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=head1 NAME

Apache2::Translation::BDB - A provider for Apache2::Translation

=head1 SYNOPSIS

  <TranslationProvider BDB>
      BDBEnv   /path/to/directory
      ReadOnly 1
  </TranslationProvider>

  or

  $provider=Apache2::Translation::BDB->new(BDBEnv=>..., ...);

  $provider->start;
  $provider->stop;

=head1 DESCRIPTION

The C<BDB> provider implements the C<Apache2::Translation> provider interface
as documented in L<Apache2::Translation::_base>. It provides for all optional
functions.

Other than the C<DB> providers C<BDB> doesn't implement a cache.
BerkeleyDB is fast enough on its own. Neither does it monitor the timestamp
of a file on disk. Hence it doesn't need a C<version> or C<timestamp> field.

Nevertheless it implements a C<timestamp> method that can be used by external
tools to synchronize the database state with external sources.

=head2 B<Parameters>

=over 2

=item B<bdbenv /path/to/directory>

Here you can pass a directory name or a C<BerkeleyDB::Env> object. In the
latter case, the environment must be initialized with DB_INIT_MPOOL,
DB_INIT_LOCK, DB_INIT_TXN and DB_INIT_LOG. Further, you need to specify a
deadlock detection method.

If a directory is passed (the normal case) the provider initializes the
environment if it is not already set up. It creates 3 databases,
C<Apache2::Translation::BDB-id.db>, C<Apache2::Translation::BDB-keyuri.db> and
C<Apache2::Translation::BDB-extra.db>. C<Apache2::Translation::BDB-keyuri.db>
is used as an associated database for C<Apache2::Translation::BDB-id.db>.
That means it is a secondary index.

The extra database holds only the timestamp value. But the provider offers
an C<extra> method to store more information in this database.

See L<CONFIGFURATION> below for performance tuning.

=item B<readonly 1>

If set to true the databases are opened in readonly mode. Please note that
the program needs write permission to the database files even if this flag
is set.

=back

=head2 B<Additional Methods>

=over 2

=item B<parent_txn>

BerkeleyDB supports nested transactions. If you provide a parent transaction
the provider wraps its changes in a child transaction. Otherwise it works in
an unrelated transaction.

=item B<extra_db>

returns the database handle of the extra database.

=item B<extra key value>

stores and retrieves information from the extra database. If value is given
it is written as value for the key to the database.

returns the previous value of the key.

Note, the key C<\ttmstmp> is reserved.

=item B<timestamp time>

sets or retrieves the timestamp from the extra database.

=back