METODO PARA REPETICAO DE TRANSACAO,METODO E SISTEMA PARA USAR NO ARMAZENAMENTO,MANUTENCAO E ACESSO DE CAMPOS DE BANCOS DE DADOS,METODO DE TRANSFERENCIA,METODO PARA RECUPERAR UM BANCO DE DADOS,METODO PARA ARMAZENAR CAMPOS LONGOS E METODO PARA O GERENCIAMENTO DE CAMPOS LONGOS

摘要

A long field file, managed using log-based recovery mechanisms, contains values associated with large data set items and contains allocation information controlling long field file space. Each long field has a compact descriptor pointing to associated multi-page block(s) of data in the long field file. The descriptor is in the database record which logically contains the long field. Long field data is shadowed in the long field file during updates and changes to the descriptor and long field file allocation information are logged. During long field data value deletion or replacement, the allocation information for the corresponding space in the long field file is marked free and locked until the deleting transaction completes, thereby insuring that deletes are undoable. Support for storage, access and maintenance of long fields as logically integral components of recoverable database records is provided as well as row-level concurrency in minimization of long field data in the recovery log. Duplication in storing before and after images of long field data in the log is avoided. More efficient management of memory space freed by deletion of long field records is provided. Long field data is transferable directly without intermediate buffering including entire multi-page blocks of data and such transfer is effected with a single access to the storage device containing the data.