env_open.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: env_open.so,v 1.4 2002/06/24 14:51:07 bostic Exp $])

m4_ref_title(m4_tam Applications,
    Opening the environment,, transapp/app, transapp/data_open)

m4_p([dnl
Creating transaction-protected applications using the m4_db library is
quite easy.  Applications first use m4_ref(dbenv_open) to initialize
the database environment.  Transaction-protected applications normally
require all four m4_db subsystems, so the m4_ref(DB_INIT_MPOOL),
m4_ref(DB_INIT_LOCK), m4_ref(DB_INIT_LOG), and m4_ref(DB_INIT_TXN) flags
should be specified.])

m4_p([dnl
Once the application has called m4_ref(dbenv_open), it opens its
databases within the environment.  Once the databases are opened, the
application makes changes to the databases inside of transactions.  Each
set of changes that entails a unit of work should be surrounded by the
appropriate m4_ref(txn_begin), m4_ref(txn_commit), and m4_ref(txn_abort)
calls.  The m4_db access methods will make the appropriate calls into
the Lock, Log and Memory Pool subsystems in order to guarantee
transaction semantics.  When the application is ready to exit, all
outstanding transactions should have been committed or aborted.])

m4_p([dnl
Databases accessed by a transaction must not be closed during the
transaction.  Once all outstanding transactions are finished, all open
m4_db files should be closed.  When the m4_db database files have been
closed, the environment should be closed by calling
m4_ref(dbenv_close).])

m4_p([dnl
The following code fragment creates the database environment directory
then opens the environment, running recovery.  Our m4_ref(DbEnv)
database environment handle is declared to be free-threaded using the
m4_ref(DB_THREAD) flag, and so may be used by any number of threads that
we may subsequently create.])

include(ref/transapp/env_open.cs)

m4_p([dnl
After running this initial program, we can use the m4_ref(db_stat)
utility to display the contents of the environment directory:])

m4_indent([dnl
prompt__GT__ db_stat -e -h TXNAPP
3.2.1   Environment version.
120897  Magic number.
0       Panic value.
1       References.
6       Locks granted without waiting.
0       Locks granted after waiting.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Mpool Region: 4.
264KB   Size (270336 bytes).
-1      Segment ID.
1       Locks granted without waiting.
0       Locks granted after waiting.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Log Region: 3.
96KB    Size (98304 bytes).
-1      Segment ID.
3       Locks granted without waiting.
0       Locks granted after waiting.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Lock Region: 2.
240KB   Size (245760 bytes).
-1      Segment ID.
1       Locks granted without waiting.
0       Locks granted after waiting.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Txn Region: 5.
8KB     Size (8192 bytes).
-1      Segment ID.
1       Locks granted without waiting.
0       Locks granted after waiting.])

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