upgrade.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: upgrade.so,v 10.17 2001/03/10 19:05:22 bostic Exp $])

m4_ref_title(Access Methods,
    Database upgrade, @upgrading databases, am/truncate, am/verify)

m4_p([dnl
When upgrading to a new release of m4_db, it may be necessary to upgrade
the on-disk format of already-created database files.  m4_bold([m4_db
database upgrades are done in place, and so are potentially
destructive.])  This means that if the system crashes during the upgrade
procedure, or if the upgrade procedure runs out of disk space, the
databases may be left in an inconsistent and unrecoverable state.  To
guard against failure, the procedures outlined in
m4_link(M4RELDIR/ref/upgrade/process, Upgrading m4_db installations)
should be carefully followed.  If you are not performing catastrophic
archival as part of your application upgrade process, you should at
least copy your database to archival media, verify that your archival
media is error-free and readable, and that copies of your backups are
stored offsite!])

m4_p([dnl
The actual database upgrade is done using the m4_ref(dbh_upgrade)
method, or by dumping the database using the old version of the m4_db
software and reloading it using the current version.])

m4_p([dnl
After an upgrade, m4_db applications must be recompiled to use the new
m4_db library before they can access an upgraded database.
m4_bold([There is no guarantee that applications compiled against
previous releases of m4_db will work correctly with an upgraded database
format.  Nor is there any guarantee that applications compiled against
newer releases of m4_db will work correctly with the previous database
format.]) We do guarantee that any archived database may be upgraded
using a current m4_db software release and the m4_ref(dbh_upgrade)
method, and there is no need to step-wise upgrade the database using
intermediate releases of m4_db.  Sites should consider archiving
appropriate copies of their application or application sources if they
may need to access archived databases without first upgrading them.])

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