes for such checking are possible, depending on the transaction termination alternative being chosen [21]: either a voting phase is needed in the transaction termination, or all replicas behave deterministically in the certification phase and all arrive to the same decision without needing any explicit coordination. But protocols based on voting can be divided in two different subclasses: those that are symmetrical, requiring a vote by every replica (for instance, in order to cope with unilateral abortions [16] or other sources of non-determinism), or others that rely on a delegate server 3 , who imposes its decision to the rest of replicas (this approach is referred to as weak voting replication in [22]).…”

“…The second approach consists in selecting a set of modern protocols with similar techniques and different isolation levels, defining from scratch the rules to be followed when different levels must be combined. This may be achieved when such protocols use similar solutions for the most important parameters that define a replication protocol [21]: server architecture, replica interaction, and transaction termination. The last option consists in supporting a single isolation level -the strictest one being needed-, thus requiring that all transactions were executed using such level.…”

Reviewing Amnesia Support in Database Recovery Protocols

“…According to the classification in [27], these are eager update everywhere and non-voting protocols. Concurrency control is performed by the DBMS with Strict 2PL.…”