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 10.32 2003/04/15 16:48:42 bostic Exp $])

m4_ref_title(Environment, Database environment introduction,
    introduction to database @environments, arch/utilities, env/create)

m4_p([dnl
A m4_db environment is an encapsulation of one or more databases, log
files and region files.  Region files are the shared memory areas that
contain information about the database environment such as memory pool
cache pages.  Only databases are byte-order independent and only
database files can be moved between machines of different byte orders.
Log files can be moved between machines of the same byte order.  Region
files are usually unique to a specific machine and potentially to a
specific operating system release.])

m4_p([dnl
The simplest way to administer a m4_db application environment is to
create a single m4_bold(home) directory that stores the files for the
applications that will share the environment.  The environment home
directory must be created before any m4_db applications are run.  m4_db
itself never creates the environment home directory.  The environment can
then be identified by the name of that directory.])

m4_p([dnl
An environment may be shared by any number of processes, as well as by
any number of threads within those processes.  It is possible for an
environment to include resources from other directories on the system,
and applications often choose to distribute resources to other
directories or disks for performance or other reasons.  However, by
default, the databases, shared regions (the locking, logging, memory
pool, and transaction shared memory areas) and log files will be stored
in a single directory hierarchy.])

m4_p([dnl
It is important to realize that all applications sharing a database
environment implicitly trust each other.  They have access to each
other's data as it resides in the shared regions, and they will share
resources such as buffer space and locks.  At the same time, any
applications using the same databases m4_bold(must) share an environment
if consistency is to be maintained between them.])

include(env/m4.methods)

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