Access Methods
Introduction
An access method (or index) facilitates retrieval of a desired record
from a relation. In Minibase, all records in a relation are stored in
a Heap File. An index consists of a collection of records of the
form <key value,rid>, where `key value' is a value for the
search key of the index, and `rid' is the id of a record
in the relation being indexed. Any number of indexes can be
defined on a relation.
Only B+ Tree
indexes are currently supported.
Minibase only supports unclustered indexes.
(In fact, dense, unclustered indexes storing
key/rid-of-data-record pairs; Alternative 2, in terms of the
text.)
Implementing clustered indexes would require major changes.
(The optimizer,
however, can correctly handle clustered vs. unclustered
indexes. Of course, this is only useful while running the optimizer
in stand-alone mode against synthetic catalogs.)
Design Decisions
All access methods are based on a common C++ base class.
A particular access method can be understood in terms of its
file structure (which determines how the pages in the index file
are organized), page structures (typical page format), and
the functionality of scans (e.g., whether range scans are
supported).
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