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This article describes the basis of a system providing automatic migration between locations in a distributed database of data and the right to update it.
English (United States)
This text was extracted from a PDF file.
This is the abbreviated version, containing approximately
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Automatic Data Migration in Distributed Database System
This article describes the basis of a system providing automatic migration
between locations in a distributed database of data and the right to update it.
Each location consists of a transaction processor and a page processor.
The page processor sees the database as a set of pages; the interpretation of
data on these pages is carried out by an access method within the transaction
processor. The transaction processor has no knowledge of data distribution.
The page processor includes a store which holds the values of certain pages of
the database. The value of every page is held in at least one of these stores. The
page processors are connected via a teleprocessing network.
When a transaction processor reads a page, its local page processor first
accesses its local store. If the value for the page is held, this is given to the
transaction processor. Otherwise, a broadcast is made over the network
requesting the page. (We do not discuss a detailed broadcast mechanism.)
When a page processor holding the value receives the request, the page is
To avoid the "missing update" problem, a concept of originals and versions of
pages is used. When a page value is held in several locations, one of these is
the original, the others copies. If the value is held only once, this is the original.
A page value may only be updated by the location holding the original.
Ownership of the original is analogous to holding a lock. If a transaction
processor wishes to update a page which is not locally held, a broadcast for the
original is made. The holder of the o...