Alternately, you can create a DBM::Deep handle by using Perl's built-in
tie() function. The object returned from tie() can be used to call methods,
such as lock() and unlock(). (That object can be retrieved from the tied
-variable at any time using tied() - please see L<perltie/> for more info.
+variable at any time using tied() - please see L<perltie> for more info.
my %hash;
my $db = tie %hash, "DBM::Deep", "foo.db";
=over 4
-=item * C<DBM::Deep-E<gt>TYPE_HASH>
+=item * C<<DBM::Deep->TYPE_HASH>>
-=item * C<DBM::Deep-E<gt>TYPE_ARRAY>.
+=item * C<<DBM::Deep->TYPE_ARRAY>>
=back
This only takes effect when beginning a new file. This is an optional
-parameter, and defaults to C<DBM::Deep-E<gt>TYPE_HASH>.
+parameter, and defaults to C<<DBM::Deep->TYPE_HASH>>.
=item * locking
As with hashes, you can treat any DBM::Deep object like a normal Perl array
reference. This includes inserting, removing and manipulating elements,
and the C<push()>, C<pop()>, C<shift()>, C<unshift()> and C<splice()> functions.
-The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>,
+The object must have first been created using type C<<DBM::Deep->TYPE_ARRAY>>,
or simply be a nested array reference inside a hash. Example:
my $db = DBM::Deep->new(
push @$db, "bar", "baz";
unshift @$db, "bah";
- my $last_elem = pop @$db; # baz
- my $first_elem = shift @$db; # bah
- my $second_elem = $db->[1]; # bar
+ my $last_elem = pop @$db; # baz
+ my $first_elem = shift @$db; # bah
+ my $second_elem = $db->[1]; # bar
my $num_elements = scalar @$db;
$db->clear(); # hashes or arrays
-=item * lock() / unlock()
+=item * lock() / unlock() / lock_exclusive() / lock_shared()
-q.v. Locking.
+q.v. L</LOCKING> for more info.
=item * optimize()
-Recover lost disk space. This is important to do, especially if you use
-transactions.
+This will compress the datafile so that it takes up as little space as possible.
+There is a freespace manager so that when space is freed up, it is used before
+extending the size of the datafile. But, that freespace just sits in the datafile
+unless C<optimize()> is called.
-=item * import() / export()
+=item * import()
-Data going in and out.
+Unlike simple assignment, C<import()> does not tie the right-hand side. Instead,
+a copy of your data is put into the DB. C<import()> takes either an arrayref (if
+your DB is an array) or a hashref (if your DB is a hash). C<import()> will die
+if anything else is passed in.
+
+=item * export()
+
+This returns a complete copy of the data structure at the point you do the export.
+This copy is in RAM, not on disk like the DB is.
=item * begin_work() / commit() / rollback()
These are the transactional functions. L</TRANSACTIONS> for more information.
+=item * supports( $option )
+
+This returns a boolean depending on if this instance of DBM::Dep supports
+that feature. C<$option> can be one of:
+
+=over 4
+
+=item * transactions
+
+=back
+
=back
=head2 Hashes
=head2 Explicit Locking
You can explicitly lock a database, so it remains locked for multiple
-actions. This is done by calling the C<lock()> method, and passing an
-optional lock mode argument (defaults to exclusive mode). This is particularly
-useful for things like counters, where the current value needs to be fetched,
-then incremented, then stored again.
+actions. This is done by calling the C<lock_exclusive()> method (for when you
+want to write) or the C<lock_shared()> method (for when you want to read).
+This is particularly useful for things like counters, where the current value
+needs to be fetched, then incremented, then stored again.
- $db->lock();
+ $db->lock_exclusive();
my $counter = $db->get("counter");
$counter++;
$db->put("counter", $counter);
# or...
- $db->lock();
+ $db->lock_exclusive();
$db->{counter}++;
$db->unlock();
-You can pass C<lock()> an optional argument, which specifies which mode to use
-(exclusive or shared). Use one of these two constants:
-C<DBM::Deep-E<gt>LOCK_EX> or C<DBM::Deep-E<gt>LOCK_SH>. These are passed
-directly to C<flock()>, and are the same as the constants defined in Perl's
-L<Fcntl/> module.
+=head2 Win32/Cygwin
- $db->lock( $db->LOCK_SH );
- # something here
- $db->unlock();
+Due to Win32 actually enforcing the read-only status of a shared lock, all
+locks on Win32 and cygwin are exclusive. This is because of how autovivification
+currently works. Hopefully, this will go away in a future release.
=head1 IMPORTING/EXPORTING
=head2 Examples
-Please read L<DBM::Deep::Manual/> for examples of filters.
+Please read L<DBM::Deep::Manual> for examples of filters.
=head1 ERROR HANDLING
by specifying the 'pack_size' parameter when constructing the file.
DBM::Deep->new(
- filename => $filename,
+ file => $filename,
pack_size => 'large',
);
instead of 32-bit longs. After setting these values your DB files have a
theoretical maximum size of 16 XB (exabytes).
-You can also use C<pack_size =E<gt> 'small'> in order to use 16-bit file
+You can also use C<<pack_size => 'small'>> in order to use 16-bit file
offsets.
B<Note:> Changing these values will B<NOT> work for existing database files.
=head2 Caching
-If a user is willing to assert upon opening the file that this process will be
+If a client is willing to assert upon opening the file that this process will be
the only consumer of that datafile, then there are a number of caching
possibilities that can be taken advantage of. This does, however, mean that
DBM::Deep is more vulnerable to losing data due to unflushed changes. It also
single-process. I have no idea how I'd specify this, though. Suggestions are
welcome.
-=head2 Importing using Data::Walker
-
-Right now, importing is done using C<Clone::clone()> to make a complete copy
-in memory, then tying that copy. It would be much better to use
-L<Data::Walker/> to walk the data structure instead, particularly in the case
-of large datastructures.
-
=head2 Different contention resolution mechanisms
Currently, the only contention resolution mechanism is last-write-wins. This
=item * CODE
-L<Data::Dump::Streamer/> provides a mechanism for serializing coderefs,
+L<Data::Dump::Streamer> provides a mechanism for serializing coderefs,
including saving off all closure state. This would allow for DBM::Deep to
store the code for a subroutine. Then, whenever the subroutine is read, the
code could be C<eval()>'ed into being. However, just as for SCALAR and REF,
=back
-=head2 Data::Dumper and references
+=head2 External references and transactions
-As of 1.0003, support for independent Perl datastructures was added (q.v. L</CIRCULAR REFERENCES>
-for more info). However, because DBM::Deep doesn't properly provide the same
-in-memory data-structure for a given location on disk, Data::Dumper (and
-friends) doesn't properly note this. This will be addressed in a future release.
+If you do C<<my $x = $db->{foo};>>, then start a transaction, $x will be
+referencing the database from outside the transaction. A fix for this (and other
+issues with how external references into the database) is being looked into. This
+is the skipped set of tests in t/39_singletons.t and a related issue is the focus
+of t/37_delete_edge_cases.t
=head2 File corruption
on DBM::Deep, as every element has to be fetched from disk, then stored again in
a different location. This will be addressed in a future version.
+This has been somewhat addressed so that the cost is constant, regardless of
+what is stored at those locations. So, small arrays with huge data structures in
+them are faster. But, large arrays are still large.
+
=head2 Writeonly Files
-If you pass in a filehandle to new(), you may have opened it in either a readonly or
-writeonly mode. STORE will verify that the filehandle is writable. However, there
-doesn't seem to be a good way to determine if a filehandle is readable. And, if the
-filehandle isn't readable, it's not clear what will happen. So, don't do that.
+If you pass in a filehandle to new(), you may have opened it in either a
+readonly or writeonly mode. STORE will verify that the filehandle is writable.
+However, there doesn't seem to be a good way to determine if a filehandle is
+readable. And, if the filehandle isn't readable, it's not clear what will
+happen. So, don't do that.
=head2 Assignments Within Transactions
=head1 CODE COVERAGE
-B<Devel::Cover> is used to test the code coverage of the tests. Below is the
-B<Devel::Cover> report on this distribution's test suite.
+L<Devel::Cover> is used to test the code coverage of the tests. Below is the
+L<Devel::Cover> report on this distribution's test suite.
------------------------------------------ ------ ------ ------ ------ ------
File stmt bran cond sub total
------------------------------------------ ------ ------ ------ ------ ------
- blib/lib/DBM/Deep.pm 94.5 85.0 90.5 100.0 93.6
- blib/lib/DBM/Deep/Array.pm 100.0 94.3 100.0 100.0 98.7
- blib/lib/DBM/Deep/Engine.pm 95.9 84.9 81.7 100.0 92.8
+ blib/lib/DBM/Deep.pm 97.2 90.9 83.3 100.0 95.4
+ blib/lib/DBM/Deep/Array.pm 100.0 95.7 100.0 100.0 99.0
+ blib/lib/DBM/Deep/Engine.pm 95.6 84.7 81.6 98.4 92.5
blib/lib/DBM/Deep/File.pm 97.2 81.6 66.7 100.0 91.9
blib/lib/DBM/Deep/Hash.pm 100.0 100.0 100.0 100.0 100.0
- Total 96.5 86.5 83.5 100.0 94.0
+ Total 96.7 87.5 82.2 99.2 94.1
------------------------------------------ ------ ------ ------ ------ ------
=head1 MORE INFORMATION
or send email to L<DBM-Deep@googlegroups.com>. You can also visit #dbm-deep on
irc.perl.org
-The source code repository is at L<http://svn.perl.org/modules/DBM-Deep>
+The source code repository is at L<http://github.com/robkinyon/dbm-deep>
=head1 MAINTAINERS
projects / dbsrgits/DBM-Deep.git / blobdiff