faq.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: faq.so,v 10.6 2006/05/01 15:32:01 bostic Exp $])

m4_ref_title(Environment,
    Environment FAQ, database @environment FAQ, env/remote, cam/intro)

m4_nlistbegin

m4_nlist([dnl
m4_bold([I'm using multiple processes to access an m4_db database
environment; is there any way to ensure that two processes don't run
transactional recovery at the same time, or that all processes have
exited the database environment so that recovery can be run?])

m4_p([dnl
See m4_link(M4RELDIR/ref/transapp/fail, Handling failure in
Transactional Data Store applications) and
m4_link(M4RELDIR/ref/transapp/app, Architecting Transactional Data Store
applications) for a full discussion of this topic.])])

m4_nlist([dnl
m4_bold([How can I associate application information with a m4_ref(Db)
or m4_ref(DbEnv) handle?])

m4_p([dnl
In the C API, the m4_ref(Db) and m4_ref(DbEnv) structures each contain
an "app_private" field intended to be used to reference
application-specific information.  See the m4_ref(dbh_create) and
m4_ref(dbenv_create) documentation for more information.])

m4_p([dnl
In the C++ or Java APIs, the easiest way to associate
application-specific data with a handle is to subclass the m4_refcxx(Db)
or m4_refcxx(DbEnv), for example subclassing m4_refcxx(Db) to get MyDb.
Objects of type MyDb will still have the m4_db API methods available on
them, and you can put any extra data or methods you want into the MyDb
class.  If you are using "callback" APIs that take m4_refcxx(Db) or
m4_refcxx(DbEnv) arguments (for example, m4_refcxx(dbh_set_bt_compare))
these will always be called with the m4_refcxx(Db) or m4_refcxx(DbEnv)
objects you create.  So if you always use MyDb objects, you will be able
to take the first argument to the callback function and cast it to a
MyDb (in C++, cast it to (MyDb*)).  That will allow you to access your
data members or methods.])])

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