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( $self ); }
192 require DBM::Deep::Hash;
193 return DBM::Deep::Hash->TIEHASH( @_ );
198 require DBM::Deep::Array;
199 return DBM::Deep::Array->TIEARRAY( @_ );
202 #XXX Unneeded now ...
208 # Given offset, signature and content, create tag and write to disk
210 my ($self, $offset, $sig, $content) = @_;
211 my $size = length($content);
215 seek($fh, $offset + $self->_root->{file_offset}, SEEK_SET);
216 print( $fh $sig . pack($DATA_LENGTH_PACK, $size) . $content );
218 if ($offset == $self->_root->{end}) {
219 $self->_root->{end} += SIG_SIZE + $DATA_LENGTH_SIZE + $size;
225 offset => $offset + SIG_SIZE + $DATA_LENGTH_SIZE,
232 # Given offset, load single tag and return signature, size and data
239 seek($fh, $offset + $self->_root->{file_offset}, SEEK_SET);
240 if (eof $fh) { return undef; }
243 read( $fh, $b, SIG_SIZE + $DATA_LENGTH_SIZE );
244 my ($sig, $size) = unpack( "A $DATA_LENGTH_PACK", $b );
247 read( $fh, $buffer, $size);
252 offset => $offset + SIG_SIZE + $DATA_LENGTH_SIZE,
259 # Given index tag, lookup single entry in index and return .
262 my ($tag, $index) = @_;
264 my $location = unpack($LONG_PACK, substr($tag->{content}, $index * $LONG_SIZE, $LONG_SIZE) );
265 if (!$location) { return; }
267 return $self->_load_tag( $location );
272 # Adds one key/value pair to bucket list, given offset, MD5 digest of key,
273 # plain (undigested) key and value.
276 my ($tag, $md5, $plain_key, $value) = @_;
277 my $keys = $tag->{content};
281 my $root = $self->_root;
283 my $is_dbm_deep = eval { local $SIG{'__DIE__'}; $value->isa( 'DBM::Deep' ) };
284 my $internal_ref = $is_dbm_deep && ($value->_root eq $root);
289 # Iterate through buckets, seeing if this is a new entry or a replace.
291 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
292 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
295 # Found empty bucket (end of list). Populate and exit loop.
299 $location = $internal_ref
300 ? $value->_base_offset
303 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $root->{file_offset}, SEEK_SET);
304 print( $fh $md5 . pack($LONG_PACK, $location) );
308 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
311 # Found existing bucket with same key. Replace with new value.
316 $location = $value->_base_offset;
317 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $root->{file_offset}, SEEK_SET);
318 print( $fh $md5 . pack($LONG_PACK, $location) );
322 seek($fh, $subloc + SIG_SIZE + $root->{file_offset}, SEEK_SET);
324 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
327 # If value is a hash, array, or raw value with equal or less size, we can
328 # reuse the same content area of the database. Otherwise, we have to create
329 # a new content area at the EOF.
332 my $r = Scalar::Util::reftype( $value ) || '';
333 if ( $r eq 'HASH' || $r eq 'ARRAY' ) {
334 $actual_length = $INDEX_SIZE;
336 # if autobless is enabled, must also take into consideration
337 # the class name, as it is stored along with key/value.
338 if ( $root->{autobless} ) {
339 my $value_class = Scalar::Util::blessed($value);
340 if ( defined $value_class && !$value->isa('DBM::Deep') ) {
341 $actual_length += length($value_class);
345 else { $actual_length = length($value); }
347 if ($actual_length <= $size) {
351 $location = $root->{end};
352 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $HASH_SIZE + $root->{file_offset}, SEEK_SET);
353 print( $fh pack($LONG_PACK, $location) );
361 # If this is an internal reference, return now.
362 # No need to write value or plain key
369 # If bucket didn't fit into list, split into a new index level
372 seek($fh, $tag->{ref_loc} + $root->{file_offset}, SEEK_SET);
373 print( $fh pack($LONG_PACK, $root->{end}) );
375 my $index_tag = $self->_create_tag($root->{end}, SIG_INDEX, chr(0) x $INDEX_SIZE);
378 $keys .= $md5 . pack($LONG_PACK, 0);
380 for (my $i=0; $i<=$MAX_BUCKETS; $i++) {
381 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
383 my $old_subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
384 my $num = ord(substr($key, $tag->{ch} + 1, 1));
386 if ($offsets[$num]) {
387 my $offset = $offsets[$num] + SIG_SIZE + $DATA_LENGTH_SIZE;
388 seek($fh, $offset + $root->{file_offset}, SEEK_SET);
390 read( $fh, $subkeys, $BUCKET_LIST_SIZE);
392 for (my $k=0; $k<$MAX_BUCKETS; $k++) {
393 my $subloc = unpack($LONG_PACK, substr($subkeys, ($k * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
395 seek($fh, $offset + ($k * $BUCKET_SIZE) + $root->{file_offset}, SEEK_SET);
396 print( $fh $key . pack($LONG_PACK, $old_subloc || $root->{end}) );
402 $offsets[$num] = $root->{end};
403 seek($fh, $index_tag->{offset} + ($num * $LONG_SIZE) + $root->{file_offset}, SEEK_SET);
404 print( $fh pack($LONG_PACK, $root->{end}) );
406 my $blist_tag = $self->_create_tag($root->{end}, SIG_BLIST, chr(0) x $BUCKET_LIST_SIZE);
408 seek($fh, $blist_tag->{offset} + $root->{file_offset}, SEEK_SET);
409 print( $fh $key . pack($LONG_PACK, $old_subloc || $root->{end}) );
414 $location ||= $root->{end};
415 } # re-index bucket list
418 # Seek to content area and store signature, value and plaintext key
422 seek($fh, $location + $root->{file_offset}, SEEK_SET);
425 # Write signature based on content type, set content length and write actual value.
427 my $r = Scalar::Util::reftype($value) || '';
429 print( $fh TYPE_HASH );
430 print( $fh pack($DATA_LENGTH_PACK, $INDEX_SIZE) . chr(0) x $INDEX_SIZE );
431 $content_length = $INDEX_SIZE;
433 elsif ($r eq 'ARRAY') {
434 print( $fh TYPE_ARRAY );
435 print( $fh pack($DATA_LENGTH_PACK, $INDEX_SIZE) . chr(0) x $INDEX_SIZE );
436 $content_length = $INDEX_SIZE;
438 elsif (!defined($value)) {
439 print( $fh SIG_NULL );
440 print( $fh pack($DATA_LENGTH_PACK, 0) );
444 print( $fh SIG_DATA );
445 print( $fh pack($DATA_LENGTH_PACK, length($value)) . $value );
446 $content_length = length($value);
450 # Plain key is stored AFTER value, as keys are typically fetched less often.
452 print( $fh pack($DATA_LENGTH_PACK, length($plain_key)) . $plain_key );
455 # If value is blessed, preserve class name
457 if ( $root->{autobless} ) {
458 my $value_class = Scalar::Util::blessed($value);
459 if ( defined $value_class && $value_class ne 'DBM::Deep' ) {
461 # Blessed ref -- will restore later
464 print( $fh pack($DATA_LENGTH_PACK, length($value_class)) . $value_class );
465 $content_length += 1;
466 $content_length += $DATA_LENGTH_SIZE + length($value_class);
470 $content_length += 1;
475 # If this is a new content area, advance EOF counter
477 if ($location == $root->{end}) {
478 $root->{end} += SIG_SIZE;
479 $root->{end} += $DATA_LENGTH_SIZE + $content_length;
480 $root->{end} += $DATA_LENGTH_SIZE + length($plain_key);
484 # If content is a hash or array, create new child DBM::Deep object and
485 # pass each key or element to it.
488 my $branch = DBM::Deep->new(
490 base_offset => $location,
493 foreach my $key (keys %{$value}) {
494 $branch->STORE( $key, $value->{$key} );
497 elsif ($r eq 'ARRAY') {
498 my $branch = DBM::Deep->new(
500 base_offset => $location,
504 foreach my $element (@{$value}) {
505 $branch->STORE( $index, $element );
513 return $self->_throw_error("Fatal error: indexing failed -- possibly due to corruption in file");
516 sub _get_bucket_value {
518 # Fetch single value given tag and MD5 digested key.
521 my ($tag, $md5) = @_;
522 my $keys = $tag->{content};
527 # Iterate through buckets, looking for a key match
530 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
531 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
532 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
536 # Hit end of list, no match
541 if ( $md5 ne $key ) {
546 # Found match -- seek to offset and read signature
549 seek($fh, $subloc + $self->_root->{file_offset}, SEEK_SET);
550 read( $fh, $signature, SIG_SIZE);
553 # If value is a hash or array, return new DBM::Deep object with correct offset
555 if (($signature eq TYPE_HASH) || ($signature eq TYPE_ARRAY)) {
556 my $obj = DBM::Deep->new(
558 base_offset => $subloc,
562 if ($self->_root->{autobless}) {
564 # Skip over value and plain key to see if object needs
567 seek($fh, $DATA_LENGTH_SIZE + $INDEX_SIZE, SEEK_CUR);
570 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
571 if ($size) { seek($fh, $size, SEEK_CUR); }
574 read( $fh, $bless_bit, 1);
575 if (ord($bless_bit)) {
577 # Yes, object needs to be re-blessed
580 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
581 if ($size) { read( $fh, $class_name, $size); }
582 if ($class_name) { $obj = bless( $obj, $class_name ); }
590 # Otherwise return actual value
592 elsif ($signature eq SIG_DATA) {
595 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
596 if ($size) { read( $fh, $value, $size); }
601 # Key exists, but content is null
611 # Delete single key/value pair given tag and MD5 digested key.
614 my ($tag, $md5) = @_;
615 my $keys = $tag->{content};
620 # Iterate through buckets, looking for a key match
623 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
624 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
625 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
629 # Hit end of list, no match
634 if ( $md5 ne $key ) {
639 # Matched key -- delete bucket and return
641 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $self->_root->{file_offset}, SEEK_SET);
642 print( $fh substr($keys, ($i+1) * $BUCKET_SIZE ) );
643 print( $fh chr(0) x $BUCKET_SIZE );
653 # Check existence of single key given tag and MD5 digested key.
656 my ($tag, $md5) = @_;
657 my $keys = $tag->{content};
660 # Iterate through buckets, looking for a key match
663 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
664 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
665 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
669 # Hit end of list, no match
674 if ( $md5 ne $key ) {
679 # Matched key -- return true
687 sub _find_bucket_list {
689 # Locate offset for bucket list, given digested key
695 # Locate offset for bucket list using digest index system
698 my $tag = $self->_load_tag($self->_base_offset);
699 if (!$tag) { return; }
701 while ($tag->{signature} ne SIG_BLIST) {
702 $tag = $self->_index_lookup($tag, ord(substr($md5, $ch, 1)));
703 if (!$tag) { return; }
710 sub _traverse_index {
712 # Scan index and recursively step into deeper levels, looking for next key.
714 my ($self, $offset, $ch, $force_return_next) = @_;
715 $force_return_next = undef unless $force_return_next;
717 my $tag = $self->_load_tag( $offset );
721 if ($tag->{signature} ne SIG_BLIST) {
722 my $content = $tag->{content};
724 if ($self->{return_next}) { $start = 0; }
725 else { $start = ord(substr($self->{prev_md5}, $ch, 1)); }
727 for (my $index = $start; $index < 256; $index++) {
728 my $subloc = unpack($LONG_PACK, substr($content, $index * $LONG_SIZE, $LONG_SIZE) );
730 my $result = $self->_traverse_index( $subloc, $ch + 1, $force_return_next );
731 if (defined($result)) { return $result; }
735 $self->{return_next} = 1;
738 elsif ($tag->{signature} eq SIG_BLIST) {
739 my $keys = $tag->{content};
740 if ($force_return_next) { $self->{return_next} = 1; }
743 # Iterate through buckets, looking for a key match
745 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
746 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
747 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
751 # End of bucket list -- return to outer loop
753 $self->{return_next} = 1;
756 elsif ($key eq $self->{prev_md5}) {
758 # Located previous key -- return next one found
760 $self->{return_next} = 1;
763 elsif ($self->{return_next}) {
765 # Seek to bucket location and skip over signature
767 seek($fh, $subloc + SIG_SIZE + $self->_root->{file_offset}, SEEK_SET);
770 # Skip over value to get to plain key
773 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
774 if ($size) { seek($fh, $size, SEEK_CUR); }
777 # Read in plain key and return as scalar
780 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
781 if ($size) { read( $fh, $plain_key, $size); }
787 $self->{return_next} = 1;
788 } # tag is a bucket list
795 # Locate next key, given digested previous one
797 my $self = $_[0]->_get_self;
799 $self->{prev_md5} = $_[1] ? $_[1] : undef;
800 $self->{return_next} = 0;
803 # If the previous key was not specifed, start at the top and
804 # return the first one found.
806 if (!$self->{prev_md5}) {
807 $self->{prev_md5} = chr(0) x $HASH_SIZE;
808 $self->{return_next} = 1;
811 return $self->_traverse_index( $self->_base_offset, 0 );
816 # If db locking is set, flock() the db file. If called multiple
817 # times before unlock(), then the same number of unlocks() must
818 # be called before the lock is released.
820 my $self = $_[0]->_get_self;
822 $type = LOCK_EX unless defined $type;
824 if (!defined($self->_fh)) { return; }
826 if ($self->_root->{locking}) {
827 if (!$self->_root->{locked}) {
828 flock($self->_fh, $type);
830 # refresh end counter in case file has changed size
831 my @stats = stat($self->_root->{file});
832 $self->_root->{end} = $stats[7];
834 # double-check file inode, in case another process
835 # has optimize()d our file while we were waiting.
836 if ($stats[1] != $self->_root->{inode}) {
837 $self->{engine}->open( $self ); # re-open
838 flock($self->_fh, $type); # re-lock
839 $self->_root->{end} = (stat($self->_fh))[7]; # re-end
842 $self->_root->{locked}++;
852 # If db locking is set, unlock the db file. See note in lock()
853 # regarding calling lock() multiple times.
855 my $self = $_[0]->_get_self;
857 if (!defined($self->_fh)) { return; }
859 if ($self->_root->{locking} && $self->_root->{locked} > 0) {
860 $self->_root->{locked}--;
861 if (!$self->_root->{locked}) { flock($self->_fh, LOCK_UN); }
870 my $self = shift->_get_self;
871 my ($spot, $value) = @_;
876 elsif ( eval { local $SIG{__DIE__}; $value->isa( 'DBM::Deep' ) } ) {
877 my $type = $value->_type;
878 ${$spot} = $type eq TYPE_HASH ? {} : [];
879 $value->_copy_node( ${$spot} );
882 my $r = Scalar::Util::reftype( $value );
883 my $c = Scalar::Util::blessed( $value );
884 if ( $r eq 'ARRAY' ) {
885 ${$spot} = [ @{$value} ];
888 ${$spot} = { %{$value} };
890 ${$spot} = bless ${$spot}, $c
899 # Copy single level of keys or elements to new DB handle.
900 # Recurse for nested structures
902 my $self = shift->_get_self;
905 if ($self->_type eq TYPE_HASH) {
906 my $key = $self->first_key();
908 my $value = $self->get($key);
909 $self->_copy_value( \$db_temp->{$key}, $value );
910 $key = $self->next_key($key);
914 my $length = $self->length();
915 for (my $index = 0; $index < $length; $index++) {
916 my $value = $self->get($index);
917 $self->_copy_value( \$db_temp->[$index], $value );
926 # Recursively export into standard Perl hashes and arrays.
928 my $self = $_[0]->_get_self;
931 if ($self->_type eq TYPE_HASH) { $temp = {}; }
932 elsif ($self->_type eq TYPE_ARRAY) { $temp = []; }
935 $self->_copy_node( $temp );
943 # Recursively import Perl hash/array structure
945 #XXX This use of ref() seems to be ok
946 if (!ref($_[0])) { return; } # Perl calls import() on use -- ignore
948 my $self = $_[0]->_get_self;
951 #XXX This use of ref() seems to be ok
954 # struct is not a reference, so just import based on our type
958 if ($self->_type eq TYPE_HASH) { $struct = {@_}; }
959 elsif ($self->_type eq TYPE_ARRAY) { $struct = [@_]; }
962 my $r = Scalar::Util::reftype($struct) || '';
963 if ($r eq "HASH" && $self->_type eq TYPE_HASH) {
964 foreach my $key (keys %$struct) { $self->put($key, $struct->{$key}); }
966 elsif ($r eq "ARRAY" && $self->_type eq TYPE_ARRAY) {
967 $self->push( @$struct );
970 return $self->_throw_error("Cannot import: type mismatch");
978 # Rebuild entire database into new file, then move
979 # it back on top of original.
981 my $self = $_[0]->_get_self;
983 #XXX Need to create a new test for this
984 # if ($self->_root->{links} > 1) {
985 # return $self->_throw_error("Cannot optimize: reference count is greater than 1");
988 my $db_temp = DBM::Deep->new(
989 file => $self->_root->{file} . '.tmp',
993 return $self->_throw_error("Cannot optimize: failed to open temp file: $!");
997 $self->_copy_node( $db_temp );
1001 # Attempt to copy user, group and permissions over to new file
1003 my @stats = stat($self->_fh);
1004 my $perms = $stats[2] & 07777;
1005 my $uid = $stats[4];
1006 my $gid = $stats[5];
1007 chown( $uid, $gid, $self->_root->{file} . '.tmp' );
1008 chmod( $perms, $self->_root->{file} . '.tmp' );
1010 # q.v. perlport for more information on this variable
1011 if ( $^O eq 'MSWin32' || $^O eq 'cygwin' ) {
1013 # Potential race condition when optmizing on Win32 with locking.
1014 # The Windows filesystem requires that the filehandle be closed
1015 # before it is overwritten with rename(). This could be redone
1019 $self->{engine}->close( $self );
1022 if (!rename $self->_root->{file} . '.tmp', $self->_root->{file}) {
1023 unlink $self->_root->{file} . '.tmp';
1025 return $self->_throw_error("Optimize failed: Cannot copy temp file over original: $!");
1029 $self->{engine}->close( $self );
1030 $self->{engine}->open( $self );
1037 # Make copy of object and return
1039 my $self = $_[0]->_get_self;
1041 return DBM::Deep->new(
1042 type => $self->_type,
1043 base_offset => $self->_base_offset,
1044 root => $self->_root
1049 my %is_legal_filter = map {
1052 store_key store_value
1053 fetch_key fetch_value
1058 # Setup filter function for storing or fetching the key or value
1060 my $self = $_[0]->_get_self;
1061 my $type = lc $_[1];
1062 my $func = $_[2] ? $_[2] : undef;
1064 if ( $is_legal_filter{$type} ) {
1065 $self->_root->{"filter_$type"} = $func;
1079 # Get access to the root structure
1081 my $self = $_[0]->_get_self;
1082 return $self->{root};
1087 # Get access to the raw fh
1089 #XXX It will be useful, though, when we split out HASH and ARRAY
1090 my $self = $_[0]->_get_self;
1091 return $self->_root->{fh};
1096 # Get type of current node (TYPE_HASH or TYPE_ARRAY)
1098 my $self = $_[0]->_get_self;
1099 return $self->{type};
1104 # Get base_offset of current node (TYPE_HASH or TYPE_ARRAY)
1106 my $self = $_[0]->_get_self;
1107 return $self->{base_offset};
1115 die "DBM::Deep: $_[1]\n";
1118 sub _precalc_sizes {
1120 # Precalculate index, bucket and bucket list sizes
1123 #XXX I don't like this ...
1124 set_pack() unless defined $LONG_SIZE;
1126 $INDEX_SIZE = 256 * $LONG_SIZE;
1127 $BUCKET_SIZE = $HASH_SIZE + $LONG_SIZE;
1128 $BUCKET_LIST_SIZE = $MAX_BUCKETS * $BUCKET_SIZE;
1133 # Set pack/unpack modes (see file header for more)
1135 my ($long_s, $long_p, $data_s, $data_p) = @_;
1137 $LONG_SIZE = $long_s ? $long_s : 4;
1138 $LONG_PACK = $long_p ? $long_p : 'N';
1140 $DATA_LENGTH_SIZE = $data_s ? $data_s : 4;
1141 $DATA_LENGTH_PACK = $data_p ? $data_p : 'N';
1148 # Set key digest function (default is MD5)
1150 my ($digest_func, $hash_size) = @_;
1152 $DIGEST_FUNC = $digest_func ? $digest_func : \&Digest::MD5::md5;
1153 $HASH_SIZE = $hash_size ? $hash_size : 16;
1160 (O_WRONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0);
1165 # (O_RDONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0);
1169 # tie() methods (hashes and arrays)
1174 # Store single hash key/value or array element in database.
1176 my $self = $_[0]->_get_self;
1179 # User may be storing a hash, in which case we do not want it run
1180 # through the filtering system
1181 my $value = ($self->_root->{filter_store_value} && !ref($_[2]))
1182 ? $self->_root->{filter_store_value}->($_[2])
1185 my $md5 = $DIGEST_FUNC->($key);
1187 unless ( _is_writable( $self->_fh ) ) {
1188 $self->_throw_error( 'Cannot write to a readonly filehandle' );
1192 # Request exclusive lock for writing
1194 $self->lock( LOCK_EX );
1196 my $fh = $self->_fh;
1199 # Locate offset for bucket list using digest index system
1201 my $tag = $self->_load_tag($self->_base_offset);
1203 $tag = $self->_create_tag($self->_base_offset, SIG_INDEX, chr(0) x $INDEX_SIZE);
1207 while ($tag->{signature} ne SIG_BLIST) {
1208 my $num = ord(substr($md5, $ch, 1));
1210 my $ref_loc = $tag->{offset} + ($num * $LONG_SIZE);
1211 my $new_tag = $self->_index_lookup($tag, $num);
1214 seek($fh, $ref_loc + $self->_root->{file_offset}, SEEK_SET);
1215 print( $fh pack($LONG_PACK, $self->_root->{end}) );
1217 $tag = $self->_create_tag($self->_root->{end}, SIG_BLIST, chr(0) x $BUCKET_LIST_SIZE);
1219 $tag->{ref_loc} = $ref_loc;
1227 $tag->{ref_loc} = $ref_loc;
1234 # Add key/value to bucket list
1236 my $result = $self->_add_bucket( $tag, $md5, $key, $value );
1245 # Fetch single value or element given plain key or array index
1247 my $self = shift->_get_self;
1250 my $md5 = $DIGEST_FUNC->($key);
1253 # Request shared lock for reading
1255 $self->lock( LOCK_SH );
1257 my $tag = $self->_find_bucket_list( $md5 );
1264 # Get value from bucket list
1266 my $result = $self->_get_bucket_value( $tag, $md5 );
1270 #XXX What is ref() checking here?
1271 #YYY Filters only apply on scalar values, so the ref check is making
1272 #YYY sure the fetched bucket is a scalar, not a child hash or array.
1273 return ($result && !ref($result) && $self->_root->{filter_fetch_value})
1274 ? $self->_root->{filter_fetch_value}->($result)
1280 # Delete single key/value pair or element given plain key or array index
1282 my $self = $_[0]->_get_self;
1285 my $md5 = $DIGEST_FUNC->($key);
1288 # Request exclusive lock for writing
1290 $self->lock( LOCK_EX );
1292 my $tag = $self->_find_bucket_list( $md5 );
1301 my $value = $self->_get_bucket_value( $tag, $md5 );
1302 if ($value && !ref($value) && $self->_root->{filter_fetch_value}) {
1303 $value = $self->_root->{filter_fetch_value}->($value);
1306 my $result = $self->_delete_bucket( $tag, $md5 );
1309 # If this object is an array and the key deleted was on the end of the stack,
1310 # decrement the length variable.
1320 # Check if a single key or element exists given plain key or array index
1322 my $self = $_[0]->_get_self;
1325 my $md5 = $DIGEST_FUNC->($key);
1328 # Request shared lock for reading
1330 $self->lock( LOCK_SH );
1332 my $tag = $self->_find_bucket_list( $md5 );
1335 # For some reason, the built-in exists() function returns '' for false
1343 # Check if bucket exists and return 1 or ''
1345 my $result = $self->_bucket_exists( $tag, $md5 ) || '';
1354 # Clear all keys from hash, or all elements from array.
1356 my $self = $_[0]->_get_self;
1359 # Request exclusive lock for writing
1361 $self->lock( LOCK_EX );
1363 my $fh = $self->_fh;
1365 seek($fh, $self->_base_offset + $self->_root->{file_offset}, SEEK_SET);
1371 $self->_create_tag($self->_base_offset, $self->_type, chr(0) x $INDEX_SIZE);
1379 # Public method aliases
1381 sub put { (shift)->STORE( @_ ) }
1382 sub store { (shift)->STORE( @_ ) }
1383 sub get { (shift)->FETCH( @_ ) }
1384 sub fetch { (shift)->FETCH( @_ ) }
1385 sub delete { (shift)->DELETE( @_ ) }
1386 sub exists { (shift)->EXISTS( @_ ) }
1387 sub clear { (shift)->CLEAR( @_ ) }
1389 package DBM::Deep::_::Root;
1403 filter_store_key => undef,
1404 filter_store_value => undef,
1405 filter_fetch_key => undef,
1406 filter_fetch_value => undef,
1412 if ( $self->{fh} && !$self->{file_offset} ) {
1413 $self->{file_offset} = tell( $self->{fh} );
1421 return unless $self;
1423 close $self->{fh} if $self->{fh};
1434 DBM::Deep - A pure perl multi-level hash/array DBM
1439 my $db = DBM::Deep->new( "foo.db" );
1441 $db->{key} = 'value'; # tie() style
1444 $db->put('key' => 'value'); # OO style
1445 print $db->get('key');
1447 # true multi-level support
1448 $db->{my_complex} = [
1449 'hello', { perl => 'rules' },
1455 A unique flat-file database module, written in pure perl. True
1456 multi-level hash/array support (unlike MLDBM, which is faked), hybrid
1457 OO / tie() interface, cross-platform FTPable files, and quite fast. Can
1458 handle millions of keys and unlimited hash levels without significant
1459 slow-down. Written from the ground-up in pure perl -- this is NOT a
1460 wrapper around a C-based DBM. Out-of-the-box compatibility with Unix,
1461 Mac OS X and Windows.
1465 Hopefully you are using Perl's excellent CPAN module, which will download
1466 and install the module for you. If not, get the tarball, and run these
1478 Construction can be done OO-style (which is the recommended way), or using
1479 Perl's tie() function. Both are examined here.
1481 =head2 OO CONSTRUCTION
1483 The recommended way to construct a DBM::Deep object is to use the new()
1484 method, which gets you a blessed, tied hash or array reference.
1486 my $db = DBM::Deep->new( "foo.db" );
1488 This opens a new database handle, mapped to the file "foo.db". If this
1489 file does not exist, it will automatically be created. DB files are
1490 opened in "r+" (read/write) mode, and the type of object returned is a
1491 hash, unless otherwise specified (see L<OPTIONS> below).
1493 You can pass a number of options to the constructor to specify things like
1494 locking, autoflush, etc. This is done by passing an inline hash:
1496 my $db = DBM::Deep->new(
1502 Notice that the filename is now specified I<inside> the hash with
1503 the "file" parameter, as opposed to being the sole argument to the
1504 constructor. This is required if any options are specified.
1505 See L<OPTIONS> below for the complete list.
1509 You can also start with an array instead of a hash. For this, you must
1510 specify the C<type> parameter:
1512 my $db = DBM::Deep->new(
1514 type => DBM::Deep->TYPE_ARRAY
1517 B<Note:> Specifing the C<type> parameter only takes effect when beginning
1518 a new DB file. If you create a DBM::Deep object with an existing file, the
1519 C<type> will be loaded from the file header, and an error will be thrown if
1520 the wrong type is passed in.
1522 =head2 TIE CONSTRUCTION
1524 Alternately, you can create a DBM::Deep handle by using Perl's built-in
1525 tie() function. The object returned from tie() can be used to call methods,
1526 such as lock() and unlock(), but cannot be used to assign to the DBM::Deep
1527 file (as expected with most tie'd objects).
1530 my $db = tie %hash, "DBM::Deep", "foo.db";
1533 my $db = tie @array, "DBM::Deep", "bar.db";
1535 As with the OO constructor, you can replace the DB filename parameter with
1536 a hash containing one or more options (see L<OPTIONS> just below for the
1539 tie %hash, "DBM::Deep", {
1547 There are a number of options that can be passed in when constructing your
1548 DBM::Deep objects. These apply to both the OO- and tie- based approaches.
1554 Filename of the DB file to link the handle to. You can pass a full absolute
1555 filesystem path, partial path, or a plain filename if the file is in the
1556 current working directory. This is a required parameter (though q.v. fh).
1560 If you want, you can pass in the fh instead of the file. This is most useful for doing
1563 my $db = DBM::Deep->new( { fh => \*DATA } );
1565 You are responsible for making sure that the fh has been opened appropriately for your
1566 needs. If you open it read-only and attempt to write, an exception will be thrown. If you
1567 open it write-only or append-only, an exception will be thrown immediately as DBM::Deep
1568 needs to read from the fh.
1572 This is the offset within the file that the DBM::Deep db starts. Most of the time, you will
1573 not need to set this. However, it's there if you want it.
1575 If you pass in fh and do not set this, it will be set appropriately.
1579 This parameter specifies what type of object to create, a hash or array. Use
1580 one of these two constants: C<DBM::Deep-E<gt>TYPE_HASH> or C<DBM::Deep-E<gt>TYPE_ARRAY>.
1581 This only takes effect when beginning a new file. This is an optional
1582 parameter, and defaults to C<DBM::Deep-E<gt>TYPE_HASH>.
1586 Specifies whether locking is to be enabled. DBM::Deep uses Perl's Fnctl flock()
1587 function to lock the database in exclusive mode for writes, and shared mode for
1588 reads. Pass any true value to enable. This affects the base DB handle I<and
1589 any child hashes or arrays> that use the same DB file. This is an optional
1590 parameter, and defaults to 0 (disabled). See L<LOCKING> below for more.
1594 Specifies whether autoflush is to be enabled on the underlying filehandle.
1595 This obviously slows down write operations, but is required if you may have
1596 multiple processes accessing the same DB file (also consider enable I<locking>).
1597 Pass any true value to enable. This is an optional parameter, and defaults to 0
1602 If I<autobless> mode is enabled, DBM::Deep will preserve blessed hashes, and
1603 restore them when fetched. This is an B<experimental> feature, and does have
1604 side-effects. Basically, when hashes are re-blessed into their original
1605 classes, they are no longer blessed into the DBM::Deep class! So you won't be
1606 able to call any DBM::Deep methods on them. You have been warned.
1607 This is an optional parameter, and defaults to 0 (disabled).
1611 See L<FILTERS> below.
1615 Setting I<debug> mode will make all errors non-fatal, dump them out to
1616 STDERR, and continue on. This is for debugging purposes only, and probably
1617 not what you want. This is an optional parameter, and defaults to 0 (disabled).
1619 B<NOTE>: This parameter is considered deprecated and should not be used anymore.
1623 =head1 TIE INTERFACE
1625 With DBM::Deep you can access your databases using Perl's standard hash/array
1626 syntax. Because all DBM::Deep objects are I<tied> to hashes or arrays, you can
1627 treat them as such. DBM::Deep will intercept all reads/writes and direct them
1628 to the right place -- the DB file. This has nothing to do with the
1629 L<TIE CONSTRUCTION> section above. This simply tells you how to use DBM::Deep
1630 using regular hashes and arrays, rather than calling functions like C<get()>
1631 and C<put()> (although those work too). It is entirely up to you how to want
1632 to access your databases.
1636 You can treat any DBM::Deep object like a normal Perl hash reference. Add keys,
1637 or even nested hashes (or arrays) using standard Perl syntax:
1639 my $db = DBM::Deep->new( "foo.db" );
1641 $db->{mykey} = "myvalue";
1643 $db->{myhash}->{subkey} = "subvalue";
1645 print $db->{myhash}->{subkey} . "\n";
1647 You can even step through hash keys using the normal Perl C<keys()> function:
1649 foreach my $key (keys %$db) {
1650 print "$key: " . $db->{$key} . "\n";
1653 Remember that Perl's C<keys()> function extracts I<every> key from the hash and
1654 pushes them onto an array, all before the loop even begins. If you have an
1655 extra large hash, this may exhaust Perl's memory. Instead, consider using
1656 Perl's C<each()> function, which pulls keys/values one at a time, using very
1659 while (my ($key, $value) = each %$db) {
1660 print "$key: $value\n";
1663 Please note that when using C<each()>, you should always pass a direct
1664 hash reference, not a lookup. Meaning, you should B<never> do this:
1667 while (my ($key, $value) = each %{$db->{foo}}) { # BAD
1669 This causes an infinite loop, because for each iteration, Perl is calling
1670 FETCH() on the $db handle, resulting in a "new" hash for foo every time, so
1671 it effectively keeps returning the first key over and over again. Instead,
1672 assign a temporary variable to C<$db->{foo}>, then pass that to each().
1676 As with hashes, you can treat any DBM::Deep object like a normal Perl array
1677 reference. This includes inserting, removing and manipulating elements,
1678 and the C<push()>, C<pop()>, C<shift()>, C<unshift()> and C<splice()> functions.
1679 The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>,
1680 or simply be a nested array reference inside a hash. Example:
1682 my $db = DBM::Deep->new(
1683 file => "foo-array.db",
1684 type => DBM::Deep->TYPE_ARRAY
1688 push @$db, "bar", "baz";
1689 unshift @$db, "bah";
1691 my $last_elem = pop @$db; # baz
1692 my $first_elem = shift @$db; # bah
1693 my $second_elem = $db->[1]; # bar
1695 my $num_elements = scalar @$db;
1699 In addition to the I<tie()> interface, you can also use a standard OO interface
1700 to manipulate all aspects of DBM::Deep databases. Each type of object (hash or
1701 array) has its own methods, but both types share the following common methods:
1702 C<put()>, C<get()>, C<exists()>, C<delete()> and C<clear()>.
1706 =item * new() / clone()
1708 These are the constructor and copy-functions.
1710 =item * put() / store()
1712 Stores a new hash key/value pair, or sets an array element value. Takes two
1713 arguments, the hash key or array index, and the new value. The value can be
1714 a scalar, hash ref or array ref. Returns true on success, false on failure.
1716 $db->put("foo", "bar"); # for hashes
1717 $db->put(1, "bar"); # for arrays
1719 =item * get() / fetch()
1721 Fetches the value of a hash key or array element. Takes one argument: the hash
1722 key or array index. Returns a scalar, hash ref or array ref, depending on the
1725 my $value = $db->get("foo"); # for hashes
1726 my $value = $db->get(1); # for arrays
1730 Checks if a hash key or array index exists. Takes one argument: the hash key
1731 or array index. Returns true if it exists, false if not.
1733 if ($db->exists("foo")) { print "yay!\n"; } # for hashes
1734 if ($db->exists(1)) { print "yay!\n"; } # for arrays
1738 Deletes one hash key/value pair or array element. Takes one argument: the hash
1739 key or array index. Returns true on success, false if not found. For arrays,
1740 the remaining elements located after the deleted element are NOT moved over.
1741 The deleted element is essentially just undefined, which is exactly how Perl's
1742 internal arrays work. Please note that the space occupied by the deleted
1743 key/value or element is B<not> reused again -- see L<UNUSED SPACE RECOVERY>
1744 below for details and workarounds.
1746 $db->delete("foo"); # for hashes
1747 $db->delete(1); # for arrays
1751 Deletes B<all> hash keys or array elements. Takes no arguments. No return
1752 value. Please note that the space occupied by the deleted keys/values or
1753 elements is B<not> reused again -- see L<UNUSED SPACE RECOVERY> below for
1754 details and workarounds.
1756 $db->clear(); # hashes or arrays
1758 =item * lock() / unlock()
1764 Recover lost disk space.
1766 =item * import() / export()
1768 Data going in and out.
1770 =item * set_digest() / set_pack() / set_filter()
1772 q.v. adjusting the interal parameters.
1778 For hashes, DBM::Deep supports all the common methods described above, and the
1779 following additional methods: C<first_key()> and C<next_key()>.
1785 Returns the "first" key in the hash. As with built-in Perl hashes, keys are
1786 fetched in an undefined order (which appears random). Takes no arguments,
1787 returns the key as a scalar value.
1789 my $key = $db->first_key();
1793 Returns the "next" key in the hash, given the previous one as the sole argument.
1794 Returns undef if there are no more keys to be fetched.
1796 $key = $db->next_key($key);
1800 Here are some examples of using hashes:
1802 my $db = DBM::Deep->new( "foo.db" );
1804 $db->put("foo", "bar");
1805 print "foo: " . $db->get("foo") . "\n";
1807 $db->put("baz", {}); # new child hash ref
1808 $db->get("baz")->put("buz", "biz");
1809 print "buz: " . $db->get("baz")->get("buz") . "\n";
1811 my $key = $db->first_key();
1813 print "$key: " . $db->get($key) . "\n";
1814 $key = $db->next_key($key);
1817 if ($db->exists("foo")) { $db->delete("foo"); }
1821 For arrays, DBM::Deep supports all the common methods described above, and the
1822 following additional methods: C<length()>, C<push()>, C<pop()>, C<shift()>,
1823 C<unshift()> and C<splice()>.
1829 Returns the number of elements in the array. Takes no arguments.
1831 my $len = $db->length();
1835 Adds one or more elements onto the end of the array. Accepts scalars, hash
1836 refs or array refs. No return value.
1838 $db->push("foo", "bar", {});
1842 Fetches the last element in the array, and deletes it. Takes no arguments.
1843 Returns undef if array is empty. Returns the element value.
1845 my $elem = $db->pop();
1849 Fetches the first element in the array, deletes it, then shifts all the
1850 remaining elements over to take up the space. Returns the element value. This
1851 method is not recommended with large arrays -- see L<LARGE ARRAYS> below for
1854 my $elem = $db->shift();
1858 Inserts one or more elements onto the beginning of the array, shifting all
1859 existing elements over to make room. Accepts scalars, hash refs or array refs.
1860 No return value. This method is not recommended with large arrays -- see
1861 <LARGE ARRAYS> below for details.
1863 $db->unshift("foo", "bar", {});
1867 Performs exactly like Perl's built-in function of the same name. See L<perldoc
1868 -f splice> for usage -- it is too complicated to document here. This method is
1869 not recommended with large arrays -- see L<LARGE ARRAYS> below for details.
1873 Here are some examples of using arrays:
1875 my $db = DBM::Deep->new(
1877 type => DBM::Deep->TYPE_ARRAY
1880 $db->push("bar", "baz");
1881 $db->unshift("foo");
1884 my $len = $db->length();
1885 print "length: $len\n"; # 4
1887 for (my $k=0; $k<$len; $k++) {
1888 print "$k: " . $db->get($k) . "\n";
1891 $db->splice(1, 2, "biz", "baf");
1893 while (my $elem = shift @$db) {
1894 print "shifted: $elem\n";
1899 Enable automatic file locking by passing a true value to the C<locking>
1900 parameter when constructing your DBM::Deep object (see L<SETUP> above).
1902 my $db = DBM::Deep->new(
1907 This causes DBM::Deep to C<flock()> the underlying filehandle with exclusive
1908 mode for writes, and shared mode for reads. This is required if you have
1909 multiple processes accessing the same database file, to avoid file corruption.
1910 Please note that C<flock()> does NOT work for files over NFS. See L<DB OVER
1911 NFS> below for more.
1913 =head2 EXPLICIT LOCKING
1915 You can explicitly lock a database, so it remains locked for multiple
1916 transactions. This is done by calling the C<lock()> method, and passing an
1917 optional lock mode argument (defaults to exclusive mode). This is particularly
1918 useful for things like counters, where the current value needs to be fetched,
1919 then incremented, then stored again.
1922 my $counter = $db->get("counter");
1924 $db->put("counter", $counter);
1933 You can pass C<lock()> an optional argument, which specifies which mode to use
1934 (exclusive or shared). Use one of these two constants: C<DBM::Deep-E<gt>LOCK_EX>
1935 or C<DBM::Deep-E<gt>LOCK_SH>. These are passed directly to C<flock()>, and are the
1936 same as the constants defined in Perl's C<Fcntl> module.
1938 $db->lock( DBM::Deep->LOCK_SH );
1942 =head1 IMPORTING/EXPORTING
1944 You can import existing complex structures by calling the C<import()> method,
1945 and export an entire database into an in-memory structure using the C<export()>
1946 method. Both are examined here.
1950 Say you have an existing hash with nested hashes/arrays inside it. Instead of
1951 walking the structure and adding keys/elements to the database as you go,
1952 simply pass a reference to the C<import()> method. This recursively adds
1953 everything to an existing DBM::Deep object for you. Here is an example:
1958 array1 => [ "elem0", "elem1", "elem2" ],
1960 subkey1 => "subvalue1",
1961 subkey2 => "subvalue2"
1965 my $db = DBM::Deep->new( "foo.db" );
1966 $db->import( $struct );
1968 print $db->{key1} . "\n"; # prints "value1"
1970 This recursively imports the entire C<$struct> object into C<$db>, including
1971 all nested hashes and arrays. If the DBM::Deep object contains exsiting data,
1972 keys are merged with the existing ones, replacing if they already exist.
1973 The C<import()> method can be called on any database level (not just the base
1974 level), and works with both hash and array DB types.
1976 B<Note:> Make sure your existing structure has no circular references in it.
1977 These will cause an infinite loop when importing.
1981 Calling the C<export()> method on an existing DBM::Deep object will return
1982 a reference to a new in-memory copy of the database. The export is done
1983 recursively, so all nested hashes/arrays are all exported to standard Perl
1984 objects. Here is an example:
1986 my $db = DBM::Deep->new( "foo.db" );
1988 $db->{key1} = "value1";
1989 $db->{key2} = "value2";
1991 $db->{hash1}->{subkey1} = "subvalue1";
1992 $db->{hash1}->{subkey2} = "subvalue2";
1994 my $struct = $db->export();
1996 print $struct->{key1} . "\n"; # prints "value1"
1998 This makes a complete copy of the database in memory, and returns a reference
1999 to it. The C<export()> method can be called on any database level (not just
2000 the base level), and works with both hash and array DB types. Be careful of
2001 large databases -- you can store a lot more data in a DBM::Deep object than an
2002 in-memory Perl structure.
2004 B<Note:> Make sure your database has no circular references in it.
2005 These will cause an infinite loop when exporting.
2009 DBM::Deep has a number of hooks where you can specify your own Perl function
2010 to perform filtering on incoming or outgoing data. This is a perfect
2011 way to extend the engine, and implement things like real-time compression or
2012 encryption. Filtering applies to the base DB level, and all child hashes /
2013 arrays. Filter hooks can be specified when your DBM::Deep object is first
2014 constructed, or by calling the C<set_filter()> method at any time. There are
2015 four available filter hooks, described below:
2019 =item * filter_store_key
2021 This filter is called whenever a hash key is stored. It
2022 is passed the incoming key, and expected to return a transformed key.
2024 =item * filter_store_value
2026 This filter is called whenever a hash key or array element is stored. It
2027 is passed the incoming value, and expected to return a transformed value.
2029 =item * filter_fetch_key
2031 This filter is called whenever a hash key is fetched (i.e. via
2032 C<first_key()> or C<next_key()>). It is passed the transformed key,
2033 and expected to return the plain key.
2035 =item * filter_fetch_value
2037 This filter is called whenever a hash key or array element is fetched.
2038 It is passed the transformed value, and expected to return the plain value.
2042 Here are the two ways to setup a filter hook:
2044 my $db = DBM::Deep->new(
2046 filter_store_value => \&my_filter_store,
2047 filter_fetch_value => \&my_filter_fetch
2052 $db->set_filter( "filter_store_value", \&my_filter_store );
2053 $db->set_filter( "filter_fetch_value", \&my_filter_fetch );
2055 Your filter function will be called only when dealing with SCALAR keys or
2056 values. When nested hashes and arrays are being stored/fetched, filtering
2057 is bypassed. Filters are called as static functions, passed a single SCALAR
2058 argument, and expected to return a single SCALAR value. If you want to
2059 remove a filter, set the function reference to C<undef>:
2061 $db->set_filter( "filter_store_value", undef );
2063 =head2 REAL-TIME ENCRYPTION EXAMPLE
2065 Here is a working example that uses the I<Crypt::Blowfish> module to
2066 do real-time encryption / decryption of keys & values with DBM::Deep Filters.
2067 Please visit L<http://search.cpan.org/search?module=Crypt::Blowfish> for more
2068 on I<Crypt::Blowfish>. You'll also need the I<Crypt::CBC> module.
2071 use Crypt::Blowfish;
2074 my $cipher = Crypt::CBC->new({
2075 'key' => 'my secret key',
2076 'cipher' => 'Blowfish',
2078 'regenerate_key' => 0,
2079 'padding' => 'space',
2083 my $db = DBM::Deep->new(
2084 file => "foo-encrypt.db",
2085 filter_store_key => \&my_encrypt,
2086 filter_store_value => \&my_encrypt,
2087 filter_fetch_key => \&my_decrypt,
2088 filter_fetch_value => \&my_decrypt,
2091 $db->{key1} = "value1";
2092 $db->{key2} = "value2";
2093 print "key1: " . $db->{key1} . "\n";
2094 print "key2: " . $db->{key2} . "\n";
2100 return $cipher->encrypt( $_[0] );
2103 return $cipher->decrypt( $_[0] );
2106 =head2 REAL-TIME COMPRESSION EXAMPLE
2108 Here is a working example that uses the I<Compress::Zlib> module to do real-time
2109 compression / decompression of keys & values with DBM::Deep Filters.
2110 Please visit L<http://search.cpan.org/search?module=Compress::Zlib> for
2111 more on I<Compress::Zlib>.
2116 my $db = DBM::Deep->new(
2117 file => "foo-compress.db",
2118 filter_store_key => \&my_compress,
2119 filter_store_value => \&my_compress,
2120 filter_fetch_key => \&my_decompress,
2121 filter_fetch_value => \&my_decompress,
2124 $db->{key1} = "value1";
2125 $db->{key2} = "value2";
2126 print "key1: " . $db->{key1} . "\n";
2127 print "key2: " . $db->{key2} . "\n";
2133 return Compress::Zlib::memGzip( $_[0] ) ;
2136 return Compress::Zlib::memGunzip( $_[0] ) ;
2139 B<Note:> Filtering of keys only applies to hashes. Array "keys" are
2140 actually numerical index numbers, and are not filtered.
2142 =head1 ERROR HANDLING
2144 Most DBM::Deep methods return a true value for success, and call die() on
2145 failure. You can wrap calls in an eval block to catch the die.
2147 my $db = DBM::Deep->new( "foo.db" ); # create hash
2148 eval { $db->push("foo"); }; # ILLEGAL -- push is array-only call
2150 print $@; # prints error message
2152 =head1 LARGEFILE SUPPORT
2154 If you have a 64-bit system, and your Perl is compiled with both LARGEFILE
2155 and 64-bit support, you I<may> be able to create databases larger than 2 GB.
2156 DBM::Deep by default uses 32-bit file offset tags, but these can be changed
2157 by calling the static C<set_pack()> method before you do anything else.
2159 DBM::Deep::set_pack(8, 'Q');
2161 This tells DBM::Deep to pack all file offsets with 8-byte (64-bit) quad words
2162 instead of 32-bit longs. After setting these values your DB files have a
2163 theoretical maximum size of 16 XB (exabytes).
2165 B<Note:> Changing these values will B<NOT> work for existing database files.
2166 Only change this for new files, and make sure it stays set consistently
2167 throughout the file's life. If you do set these values, you can no longer
2168 access 32-bit DB files. You can, however, call C<set_pack(4, 'N')> to change
2169 back to 32-bit mode.
2171 B<Note:> I have not personally tested files > 2 GB -- all my systems have
2172 only a 32-bit Perl. However, I have received user reports that this does
2175 =head1 LOW-LEVEL ACCESS
2177 If you require low-level access to the underlying filehandle that DBM::Deep uses,
2178 you can call the C<_fh()> method, which returns the handle:
2180 my $fh = $db->_fh();
2182 This method can be called on the root level of the datbase, or any child
2183 hashes or arrays. All levels share a I<root> structure, which contains things
2184 like the filehandle, a reference counter, and all the options specified
2185 when you created the object. You can get access to this root structure by
2186 calling the C<root()> method.
2188 my $root = $db->_root();
2190 This is useful for changing options after the object has already been created,
2191 such as enabling/disabling locking, or debug modes. You can also
2192 store your own temporary user data in this structure (be wary of name
2193 collision), which is then accessible from any child hash or array.
2195 =head1 CUSTOM DIGEST ALGORITHM
2197 DBM::Deep by default uses the I<Message Digest 5> (MD5) algorithm for hashing
2198 keys. However you can override this, and use another algorithm (such as SHA-256)
2199 or even write your own. But please note that DBM::Deep currently expects zero
2200 collisions, so your algorithm has to be I<perfect>, so to speak.
2201 Collision detection may be introduced in a later version.
2205 You can specify a custom digest algorithm by calling the static C<set_digest()>
2206 function, passing a reference to a subroutine, and the length of the algorithm's
2207 hashes (in bytes). This is a global static function, which affects ALL DBM::Deep
2208 objects. Here is a working example that uses a 256-bit hash from the
2209 I<Digest::SHA256> module. Please see
2210 L<http://search.cpan.org/search?module=Digest::SHA256> for more.
2215 my $context = Digest::SHA256::new(256);
2217 DBM::Deep::set_digest( \&my_digest, 32 );
2219 my $db = DBM::Deep->new( "foo-sha.db" );
2221 $db->{key1} = "value1";
2222 $db->{key2} = "value2";
2223 print "key1: " . $db->{key1} . "\n";
2224 print "key2: " . $db->{key2} . "\n";
2230 return substr( $context->hash($_[0]), 0, 32 );
2233 B<Note:> Your returned digest strings must be B<EXACTLY> the number
2234 of bytes you specify in the C<set_digest()> function (in this case 32).
2236 =head1 CIRCULAR REFERENCES
2238 DBM::Deep has B<experimental> support for circular references. Meaning you
2239 can have a nested hash key or array element that points to a parent object.
2240 This relationship is stored in the DB file, and is preserved between sessions.
2243 my $db = DBM::Deep->new( "foo.db" );
2246 $db->{circle} = $db; # ref to self
2248 print $db->{foo} . "\n"; # prints "foo"
2249 print $db->{circle}->{foo} . "\n"; # prints "foo" again
2251 One catch is, passing the object to a function that recursively walks the
2252 object tree (such as I<Data::Dumper> or even the built-in C<optimize()> or
2253 C<export()> methods) will result in an infinite loop. The other catch is,
2254 if you fetch the I<key> of a circular reference (i.e. using the C<first_key()>
2255 or C<next_key()> methods), you will get the I<target object's key>, not the
2256 ref's key. This gets even more interesting with the above example, where
2257 the I<circle> key points to the base DB object, which technically doesn't
2258 have a key. So I made DBM::Deep return "[base]" as the key name in that
2261 =head1 CAVEATS / ISSUES / BUGS
2263 This section describes all the known issues with DBM::Deep. It you have found
2264 something that is not listed here, please send e-mail to L<jhuckaby@cpan.org>.
2266 =head2 UNUSED SPACE RECOVERY
2268 One major caveat with DBM::Deep is that space occupied by existing keys and
2269 values is not recovered when they are deleted. Meaning if you keep deleting
2270 and adding new keys, your file will continuously grow. I am working on this,
2271 but in the meantime you can call the built-in C<optimize()> method from time to
2272 time (perhaps in a crontab or something) to recover all your unused space.
2274 $db->optimize(); # returns true on success
2276 This rebuilds the ENTIRE database into a new file, then moves it on top of
2277 the original. The new file will have no unused space, thus it will take up as
2278 little disk space as possible. Please note that this operation can take
2279 a long time for large files, and you need enough disk space to temporarily hold
2280 2 copies of your DB file. The temporary file is created in the same directory
2281 as the original, named with a ".tmp" extension, and is deleted when the
2282 operation completes. Oh, and if locking is enabled, the DB is automatically
2283 locked for the entire duration of the copy.
2285 B<WARNING:> Only call optimize() on the top-level node of the database, and
2286 make sure there are no child references lying around. DBM::Deep keeps a reference
2287 counter, and if it is greater than 1, optimize() will abort and return undef.
2289 =head2 AUTOVIVIFICATION
2291 Unfortunately, autovivification doesn't work with tied hashes. This appears to
2292 be a bug in Perl's tie() system, as I<Jakob Schmidt> encountered the very same
2293 issue with his I<DWH_FIle> module (see L<http://search.cpan.org/search?module=DWH_File>),
2294 and it is also mentioned in the BUGS section for the I<MLDBM> module <see
2295 L<http://search.cpan.org/search?module=MLDBM>). Basically, on a new db file,
2298 $db->{foo}->{bar} = "hello";
2300 Since "foo" doesn't exist, you cannot add "bar" to it. You end up with "foo"
2301 being an empty hash. Try this instead, which works fine:
2303 $db->{foo} = { bar => "hello" };
2305 As of Perl 5.8.7, this bug still exists. I have walked very carefully through
2306 the execution path, and Perl indeed passes an empty hash to the STORE() method.
2307 Probably a bug in Perl.
2309 =head2 FILE CORRUPTION
2311 The current level of error handling in DBM::Deep is minimal. Files I<are> checked
2312 for a 32-bit signature when opened, but other corruption in files can cause
2313 segmentation faults. DBM::Deep may try to seek() past the end of a file, or get
2314 stuck in an infinite loop depending on the level of corruption. File write
2315 operations are not checked for failure (for speed), so if you happen to run
2316 out of disk space, DBM::Deep will probably fail in a bad way. These things will
2317 be addressed in a later version of DBM::Deep.
2321 Beware of using DB files over NFS. DBM::Deep uses flock(), which works well on local
2322 filesystems, but will NOT protect you from file corruption over NFS. I've heard
2323 about setting up your NFS server with a locking daemon, then using lockf() to
2324 lock your files, but your mileage may vary there as well. From what I
2325 understand, there is no real way to do it. However, if you need access to the
2326 underlying filehandle in DBM::Deep for using some other kind of locking scheme like
2327 lockf(), see the L<LOW-LEVEL ACCESS> section above.
2329 =head2 COPYING OBJECTS
2331 Beware of copying tied objects in Perl. Very strange things can happen.
2332 Instead, use DBM::Deep's C<clone()> method which safely copies the object and
2333 returns a new, blessed, tied hash or array to the same level in the DB.
2335 my $copy = $db->clone();
2337 B<Note>: Since clone() here is cloning the object, not the database location, any
2338 modifications to either $db or $copy will be visible in both.
2342 Beware of using C<shift()>, C<unshift()> or C<splice()> with large arrays.
2343 These functions cause every element in the array to move, which can be murder
2344 on DBM::Deep, as every element has to be fetched from disk, then stored again in
2345 a different location. This will be addressed in the forthcoming version 1.00.
2347 =head2 WRITEONLY FILES
2349 If you pass in a filehandle to new(), you may have opened it in either a readonly or
2350 writeonly mode. STORE will verify that the filehandle is writable. However, there
2351 doesn't seem to be a good way to determine if a filehandle is readable. And, if the
2352 filehandle isn't readable, it's not clear what will happen. So, don't do that.
2356 This section discusses DBM::Deep's speed and memory usage.
2360 Obviously, DBM::Deep isn't going to be as fast as some C-based DBMs, such as
2361 the almighty I<BerkeleyDB>. But it makes up for it in features like true
2362 multi-level hash/array support, and cross-platform FTPable files. Even so,
2363 DBM::Deep is still pretty fast, and the speed stays fairly consistent, even
2364 with huge databases. Here is some test data:
2366 Adding 1,000,000 keys to new DB file...
2368 At 100 keys, avg. speed is 2,703 keys/sec
2369 At 200 keys, avg. speed is 2,642 keys/sec
2370 At 300 keys, avg. speed is 2,598 keys/sec
2371 At 400 keys, avg. speed is 2,578 keys/sec
2372 At 500 keys, avg. speed is 2,722 keys/sec
2373 At 600 keys, avg. speed is 2,628 keys/sec
2374 At 700 keys, avg. speed is 2,700 keys/sec
2375 At 800 keys, avg. speed is 2,607 keys/sec
2376 At 900 keys, avg. speed is 2,190 keys/sec
2377 At 1,000 keys, avg. speed is 2,570 keys/sec
2378 At 2,000 keys, avg. speed is 2,417 keys/sec
2379 At 3,000 keys, avg. speed is 1,982 keys/sec
2380 At 4,000 keys, avg. speed is 1,568 keys/sec
2381 At 5,000 keys, avg. speed is 1,533 keys/sec
2382 At 6,000 keys, avg. speed is 1,787 keys/sec
2383 At 7,000 keys, avg. speed is 1,977 keys/sec
2384 At 8,000 keys, avg. speed is 2,028 keys/sec
2385 At 9,000 keys, avg. speed is 2,077 keys/sec
2386 At 10,000 keys, avg. speed is 2,031 keys/sec
2387 At 20,000 keys, avg. speed is 1,970 keys/sec
2388 At 30,000 keys, avg. speed is 2,050 keys/sec
2389 At 40,000 keys, avg. speed is 2,073 keys/sec
2390 At 50,000 keys, avg. speed is 1,973 keys/sec
2391 At 60,000 keys, avg. speed is 1,914 keys/sec
2392 At 70,000 keys, avg. speed is 2,091 keys/sec
2393 At 80,000 keys, avg. speed is 2,103 keys/sec
2394 At 90,000 keys, avg. speed is 1,886 keys/sec
2395 At 100,000 keys, avg. speed is 1,970 keys/sec
2396 At 200,000 keys, avg. speed is 2,053 keys/sec
2397 At 300,000 keys, avg. speed is 1,697 keys/sec
2398 At 400,000 keys, avg. speed is 1,838 keys/sec
2399 At 500,000 keys, avg. speed is 1,941 keys/sec
2400 At 600,000 keys, avg. speed is 1,930 keys/sec
2401 At 700,000 keys, avg. speed is 1,735 keys/sec
2402 At 800,000 keys, avg. speed is 1,795 keys/sec
2403 At 900,000 keys, avg. speed is 1,221 keys/sec
2404 At 1,000,000 keys, avg. speed is 1,077 keys/sec
2406 This test was performed on a PowerMac G4 1gHz running Mac OS X 10.3.2 & Perl
2407 5.8.1, with an 80GB Ultra ATA/100 HD spinning at 7200RPM. The hash keys and
2408 values were between 6 - 12 chars in length. The DB file ended up at 210MB.
2409 Run time was 12 min 3 sec.
2413 One of the great things about DBM::Deep is that it uses very little memory.
2414 Even with huge databases (1,000,000+ keys) you will not see much increased
2415 memory on your process. DBM::Deep relies solely on the filesystem for storing
2416 and fetching data. Here is output from I</usr/bin/top> before even opening a
2419 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
2420 22831 root 11 0 2716 2716 1296 R 0.0 0.2 0:07 perl
2422 Basically the process is taking 2,716K of memory. And here is the same
2423 process after storing and fetching 1,000,000 keys:
2425 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
2426 22831 root 14 0 2772 2772 1328 R 0.0 0.2 13:32 perl
2428 Notice the memory usage increased by only 56K. Test was performed on a 700mHz
2429 x86 box running Linux RedHat 7.2 & Perl 5.6.1.
2431 =head1 DB FILE FORMAT
2433 In case you were interested in the underlying DB file format, it is documented
2434 here in this section. You don't need to know this to use the module, it's just
2435 included for reference.
2439 DBM::Deep files always start with a 32-bit signature to identify the file type.
2440 This is at offset 0. The signature is "DPDB" in network byte order. This is
2441 checked for when the file is opened and an error will be thrown if it's not found.
2445 The DBM::Deep file is in a I<tagged format>, meaning each section of the file
2446 has a standard header containing the type of data, the length of data, and then
2447 the data itself. The type is a single character (1 byte), the length is a
2448 32-bit unsigned long in network byte order, and the data is, well, the data.
2449 Here is how it unfolds:
2453 Immediately after the 32-bit file signature is the I<Master Index> record.
2454 This is a standard tag header followed by 1024 bytes (in 32-bit mode) or 2048
2455 bytes (in 64-bit mode) of data. The type is I<H> for hash or I<A> for array,
2456 depending on how the DBM::Deep object was constructed.
2458 The index works by looking at a I<MD5 Hash> of the hash key (or array index
2459 number). The first 8-bit char of the MD5 signature is the offset into the
2460 index, multipled by 4 in 32-bit mode, or 8 in 64-bit mode. The value of the
2461 index element is a file offset of the next tag for the key/element in question,
2462 which is usually a I<Bucket List> tag (see below).
2464 The next tag I<could> be another index, depending on how many keys/elements
2465 exist. See L<RE-INDEXING> below for details.
2469 A I<Bucket List> is a collection of 16 MD5 hashes for keys/elements, plus
2470 file offsets to where the actual data is stored. It starts with a standard
2471 tag header, with type I<B>, and a data size of 320 bytes in 32-bit mode, or
2472 384 bytes in 64-bit mode. Each MD5 hash is stored in full (16 bytes), plus
2473 the 32-bit or 64-bit file offset for the I<Bucket> containing the actual data.
2474 When the list fills up, a I<Re-Index> operation is performed (See
2475 L<RE-INDEXING> below).
2479 A I<Bucket> is a tag containing a key/value pair (in hash mode), or a
2480 index/value pair (in array mode). It starts with a standard tag header with
2481 type I<D> for scalar data (string, binary, etc.), or it could be a nested
2482 hash (type I<H>) or array (type I<A>). The value comes just after the tag
2483 header. The size reported in the tag header is only for the value, but then,
2484 just after the value is another size (32-bit unsigned long) and then the plain
2485 key itself. Since the value is likely to be fetched more often than the plain
2486 key, I figured it would be I<slightly> faster to store the value first.
2488 If the type is I<H> (hash) or I<A> (array), the value is another I<Master Index>
2489 record for the nested structure, where the process begins all over again.
2493 After a I<Bucket List> grows to 16 records, its allocated space in the file is
2494 exhausted. Then, when another key/element comes in, the list is converted to a
2495 new index record. However, this index will look at the next char in the MD5
2496 hash, and arrange new Bucket List pointers accordingly. This process is called
2497 I<Re-Indexing>. Basically, a new index tag is created at the file EOF, and all
2498 17 (16 + new one) keys/elements are removed from the old Bucket List and
2499 inserted into the new index. Several new Bucket Lists are created in the
2500 process, as a new MD5 char from the key is being examined (it is unlikely that
2501 the keys will all share the same next char of their MD5s).
2503 Because of the way the I<MD5> algorithm works, it is impossible to tell exactly
2504 when the Bucket Lists will turn into indexes, but the first round tends to
2505 happen right around 4,000 keys. You will see a I<slight> decrease in
2506 performance here, but it picks back up pretty quick (see L<SPEED> above). Then
2507 it takes B<a lot> more keys to exhaust the next level of Bucket Lists. It's
2508 right around 900,000 keys. This process can continue nearly indefinitely --
2509 right up until the point the I<MD5> signatures start colliding with each other,
2510 and this is B<EXTREMELY> rare -- like winning the lottery 5 times in a row AND
2511 getting struck by lightning while you are walking to cash in your tickets.
2512 Theoretically, since I<MD5> hashes are 128-bit values, you I<could> have up to
2513 340,282,366,921,000,000,000,000,000,000,000,000,000 keys/elements (I believe
2514 this is 340 unodecillion, but don't quote me).
2518 When a new key/element is stored, the key (or index number) is first run through
2519 I<Digest::MD5> to get a 128-bit signature (example, in hex:
2520 b05783b0773d894396d475ced9d2f4f6). Then, the I<Master Index> record is checked
2521 for the first char of the signature (in this case I<b0>). If it does not exist,
2522 a new I<Bucket List> is created for our key (and the next 15 future keys that
2523 happen to also have I<b> as their first MD5 char). The entire MD5 is written
2524 to the I<Bucket List> along with the offset of the new I<Bucket> record (EOF at
2525 this point, unless we are replacing an existing I<Bucket>), where the actual
2526 data will be stored.
2530 Fetching an existing key/element involves getting a I<Digest::MD5> of the key
2531 (or index number), then walking along the indexes. If there are enough
2532 keys/elements in this DB level, there might be nested indexes, each linked to
2533 a particular char of the MD5. Finally, a I<Bucket List> is pointed to, which
2534 contains up to 16 full MD5 hashes. Each is checked for equality to the key in
2535 question. If we found a match, the I<Bucket> tag is loaded, where the value and
2536 plain key are stored.
2538 Fetching the plain key occurs when calling the I<first_key()> and I<next_key()>
2539 methods. In this process the indexes are walked systematically, and each key
2540 fetched in increasing MD5 order (which is why it appears random). Once the
2541 I<Bucket> is found, the value is skipped and the plain key returned instead.
2542 B<Note:> Do not count on keys being fetched as if the MD5 hashes were
2543 alphabetically sorted. This only happens on an index-level -- as soon as the
2544 I<Bucket Lists> are hit, the keys will come out in the order they went in --
2545 so it's pretty much undefined how the keys will come out -- just like Perl's
2548 =head1 CODE COVERAGE
2550 We use B<Devel::Cover> to test the code coverage of our tests, below is the
2551 B<Devel::Cover> report on this module's test suite.
2553 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2554 File stmt bran cond sub pod time total
2555 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2556 blib/lib/DBM/Deep.pm 95.2 83.8 70.0 98.2 100.0 58.0 91.0
2557 blib/lib/DBM/Deep/Array.pm 100.0 91.1 100.0 100.0 n/a 26.7 98.0
2558 blib/lib/DBM/Deep/Hash.pm 95.3 80.0 100.0 100.0 n/a 15.3 92.4
2559 Total 96.2 84.8 74.4 98.8 100.0 100.0 92.4
2560 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2562 =head1 MORE INFORMATION
2564 Check out the DBM::Deep Google Group at L<http://groups.google.com/group/DBM-Deep>
2565 or send email to L<DBM-Deep@googlegroups.com>.
2569 Joseph Huckaby, L<jhuckaby@cpan.org>
2571 Rob Kinyon, L<rkinyon@cpan.org>
2573 Special thanks to Adam Sah and Rich Gaushell! You know why :-)
2577 perltie(1), Tie::Hash(3), Digest::MD5(3), Fcntl(3), flock(2), lockf(3), nfs(5),
2578 Digest::SHA256(3), Crypt::Blowfish(3), Compress::Zlib(3)
2582 Copyright (c) 2002-2006 Joseph Huckaby. All Rights Reserved.
2583 This is free software, you may use it and distribute it under the
2584 same terms as Perl itself.