openldap-2.4.45.rar_openldap

/*

* Copyright 2015-2017 Howard Chu, Symas Corp.

* All rights reserved.

*

* Redistribution and use in source and binary forms, with or without

* modification, are permitted only as authorized by the OpenLDAP

* Public License.

*

* A copy of this license is available in the file LICENSE in the

verbosely

documented in its own right.) After reading this page, the main

ef mdb documentation should make sense. Thanks to Bert Hubert

for creating the

<a href="https://github.com/ahupowerdns/ahutils/blob/master/lmdb-

semantics.md">

initial version</a> of this writeup.

Everything starts with an environment, created by #mdb_env_create().

Once created, this environment must also be opened with #mdb_env_open().

#mdb_env_open() gets passed a name which is interpreted as a directory

Once the environment is open, a transaction can be created within it

using #mdb_txn_begin(). Transactions may be read-write or read-only,

and read-write transactions may be nested. A transaction must only

be used by one thread at a time. Transactions are always required,

even for read-only access. The transaction provides a consistent

view of the data.

Once a transaction has been created, a database can be opened within it

using #mdb_dbi_open(). If only one database will ever be used in the

environment, a NULL can be passed as the database name. For named

databases, the #MDB_CREATE flag must be used to create the database

handles can freely be used by all subsequent transactions.

Within a transaction, #mdb_get() and #mdb_put() can store single

key/value pairs if that is all you need to do (but see \ref Cursors

below if you want to do more).

A key/value pair is expressed as two #MDB_val structures. This struct

has two fields, \c mv_size and \c mv_data. The data is a \c void pointer

to

an array of \c mv_size bytes.

Once a transaction is closed, the values can no longer be used, so

@section Cursors Cursors

To do more powerful things, we must use a cursor.

Within the transaction, a cursor can be created with #mdb_cursor_open().

With this cursor we can store/retrieve/delete (multiple) values using

#mdb_cursor_get(), #mdb_cursor_put(), and #mdb_cursor_del().

#mdb_cursor_get() positions itself depending on the cursor operation

requested, and for some operations, on the supplied key. For example,

to list all key/value pairs in a database, use operation #MDB_FIRST for

the first call to #mdb_cursor_get(), and #MDB_NEXT on subsequent calls,

cursor for you based on the \b key, or you can use operation

#MDB_CURRENT to use the current position of the cursor. Note that

\b key must then match the current position's key.

@subsection summary Summarizing the Opening

So we have a cursor in a transaction which opened a database in an

environment which is opened from a filesystem after it was

separately created.

Or, we create an environment, open it from a filesystem, create a

transaction within it, open a database within that transaction,

process opens a file multiple times. Because of this, do not