intro.so

berkeley db 4.6.21的源码。berkeley db是一个简单的数据库管理系统

m4_comment([$Id: intro.so,v 10.25 2004/09/17 19:51:50 bostic Exp $])

m4_ref_title(Access Methods,
    What are the available access methods?,
    introduction to the @access methods, intro/products, am_conf/select)

m4_p([dnl
m4_db currently offers four access methods: Btree, Hash, Queue and Recno.])

m4_section(Btree)
m4_p([dnl
The Btree access method is an implementation of a sorted, balanced tree
structure.  Searches, insertions, and deletions in the tree all take O(log
base_b N) time, where base_b is the average number of keys per page, and
N is the total number of keys stored.  Often, inserting ordered data into
Btree implementations results in pages that are only half-full.  m4_db
makes ordered (or inverse ordered) insertion the best case, resulting in
nearly full-page space utilization.])

m4_section(Hash)
m4_p([dnl
The Hash access method data structure is an implementation of Extended
Linear Hashing, as described in "Linear Hashing: A New Tool for File and
Table Addressing", Witold Litwin, m4_italic([Proceedings of the 6th
International Conference on Very Large Databases (VLDB)]), 1980.])

m4_section(Queue)
m4_p([dnl
The Queue access method stores fixed-length records with logical record
numbers as keys.  It is designed for fast inserts at the tail and has a
special cursor consume operation that deletes and returns a record from
the head of the queue.  The Queue access method uses record level locking.])

m4_section(Recno)
m4_p([dnl
The Recno access method stores both fixed and variable-length records with
logical record numbers as keys, optionally backed by a flat text (byte
stream) file.])

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