7 # Multi-level database module for storing hash trees, arrays and simple
8 # key/value pairs into FTP-able, cross-platform binary database files.
10 # Type `perldoc DBM::Deep` for complete documentation.
14 # tie %db, 'DBM::Deep', 'my_database.db'; # standard tie() method
16 # my $db = new DBM::Deep( 'my_database.db' ); # preferred OO method
18 # $db->{my_scalar} = 'hello world';
19 # $db->{my_hash} = { larry => 'genius', hashes => 'fast' };
20 # $db->{my_array} = [ 1, 2, 3, time() ];
21 # $db->{my_complex} = [ 'hello', { perl => 'rules' }, 42, 99 ];
22 # push @{$db->{my_array}}, 'another value';
23 # my @key_list = keys %{$db->{my_hash}};
24 # print "This module " . $db->{my_complex}->[1]->{perl} . "!\n";
27 # (c) 2002-2006 Joseph Huckaby. All Rights Reserved.
28 # This program is free software; you can redistribute it and/or
29 # modify it under the same terms as Perl itself.
34 use Fcntl qw( :DEFAULT :flock :seek );
38 use DBM::Deep::Engine;
40 use vars qw( $VERSION );
41 $VERSION = q(0.99_01);
44 # Set to 4 and 'N' for 32-bit offset tags (default). Theoretical limit of 4 GB per file.
45 # (Perl must be compiled with largefile support for files > 2 GB)
47 # Set to 8 and 'Q' for 64-bit offsets. Theoretical limit of 16 XB per file.
48 # (Perl must be compiled with largefile and 64-bit long support)
54 # Set to 4 and 'N' for 32-bit data length prefixes. Limit of 4 GB for each key/value.
55 # Upgrading this is possible (see above) but probably not necessary. If you need
56 # more than 4 GB for a single key or value, this module is really not for you :-)
58 #my $DATA_LENGTH_SIZE = 4;
59 #my $DATA_LENGTH_PACK = 'N';
60 our ($LONG_SIZE, $LONG_PACK, $DATA_LENGTH_SIZE, $DATA_LENGTH_PACK);
63 # Maximum number of buckets per list before another level of indexing is done.
64 # Increase this value for slightly greater speed, but larger database files.
65 # DO NOT decrease this value below 16, due to risk of recursive reindex overrun.
70 # Better not adjust anything below here, unless you're me :-)
74 # Setup digest function for keys
76 our ($DIGEST_FUNC, $HASH_SIZE);
77 #my $DIGEST_FUNC = \&Digest::MD5::md5;
80 # Precalculate index and bucket sizes based on values above.
83 our ($INDEX_SIZE, $BUCKET_SIZE, $BUCKET_LIST_SIZE);
90 # Setup file and tag signatures. These should never change.
92 sub SIG_FILE () { 'DPDB' }
93 sub SIG_HASH () { 'H' }
94 sub SIG_ARRAY () { 'A' }
95 sub SIG_SCALAR () { 'S' }
96 sub SIG_NULL () { 'N' }
97 sub SIG_DATA () { 'D' }
98 sub SIG_INDEX () { 'I' }
99 sub SIG_BLIST () { 'B' }
100 sub SIG_SIZE () { 1 }
103 # Setup constants for users to pass to new()
105 sub TYPE_HASH () { SIG_HASH }
106 sub TYPE_ARRAY () { SIG_ARRAY }
107 sub TYPE_SCALAR () { SIG_SCALAR }
113 if (scalar(@_) > 1) {
115 $proto->_throw_error( "Odd number of parameters to " . (caller(1))[2] );
119 elsif ( ref $_[0] ) {
120 unless ( eval { local $SIG{'__DIE__'}; %{$_[0]} || 1 } ) {
121 $proto->_throw_error( "Not a hashref in args to " . (caller(1))[2] );
126 $args = { file => shift };
134 # Class constructor method for Perl OO interface.
135 # Calls tie() and returns blessed reference to tied hash or array,
136 # providing a hybrid OO/tie interface.
139 my $args = $class->_get_args( @_ );
142 # Check if we want a tied hash or array.
145 if (defined($args->{type}) && $args->{type} eq TYPE_ARRAY) {
146 $class = 'DBM::Deep::Array';
147 require DBM::Deep::Array;
148 tie @$self, $class, %$args;
151 $class = 'DBM::Deep::Hash';
152 require DBM::Deep::Hash;
153 tie %$self, $class, %$args;
156 return bless $self, $class;
161 # Setup $self and bless into this class.
166 # These are the defaults to be optionally overridden below
169 base_offset => length(SIG_FILE),
170 engine => 'DBM::Deep::Engine',
173 foreach my $param ( keys %$self ) {
174 next unless exists $args->{$param};
175 $self->{$param} = delete $args->{$param}
178 # locking implicitly enables autoflush
179 if ($args->{locking}) { $args->{autoflush} = 1; }
181 $self->{root} = exists $args->{root}
183 : DBM::Deep::_::Root->new( $args );
185 if (!defined($self->_fh)) { $self->{engine}->open( $self ); }
192 require DBM::Deep::Hash;
193 return DBM::Deep::Hash->TIEHASH( @_ );
198 require DBM::Deep::Array;
199 return DBM::Deep::Array->TIEARRAY( @_ );
202 #XXX Unneeded now ...
210 my $self = $_[0]->_get_self;
211 close $self->_root->{fh} if $self->_root->{fh};
212 $self->_root->{fh} = undef;
217 # Given offset, signature and content, create tag and write to disk
219 my ($self, $offset, $sig, $content) = @_;
220 my $size = length($content);
224 seek($fh, $offset + $self->_root->{file_offset}, SEEK_SET);
225 print( $fh $sig . pack($DATA_LENGTH_PACK, $size) . $content );
227 if ($offset == $self->_root->{end}) {
228 $self->_root->{end} += SIG_SIZE + $DATA_LENGTH_SIZE + $size;
234 offset => $offset + SIG_SIZE + $DATA_LENGTH_SIZE,
241 # Given offset, load single tag and return signature, size and data
248 seek($fh, $offset + $self->_root->{file_offset}, SEEK_SET);
249 if (eof $fh) { return undef; }
252 read( $fh, $b, SIG_SIZE + $DATA_LENGTH_SIZE );
253 my ($sig, $size) = unpack( "A $DATA_LENGTH_PACK", $b );
256 read( $fh, $buffer, $size);
261 offset => $offset + SIG_SIZE + $DATA_LENGTH_SIZE,
268 # Given index tag, lookup single entry in index and return .
271 my ($tag, $index) = @_;
273 my $location = unpack($LONG_PACK, substr($tag->{content}, $index * $LONG_SIZE, $LONG_SIZE) );
274 if (!$location) { return; }
276 return $self->_load_tag( $location );
281 # Adds one key/value pair to bucket list, given offset, MD5 digest of key,
282 # plain (undigested) key and value.
285 my ($tag, $md5, $plain_key, $value) = @_;
286 my $keys = $tag->{content};
290 my $root = $self->_root;
292 my $is_dbm_deep = eval { local $SIG{'__DIE__'}; $value->isa( 'DBM::Deep' ) };
293 my $internal_ref = $is_dbm_deep && ($value->_root eq $root);
298 # Iterate through buckets, seeing if this is a new entry or a replace.
300 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
301 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
304 # Found empty bucket (end of list). Populate and exit loop.
308 $location = $internal_ref
309 ? $value->_base_offset
312 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $root->{file_offset}, SEEK_SET);
313 print( $fh $md5 . pack($LONG_PACK, $location) );
317 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
320 # Found existing bucket with same key. Replace with new value.
325 $location = $value->_base_offset;
326 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $root->{file_offset}, SEEK_SET);
327 print( $fh $md5 . pack($LONG_PACK, $location) );
331 seek($fh, $subloc + SIG_SIZE + $root->{file_offset}, SEEK_SET);
333 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
336 # If value is a hash, array, or raw value with equal or less size, we can
337 # reuse the same content area of the database. Otherwise, we have to create
338 # a new content area at the EOF.
341 my $r = Scalar::Util::reftype( $value ) || '';
342 if ( $r eq 'HASH' || $r eq 'ARRAY' ) {
343 $actual_length = $INDEX_SIZE;
345 # if autobless is enabled, must also take into consideration
346 # the class name, as it is stored along with key/value.
347 if ( $root->{autobless} ) {
348 my $value_class = Scalar::Util::blessed($value);
349 if ( defined $value_class && !$value->isa('DBM::Deep') ) {
350 $actual_length += length($value_class);
354 else { $actual_length = length($value); }
356 if ($actual_length <= $size) {
360 $location = $root->{end};
361 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $HASH_SIZE + $root->{file_offset}, SEEK_SET);
362 print( $fh pack($LONG_PACK, $location) );
370 # If this is an internal reference, return now.
371 # No need to write value or plain key
378 # If bucket didn't fit into list, split into a new index level
381 seek($fh, $tag->{ref_loc} + $root->{file_offset}, SEEK_SET);
382 print( $fh pack($LONG_PACK, $root->{end}) );
384 my $index_tag = $self->_create_tag($root->{end}, SIG_INDEX, chr(0) x $INDEX_SIZE);
387 $keys .= $md5 . pack($LONG_PACK, 0);
389 for (my $i=0; $i<=$MAX_BUCKETS; $i++) {
390 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
392 my $old_subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
393 my $num = ord(substr($key, $tag->{ch} + 1, 1));
395 if ($offsets[$num]) {
396 my $offset = $offsets[$num] + SIG_SIZE + $DATA_LENGTH_SIZE;
397 seek($fh, $offset + $root->{file_offset}, SEEK_SET);
399 read( $fh, $subkeys, $BUCKET_LIST_SIZE);
401 for (my $k=0; $k<$MAX_BUCKETS; $k++) {
402 my $subloc = unpack($LONG_PACK, substr($subkeys, ($k * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
404 seek($fh, $offset + ($k * $BUCKET_SIZE) + $root->{file_offset}, SEEK_SET);
405 print( $fh $key . pack($LONG_PACK, $old_subloc || $root->{end}) );
411 $offsets[$num] = $root->{end};
412 seek($fh, $index_tag->{offset} + ($num * $LONG_SIZE) + $root->{file_offset}, SEEK_SET);
413 print( $fh pack($LONG_PACK, $root->{end}) );
415 my $blist_tag = $self->_create_tag($root->{end}, SIG_BLIST, chr(0) x $BUCKET_LIST_SIZE);
417 seek($fh, $blist_tag->{offset} + $root->{file_offset}, SEEK_SET);
418 print( $fh $key . pack($LONG_PACK, $old_subloc || $root->{end}) );
423 $location ||= $root->{end};
424 } # re-index bucket list
427 # Seek to content area and store signature, value and plaintext key
431 seek($fh, $location + $root->{file_offset}, SEEK_SET);
434 # Write signature based on content type, set content length and write actual value.
436 my $r = Scalar::Util::reftype($value) || '';
438 print( $fh TYPE_HASH );
439 print( $fh pack($DATA_LENGTH_PACK, $INDEX_SIZE) . chr(0) x $INDEX_SIZE );
440 $content_length = $INDEX_SIZE;
442 elsif ($r eq 'ARRAY') {
443 print( $fh TYPE_ARRAY );
444 print( $fh pack($DATA_LENGTH_PACK, $INDEX_SIZE) . chr(0) x $INDEX_SIZE );
445 $content_length = $INDEX_SIZE;
447 elsif (!defined($value)) {
448 print( $fh SIG_NULL );
449 print( $fh pack($DATA_LENGTH_PACK, 0) );
453 print( $fh SIG_DATA );
454 print( $fh pack($DATA_LENGTH_PACK, length($value)) . $value );
455 $content_length = length($value);
459 # Plain key is stored AFTER value, as keys are typically fetched less often.
461 print( $fh pack($DATA_LENGTH_PACK, length($plain_key)) . $plain_key );
464 # If value is blessed, preserve class name
466 if ( $root->{autobless} ) {
467 my $value_class = Scalar::Util::blessed($value);
468 if ( defined $value_class && $value_class ne 'DBM::Deep' ) {
470 # Blessed ref -- will restore later
473 print( $fh pack($DATA_LENGTH_PACK, length($value_class)) . $value_class );
474 $content_length += 1;
475 $content_length += $DATA_LENGTH_SIZE + length($value_class);
479 $content_length += 1;
484 # If this is a new content area, advance EOF counter
486 if ($location == $root->{end}) {
487 $root->{end} += SIG_SIZE;
488 $root->{end} += $DATA_LENGTH_SIZE + $content_length;
489 $root->{end} += $DATA_LENGTH_SIZE + length($plain_key);
493 # If content is a hash or array, create new child DBM::Deep object and
494 # pass each key or element to it.
497 my $branch = DBM::Deep->new(
499 base_offset => $location,
502 foreach my $key (keys %{$value}) {
503 $branch->STORE( $key, $value->{$key} );
506 elsif ($r eq 'ARRAY') {
507 my $branch = DBM::Deep->new(
509 base_offset => $location,
513 foreach my $element (@{$value}) {
514 $branch->STORE( $index, $element );
522 return $self->_throw_error("Fatal error: indexing failed -- possibly due to corruption in file");
525 sub _get_bucket_value {
527 # Fetch single value given tag and MD5 digested key.
530 my ($tag, $md5) = @_;
531 my $keys = $tag->{content};
536 # Iterate through buckets, looking for a key match
539 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
540 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
541 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
545 # Hit end of list, no match
550 if ( $md5 ne $key ) {
555 # Found match -- seek to offset and read signature
558 seek($fh, $subloc + $self->_root->{file_offset}, SEEK_SET);
559 read( $fh, $signature, SIG_SIZE);
562 # If value is a hash or array, return new DBM::Deep object with correct offset
564 if (($signature eq TYPE_HASH) || ($signature eq TYPE_ARRAY)) {
565 my $obj = DBM::Deep->new(
567 base_offset => $subloc,
571 if ($self->_root->{autobless}) {
573 # Skip over value and plain key to see if object needs
576 seek($fh, $DATA_LENGTH_SIZE + $INDEX_SIZE, SEEK_CUR);
579 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
580 if ($size) { seek($fh, $size, SEEK_CUR); }
583 read( $fh, $bless_bit, 1);
584 if (ord($bless_bit)) {
586 # Yes, object needs to be re-blessed
589 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
590 if ($size) { read( $fh, $class_name, $size); }
591 if ($class_name) { $obj = bless( $obj, $class_name ); }
599 # Otherwise return actual value
601 elsif ($signature eq SIG_DATA) {
604 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
605 if ($size) { read( $fh, $value, $size); }
610 # Key exists, but content is null
620 # Delete single key/value pair given tag and MD5 digested key.
623 my ($tag, $md5) = @_;
624 my $keys = $tag->{content};
629 # Iterate through buckets, looking for a key match
632 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
633 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
634 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
638 # Hit end of list, no match
643 if ( $md5 ne $key ) {
648 # Matched key -- delete bucket and return
650 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $self->_root->{file_offset}, SEEK_SET);
651 print( $fh substr($keys, ($i+1) * $BUCKET_SIZE ) );
652 print( $fh chr(0) x $BUCKET_SIZE );
662 # Check existence of single key given tag and MD5 digested key.
665 my ($tag, $md5) = @_;
666 my $keys = $tag->{content};
669 # Iterate through buckets, looking for a key match
672 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
673 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
674 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
678 # Hit end of list, no match
683 if ( $md5 ne $key ) {
688 # Matched key -- return true
696 sub _find_bucket_list {
698 # Locate offset for bucket list, given digested key
704 # Locate offset for bucket list using digest index system
707 my $tag = $self->_load_tag($self->_base_offset);
708 if (!$tag) { return; }
710 while ($tag->{signature} ne SIG_BLIST) {
711 $tag = $self->_index_lookup($tag, ord(substr($md5, $ch, 1)));
712 if (!$tag) { return; }
719 sub _traverse_index {
721 # Scan index and recursively step into deeper levels, looking for next key.
723 my ($self, $offset, $ch, $force_return_next) = @_;
724 $force_return_next = undef unless $force_return_next;
726 my $tag = $self->_load_tag( $offset );
730 if ($tag->{signature} ne SIG_BLIST) {
731 my $content = $tag->{content};
733 if ($self->{return_next}) { $start = 0; }
734 else { $start = ord(substr($self->{prev_md5}, $ch, 1)); }
736 for (my $index = $start; $index < 256; $index++) {
737 my $subloc = unpack($LONG_PACK, substr($content, $index * $LONG_SIZE, $LONG_SIZE) );
739 my $result = $self->_traverse_index( $subloc, $ch + 1, $force_return_next );
740 if (defined($result)) { return $result; }
744 $self->{return_next} = 1;
747 elsif ($tag->{signature} eq SIG_BLIST) {
748 my $keys = $tag->{content};
749 if ($force_return_next) { $self->{return_next} = 1; }
752 # Iterate through buckets, looking for a key match
754 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
755 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
756 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
760 # End of bucket list -- return to outer loop
762 $self->{return_next} = 1;
765 elsif ($key eq $self->{prev_md5}) {
767 # Located previous key -- return next one found
769 $self->{return_next} = 1;
772 elsif ($self->{return_next}) {
774 # Seek to bucket location and skip over signature
776 seek($fh, $subloc + SIG_SIZE + $self->_root->{file_offset}, SEEK_SET);
779 # Skip over value to get to plain key
782 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
783 if ($size) { seek($fh, $size, SEEK_CUR); }
786 # Read in plain key and return as scalar
789 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
790 if ($size) { read( $fh, $plain_key, $size); }
796 $self->{return_next} = 1;
797 } # tag is a bucket list
804 # Locate next key, given digested previous one
806 my $self = $_[0]->_get_self;
808 $self->{prev_md5} = $_[1] ? $_[1] : undef;
809 $self->{return_next} = 0;
812 # If the previous key was not specifed, start at the top and
813 # return the first one found.
815 if (!$self->{prev_md5}) {
816 $self->{prev_md5} = chr(0) x $HASH_SIZE;
817 $self->{return_next} = 1;
820 return $self->_traverse_index( $self->_base_offset, 0 );
825 # If db locking is set, flock() the db file. If called multiple
826 # times before unlock(), then the same number of unlocks() must
827 # be called before the lock is released.
829 my $self = $_[0]->_get_self;
831 $type = LOCK_EX unless defined $type;
833 if (!defined($self->_fh)) { return; }
835 if ($self->_root->{locking}) {
836 if (!$self->_root->{locked}) {
837 flock($self->_fh, $type);
839 # refresh end counter in case file has changed size
840 my @stats = stat($self->_root->{file});
841 $self->_root->{end} = $stats[7];
843 # double-check file inode, in case another process
844 # has optimize()d our file while we were waiting.
845 if ($stats[1] != $self->_root->{inode}) {
846 $self->{engine}->open($self); # re-open
847 flock($self->_fh, $type); # re-lock
848 $self->_root->{end} = (stat($self->_fh))[7]; # re-end
851 $self->_root->{locked}++;
861 # If db locking is set, unlock the db file. See note in lock()
862 # regarding calling lock() multiple times.
864 my $self = $_[0]->_get_self;
866 if (!defined($self->_fh)) { return; }
868 if ($self->_root->{locking} && $self->_root->{locked} > 0) {
869 $self->_root->{locked}--;
870 if (!$self->_root->{locked}) { flock($self->_fh, LOCK_UN); }
879 my $self = shift->_get_self;
880 my ($spot, $value) = @_;
885 elsif ( eval { local $SIG{__DIE__}; $value->isa( 'DBM::Deep' ) } ) {
886 my $type = $value->_type;
887 ${$spot} = $type eq TYPE_HASH ? {} : [];
888 $value->_copy_node( ${$spot} );
891 my $r = Scalar::Util::reftype( $value );
892 my $c = Scalar::Util::blessed( $value );
893 if ( $r eq 'ARRAY' ) {
894 ${$spot} = [ @{$value} ];
897 ${$spot} = { %{$value} };
899 ${$spot} = bless ${$spot}, $c
908 # Copy single level of keys or elements to new DB handle.
909 # Recurse for nested structures
911 my $self = shift->_get_self;
914 if ($self->_type eq TYPE_HASH) {
915 my $key = $self->first_key();
917 my $value = $self->get($key);
918 $self->_copy_value( \$db_temp->{$key}, $value );
919 $key = $self->next_key($key);
923 my $length = $self->length();
924 for (my $index = 0; $index < $length; $index++) {
925 my $value = $self->get($index);
926 $self->_copy_value( \$db_temp->[$index], $value );
935 # Recursively export into standard Perl hashes and arrays.
937 my $self = $_[0]->_get_self;
940 if ($self->_type eq TYPE_HASH) { $temp = {}; }
941 elsif ($self->_type eq TYPE_ARRAY) { $temp = []; }
944 $self->_copy_node( $temp );
952 # Recursively import Perl hash/array structure
954 #XXX This use of ref() seems to be ok
955 if (!ref($_[0])) { return; } # Perl calls import() on use -- ignore
957 my $self = $_[0]->_get_self;
960 #XXX This use of ref() seems to be ok
963 # struct is not a reference, so just import based on our type
967 if ($self->_type eq TYPE_HASH) { $struct = {@_}; }
968 elsif ($self->_type eq TYPE_ARRAY) { $struct = [@_]; }
971 my $r = Scalar::Util::reftype($struct) || '';
972 if ($r eq "HASH" && $self->_type eq TYPE_HASH) {
973 foreach my $key (keys %$struct) { $self->put($key, $struct->{$key}); }
975 elsif ($r eq "ARRAY" && $self->_type eq TYPE_ARRAY) {
976 $self->push( @$struct );
979 return $self->_throw_error("Cannot import: type mismatch");
987 # Rebuild entire database into new file, then move
988 # it back on top of original.
990 my $self = $_[0]->_get_self;
992 #XXX Need to create a new test for this
993 # if ($self->_root->{links} > 1) {
994 # return $self->_throw_error("Cannot optimize: reference count is greater than 1");
997 my $db_temp = DBM::Deep->new(
998 file => $self->_root->{file} . '.tmp',
1002 return $self->_throw_error("Cannot optimize: failed to open temp file: $!");
1006 $self->_copy_node( $db_temp );
1010 # Attempt to copy user, group and permissions over to new file
1012 my @stats = stat($self->_fh);
1013 my $perms = $stats[2] & 07777;
1014 my $uid = $stats[4];
1015 my $gid = $stats[5];
1016 chown( $uid, $gid, $self->_root->{file} . '.tmp' );
1017 chmod( $perms, $self->_root->{file} . '.tmp' );
1019 # q.v. perlport for more information on this variable
1020 if ( $^O eq 'MSWin32' || $^O eq 'cygwin' ) {
1022 # Potential race condition when optmizing on Win32 with locking.
1023 # The Windows filesystem requires that the filehandle be closed
1024 # before it is overwritten with rename(). This could be redone
1031 if (!rename $self->_root->{file} . '.tmp', $self->_root->{file}) {
1032 unlink $self->_root->{file} . '.tmp';
1034 return $self->_throw_error("Optimize failed: Cannot copy temp file over original: $!");
1039 $self->{engine}->open($self);
1046 # Make copy of object and return
1048 my $self = $_[0]->_get_self;
1050 return DBM::Deep->new(
1051 type => $self->_type,
1052 base_offset => $self->_base_offset,
1053 root => $self->_root
1058 my %is_legal_filter = map {
1061 store_key store_value
1062 fetch_key fetch_value
1067 # Setup filter function for storing or fetching the key or value
1069 my $self = $_[0]->_get_self;
1070 my $type = lc $_[1];
1071 my $func = $_[2] ? $_[2] : undef;
1073 if ( $is_legal_filter{$type} ) {
1074 $self->_root->{"filter_$type"} = $func;
1088 # Get access to the root structure
1090 my $self = $_[0]->_get_self;
1091 return $self->{root};
1096 # Get access to the raw fh
1098 #XXX It will be useful, though, when we split out HASH and ARRAY
1099 my $self = $_[0]->_get_self;
1100 return $self->_root->{fh};
1105 # Get type of current node (TYPE_HASH or TYPE_ARRAY)
1107 my $self = $_[0]->_get_self;
1108 return $self->{type};
1113 # Get base_offset of current node (TYPE_HASH or TYPE_ARRAY)
1115 my $self = $_[0]->_get_self;
1116 return $self->{base_offset};
1124 die "DBM::Deep: $_[1]\n";
1127 sub _precalc_sizes {
1129 # Precalculate index, bucket and bucket list sizes
1132 #XXX I don't like this ...
1133 set_pack() unless defined $LONG_SIZE;
1135 $INDEX_SIZE = 256 * $LONG_SIZE;
1136 $BUCKET_SIZE = $HASH_SIZE + $LONG_SIZE;
1137 $BUCKET_LIST_SIZE = $MAX_BUCKETS * $BUCKET_SIZE;
1142 # Set pack/unpack modes (see file header for more)
1144 my ($long_s, $long_p, $data_s, $data_p) = @_;
1146 $LONG_SIZE = $long_s ? $long_s : 4;
1147 $LONG_PACK = $long_p ? $long_p : 'N';
1149 $DATA_LENGTH_SIZE = $data_s ? $data_s : 4;
1150 $DATA_LENGTH_PACK = $data_p ? $data_p : 'N';
1157 # Set key digest function (default is MD5)
1159 my ($digest_func, $hash_size) = @_;
1161 $DIGEST_FUNC = $digest_func ? $digest_func : \&Digest::MD5::md5;
1162 $HASH_SIZE = $hash_size ? $hash_size : 16;
1169 (O_WRONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0);
1174 # (O_RDONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0);
1178 # tie() methods (hashes and arrays)
1183 # Store single hash key/value or array element in database.
1185 my $self = $_[0]->_get_self;
1188 # User may be storing a hash, in which case we do not want it run
1189 # through the filtering system
1190 my $value = ($self->_root->{filter_store_value} && !ref($_[2]))
1191 ? $self->_root->{filter_store_value}->($_[2])
1194 my $md5 = $DIGEST_FUNC->($key);
1196 unless ( _is_writable( $self->_fh ) ) {
1197 $self->_throw_error( 'Cannot write to a readonly filehandle' );
1201 # Request exclusive lock for writing
1203 $self->lock( LOCK_EX );
1205 my $fh = $self->_fh;
1208 # Locate offset for bucket list using digest index system
1210 my $tag = $self->_load_tag($self->_base_offset);
1212 $tag = $self->_create_tag($self->_base_offset, SIG_INDEX, chr(0) x $INDEX_SIZE);
1216 while ($tag->{signature} ne SIG_BLIST) {
1217 my $num = ord(substr($md5, $ch, 1));
1219 my $ref_loc = $tag->{offset} + ($num * $LONG_SIZE);
1220 my $new_tag = $self->_index_lookup($tag, $num);
1223 seek($fh, $ref_loc + $self->_root->{file_offset}, SEEK_SET);
1224 print( $fh pack($LONG_PACK, $self->_root->{end}) );
1226 $tag = $self->_create_tag($self->_root->{end}, SIG_BLIST, chr(0) x $BUCKET_LIST_SIZE);
1228 $tag->{ref_loc} = $ref_loc;
1236 $tag->{ref_loc} = $ref_loc;
1243 # Add key/value to bucket list
1245 my $result = $self->_add_bucket( $tag, $md5, $key, $value );
1254 # Fetch single value or element given plain key or array index
1256 my $self = shift->_get_self;
1259 my $md5 = $DIGEST_FUNC->($key);
1262 # Request shared lock for reading
1264 $self->lock( LOCK_SH );
1266 my $tag = $self->_find_bucket_list( $md5 );
1273 # Get value from bucket list
1275 my $result = $self->_get_bucket_value( $tag, $md5 );
1279 #XXX What is ref() checking here?
1280 #YYY Filters only apply on scalar values, so the ref check is making
1281 #YYY sure the fetched bucket is a scalar, not a child hash or array.
1282 return ($result && !ref($result) && $self->_root->{filter_fetch_value})
1283 ? $self->_root->{filter_fetch_value}->($result)
1289 # Delete single key/value pair or element given plain key or array index
1291 my $self = $_[0]->_get_self;
1294 my $md5 = $DIGEST_FUNC->($key);
1297 # Request exclusive lock for writing
1299 $self->lock( LOCK_EX );
1301 my $tag = $self->_find_bucket_list( $md5 );
1310 my $value = $self->_get_bucket_value( $tag, $md5 );
1311 if ($value && !ref($value) && $self->_root->{filter_fetch_value}) {
1312 $value = $self->_root->{filter_fetch_value}->($value);
1315 my $result = $self->_delete_bucket( $tag, $md5 );
1318 # If this object is an array and the key deleted was on the end of the stack,
1319 # decrement the length variable.
1329 # Check if a single key or element exists given plain key or array index
1331 my $self = $_[0]->_get_self;
1334 my $md5 = $DIGEST_FUNC->($key);
1337 # Request shared lock for reading
1339 $self->lock( LOCK_SH );
1341 my $tag = $self->_find_bucket_list( $md5 );
1344 # For some reason, the built-in exists() function returns '' for false
1352 # Check if bucket exists and return 1 or ''
1354 my $result = $self->_bucket_exists( $tag, $md5 ) || '';
1363 # Clear all keys from hash, or all elements from array.
1365 my $self = $_[0]->_get_self;
1368 # Request exclusive lock for writing
1370 $self->lock( LOCK_EX );
1372 my $fh = $self->_fh;
1374 seek($fh, $self->_base_offset + $self->_root->{file_offset}, SEEK_SET);
1380 $self->_create_tag($self->_base_offset, $self->_type, chr(0) x $INDEX_SIZE);
1388 # Public method aliases
1390 sub put { (shift)->STORE( @_ ) }
1391 sub store { (shift)->STORE( @_ ) }
1392 sub get { (shift)->FETCH( @_ ) }
1393 sub fetch { (shift)->FETCH( @_ ) }
1394 sub delete { (shift)->DELETE( @_ ) }
1395 sub exists { (shift)->EXISTS( @_ ) }
1396 sub clear { (shift)->CLEAR( @_ ) }
1398 package DBM::Deep::_::Root;
1412 filter_store_key => undef,
1413 filter_store_value => undef,
1414 filter_fetch_key => undef,
1415 filter_fetch_value => undef,
1421 if ( $self->{fh} && !$self->{file_offset} ) {
1422 $self->{file_offset} = tell( $self->{fh} );
1430 return unless $self;
1432 close $self->{fh} if $self->{fh};
1443 DBM::Deep - A pure perl multi-level hash/array DBM
1448 my $db = DBM::Deep->new( "foo.db" );
1450 $db->{key} = 'value'; # tie() style
1453 $db->put('key' => 'value'); # OO style
1454 print $db->get('key');
1456 # true multi-level support
1457 $db->{my_complex} = [
1458 'hello', { perl => 'rules' },
1464 A unique flat-file database module, written in pure perl. True
1465 multi-level hash/array support (unlike MLDBM, which is faked), hybrid
1466 OO / tie() interface, cross-platform FTPable files, and quite fast. Can
1467 handle millions of keys and unlimited hash levels without significant
1468 slow-down. Written from the ground-up in pure perl -- this is NOT a
1469 wrapper around a C-based DBM. Out-of-the-box compatibility with Unix,
1470 Mac OS X and Windows.
1474 Hopefully you are using Perl's excellent CPAN module, which will download
1475 and install the module for you. If not, get the tarball, and run these
1487 Construction can be done OO-style (which is the recommended way), or using
1488 Perl's tie() function. Both are examined here.
1490 =head2 OO CONSTRUCTION
1492 The recommended way to construct a DBM::Deep object is to use the new()
1493 method, which gets you a blessed, tied hash or array reference.
1495 my $db = DBM::Deep->new( "foo.db" );
1497 This opens a new database handle, mapped to the file "foo.db". If this
1498 file does not exist, it will automatically be created. DB files are
1499 opened in "r+" (read/write) mode, and the type of object returned is a
1500 hash, unless otherwise specified (see L<OPTIONS> below).
1502 You can pass a number of options to the constructor to specify things like
1503 locking, autoflush, etc. This is done by passing an inline hash:
1505 my $db = DBM::Deep->new(
1511 Notice that the filename is now specified I<inside> the hash with
1512 the "file" parameter, as opposed to being the sole argument to the
1513 constructor. This is required if any options are specified.
1514 See L<OPTIONS> below for the complete list.
1518 You can also start with an array instead of a hash. For this, you must
1519 specify the C<type> parameter:
1521 my $db = DBM::Deep->new(
1523 type => DBM::Deep->TYPE_ARRAY
1526 B<Note:> Specifing the C<type> parameter only takes effect when beginning
1527 a new DB file. If you create a DBM::Deep object with an existing file, the
1528 C<type> will be loaded from the file header, and an error will be thrown if
1529 the wrong type is passed in.
1531 =head2 TIE CONSTRUCTION
1533 Alternately, you can create a DBM::Deep handle by using Perl's built-in
1534 tie() function. The object returned from tie() can be used to call methods,
1535 such as lock() and unlock(), but cannot be used to assign to the DBM::Deep
1536 file (as expected with most tie'd objects).
1539 my $db = tie %hash, "DBM::Deep", "foo.db";
1542 my $db = tie @array, "DBM::Deep", "bar.db";
1544 As with the OO constructor, you can replace the DB filename parameter with
1545 a hash containing one or more options (see L<OPTIONS> just below for the
1548 tie %hash, "DBM::Deep", {
1556 There are a number of options that can be passed in when constructing your
1557 DBM::Deep objects. These apply to both the OO- and tie- based approaches.
1563 Filename of the DB file to link the handle to. You can pass a full absolute
1564 filesystem path, partial path, or a plain filename if the file is in the
1565 current working directory. This is a required parameter (though q.v. fh).
1569 If you want, you can pass in the fh instead of the file. This is most useful for doing
1572 my $db = DBM::Deep->new( { fh => \*DATA } );
1574 You are responsible for making sure that the fh has been opened appropriately for your
1575 needs. If you open it read-only and attempt to write, an exception will be thrown. If you
1576 open it write-only or append-only, an exception will be thrown immediately as DBM::Deep
1577 needs to read from the fh.
1581 This is the offset within the file that the DBM::Deep db starts. Most of the time, you will
1582 not need to set this. However, it's there if you want it.
1584 If you pass in fh and do not set this, it will be set appropriately.
1588 This parameter specifies what type of object to create, a hash or array. Use
1589 one of these two constants: C<DBM::Deep-E<gt>TYPE_HASH> or C<DBM::Deep-E<gt>TYPE_ARRAY>.
1590 This only takes effect when beginning a new file. This is an optional
1591 parameter, and defaults to C<DBM::Deep-E<gt>TYPE_HASH>.
1595 Specifies whether locking is to be enabled. DBM::Deep uses Perl's Fnctl flock()
1596 function to lock the database in exclusive mode for writes, and shared mode for
1597 reads. Pass any true value to enable. This affects the base DB handle I<and
1598 any child hashes or arrays> that use the same DB file. This is an optional
1599 parameter, and defaults to 0 (disabled). See L<LOCKING> below for more.
1603 Specifies whether autoflush is to be enabled on the underlying filehandle.
1604 This obviously slows down write operations, but is required if you may have
1605 multiple processes accessing the same DB file (also consider enable I<locking>).
1606 Pass any true value to enable. This is an optional parameter, and defaults to 0
1611 If I<autobless> mode is enabled, DBM::Deep will preserve blessed hashes, and
1612 restore them when fetched. This is an B<experimental> feature, and does have
1613 side-effects. Basically, when hashes are re-blessed into their original
1614 classes, they are no longer blessed into the DBM::Deep class! So you won't be
1615 able to call any DBM::Deep methods on them. You have been warned.
1616 This is an optional parameter, and defaults to 0 (disabled).
1620 See L<FILTERS> below.
1624 Setting I<debug> mode will make all errors non-fatal, dump them out to
1625 STDERR, and continue on. This is for debugging purposes only, and probably
1626 not what you want. This is an optional parameter, and defaults to 0 (disabled).
1628 B<NOTE>: This parameter is considered deprecated and should not be used anymore.
1632 =head1 TIE INTERFACE
1634 With DBM::Deep you can access your databases using Perl's standard hash/array
1635 syntax. Because all DBM::Deep objects are I<tied> to hashes or arrays, you can
1636 treat them as such. DBM::Deep will intercept all reads/writes and direct them
1637 to the right place -- the DB file. This has nothing to do with the
1638 L<TIE CONSTRUCTION> section above. This simply tells you how to use DBM::Deep
1639 using regular hashes and arrays, rather than calling functions like C<get()>
1640 and C<put()> (although those work too). It is entirely up to you how to want
1641 to access your databases.
1645 You can treat any DBM::Deep object like a normal Perl hash reference. Add keys,
1646 or even nested hashes (or arrays) using standard Perl syntax:
1648 my $db = DBM::Deep->new( "foo.db" );
1650 $db->{mykey} = "myvalue";
1652 $db->{myhash}->{subkey} = "subvalue";
1654 print $db->{myhash}->{subkey} . "\n";
1656 You can even step through hash keys using the normal Perl C<keys()> function:
1658 foreach my $key (keys %$db) {
1659 print "$key: " . $db->{$key} . "\n";
1662 Remember that Perl's C<keys()> function extracts I<every> key from the hash and
1663 pushes them onto an array, all before the loop even begins. If you have an
1664 extra large hash, this may exhaust Perl's memory. Instead, consider using
1665 Perl's C<each()> function, which pulls keys/values one at a time, using very
1668 while (my ($key, $value) = each %$db) {
1669 print "$key: $value\n";
1672 Please note that when using C<each()>, you should always pass a direct
1673 hash reference, not a lookup. Meaning, you should B<never> do this:
1676 while (my ($key, $value) = each %{$db->{foo}}) { # BAD
1678 This causes an infinite loop, because for each iteration, Perl is calling
1679 FETCH() on the $db handle, resulting in a "new" hash for foo every time, so
1680 it effectively keeps returning the first key over and over again. Instead,
1681 assign a temporary variable to C<$db->{foo}>, then pass that to each().
1685 As with hashes, you can treat any DBM::Deep object like a normal Perl array
1686 reference. This includes inserting, removing and manipulating elements,
1687 and the C<push()>, C<pop()>, C<shift()>, C<unshift()> and C<splice()> functions.
1688 The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>,
1689 or simply be a nested array reference inside a hash. Example:
1691 my $db = DBM::Deep->new(
1692 file => "foo-array.db",
1693 type => DBM::Deep->TYPE_ARRAY
1697 push @$db, "bar", "baz";
1698 unshift @$db, "bah";
1700 my $last_elem = pop @$db; # baz
1701 my $first_elem = shift @$db; # bah
1702 my $second_elem = $db->[1]; # bar
1704 my $num_elements = scalar @$db;
1708 In addition to the I<tie()> interface, you can also use a standard OO interface
1709 to manipulate all aspects of DBM::Deep databases. Each type of object (hash or
1710 array) has its own methods, but both types share the following common methods:
1711 C<put()>, C<get()>, C<exists()>, C<delete()> and C<clear()>.
1715 =item * new() / clone()
1717 These are the constructor and copy-functions.
1719 =item * put() / store()
1721 Stores a new hash key/value pair, or sets an array element value. Takes two
1722 arguments, the hash key or array index, and the new value. The value can be
1723 a scalar, hash ref or array ref. Returns true on success, false on failure.
1725 $db->put("foo", "bar"); # for hashes
1726 $db->put(1, "bar"); # for arrays
1728 =item * get() / fetch()
1730 Fetches the value of a hash key or array element. Takes one argument: the hash
1731 key or array index. Returns a scalar, hash ref or array ref, depending on the
1734 my $value = $db->get("foo"); # for hashes
1735 my $value = $db->get(1); # for arrays
1739 Checks if a hash key or array index exists. Takes one argument: the hash key
1740 or array index. Returns true if it exists, false if not.
1742 if ($db->exists("foo")) { print "yay!\n"; } # for hashes
1743 if ($db->exists(1)) { print "yay!\n"; } # for arrays
1747 Deletes one hash key/value pair or array element. Takes one argument: the hash
1748 key or array index. Returns true on success, false if not found. For arrays,
1749 the remaining elements located after the deleted element are NOT moved over.
1750 The deleted element is essentially just undefined, which is exactly how Perl's
1751 internal arrays work. Please note that the space occupied by the deleted
1752 key/value or element is B<not> reused again -- see L<UNUSED SPACE RECOVERY>
1753 below for details and workarounds.
1755 $db->delete("foo"); # for hashes
1756 $db->delete(1); # for arrays
1760 Deletes B<all> hash keys or array elements. Takes no arguments. No return
1761 value. Please note that the space occupied by the deleted keys/values or
1762 elements is B<not> reused again -- see L<UNUSED SPACE RECOVERY> below for
1763 details and workarounds.
1765 $db->clear(); # hashes or arrays
1767 =item * lock() / unlock()
1773 Recover lost disk space.
1775 =item * import() / export()
1777 Data going in and out.
1779 =item * set_digest() / set_pack() / set_filter()
1781 q.v. adjusting the interal parameters.
1787 For hashes, DBM::Deep supports all the common methods described above, and the
1788 following additional methods: C<first_key()> and C<next_key()>.
1794 Returns the "first" key in the hash. As with built-in Perl hashes, keys are
1795 fetched in an undefined order (which appears random). Takes no arguments,
1796 returns the key as a scalar value.
1798 my $key = $db->first_key();
1802 Returns the "next" key in the hash, given the previous one as the sole argument.
1803 Returns undef if there are no more keys to be fetched.
1805 $key = $db->next_key($key);
1809 Here are some examples of using hashes:
1811 my $db = DBM::Deep->new( "foo.db" );
1813 $db->put("foo", "bar");
1814 print "foo: " . $db->get("foo") . "\n";
1816 $db->put("baz", {}); # new child hash ref
1817 $db->get("baz")->put("buz", "biz");
1818 print "buz: " . $db->get("baz")->get("buz") . "\n";
1820 my $key = $db->first_key();
1822 print "$key: " . $db->get($key) . "\n";
1823 $key = $db->next_key($key);
1826 if ($db->exists("foo")) { $db->delete("foo"); }
1830 For arrays, DBM::Deep supports all the common methods described above, and the
1831 following additional methods: C<length()>, C<push()>, C<pop()>, C<shift()>,
1832 C<unshift()> and C<splice()>.
1838 Returns the number of elements in the array. Takes no arguments.
1840 my $len = $db->length();
1844 Adds one or more elements onto the end of the array. Accepts scalars, hash
1845 refs or array refs. No return value.
1847 $db->push("foo", "bar", {});
1851 Fetches the last element in the array, and deletes it. Takes no arguments.
1852 Returns undef if array is empty. Returns the element value.
1854 my $elem = $db->pop();
1858 Fetches the first element in the array, deletes it, then shifts all the
1859 remaining elements over to take up the space. Returns the element value. This
1860 method is not recommended with large arrays -- see L<LARGE ARRAYS> below for
1863 my $elem = $db->shift();
1867 Inserts one or more elements onto the beginning of the array, shifting all
1868 existing elements over to make room. Accepts scalars, hash refs or array refs.
1869 No return value. This method is not recommended with large arrays -- see
1870 <LARGE ARRAYS> below for details.
1872 $db->unshift("foo", "bar", {});
1876 Performs exactly like Perl's built-in function of the same name. See L<perldoc
1877 -f splice> for usage -- it is too complicated to document here. This method is
1878 not recommended with large arrays -- see L<LARGE ARRAYS> below for details.
1882 Here are some examples of using arrays:
1884 my $db = DBM::Deep->new(
1886 type => DBM::Deep->TYPE_ARRAY
1889 $db->push("bar", "baz");
1890 $db->unshift("foo");
1893 my $len = $db->length();
1894 print "length: $len\n"; # 4
1896 for (my $k=0; $k<$len; $k++) {
1897 print "$k: " . $db->get($k) . "\n";
1900 $db->splice(1, 2, "biz", "baf");
1902 while (my $elem = shift @$db) {
1903 print "shifted: $elem\n";
1908 Enable automatic file locking by passing a true value to the C<locking>
1909 parameter when constructing your DBM::Deep object (see L<SETUP> above).
1911 my $db = DBM::Deep->new(
1916 This causes DBM::Deep to C<flock()> the underlying filehandle with exclusive
1917 mode for writes, and shared mode for reads. This is required if you have
1918 multiple processes accessing the same database file, to avoid file corruption.
1919 Please note that C<flock()> does NOT work for files over NFS. See L<DB OVER
1920 NFS> below for more.
1922 =head2 EXPLICIT LOCKING
1924 You can explicitly lock a database, so it remains locked for multiple
1925 transactions. This is done by calling the C<lock()> method, and passing an
1926 optional lock mode argument (defaults to exclusive mode). This is particularly
1927 useful for things like counters, where the current value needs to be fetched,
1928 then incremented, then stored again.
1931 my $counter = $db->get("counter");
1933 $db->put("counter", $counter);
1942 You can pass C<lock()> an optional argument, which specifies which mode to use
1943 (exclusive or shared). Use one of these two constants: C<DBM::Deep-E<gt>LOCK_EX>
1944 or C<DBM::Deep-E<gt>LOCK_SH>. These are passed directly to C<flock()>, and are the
1945 same as the constants defined in Perl's C<Fcntl> module.
1947 $db->lock( DBM::Deep->LOCK_SH );
1951 =head1 IMPORTING/EXPORTING
1953 You can import existing complex structures by calling the C<import()> method,
1954 and export an entire database into an in-memory structure using the C<export()>
1955 method. Both are examined here.
1959 Say you have an existing hash with nested hashes/arrays inside it. Instead of
1960 walking the structure and adding keys/elements to the database as you go,
1961 simply pass a reference to the C<import()> method. This recursively adds
1962 everything to an existing DBM::Deep object for you. Here is an example:
1967 array1 => [ "elem0", "elem1", "elem2" ],
1969 subkey1 => "subvalue1",
1970 subkey2 => "subvalue2"
1974 my $db = DBM::Deep->new( "foo.db" );
1975 $db->import( $struct );
1977 print $db->{key1} . "\n"; # prints "value1"
1979 This recursively imports the entire C<$struct> object into C<$db>, including
1980 all nested hashes and arrays. If the DBM::Deep object contains exsiting data,
1981 keys are merged with the existing ones, replacing if they already exist.
1982 The C<import()> method can be called on any database level (not just the base
1983 level), and works with both hash and array DB types.
1985 B<Note:> Make sure your existing structure has no circular references in it.
1986 These will cause an infinite loop when importing.
1990 Calling the C<export()> method on an existing DBM::Deep object will return
1991 a reference to a new in-memory copy of the database. The export is done
1992 recursively, so all nested hashes/arrays are all exported to standard Perl
1993 objects. Here is an example:
1995 my $db = DBM::Deep->new( "foo.db" );
1997 $db->{key1} = "value1";
1998 $db->{key2} = "value2";
2000 $db->{hash1}->{subkey1} = "subvalue1";
2001 $db->{hash1}->{subkey2} = "subvalue2";
2003 my $struct = $db->export();
2005 print $struct->{key1} . "\n"; # prints "value1"
2007 This makes a complete copy of the database in memory, and returns a reference
2008 to it. The C<export()> method can be called on any database level (not just
2009 the base level), and works with both hash and array DB types. Be careful of
2010 large databases -- you can store a lot more data in a DBM::Deep object than an
2011 in-memory Perl structure.
2013 B<Note:> Make sure your database has no circular references in it.
2014 These will cause an infinite loop when exporting.
2018 DBM::Deep has a number of hooks where you can specify your own Perl function
2019 to perform filtering on incoming or outgoing data. This is a perfect
2020 way to extend the engine, and implement things like real-time compression or
2021 encryption. Filtering applies to the base DB level, and all child hashes /
2022 arrays. Filter hooks can be specified when your DBM::Deep object is first
2023 constructed, or by calling the C<set_filter()> method at any time. There are
2024 four available filter hooks, described below:
2028 =item * filter_store_key
2030 This filter is called whenever a hash key is stored. It
2031 is passed the incoming key, and expected to return a transformed key.
2033 =item * filter_store_value
2035 This filter is called whenever a hash key or array element is stored. It
2036 is passed the incoming value, and expected to return a transformed value.
2038 =item * filter_fetch_key
2040 This filter is called whenever a hash key is fetched (i.e. via
2041 C<first_key()> or C<next_key()>). It is passed the transformed key,
2042 and expected to return the plain key.
2044 =item * filter_fetch_value
2046 This filter is called whenever a hash key or array element is fetched.
2047 It is passed the transformed value, and expected to return the plain value.
2051 Here are the two ways to setup a filter hook:
2053 my $db = DBM::Deep->new(
2055 filter_store_value => \&my_filter_store,
2056 filter_fetch_value => \&my_filter_fetch
2061 $db->set_filter( "filter_store_value", \&my_filter_store );
2062 $db->set_filter( "filter_fetch_value", \&my_filter_fetch );
2064 Your filter function will be called only when dealing with SCALAR keys or
2065 values. When nested hashes and arrays are being stored/fetched, filtering
2066 is bypassed. Filters are called as static functions, passed a single SCALAR
2067 argument, and expected to return a single SCALAR value. If you want to
2068 remove a filter, set the function reference to C<undef>:
2070 $db->set_filter( "filter_store_value", undef );
2072 =head2 REAL-TIME ENCRYPTION EXAMPLE
2074 Here is a working example that uses the I<Crypt::Blowfish> module to
2075 do real-time encryption / decryption of keys & values with DBM::Deep Filters.
2076 Please visit L<http://search.cpan.org/search?module=Crypt::Blowfish> for more
2077 on I<Crypt::Blowfish>. You'll also need the I<Crypt::CBC> module.
2080 use Crypt::Blowfish;
2083 my $cipher = Crypt::CBC->new({
2084 'key' => 'my secret key',
2085 'cipher' => 'Blowfish',
2087 'regenerate_key' => 0,
2088 'padding' => 'space',
2092 my $db = DBM::Deep->new(
2093 file => "foo-encrypt.db",
2094 filter_store_key => \&my_encrypt,
2095 filter_store_value => \&my_encrypt,
2096 filter_fetch_key => \&my_decrypt,
2097 filter_fetch_value => \&my_decrypt,
2100 $db->{key1} = "value1";
2101 $db->{key2} = "value2";
2102 print "key1: " . $db->{key1} . "\n";
2103 print "key2: " . $db->{key2} . "\n";
2109 return $cipher->encrypt( $_[0] );
2112 return $cipher->decrypt( $_[0] );
2115 =head2 REAL-TIME COMPRESSION EXAMPLE
2117 Here is a working example that uses the I<Compress::Zlib> module to do real-time
2118 compression / decompression of keys & values with DBM::Deep Filters.
2119 Please visit L<http://search.cpan.org/search?module=Compress::Zlib> for
2120 more on I<Compress::Zlib>.
2125 my $db = DBM::Deep->new(
2126 file => "foo-compress.db",
2127 filter_store_key => \&my_compress,
2128 filter_store_value => \&my_compress,
2129 filter_fetch_key => \&my_decompress,
2130 filter_fetch_value => \&my_decompress,
2133 $db->{key1} = "value1";
2134 $db->{key2} = "value2";
2135 print "key1: " . $db->{key1} . "\n";
2136 print "key2: " . $db->{key2} . "\n";
2142 return Compress::Zlib::memGzip( $_[0] ) ;
2145 return Compress::Zlib::memGunzip( $_[0] ) ;
2148 B<Note:> Filtering of keys only applies to hashes. Array "keys" are
2149 actually numerical index numbers, and are not filtered.
2151 =head1 ERROR HANDLING
2153 Most DBM::Deep methods return a true value for success, and call die() on
2154 failure. You can wrap calls in an eval block to catch the die.
2156 my $db = DBM::Deep->new( "foo.db" ); # create hash
2157 eval { $db->push("foo"); }; # ILLEGAL -- push is array-only call
2159 print $@; # prints error message
2161 =head1 LARGEFILE SUPPORT
2163 If you have a 64-bit system, and your Perl is compiled with both LARGEFILE
2164 and 64-bit support, you I<may> be able to create databases larger than 2 GB.
2165 DBM::Deep by default uses 32-bit file offset tags, but these can be changed
2166 by calling the static C<set_pack()> method before you do anything else.
2168 DBM::Deep::set_pack(8, 'Q');
2170 This tells DBM::Deep to pack all file offsets with 8-byte (64-bit) quad words
2171 instead of 32-bit longs. After setting these values your DB files have a
2172 theoretical maximum size of 16 XB (exabytes).
2174 B<Note:> Changing these values will B<NOT> work for existing database files.
2175 Only change this for new files, and make sure it stays set consistently
2176 throughout the file's life. If you do set these values, you can no longer
2177 access 32-bit DB files. You can, however, call C<set_pack(4, 'N')> to change
2178 back to 32-bit mode.
2180 B<Note:> I have not personally tested files > 2 GB -- all my systems have
2181 only a 32-bit Perl. However, I have received user reports that this does
2184 =head1 LOW-LEVEL ACCESS
2186 If you require low-level access to the underlying filehandle that DBM::Deep uses,
2187 you can call the C<_fh()> method, which returns the handle:
2189 my $fh = $db->_fh();
2191 This method can be called on the root level of the datbase, or any child
2192 hashes or arrays. All levels share a I<root> structure, which contains things
2193 like the filehandle, a reference counter, and all the options specified
2194 when you created the object. You can get access to this root structure by
2195 calling the C<root()> method.
2197 my $root = $db->_root();
2199 This is useful for changing options after the object has already been created,
2200 such as enabling/disabling locking, or debug modes. You can also
2201 store your own temporary user data in this structure (be wary of name
2202 collision), which is then accessible from any child hash or array.
2204 =head1 CUSTOM DIGEST ALGORITHM
2206 DBM::Deep by default uses the I<Message Digest 5> (MD5) algorithm for hashing
2207 keys. However you can override this, and use another algorithm (such as SHA-256)
2208 or even write your own. But please note that DBM::Deep currently expects zero
2209 collisions, so your algorithm has to be I<perfect>, so to speak.
2210 Collision detection may be introduced in a later version.
2214 You can specify a custom digest algorithm by calling the static C<set_digest()>
2215 function, passing a reference to a subroutine, and the length of the algorithm's
2216 hashes (in bytes). This is a global static function, which affects ALL DBM::Deep
2217 objects. Here is a working example that uses a 256-bit hash from the
2218 I<Digest::SHA256> module. Please see
2219 L<http://search.cpan.org/search?module=Digest::SHA256> for more.
2224 my $context = Digest::SHA256::new(256);
2226 DBM::Deep::set_digest( \&my_digest, 32 );
2228 my $db = DBM::Deep->new( "foo-sha.db" );
2230 $db->{key1} = "value1";
2231 $db->{key2} = "value2";
2232 print "key1: " . $db->{key1} . "\n";
2233 print "key2: " . $db->{key2} . "\n";
2239 return substr( $context->hash($_[0]), 0, 32 );
2242 B<Note:> Your returned digest strings must be B<EXACTLY> the number
2243 of bytes you specify in the C<set_digest()> function (in this case 32).
2245 =head1 CIRCULAR REFERENCES
2247 DBM::Deep has B<experimental> support for circular references. Meaning you
2248 can have a nested hash key or array element that points to a parent object.
2249 This relationship is stored in the DB file, and is preserved between sessions.
2252 my $db = DBM::Deep->new( "foo.db" );
2255 $db->{circle} = $db; # ref to self
2257 print $db->{foo} . "\n"; # prints "foo"
2258 print $db->{circle}->{foo} . "\n"; # prints "foo" again
2260 One catch is, passing the object to a function that recursively walks the
2261 object tree (such as I<Data::Dumper> or even the built-in C<optimize()> or
2262 C<export()> methods) will result in an infinite loop. The other catch is,
2263 if you fetch the I<key> of a circular reference (i.e. using the C<first_key()>
2264 or C<next_key()> methods), you will get the I<target object's key>, not the
2265 ref's key. This gets even more interesting with the above example, where
2266 the I<circle> key points to the base DB object, which technically doesn't
2267 have a key. So I made DBM::Deep return "[base]" as the key name in that
2270 =head1 CAVEATS / ISSUES / BUGS
2272 This section describes all the known issues with DBM::Deep. It you have found
2273 something that is not listed here, please send e-mail to L<jhuckaby@cpan.org>.
2275 =head2 UNUSED SPACE RECOVERY
2277 One major caveat with DBM::Deep is that space occupied by existing keys and
2278 values is not recovered when they are deleted. Meaning if you keep deleting
2279 and adding new keys, your file will continuously grow. I am working on this,
2280 but in the meantime you can call the built-in C<optimize()> method from time to
2281 time (perhaps in a crontab or something) to recover all your unused space.
2283 $db->optimize(); # returns true on success
2285 This rebuilds the ENTIRE database into a new file, then moves it on top of
2286 the original. The new file will have no unused space, thus it will take up as
2287 little disk space as possible. Please note that this operation can take
2288 a long time for large files, and you need enough disk space to temporarily hold
2289 2 copies of your DB file. The temporary file is created in the same directory
2290 as the original, named with a ".tmp" extension, and is deleted when the
2291 operation completes. Oh, and if locking is enabled, the DB is automatically
2292 locked for the entire duration of the copy.
2294 B<WARNING:> Only call optimize() on the top-level node of the database, and
2295 make sure there are no child references lying around. DBM::Deep keeps a reference
2296 counter, and if it is greater than 1, optimize() will abort and return undef.
2298 =head2 AUTOVIVIFICATION
2300 Unfortunately, autovivification doesn't work with tied hashes. This appears to
2301 be a bug in Perl's tie() system, as I<Jakob Schmidt> encountered the very same
2302 issue with his I<DWH_FIle> module (see L<http://search.cpan.org/search?module=DWH_File>),
2303 and it is also mentioned in the BUGS section for the I<MLDBM> module <see
2304 L<http://search.cpan.org/search?module=MLDBM>). Basically, on a new db file,
2307 $db->{foo}->{bar} = "hello";
2309 Since "foo" doesn't exist, you cannot add "bar" to it. You end up with "foo"
2310 being an empty hash. Try this instead, which works fine:
2312 $db->{foo} = { bar => "hello" };
2314 As of Perl 5.8.7, this bug still exists. I have walked very carefully through
2315 the execution path, and Perl indeed passes an empty hash to the STORE() method.
2316 Probably a bug in Perl.
2318 =head2 FILE CORRUPTION
2320 The current level of error handling in DBM::Deep is minimal. Files I<are> checked
2321 for a 32-bit signature when opened, but other corruption in files can cause
2322 segmentation faults. DBM::Deep may try to seek() past the end of a file, or get
2323 stuck in an infinite loop depending on the level of corruption. File write
2324 operations are not checked for failure (for speed), so if you happen to run
2325 out of disk space, DBM::Deep will probably fail in a bad way. These things will
2326 be addressed in a later version of DBM::Deep.
2330 Beware of using DB files over NFS. DBM::Deep uses flock(), which works well on local
2331 filesystems, but will NOT protect you from file corruption over NFS. I've heard
2332 about setting up your NFS server with a locking daemon, then using lockf() to
2333 lock your files, but your mileage may vary there as well. From what I
2334 understand, there is no real way to do it. However, if you need access to the
2335 underlying filehandle in DBM::Deep for using some other kind of locking scheme like
2336 lockf(), see the L<LOW-LEVEL ACCESS> section above.
2338 =head2 COPYING OBJECTS
2340 Beware of copying tied objects in Perl. Very strange things can happen.
2341 Instead, use DBM::Deep's C<clone()> method which safely copies the object and
2342 returns a new, blessed, tied hash or array to the same level in the DB.
2344 my $copy = $db->clone();
2346 B<Note>: Since clone() here is cloning the object, not the database location, any
2347 modifications to either $db or $copy will be visible in both.
2351 Beware of using C<shift()>, C<unshift()> or C<splice()> with large arrays.
2352 These functions cause every element in the array to move, which can be murder
2353 on DBM::Deep, as every element has to be fetched from disk, then stored again in
2354 a different location. This will be addressed in the forthcoming version 1.00.
2356 =head2 WRITEONLY FILES
2358 If you pass in a filehandle to new(), you may have opened it in either a readonly or
2359 writeonly mode. STORE will verify that the filehandle is writable. However, there
2360 doesn't seem to be a good way to determine if a filehandle is readable. And, if the
2361 filehandle isn't readable, it's not clear what will happen. So, don't do that.
2365 This section discusses DBM::Deep's speed and memory usage.
2369 Obviously, DBM::Deep isn't going to be as fast as some C-based DBMs, such as
2370 the almighty I<BerkeleyDB>. But it makes up for it in features like true
2371 multi-level hash/array support, and cross-platform FTPable files. Even so,
2372 DBM::Deep is still pretty fast, and the speed stays fairly consistent, even
2373 with huge databases. Here is some test data:
2375 Adding 1,000,000 keys to new DB file...
2377 At 100 keys, avg. speed is 2,703 keys/sec
2378 At 200 keys, avg. speed is 2,642 keys/sec
2379 At 300 keys, avg. speed is 2,598 keys/sec
2380 At 400 keys, avg. speed is 2,578 keys/sec
2381 At 500 keys, avg. speed is 2,722 keys/sec
2382 At 600 keys, avg. speed is 2,628 keys/sec
2383 At 700 keys, avg. speed is 2,700 keys/sec
2384 At 800 keys, avg. speed is 2,607 keys/sec
2385 At 900 keys, avg. speed is 2,190 keys/sec
2386 At 1,000 keys, avg. speed is 2,570 keys/sec
2387 At 2,000 keys, avg. speed is 2,417 keys/sec
2388 At 3,000 keys, avg. speed is 1,982 keys/sec
2389 At 4,000 keys, avg. speed is 1,568 keys/sec
2390 At 5,000 keys, avg. speed is 1,533 keys/sec
2391 At 6,000 keys, avg. speed is 1,787 keys/sec
2392 At 7,000 keys, avg. speed is 1,977 keys/sec
2393 At 8,000 keys, avg. speed is 2,028 keys/sec
2394 At 9,000 keys, avg. speed is 2,077 keys/sec
2395 At 10,000 keys, avg. speed is 2,031 keys/sec
2396 At 20,000 keys, avg. speed is 1,970 keys/sec
2397 At 30,000 keys, avg. speed is 2,050 keys/sec
2398 At 40,000 keys, avg. speed is 2,073 keys/sec
2399 At 50,000 keys, avg. speed is 1,973 keys/sec
2400 At 60,000 keys, avg. speed is 1,914 keys/sec
2401 At 70,000 keys, avg. speed is 2,091 keys/sec
2402 At 80,000 keys, avg. speed is 2,103 keys/sec
2403 At 90,000 keys, avg. speed is 1,886 keys/sec
2404 At 100,000 keys, avg. speed is 1,970 keys/sec
2405 At 200,000 keys, avg. speed is 2,053 keys/sec
2406 At 300,000 keys, avg. speed is 1,697 keys/sec
2407 At 400,000 keys, avg. speed is 1,838 keys/sec
2408 At 500,000 keys, avg. speed is 1,941 keys/sec
2409 At 600,000 keys, avg. speed is 1,930 keys/sec
2410 At 700,000 keys, avg. speed is 1,735 keys/sec
2411 At 800,000 keys, avg. speed is 1,795 keys/sec
2412 At 900,000 keys, avg. speed is 1,221 keys/sec
2413 At 1,000,000 keys, avg. speed is 1,077 keys/sec
2415 This test was performed on a PowerMac G4 1gHz running Mac OS X 10.3.2 & Perl
2416 5.8.1, with an 80GB Ultra ATA/100 HD spinning at 7200RPM. The hash keys and
2417 values were between 6 - 12 chars in length. The DB file ended up at 210MB.
2418 Run time was 12 min 3 sec.
2422 One of the great things about DBM::Deep is that it uses very little memory.
2423 Even with huge databases (1,000,000+ keys) you will not see much increased
2424 memory on your process. DBM::Deep relies solely on the filesystem for storing
2425 and fetching data. Here is output from I</usr/bin/top> before even opening a
2428 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
2429 22831 root 11 0 2716 2716 1296 R 0.0 0.2 0:07 perl
2431 Basically the process is taking 2,716K of memory. And here is the same
2432 process after storing and fetching 1,000,000 keys:
2434 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
2435 22831 root 14 0 2772 2772 1328 R 0.0 0.2 13:32 perl
2437 Notice the memory usage increased by only 56K. Test was performed on a 700mHz
2438 x86 box running Linux RedHat 7.2 & Perl 5.6.1.
2440 =head1 DB FILE FORMAT
2442 In case you were interested in the underlying DB file format, it is documented
2443 here in this section. You don't need to know this to use the module, it's just
2444 included for reference.
2448 DBM::Deep files always start with a 32-bit signature to identify the file type.
2449 This is at offset 0. The signature is "DPDB" in network byte order. This is
2450 checked for when the file is opened and an error will be thrown if it's not found.
2454 The DBM::Deep file is in a I<tagged format>, meaning each section of the file
2455 has a standard header containing the type of data, the length of data, and then
2456 the data itself. The type is a single character (1 byte), the length is a
2457 32-bit unsigned long in network byte order, and the data is, well, the data.
2458 Here is how it unfolds:
2462 Immediately after the 32-bit file signature is the I<Master Index> record.
2463 This is a standard tag header followed by 1024 bytes (in 32-bit mode) or 2048
2464 bytes (in 64-bit mode) of data. The type is I<H> for hash or I<A> for array,
2465 depending on how the DBM::Deep object was constructed.
2467 The index works by looking at a I<MD5 Hash> of the hash key (or array index
2468 number). The first 8-bit char of the MD5 signature is the offset into the
2469 index, multipled by 4 in 32-bit mode, or 8 in 64-bit mode. The value of the
2470 index element is a file offset of the next tag for the key/element in question,
2471 which is usually a I<Bucket List> tag (see below).
2473 The next tag I<could> be another index, depending on how many keys/elements
2474 exist. See L<RE-INDEXING> below for details.
2478 A I<Bucket List> is a collection of 16 MD5 hashes for keys/elements, plus
2479 file offsets to where the actual data is stored. It starts with a standard
2480 tag header, with type I<B>, and a data size of 320 bytes in 32-bit mode, or
2481 384 bytes in 64-bit mode. Each MD5 hash is stored in full (16 bytes), plus
2482 the 32-bit or 64-bit file offset for the I<Bucket> containing the actual data.
2483 When the list fills up, a I<Re-Index> operation is performed (See
2484 L<RE-INDEXING> below).
2488 A I<Bucket> is a tag containing a key/value pair (in hash mode), or a
2489 index/value pair (in array mode). It starts with a standard tag header with
2490 type I<D> for scalar data (string, binary, etc.), or it could be a nested
2491 hash (type I<H>) or array (type I<A>). The value comes just after the tag
2492 header. The size reported in the tag header is only for the value, but then,
2493 just after the value is another size (32-bit unsigned long) and then the plain
2494 key itself. Since the value is likely to be fetched more often than the plain
2495 key, I figured it would be I<slightly> faster to store the value first.
2497 If the type is I<H> (hash) or I<A> (array), the value is another I<Master Index>
2498 record for the nested structure, where the process begins all over again.
2502 After a I<Bucket List> grows to 16 records, its allocated space in the file is
2503 exhausted. Then, when another key/element comes in, the list is converted to a
2504 new index record. However, this index will look at the next char in the MD5
2505 hash, and arrange new Bucket List pointers accordingly. This process is called
2506 I<Re-Indexing>. Basically, a new index tag is created at the file EOF, and all
2507 17 (16 + new one) keys/elements are removed from the old Bucket List and
2508 inserted into the new index. Several new Bucket Lists are created in the
2509 process, as a new MD5 char from the key is being examined (it is unlikely that
2510 the keys will all share the same next char of their MD5s).
2512 Because of the way the I<MD5> algorithm works, it is impossible to tell exactly
2513 when the Bucket Lists will turn into indexes, but the first round tends to
2514 happen right around 4,000 keys. You will see a I<slight> decrease in
2515 performance here, but it picks back up pretty quick (see L<SPEED> above). Then
2516 it takes B<a lot> more keys to exhaust the next level of Bucket Lists. It's
2517 right around 900,000 keys. This process can continue nearly indefinitely --
2518 right up until the point the I<MD5> signatures start colliding with each other,
2519 and this is B<EXTREMELY> rare -- like winning the lottery 5 times in a row AND
2520 getting struck by lightning while you are walking to cash in your tickets.
2521 Theoretically, since I<MD5> hashes are 128-bit values, you I<could> have up to
2522 340,282,366,921,000,000,000,000,000,000,000,000,000 keys/elements (I believe
2523 this is 340 unodecillion, but don't quote me).
2527 When a new key/element is stored, the key (or index number) is first run through
2528 I<Digest::MD5> to get a 128-bit signature (example, in hex:
2529 b05783b0773d894396d475ced9d2f4f6). Then, the I<Master Index> record is checked
2530 for the first char of the signature (in this case I<b0>). If it does not exist,
2531 a new I<Bucket List> is created for our key (and the next 15 future keys that
2532 happen to also have I<b> as their first MD5 char). The entire MD5 is written
2533 to the I<Bucket List> along with the offset of the new I<Bucket> record (EOF at
2534 this point, unless we are replacing an existing I<Bucket>), where the actual
2535 data will be stored.
2539 Fetching an existing key/element involves getting a I<Digest::MD5> of the key
2540 (or index number), then walking along the indexes. If there are enough
2541 keys/elements in this DB level, there might be nested indexes, each linked to
2542 a particular char of the MD5. Finally, a I<Bucket List> is pointed to, which
2543 contains up to 16 full MD5 hashes. Each is checked for equality to the key in
2544 question. If we found a match, the I<Bucket> tag is loaded, where the value and
2545 plain key are stored.
2547 Fetching the plain key occurs when calling the I<first_key()> and I<next_key()>
2548 methods. In this process the indexes are walked systematically, and each key
2549 fetched in increasing MD5 order (which is why it appears random). Once the
2550 I<Bucket> is found, the value is skipped and the plain key returned instead.
2551 B<Note:> Do not count on keys being fetched as if the MD5 hashes were
2552 alphabetically sorted. This only happens on an index-level -- as soon as the
2553 I<Bucket Lists> are hit, the keys will come out in the order they went in --
2554 so it's pretty much undefined how the keys will come out -- just like Perl's
2557 =head1 CODE COVERAGE
2559 We use B<Devel::Cover> to test the code coverage of our tests, below is the
2560 B<Devel::Cover> report on this module's test suite.
2562 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2563 File stmt bran cond sub pod time total
2564 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2565 blib/lib/DBM/Deep.pm 95.2 83.8 70.0 98.2 100.0 58.0 91.0
2566 blib/lib/DBM/Deep/Array.pm 100.0 91.1 100.0 100.0 n/a 26.7 98.0
2567 blib/lib/DBM/Deep/Hash.pm 95.3 80.0 100.0 100.0 n/a 15.3 92.4
2568 Total 96.2 84.8 74.4 98.8 100.0 100.0 92.4
2569 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2571 =head1 MORE INFORMATION
2573 Check out the DBM::Deep Google Group at L<http://groups.google.com/group/DBM-Deep>
2574 or send email to L<DBM-Deep@googlegroups.com>.
2578 Joseph Huckaby, L<jhuckaby@cpan.org>
2580 Rob Kinyon, L<rkinyon@cpan.org>
2582 Special thanks to Adam Sah and Rich Gaushell! You know why :-)
2586 perltie(1), Tie::Hash(3), Digest::MD5(3), Fcntl(3), flock(2), lockf(3), nfs(5),
2587 Digest::SHA256(3), Crypt::Blowfish(3), Compress::Zlib(3)
2591 Copyright (c) 2002-2006 Joseph Huckaby. All Rights Reserved.
2592 This is free software, you may use it and distribute it under the
2593 same terms as Perl itself.