Consistency in a partitioned network: a survey
ACM Computing Surveys (CSUR)
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When comparing centralized and distributed databases one of the advantages of distributed databases is said to be the greater availability of the data. Availability is defined as having access to the stored data for update and retrieval, even when some distributed sites are down due to hardware failures. We will investigate the functioning of a distributed database of which the underlying computer network may fail. A classification of transactions is given to allow an implementation of different levels of operatability. Some transactions can be guaranteed to commit in spite of a network partition, while others have to wait until the state of potential transactions in the other partitions is also known. An algorithm is given to compute a classification. Based on historics of transactions kept in the different partitions a merge of histories is computed, generating the new values for some data items when communication is re-established. Thc algorithm to compute the merge of the histories makes use of a knowledge base containing knowledge about the transactions, to decide whether to merge, delete, or delay a transaction.