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) 2002-2005 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 vars qw( $VERSION );
42 # Set to 4 and 'N' for 32-bit offset tags (default). Theoretical limit of 4 GB per file.
43 # (Perl must be compiled with largefile support for files > 2 GB)
45 # Set to 8 and 'Q' for 64-bit offsets. Theoretical limit of 16 XB per file.
46 # (Perl must be compiled with largefile and 64-bit long support)
52 # Set to 4 and 'N' for 32-bit data length prefixes. Limit of 4 GB for each key/value.
53 # Upgrading this is possible (see above) but probably not necessary. If you need
54 # more than 4 GB for a single key or value, this module is really not for you :-)
56 #my $DATA_LENGTH_SIZE = 4;
57 #my $DATA_LENGTH_PACK = 'N';
58 our ($LONG_SIZE, $LONG_PACK, $DATA_LENGTH_SIZE, $DATA_LENGTH_PACK);
61 # Maximum number of buckets per list before another level of indexing is done.
62 # Increase this value for slightly greater speed, but larger database files.
63 # DO NOT decrease this value below 16, due to risk of recursive reindex overrun.
68 # Better not adjust anything below here, unless you're me :-)
72 # Setup digest function for keys
74 our ($DIGEST_FUNC, $HASH_SIZE);
75 #my $DIGEST_FUNC = \&Digest::MD5::md5;
78 # Precalculate index and bucket sizes based on values above.
81 my ($INDEX_SIZE, $BUCKET_SIZE, $BUCKET_LIST_SIZE);
88 # Setup file and tag signatures. These should never change.
90 sub SIG_FILE () { 'DPDB' }
91 sub SIG_HASH () { 'H' }
92 sub SIG_ARRAY () { 'A' }
93 sub SIG_SCALAR () { 'S' }
94 sub SIG_NULL () { 'N' }
95 sub SIG_DATA () { 'D' }
96 sub SIG_INDEX () { 'I' }
97 sub SIG_BLIST () { 'B' }
101 # Setup constants for users to pass to new()
103 sub TYPE_HASH () { return SIG_HASH; }
104 sub TYPE_ARRAY () { return SIG_ARRAY; }
105 sub TYPE_SCALAR () { return SIG_SCALAR; }
111 if (scalar(@_) > 1) {
113 $proto->_throw_error( "Odd number of parameters to " . (caller(1))[2] );
117 elsif ( my $type = Scalar::Util::reftype($_[0]) ) {
118 if ( $type ne 'HASH' ) {
119 $proto->_throw_error( "Not a hashref in args to " . (caller(1))[2] );
124 $args = { file => shift };
132 # Class constructor method for Perl OO interface.
133 # Calls tie() and returns blessed reference to tied hash or array,
134 # providing a hybrid OO/tie interface.
137 my $args = $class->_get_args( @_ );
140 # Check if we want a tied hash or array.
143 if (defined($args->{type}) && $args->{type} eq TYPE_ARRAY) {
144 $class = 'DBM::Deep::Array';
145 require DBM::Deep::Array;
146 tie @$self, $class, %$args;
149 $class = 'DBM::Deep::Hash';
150 require DBM::Deep::Hash;
151 tie %$self, $class, %$args;
154 return bless $self, $class;
159 # Setup $self and bless into this class.
164 # These are the defaults to be optionally overridden below
167 base_offset => length(SIG_FILE),
170 foreach my $param ( keys %$self ) {
171 next unless exists $args->{$param};
172 $self->{$param} = delete $args->{$param}
175 $self->{root} = exists $args->{root}
177 : DBM::Deep::_::Root->new( $args );
179 if (!defined($self->fh)) { $self->_open(); }
186 require DBM::Deep::Hash;
187 return DBM::Deep::Hash->TIEHASH( @_ );
192 require DBM::Deep::Array;
193 return DBM::Deep::Array->TIEARRAY( @_ );
196 #XXX Unneeded now ...
202 # Open a FileHandle to the database, create if nonexistent.
203 # Make sure file signature matches DeepDB spec.
205 my $self = $_[0]->_get_self;
207 if (defined($self->fh)) { $self->_close(); }
210 # Theoretically, adding O_BINARY should remove the need for the binmode
211 # Of course, testing it is going to be ... interesting.
212 my $flags = O_RDWR | O_CREAT | O_BINARY;
214 #XXX Can the mode be anything but r+, w+, or a+??
215 #XXX ie, it has to be in read-write mode
216 #XXX So, should we verify that the mode is legitimate?
218 #XXX Maybe the mode thingy should just go away. There's no good
219 #XXX reason for it ...
220 if ( $self->root->{mode} eq 'w+' ) {
225 sysopen( $fh, $self->root->{file}, $flags )
227 $self->root->{fh} = $fh;
228 }; if ($@ ) { $self->_throw_error( "Received error: $@\n" ); }
229 if (! defined($self->fh)) {
230 return $self->_throw_error("Cannot sysopen file: " . $self->root->{file} . ": $!");
235 #XXX Can we remove this by using the right sysopen() flags?
236 # Maybe ... q.v. above
237 binmode $fh; # for win32
239 if ($self->root->{autoflush}) {
240 my $old = select $fh;
246 seek($fh, 0, SEEK_SET);
249 my $bytes_read = read( $fh, $signature, length(SIG_FILE));
252 # File is empty -- write signature and master index
255 seek($fh, 0, SEEK_SET);
257 $self->root->{end} = length(SIG_FILE);
258 $self->_create_tag($self->base_offset, $self->type, chr(0) x $INDEX_SIZE);
260 my $plain_key = "[base]";
261 print($fh pack($DATA_LENGTH_PACK, length($plain_key)) . $plain_key );
262 $self->root->{end} += $DATA_LENGTH_SIZE + length($plain_key);
264 # Flush the filehandle
265 my $old_fh = select $fh;
275 # Check signature was valid
277 unless ($signature eq SIG_FILE) {
279 return $self->_throw_error("Signature not found -- file is not a Deep DB");
282 $self->root->{end} = (stat($fh))[7];
285 # Get our type from master index signature
287 my $tag = $self->_load_tag($self->base_offset);
289 #XXX We probably also want to store the hash algorithm name and not assume anything
290 #XXX The cool thing would be to allow a different hashing algorithm at every level
293 return $self->_throw_error("Corrupted file, no master index record");
295 if ($self->{type} ne $tag->{signature}) {
296 return $self->_throw_error("File type mismatch");
304 # Close database FileHandle
306 my $self = $_[0]->_get_self;
307 close $self->root->{fh};
308 $self->root->{fh} = undef;
313 # Given offset, signature and content, create tag and write to disk
315 my ($self, $offset, $sig, $content) = @_;
316 my $size = length($content);
320 seek($fh, $offset, SEEK_SET);
321 print($fh $sig . pack($DATA_LENGTH_PACK, $size) . $content );
323 if ($offset == $self->root->{end}) {
324 $self->root->{end} += SIG_SIZE + $DATA_LENGTH_SIZE + $size;
330 offset => $offset + SIG_SIZE + $DATA_LENGTH_SIZE,
337 # Given offset, load single tag and return signature, size and data
344 seek($fh, $offset, SEEK_SET);
345 if (eof $fh) { return undef; }
348 read( $fh, $sig, SIG_SIZE);
351 read( $fh, $size, $DATA_LENGTH_SIZE);
352 $size = unpack($DATA_LENGTH_PACK, $size);
355 read( $fh, $buffer, $size);
360 offset => $offset + SIG_SIZE + $DATA_LENGTH_SIZE,
367 # Given index tag, lookup single entry in index and return .
370 my ($tag, $index) = @_;
372 my $location = unpack($LONG_PACK, substr($tag->{content}, $index * $LONG_SIZE, $LONG_SIZE) );
373 if (!$location) { return; }
375 return $self->_load_tag( $location );
380 # Adds one key/value pair to bucket list, given offset, MD5 digest of key,
381 # plain (undigested) key and value.
384 my ($tag, $md5, $plain_key, $value) = @_;
385 my $keys = $tag->{content};
389 my $is_dbm_deep = eval { $value->isa( 'DBM::Deep' ) };
390 my $internal_ref = $is_dbm_deep && ($value->root eq $self->root);
395 # Iterate through buckets, seeing if this is a new entry or a replace.
397 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
398 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
399 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
402 # Found empty bucket (end of list). Populate and exit loop.
406 $location = $internal_ref
407 ? $value->base_offset
408 : $self->root->{end};
410 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE), SEEK_SET);
411 print($fh $md5 . pack($LONG_PACK, $location) );
414 elsif ($md5 eq $key) {
416 # Found existing bucket with same key. Replace with new value.
421 $location = $value->base_offset;
422 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE), SEEK_SET);
423 print($fh $md5 . pack($LONG_PACK, $location) );
426 seek($fh, $subloc + SIG_SIZE, SEEK_SET);
428 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
431 # If value is a hash, array, or raw value with equal or less size, we can
432 # reuse the same content area of the database. Otherwise, we have to create
433 # a new content area at the EOF.
436 my $r = Scalar::Util::reftype( $value ) || '';
437 if ( $r eq 'HASH' || $r eq 'ARRAY' ) { $actual_length = $INDEX_SIZE; }
438 else { $actual_length = length($value); }
440 if ($actual_length <= $size) {
444 $location = $self->root->{end};
445 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $HASH_SIZE, SEEK_SET);
446 print($fh pack($LONG_PACK, $location) );
454 # If this is an internal reference, return now.
455 # No need to write value or plain key
462 # If bucket didn't fit into list, split into a new index level
465 seek($fh, $tag->{ref_loc}, SEEK_SET);
466 print($fh pack($LONG_PACK, $self->root->{end}) );
468 my $index_tag = $self->_create_tag($self->root->{end}, SIG_INDEX, chr(0) x $INDEX_SIZE);
471 $keys .= $md5 . pack($LONG_PACK, 0);
473 for (my $i=0; $i<=$MAX_BUCKETS; $i++) {
474 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
476 my $old_subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
477 my $num = ord(substr($key, $tag->{ch} + 1, 1));
479 if ($offsets[$num]) {
480 my $offset = $offsets[$num] + SIG_SIZE + $DATA_LENGTH_SIZE;
481 seek($fh, $offset, SEEK_SET);
483 read( $fh, $subkeys, $BUCKET_LIST_SIZE);
485 for (my $k=0; $k<$MAX_BUCKETS; $k++) {
486 my $subloc = unpack($LONG_PACK, substr($subkeys, ($k * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
488 seek($fh, $offset + ($k * $BUCKET_SIZE), SEEK_SET);
489 print($fh $key . pack($LONG_PACK, $old_subloc || $self->root->{end}) );
495 $offsets[$num] = $self->root->{end};
496 seek($fh, $index_tag->{offset} + ($num * $LONG_SIZE), SEEK_SET);
497 print($fh pack($LONG_PACK, $self->root->{end}) );
499 my $blist_tag = $self->_create_tag($self->root->{end}, SIG_BLIST, chr(0) x $BUCKET_LIST_SIZE);
501 seek($fh, $blist_tag->{offset}, SEEK_SET);
502 print($fh $key . pack($LONG_PACK, $old_subloc || $self->root->{end}) );
507 $location ||= $self->root->{end};
508 } # re-index bucket list
511 # Seek to content area and store signature, value and plaintext key
515 seek($fh, $location, SEEK_SET);
518 # Write signature based on content type, set content length and write actual value.
520 my $r = Scalar::Util::reftype($value) || '';
522 print($fh TYPE_HASH );
523 print($fh pack($DATA_LENGTH_PACK, $INDEX_SIZE) . chr(0) x $INDEX_SIZE );
524 $content_length = $INDEX_SIZE;
526 elsif ($r eq 'ARRAY') {
527 print($fh TYPE_ARRAY );
528 print($fh pack($DATA_LENGTH_PACK, $INDEX_SIZE) . chr(0) x $INDEX_SIZE );
529 $content_length = $INDEX_SIZE;
531 elsif (!defined($value)) {
532 print($fh SIG_NULL );
533 print($fh pack($DATA_LENGTH_PACK, 0) );
537 print($fh SIG_DATA );
538 print($fh pack($DATA_LENGTH_PACK, length($value)) . $value );
539 $content_length = length($value);
543 # Plain key is stored AFTER value, as keys are typically fetched less often.
545 print($fh pack($DATA_LENGTH_PACK, length($plain_key)) . $plain_key );
548 # If value is blessed, preserve class name
550 if ( $self->root->{autobless} ) {
551 my $value_class = Scalar::Util::blessed($value);
552 if ( defined $value_class && $value_class ne 'DBM::Deep' ) {
554 # Blessed ref -- will restore later
557 print($fh pack($DATA_LENGTH_PACK, length($value_class)) . $value_class );
558 $content_length += 1;
559 $content_length += $DATA_LENGTH_SIZE + length($value_class);
563 $content_length += 1;
568 # If this is a new content area, advance EOF counter
570 if ($location == $self->root->{end}) {
571 $self->root->{end} += SIG_SIZE;
572 $self->root->{end} += $DATA_LENGTH_SIZE + $content_length;
573 $self->root->{end} += $DATA_LENGTH_SIZE + length($plain_key);
577 # If content is a hash or array, create new child DeepDB object and
578 # pass each key or element to it.
581 my $branch = DBM::Deep->new(
583 base_offset => $location,
586 foreach my $key (keys %{$value}) {
587 #$branch->{$key} = $value->{$key};
588 $branch->STORE( $key, $value->{$key} );
591 elsif ($r eq 'ARRAY') {
592 my $branch = DBM::Deep->new(
594 base_offset => $location,
598 foreach my $element (@{$value}) {
599 #$branch->[$index] = $element;
600 $branch->STORE( $index, $element );
608 return $self->_throw_error("Fatal error: indexing failed -- possibly due to corruption in file");
611 sub _get_bucket_value {
613 # Fetch single value given tag and MD5 digested key.
616 my ($tag, $md5) = @_;
617 my $keys = $tag->{content};
622 # Iterate through buckets, looking for a key match
625 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
626 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
627 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
631 # Hit end of list, no match
636 if ( $md5 ne $key ) {
641 # Found match -- seek to offset and read signature
644 seek($fh, $subloc, SEEK_SET);
645 read( $fh, $signature, SIG_SIZE);
648 # If value is a hash or array, return new DeepDB object with correct offset
650 if (($signature eq TYPE_HASH) || ($signature eq TYPE_ARRAY)) {
651 my $obj = DBM::Deep->new(
653 base_offset => $subloc,
657 if ($self->root->{autobless}) {
659 # Skip over value and plain key to see if object needs
662 seek($fh, $DATA_LENGTH_SIZE + $INDEX_SIZE, SEEK_CUR);
665 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
666 if ($size) { seek($fh, $size, SEEK_CUR); }
669 read( $fh, $bless_bit, 1);
670 if (ord($bless_bit)) {
672 # Yes, object needs to be re-blessed
675 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
676 if ($size) { read( $fh, $class_name, $size); }
677 if ($class_name) { $obj = bless( $obj, $class_name ); }
685 # Otherwise return actual value
687 elsif ($signature eq SIG_DATA) {
690 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
691 if ($size) { read( $fh, $value, $size); }
696 # Key exists, but content is null
706 # Delete single key/value pair given tag and MD5 digested key.
709 my ($tag, $md5) = @_;
710 my $keys = $tag->{content};
715 # Iterate through buckets, looking for a key match
718 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
719 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
720 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
724 # Hit end of list, no match
729 if ( $md5 ne $key ) {
734 # Matched key -- delete bucket and return
736 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE), SEEK_SET);
737 print($fh substr($keys, ($i+1) * $BUCKET_SIZE ) );
738 print($fh chr(0) x $BUCKET_SIZE );
748 # Check existence of single key given tag and MD5 digested key.
751 my ($tag, $md5) = @_;
752 my $keys = $tag->{content};
755 # Iterate through buckets, looking for a key match
758 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
759 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
760 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
764 # Hit end of list, no match
769 if ( $md5 ne $key ) {
774 # Matched key -- return true
782 sub _find_bucket_list {
784 # Locate offset for bucket list, given digested key
790 # Locate offset for bucket list using digest index system
793 my $tag = $self->_load_tag($self->base_offset);
794 if (!$tag) { return; }
796 while ($tag->{signature} ne SIG_BLIST) {
797 $tag = $self->_index_lookup($tag, ord(substr($md5, $ch, 1)));
798 if (!$tag) { return; }
805 sub _traverse_index {
807 # Scan index and recursively step into deeper levels, looking for next key.
809 my ($self, $offset, $ch, $force_return_next) = @_;
810 $force_return_next = undef unless $force_return_next;
812 my $tag = $self->_load_tag( $offset );
816 if ($tag->{signature} ne SIG_BLIST) {
817 my $content = $tag->{content};
819 if ($self->{return_next}) { $start = 0; }
820 else { $start = ord(substr($self->{prev_md5}, $ch, 1)); }
822 for (my $index = $start; $index < 256; $index++) {
823 my $subloc = unpack($LONG_PACK, substr($content, $index * $LONG_SIZE, $LONG_SIZE) );
825 my $result = $self->_traverse_index( $subloc, $ch + 1, $force_return_next );
826 if (defined($result)) { return $result; }
830 $self->{return_next} = 1;
833 elsif ($tag->{signature} eq SIG_BLIST) {
834 my $keys = $tag->{content};
835 if ($force_return_next) { $self->{return_next} = 1; }
838 # Iterate through buckets, looking for a key match
840 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
841 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
842 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
846 # End of bucket list -- return to outer loop
848 $self->{return_next} = 1;
851 elsif ($key eq $self->{prev_md5}) {
853 # Located previous key -- return next one found
855 $self->{return_next} = 1;
858 elsif ($self->{return_next}) {
860 # Seek to bucket location and skip over signature
862 seek($fh, $subloc + SIG_SIZE, SEEK_SET);
865 # Skip over value to get to plain key
868 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
869 if ($size) { seek($fh, $size, SEEK_CUR); }
872 # Read in plain key and return as scalar
875 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
876 if ($size) { read( $fh, $plain_key, $size); }
882 $self->{return_next} = 1;
883 } # tag is a bucket list
890 # Locate next key, given digested previous one
892 my $self = $_[0]->_get_self;
894 $self->{prev_md5} = $_[1] ? $_[1] : undef;
895 $self->{return_next} = 0;
898 # If the previous key was not specifed, start at the top and
899 # return the first one found.
901 if (!$self->{prev_md5}) {
902 $self->{prev_md5} = chr(0) x $HASH_SIZE;
903 $self->{return_next} = 1;
906 return $self->_traverse_index( $self->base_offset, 0 );
911 # If db locking is set, flock() the db file. If called multiple
912 # times before unlock(), then the same number of unlocks() must
913 # be called before the lock is released.
915 my $self = $_[0]->_get_self;
917 $type = LOCK_EX unless defined $type;
919 if (!defined($self->fh)) { return; }
921 if ($self->root->{locking}) {
922 if (!$self->root->{locked}) { flock($self->fh, $type); }
923 $self->root->{locked}++;
933 # If db locking is set, unlock the db file. See note in lock()
934 # regarding calling lock() multiple times.
936 my $self = $_[0]->_get_self;
938 if (!defined($self->fh)) { return; }
940 if ($self->root->{locking} && $self->root->{locked} > 0) {
941 $self->root->{locked}--;
942 if (!$self->root->{locked}) { flock($self->fh, LOCK_UN); }
950 #XXX These uses of ref() need verified
953 # Copy single level of keys or elements to new DB handle.
954 # Recurse for nested structures
956 my $self = $_[0]->_get_self;
959 if ($self->type eq TYPE_HASH) {
960 my $key = $self->first_key();
962 my $value = $self->get($key);
963 #XXX This doesn't work with autobless
964 if (!ref($value)) { $db_temp->{$key} = $value; }
966 my $type = $value->type;
967 if ($type eq TYPE_HASH) { $db_temp->{$key} = {}; }
968 else { $db_temp->{$key} = []; }
969 $value->_copy_node( $db_temp->{$key} );
971 $key = $self->next_key($key);
975 my $length = $self->length();
976 for (my $index = 0; $index < $length; $index++) {
977 my $value = $self->get($index);
978 if (!ref($value)) { $db_temp->[$index] = $value; }
979 #XXX NO tests for this code
981 my $type = $value->type;
982 if ($type eq TYPE_HASH) { $db_temp->[$index] = {}; }
983 else { $db_temp->[$index] = []; }
984 $value->_copy_node( $db_temp->[$index] );
992 # Recursively export into standard Perl hashes and arrays.
994 my $self = $_[0]->_get_self;
997 if ($self->type eq TYPE_HASH) { $temp = {}; }
998 elsif ($self->type eq TYPE_ARRAY) { $temp = []; }
1001 $self->_copy_node( $temp );
1009 # Recursively import Perl hash/array structure
1011 #XXX This use of ref() seems to be ok
1012 if (!ref($_[0])) { return; } # Perl calls import() on use -- ignore
1014 my $self = $_[0]->_get_self;
1017 #XXX This use of ref() seems to be ok
1018 if (!ref($struct)) {
1020 # struct is not a reference, so just import based on our type
1024 if ($self->type eq TYPE_HASH) { $struct = {@_}; }
1025 elsif ($self->type eq TYPE_ARRAY) { $struct = [@_]; }
1028 my $r = Scalar::Util::reftype($struct) || '';
1029 if ($r eq "HASH" && $self->type eq TYPE_HASH) {
1030 foreach my $key (keys %$struct) { $self->put($key, $struct->{$key}); }
1032 elsif ($r eq "ARRAY" && $self->type eq TYPE_ARRAY) {
1033 $self->push( @$struct );
1036 return $self->_throw_error("Cannot import: type mismatch");
1044 # Rebuild entire database into new file, then move
1045 # it back on top of original.
1047 my $self = $_[0]->_get_self;
1049 #XXX Need to create a new test for this
1050 # if ($self->root->{links} > 1) {
1051 # return $self->_throw_error("Cannot optimize: reference count is greater than 1");
1054 my $db_temp = DBM::Deep->new(
1055 file => $self->root->{file} . '.tmp',
1059 return $self->_throw_error("Cannot optimize: failed to open temp file: $!");
1063 $self->_copy_node( $db_temp );
1067 # Attempt to copy user, group and permissions over to new file
1069 my @stats = stat($self->fh);
1070 my $perms = $stats[2] & 07777;
1071 my $uid = $stats[4];
1072 my $gid = $stats[5];
1073 chown( $uid, $gid, $self->root->{file} . '.tmp' );
1074 chmod( $perms, $self->root->{file} . '.tmp' );
1076 # q.v. perlport for more information on this variable
1077 if ( $^O eq 'MSWin32' ) {
1079 # Potential race condition when optmizing on Win32 with locking.
1080 # The Windows filesystem requires that the filehandle be closed
1081 # before it is overwritten with rename(). This could be redone
1088 if (!rename $self->root->{file} . '.tmp', $self->root->{file}) {
1089 unlink $self->root->{file} . '.tmp';
1091 return $self->_throw_error("Optimize failed: Cannot copy temp file over original: $!");
1103 # Make copy of object and return
1105 my $self = $_[0]->_get_self;
1107 return DBM::Deep->new(
1108 type => $self->type,
1109 base_offset => $self->base_offset,
1115 my %is_legal_filter = map {
1118 store_key store_value
1119 fetch_key fetch_value
1124 # Setup filter function for storing or fetching the key or value
1126 my $self = $_[0]->_get_self;
1127 my $type = lc $_[1];
1128 my $func = $_[2] ? $_[2] : undef;
1130 if ( $is_legal_filter{$type} ) {
1131 $self->root->{"filter_$type"} = $func;
1145 # Get access to the root structure
1147 my $self = $_[0]->_get_self;
1148 return $self->{root};
1153 # Get access to the raw FileHandle
1155 #XXX It will be useful, though, when we split out HASH and ARRAY
1156 my $self = $_[0]->_get_self;
1157 return $self->root->{fh};
1162 # Get type of current node (TYPE_HASH or TYPE_ARRAY)
1164 my $self = $_[0]->_get_self;
1165 return $self->{type};
1170 # Get base_offset of current node (TYPE_HASH or TYPE_ARRAY)
1172 my $self = $_[0]->_get_self;
1173 return $self->{base_offset};
1178 # Get last error string, or undef if no error
1181 #? ( _get_self($_[0])->{root}->{error} or undef )
1182 ? ( $_[0]->_get_self->{root}->{error} or undef )
1192 # Store error string in self
1194 my $self = $_[0]->_get_self;
1195 my $error_text = $_[1];
1197 if ( Scalar::Util::blessed $self ) {
1198 $self->root->{error} = $error_text;
1200 unless ($self->root->{debug}) {
1201 die "DBM::Deep: $error_text\n";
1204 warn "DBM::Deep: $error_text\n";
1208 die "DBM::Deep: $error_text\n";
1216 my $self = $_[0]->_get_self;
1218 undef $self->root->{error};
1223 # Precalculate index, bucket and bucket list sizes
1226 #XXX I don't like this ...
1227 set_pack() unless defined $LONG_SIZE;
1229 $INDEX_SIZE = 256 * $LONG_SIZE;
1230 $BUCKET_SIZE = $HASH_SIZE + $LONG_SIZE;
1231 $BUCKET_LIST_SIZE = $MAX_BUCKETS * $BUCKET_SIZE;
1236 # Set pack/unpack modes (see file header for more)
1238 my ($long_s, $long_p, $data_s, $data_p) = @_;
1240 $LONG_SIZE = $long_s ? $long_s : 4;
1241 $LONG_PACK = $long_p ? $long_p : 'N';
1243 $DATA_LENGTH_SIZE = $data_s ? $data_s : 4;
1244 $DATA_LENGTH_PACK = $data_p ? $data_p : 'N';
1251 # Set key digest function (default is MD5)
1253 my ($digest_func, $hash_size) = @_;
1255 $DIGEST_FUNC = $digest_func ? $digest_func : \&Digest::MD5::md5;
1256 $HASH_SIZE = $hash_size ? $hash_size : 16;
1262 # tie() methods (hashes and arrays)
1267 # Store single hash key/value or array element in database.
1269 my $self = $_[0]->_get_self;
1272 #XXX What is ref() checking here?
1273 #YYY User may be storing a hash, in which case we do not want it run
1274 #YYY through the filtering system
1275 my $value = ($self->root->{filter_store_value} && !ref($_[2]))
1276 ? $self->root->{filter_store_value}->($_[2])
1279 my $md5 = $DIGEST_FUNC->($key);
1282 # Make sure file is open
1284 if (!defined($self->fh) && !$self->_open()) {
1292 # Request exclusive lock for writing
1294 $self->lock( LOCK_EX );
1297 # If locking is enabled, set 'end' parameter again, in case another
1298 # DB instance appended to our file while we were unlocked.
1300 if ($self->root->{locking} || $self->root->{volatile}) {
1301 $self->root->{end} = (stat($fh))[7];
1305 # Locate offset for bucket list using digest index system
1307 my $tag = $self->_load_tag($self->base_offset);
1309 $tag = $self->_create_tag($self->base_offset, SIG_INDEX, chr(0) x $INDEX_SIZE);
1313 while ($tag->{signature} ne SIG_BLIST) {
1314 my $num = ord(substr($md5, $ch, 1));
1315 my $new_tag = $self->_index_lookup($tag, $num);
1317 my $ref_loc = $tag->{offset} + ($num * $LONG_SIZE);
1318 seek($fh, $ref_loc, SEEK_SET);
1319 print($fh pack($LONG_PACK, $self->root->{end}) );
1321 $tag = $self->_create_tag($self->root->{end}, SIG_BLIST, chr(0) x $BUCKET_LIST_SIZE);
1322 $tag->{ref_loc} = $ref_loc;
1327 my $ref_loc = $tag->{offset} + ($num * $LONG_SIZE);
1329 $tag->{ref_loc} = $ref_loc;
1336 # Add key/value to bucket list
1338 my $result = $self->_add_bucket( $tag, $md5, $key, $value );
1347 # Fetch single value or element given plain key or array index
1349 my $self = shift->_get_self;
1353 # Make sure file is open
1355 if (!defined($self->fh)) { $self->_open(); }
1357 my $md5 = $DIGEST_FUNC->($key);
1360 # Request shared lock for reading
1362 $self->lock( LOCK_SH );
1364 my $tag = $self->_find_bucket_list( $md5 );
1371 # Get value from bucket list
1373 my $result = $self->_get_bucket_value( $tag, $md5 );
1377 #XXX What is ref() checking here?
1378 return ($result && !ref($result) && $self->root->{filter_fetch_value})
1379 ? $self->root->{filter_fetch_value}->($result)
1385 # Delete single key/value pair or element given plain key or array index
1387 my $self = $_[0]->_get_self;
1390 my $unpacked_key = $key;
1391 if (($self->type eq TYPE_ARRAY) && ($key =~ /^\d+$/)) { $key = pack($LONG_PACK, $key); }
1392 my $md5 = $DIGEST_FUNC->($key);
1395 # Make sure file is open
1397 if (!defined($self->fh)) { $self->_open(); }
1400 # Request exclusive lock for writing
1402 $self->lock( LOCK_EX );
1404 my $tag = $self->_find_bucket_list( $md5 );
1413 my $value = $self->FETCH( $unpacked_key );
1414 my $result = $self->_delete_bucket( $tag, $md5 );
1417 # If this object is an array and the key deleted was on the end of the stack,
1418 # decrement the length variable.
1420 if ($result && ($self->type eq TYPE_ARRAY) && ($unpacked_key == $self->FETCHSIZE() - 1)) {
1421 $self->STORESIZE( $unpacked_key );
1431 # Check if a single key or element exists given plain key or array index
1433 my $self = $_[0]->_get_self;
1436 my $md5 = $DIGEST_FUNC->($key);
1439 # Make sure file is open
1441 if (!defined($self->fh)) { $self->_open(); }
1444 # Request shared lock for reading
1446 $self->lock( LOCK_SH );
1448 my $tag = $self->_find_bucket_list( $md5 );
1451 # For some reason, the built-in exists() function returns '' for false
1459 # Check if bucket exists and return 1 or ''
1461 my $result = $self->_bucket_exists( $tag, $md5 ) || '';
1470 # Clear all keys from hash, or all elements from array.
1472 my $self = $_[0]->_get_self;
1475 # Make sure file is open
1477 if (!defined($self->fh)) { $self->_open(); }
1480 # Request exclusive lock for writing
1482 $self->lock( LOCK_EX );
1486 seek($fh, $self->base_offset, SEEK_SET);
1492 $self->_create_tag($self->base_offset, $self->type, chr(0) x $INDEX_SIZE);
1500 # Public method aliases
1502 sub put { (shift)->STORE( @_ ) }
1503 sub store { (shift)->STORE( @_ ) }
1504 sub get { (shift)->FETCH( @_ ) }
1505 sub fetch { (shift)->FETCH( @_ ) }
1506 sub delete { (shift)->DELETE( @_ ) }
1507 sub exists { (shift)->EXISTS( @_ ) }
1508 sub clear { (shift)->CLEAR( @_ ) }
1510 package DBM::Deep::_::Root;
1525 filter_store_key => undef,
1526 filter_store_value => undef,
1527 filter_fetch_key => undef,
1528 filter_fetch_value => undef,
1539 return unless $self;
1541 close $self->{fh} if $self->{fh};
1552 DBM::Deep - A pure perl multi-level hash/array DBM
1557 my $db = DBM::Deep->new( "foo.db" );
1559 $db->{key} = 'value'; # tie() style
1562 $db->put('key', 'value'); # OO style
1563 print $db->get('key');
1565 # true multi-level support
1566 $db->{my_complex} = [
1567 'hello', { perl => 'rules' },
1572 A unique flat-file database module, written in pure perl. True
1573 multi-level hash/array support (unlike MLDBM, which is faked), hybrid
1574 OO / tie() interface, cross-platform FTPable files, and quite fast. Can
1575 handle millions of keys and unlimited hash levels without significant
1576 slow-down. Written from the ground-up in pure perl -- this is NOT a
1577 wrapper around a C-based DBM. Out-of-the-box compatibility with Unix,
1578 Mac OS X and Windows.
1582 Hopefully you are using CPAN's excellent Perl module, which will download
1583 and install the module for you. If not, get the tarball, and run these
1595 Construction can be done OO-style (which is the recommended way), or using
1596 Perl's tie() function. Both are examined here.
1598 =head2 OO CONSTRUCTION
1600 The recommended way to construct a DBM::Deep object is to use the new()
1601 method, which gets you a blessed, tied hash or array reference.
1603 my $db = DBM::Deep->new( "foo.db" );
1605 This opens a new database handle, mapped to the file "foo.db". If this
1606 file does not exist, it will automatically be created. DB files are
1607 opened in "r+" (read/write) mode, and the type of object returned is a
1608 hash, unless otherwise specified (see L<OPTIONS> below).
1612 You can pass a number of options to the constructor to specify things like
1613 locking, autoflush, etc. This is done by passing an inline hash:
1615 my $db = DBM::Deep->new(
1621 Notice that the filename is now specified I<inside> the hash with
1622 the "file" parameter, as opposed to being the sole argument to the
1623 constructor. This is required if any options are specified.
1624 See L<OPTIONS> below for the complete list.
1628 You can also start with an array instead of a hash. For this, you must
1629 specify the C<type> parameter:
1631 my $db = DBM::Deep->new(
1633 type => DBM::Deep->TYPE_ARRAY
1636 B<Note:> Specifing the C<type> parameter only takes effect when beginning
1637 a new DB file. If you create a DBM::Deep object with an existing file, the
1638 C<type> will be loaded from the file header, and ignored if it is passed
1641 =head2 TIE CONSTRUCTION
1643 Alternatively, you can create a DBM::Deep handle by using Perl's built-in
1644 tie() function. This is not ideal, because you get only a basic, tied hash
1645 (or array) which is not blessed, so you can't call any functions on it.
1648 tie %hash, "DBM::Deep", "foo.db";
1651 tie @array, "DBM::Deep", "bar.db";
1653 As with the OO constructor, you can replace the DB filename parameter with
1654 a hash containing one or more options (see L<OPTIONS> just below for the
1657 tie %hash, "DBM::Deep", {
1665 There are a number of options that can be passed in when constructing your
1666 DBM::Deep objects. These apply to both the OO- and tie- based approaches.
1672 Filename of the DB file to link the handle to. You can pass a full absolute
1673 filesystem path, partial path, or a plain filename if the file is in the
1674 current working directory. This is a required parameter.
1678 File open mode (read-only, read-write, etc.) string passed to Perl's FileHandle
1679 module. This is an optional parameter, and defaults to "r+" (read/write).
1680 B<Note:> If the default (r+) mode is selected, the file will also be auto-
1681 created if it doesn't exist.
1685 This parameter specifies what type of object to create, a hash or array. Use
1686 one of these two constants: C<DBM::Deep-E<gt>TYPE_HASH> or C<DBM::Deep-E<gt>TYPE_ARRAY>.
1687 This only takes effect when beginning a new file. This is an optional
1688 parameter, and defaults to C<DBM::Deep-E<gt>TYPE_HASH>.
1692 Specifies whether locking is to be enabled. DBM::Deep uses Perl's Fnctl flock()
1693 function to lock the database in exclusive mode for writes, and shared mode for
1694 reads. Pass any true value to enable. This affects the base DB handle I<and
1695 any child hashes or arrays> that use the same DB file. This is an optional
1696 parameter, and defaults to 0 (disabled). See L<LOCKING> below for more.
1700 Specifies whether autoflush is to be enabled on the underlying FileHandle.
1701 This obviously slows down write operations, but is required if you may have
1702 multiple processes accessing the same DB file (also consider enable I<locking>
1703 or at least I<volatile>). Pass any true value to enable. This is an optional
1704 parameter, and defaults to 0 (disabled).
1708 If I<volatile> mode is enabled, DBM::Deep will stat() the DB file before each
1709 STORE() operation. This is required if an outside force may change the size of
1710 the file between transactions. Locking also implicitly enables volatile. This
1711 is useful if you want to use a different locking system or write your own. Pass
1712 any true value to enable. This is an optional parameter, and defaults to 0
1717 If I<autobless> mode is enabled, DBM::Deep will preserve blessed hashes, and
1718 restore them when fetched. This is an B<experimental> feature, and does have
1719 side-effects. Basically, when hashes are re-blessed into their original
1720 classes, they are no longer blessed into the DBM::Deep class! So you won't be
1721 able to call any DBM::Deep methods on them. You have been warned.
1722 This is an optional parameter, and defaults to 0 (disabled).
1726 See L<FILTERS> below.
1730 Setting I<debug> mode will make all errors non-fatal, dump them out to
1731 STDERR, and continue on. This is for debugging purposes only, and probably
1732 not what you want. This is an optional parameter, and defaults to 0 (disabled).
1736 Instead of passing a file path, you can instead pass a handle to an pre-opened
1737 filehandle. Note: Beware of using the magick *DATA handle, as this actually
1738 contains your entire Perl script, as well as the data following the __DATA__
1739 marker. This will not work, because DBM::Deep uses absolute seek()s into the
1740 file. Instead, consider reading *DATA into an IO::Scalar handle, then passing
1745 =head1 TIE INTERFACE
1747 With DBM::Deep you can access your databases using Perl's standard hash/array
1748 syntax. Because all DBM::Deep objects are I<tied> to hashes or arrays, you can treat
1749 them as such. DBM::Deep will intercept all reads/writes and direct them to the right
1750 place -- the DB file. This has nothing to do with the L<TIE CONSTRUCTION>
1751 section above. This simply tells you how to use DBM::Deep using regular hashes
1752 and arrays, rather than calling functions like C<get()> and C<put()> (although those
1753 work too). It is entirely up to you how to want to access your databases.
1757 You can treat any DBM::Deep object like a normal Perl hash reference. Add keys,
1758 or even nested hashes (or arrays) using standard Perl syntax:
1760 my $db = DBM::Deep->new( "foo.db" );
1762 $db->{mykey} = "myvalue";
1764 $db->{myhash}->{subkey} = "subvalue";
1766 print $db->{myhash}->{subkey} . "\n";
1768 You can even step through hash keys using the normal Perl C<keys()> function:
1770 foreach my $key (keys %$db) {
1771 print "$key: " . $db->{$key} . "\n";
1774 Remember that Perl's C<keys()> function extracts I<every> key from the hash and
1775 pushes them onto an array, all before the loop even begins. If you have an
1776 extra large hash, this may exhaust Perl's memory. Instead, consider using
1777 Perl's C<each()> function, which pulls keys/values one at a time, using very
1780 while (my ($key, $value) = each %$db) {
1781 print "$key: $value\n";
1784 Please note that when using C<each()>, you should always pass a direct
1785 hash reference, not a lookup. Meaning, you should B<never> do this:
1788 while (my ($key, $value) = each %{$db->{foo}}) { # BAD
1790 This causes an infinite loop, because for each iteration, Perl is calling
1791 FETCH() on the $db handle, resulting in a "new" hash for foo every time, so
1792 it effectively keeps returning the first key over and over again. Instead,
1793 assign a temporary variable to C<$db->{foo}>, then pass that to each().
1797 As with hashes, you can treat any DBM::Deep object like a normal Perl array
1798 reference. This includes inserting, removing and manipulating elements,
1799 and the C<push()>, C<pop()>, C<shift()>, C<unshift()> and C<splice()> functions.
1800 The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>,
1801 or simply be a nested array reference inside a hash. Example:
1803 my $db = DBM::Deep->new(
1804 file => "foo-array.db",
1805 type => DBM::Deep->TYPE_ARRAY
1809 push @$db, "bar", "baz";
1810 unshift @$db, "bah";
1812 my $last_elem = pop @$db; # baz
1813 my $first_elem = shift @$db; # bah
1814 my $second_elem = $db->[1]; # bar
1816 my $num_elements = scalar @$db;
1820 In addition to the I<tie()> interface, you can also use a standard OO interface
1821 to manipulate all aspects of DBM::Deep databases. Each type of object (hash or
1822 array) has its own methods, but both types share the following common methods:
1823 C<put()>, C<get()>, C<exists()>, C<delete()> and C<clear()>.
1829 Stores a new hash key/value pair, or sets an array element value. Takes two
1830 arguments, the hash key or array index, and the new value. The value can be
1831 a scalar, hash ref or array ref. Returns true on success, false on failure.
1833 $db->put("foo", "bar"); # for hashes
1834 $db->put(1, "bar"); # for arrays
1838 Fetches the value of a hash key or array element. Takes one argument: the hash
1839 key or array index. Returns a scalar, hash ref or array ref, depending on the
1842 my $value = $db->get("foo"); # for hashes
1843 my $value = $db->get(1); # for arrays
1847 Checks if a hash key or array index exists. Takes one argument: the hash key
1848 or array index. Returns true if it exists, false if not.
1850 if ($db->exists("foo")) { print "yay!\n"; } # for hashes
1851 if ($db->exists(1)) { print "yay!\n"; } # for arrays
1855 Deletes one hash key/value pair or array element. Takes one argument: the hash
1856 key or array index. Returns true on success, false if not found. For arrays,
1857 the remaining elements located after the deleted element are NOT moved over.
1858 The deleted element is essentially just undefined, which is exactly how Perl's
1859 internal arrays work. Please note that the space occupied by the deleted
1860 key/value or element is B<not> reused again -- see L<UNUSED SPACE RECOVERY>
1861 below for details and workarounds.
1863 $db->delete("foo"); # for hashes
1864 $db->delete(1); # for arrays
1868 Deletes B<all> hash keys or array elements. Takes no arguments. No return
1869 value. Please note that the space occupied by the deleted keys/values or
1870 elements is B<not> reused again -- see L<UNUSED SPACE RECOVERY> below for
1871 details and workarounds.
1873 $db->clear(); # hashes or arrays
1879 For hashes, DBM::Deep supports all the common methods described above, and the
1880 following additional methods: C<first_key()> and C<next_key()>.
1886 Returns the "first" key in the hash. As with built-in Perl hashes, keys are
1887 fetched in an undefined order (which appears random). Takes no arguments,
1888 returns the key as a scalar value.
1890 my $key = $db->first_key();
1894 Returns the "next" key in the hash, given the previous one as the sole argument.
1895 Returns undef if there are no more keys to be fetched.
1897 $key = $db->next_key($key);
1901 Here are some examples of using hashes:
1903 my $db = DBM::Deep->new( "foo.db" );
1905 $db->put("foo", "bar");
1906 print "foo: " . $db->get("foo") . "\n";
1908 $db->put("baz", {}); # new child hash ref
1909 $db->get("baz")->put("buz", "biz");
1910 print "buz: " . $db->get("baz")->get("buz") . "\n";
1912 my $key = $db->first_key();
1914 print "$key: " . $db->get($key) . "\n";
1915 $key = $db->next_key($key);
1918 if ($db->exists("foo")) { $db->delete("foo"); }
1922 For arrays, DBM::Deep supports all the common methods described above, and the
1923 following additional methods: C<length()>, C<push()>, C<pop()>, C<shift()>,
1924 C<unshift()> and C<splice()>.
1930 Returns the number of elements in the array. Takes no arguments.
1932 my $len = $db->length();
1936 Adds one or more elements onto the end of the array. Accepts scalars, hash
1937 refs or array refs. No return value.
1939 $db->push("foo", "bar", {});
1943 Fetches the last element in the array, and deletes it. Takes no arguments.
1944 Returns undef if array is empty. Returns the element value.
1946 my $elem = $db->pop();
1950 Fetches the first element in the array, deletes it, then shifts all the
1951 remaining elements over to take up the space. Returns the element value. This
1952 method is not recommended with large arrays -- see L<LARGE ARRAYS> below for
1955 my $elem = $db->shift();
1959 Inserts one or more elements onto the beginning of the array, shifting all
1960 existing elements over to make room. Accepts scalars, hash refs or array refs.
1961 No return value. This method is not recommended with large arrays -- see
1962 <LARGE ARRAYS> below for details.
1964 $db->unshift("foo", "bar", {});
1968 Performs exactly like Perl's built-in function of the same name. See L<perldoc
1969 -f splice> for usage -- it is too complicated to document here. This method is
1970 not recommended with large arrays -- see L<LARGE ARRAYS> below for details.
1974 Here are some examples of using arrays:
1976 my $db = DBM::Deep->new(
1978 type => DBM::Deep->TYPE_ARRAY
1981 $db->push("bar", "baz");
1982 $db->unshift("foo");
1985 my $len = $db->length();
1986 print "length: $len\n"; # 4
1988 for (my $k=0; $k<$len; $k++) {
1989 print "$k: " . $db->get($k) . "\n";
1992 $db->splice(1, 2, "biz", "baf");
1994 while (my $elem = shift @$db) {
1995 print "shifted: $elem\n";
2000 Enable automatic file locking by passing a true value to the C<locking>
2001 parameter when constructing your DBM::Deep object (see L<SETUP> above).
2003 my $db = DBM::Deep->new(
2008 This causes DBM::Deep to C<flock()> the underlying FileHandle object with exclusive
2009 mode for writes, and shared mode for reads. This is required if you have
2010 multiple processes accessing the same database file, to avoid file corruption.
2011 Please note that C<flock()> does NOT work for files over NFS. See L<DB OVER
2012 NFS> below for more.
2014 =head2 EXPLICIT LOCKING
2016 You can explicitly lock a database, so it remains locked for multiple
2017 transactions. This is done by calling the C<lock()> method, and passing an
2018 optional lock mode argument (defaults to exclusive mode). This is particularly
2019 useful for things like counters, where the current value needs to be fetched,
2020 then incremented, then stored again.
2023 my $counter = $db->get("counter");
2025 $db->put("counter", $counter);
2034 You can pass C<lock()> an optional argument, which specifies which mode to use
2035 (exclusive or shared). Use one of these two constants: C<DBM::Deep-E<gt>LOCK_EX>
2036 or C<DBM::Deep-E<gt>LOCK_SH>. These are passed directly to C<flock()>, and are the
2037 same as the constants defined in Perl's C<Fcntl> module.
2039 $db->lock( DBM::Deep->LOCK_SH );
2043 If you want to implement your own file locking scheme, be sure to create your
2044 DBM::Deep objects setting the C<volatile> option to true. This hints to DBM::Deep
2045 that the DB file may change between transactions. See L<LOW-LEVEL ACCESS>
2048 =head1 IMPORTING/EXPORTING
2050 You can import existing complex structures by calling the C<import()> method,
2051 and export an entire database into an in-memory structure using the C<export()>
2052 method. Both are examined here.
2056 Say you have an existing hash with nested hashes/arrays inside it. Instead of
2057 walking the structure and adding keys/elements to the database as you go,
2058 simply pass a reference to the C<import()> method. This recursively adds
2059 everything to an existing DBM::Deep object for you. Here is an example:
2064 array1 => [ "elem0", "elem1", "elem2" ],
2066 subkey1 => "subvalue1",
2067 subkey2 => "subvalue2"
2071 my $db = DBM::Deep->new( "foo.db" );
2072 $db->import( $struct );
2074 print $db->{key1} . "\n"; # prints "value1"
2076 This recursively imports the entire C<$struct> object into C<$db>, including
2077 all nested hashes and arrays. If the DBM::Deep object contains exsiting data,
2078 keys are merged with the existing ones, replacing if they already exist.
2079 The C<import()> method can be called on any database level (not just the base
2080 level), and works with both hash and array DB types.
2084 B<Note:> Make sure your existing structure has no circular references in it.
2085 These will cause an infinite loop when importing.
2089 Calling the C<export()> method on an existing DBM::Deep object will return
2090 a reference to a new in-memory copy of the database. The export is done
2091 recursively, so all nested hashes/arrays are all exported to standard Perl
2092 objects. Here is an example:
2094 my $db = DBM::Deep->new( "foo.db" );
2096 $db->{key1} = "value1";
2097 $db->{key2} = "value2";
2099 $db->{hash1}->{subkey1} = "subvalue1";
2100 $db->{hash1}->{subkey2} = "subvalue2";
2102 my $struct = $db->export();
2104 print $struct->{key1} . "\n"; # prints "value1"
2106 This makes a complete copy of the database in memory, and returns a reference
2107 to it. The C<export()> method can be called on any database level (not just
2108 the base level), and works with both hash and array DB types. Be careful of
2109 large databases -- you can store a lot more data in a DBM::Deep object than an
2110 in-memory Perl structure.
2114 B<Note:> Make sure your database has no circular references in it.
2115 These will cause an infinite loop when exporting.
2119 DBM::Deep has a number of hooks where you can specify your own Perl function
2120 to perform filtering on incoming or outgoing data. This is a perfect
2121 way to extend the engine, and implement things like real-time compression or
2122 encryption. Filtering applies to the base DB level, and all child hashes /
2123 arrays. Filter hooks can be specified when your DBM::Deep object is first
2124 constructed, or by calling the C<set_filter()> method at any time. There are
2125 four available filter hooks, described below:
2129 =item * filter_store_key
2131 This filter is called whenever a hash key is stored. It
2132 is passed the incoming key, and expected to return a transformed key.
2134 =item * filter_store_value
2136 This filter is called whenever a hash key or array element is stored. It
2137 is passed the incoming value, and expected to return a transformed value.
2139 =item * filter_fetch_key
2141 This filter is called whenever a hash key is fetched (i.e. via
2142 C<first_key()> or C<next_key()>). It is passed the transformed key,
2143 and expected to return the plain key.
2145 =item * filter_fetch_value
2147 This filter is called whenever a hash key or array element is fetched.
2148 It is passed the transformed value, and expected to return the plain value.
2152 Here are the two ways to setup a filter hook:
2154 my $db = DBM::Deep->new(
2156 filter_store_value => \&my_filter_store,
2157 filter_fetch_value => \&my_filter_fetch
2162 $db->set_filter( "filter_store_value", \&my_filter_store );
2163 $db->set_filter( "filter_fetch_value", \&my_filter_fetch );
2165 Your filter function will be called only when dealing with SCALAR keys or
2166 values. When nested hashes and arrays are being stored/fetched, filtering
2167 is bypassed. Filters are called as static functions, passed a single SCALAR
2168 argument, and expected to return a single SCALAR value. If you want to
2169 remove a filter, set the function reference to C<undef>:
2171 $db->set_filter( "filter_store_value", undef );
2173 =head2 REAL-TIME ENCRYPTION EXAMPLE
2175 Here is a working example that uses the I<Crypt::Blowfish> module to
2176 do real-time encryption / decryption of keys & values with DBM::Deep Filters.
2177 Please visit L<http://search.cpan.org/search?module=Crypt::Blowfish> for more
2178 on I<Crypt::Blowfish>. You'll also need the I<Crypt::CBC> module.
2181 use Crypt::Blowfish;
2184 my $cipher = Crypt::CBC->new({
2185 'key' => 'my secret key',
2186 'cipher' => 'Blowfish',
2188 'regenerate_key' => 0,
2189 'padding' => 'space',
2193 my $db = DBM::Deep->new(
2194 file => "foo-encrypt.db",
2195 filter_store_key => \&my_encrypt,
2196 filter_store_value => \&my_encrypt,
2197 filter_fetch_key => \&my_decrypt,
2198 filter_fetch_value => \&my_decrypt,
2201 $db->{key1} = "value1";
2202 $db->{key2} = "value2";
2203 print "key1: " . $db->{key1} . "\n";
2204 print "key2: " . $db->{key2} . "\n";
2210 return $cipher->encrypt( $_[0] );
2213 return $cipher->decrypt( $_[0] );
2216 =head2 REAL-TIME COMPRESSION EXAMPLE
2218 Here is a working example that uses the I<Compress::Zlib> module to do real-time
2219 compression / decompression of keys & values with DBM::Deep Filters.
2220 Please visit L<http://search.cpan.org/search?module=Compress::Zlib> for
2221 more on I<Compress::Zlib>.
2226 my $db = DBM::Deep->new(
2227 file => "foo-compress.db",
2228 filter_store_key => \&my_compress,
2229 filter_store_value => \&my_compress,
2230 filter_fetch_key => \&my_decompress,
2231 filter_fetch_value => \&my_decompress,
2234 $db->{key1} = "value1";
2235 $db->{key2} = "value2";
2236 print "key1: " . $db->{key1} . "\n";
2237 print "key2: " . $db->{key2} . "\n";
2243 return Compress::Zlib::memGzip( $_[0] ) ;
2246 return Compress::Zlib::memGunzip( $_[0] ) ;
2249 B<Note:> Filtering of keys only applies to hashes. Array "keys" are
2250 actually numerical index numbers, and are not filtered.
2252 =head1 ERROR HANDLING
2254 Most DBM::Deep methods return a true value for success, and call die() on
2255 failure. You can wrap calls in an eval block to catch the die. Also, the
2256 actual error message is stored in an internal scalar, which can be fetched by
2257 calling the C<error()> method.
2259 my $db = DBM::Deep->new( "foo.db" ); # create hash
2260 eval { $db->push("foo"); }; # ILLEGAL -- push is array-only call
2262 print $db->error(); # prints error message
2264 You can then call C<clear_error()> to clear the current error state.
2268 If you set the C<debug> option to true when creating your DBM::Deep object,
2269 all errors are considered NON-FATAL, and dumped to STDERR. This is only
2270 for debugging purposes.
2272 =head1 LARGEFILE SUPPORT
2274 If you have a 64-bit system, and your Perl is compiled with both LARGEFILE
2275 and 64-bit support, you I<may> be able to create databases larger than 2 GB.
2276 DBM::Deep by default uses 32-bit file offset tags, but these can be changed
2277 by calling the static C<set_pack()> method before you do anything else.
2279 DBM::Deep::set_pack(8, 'Q');
2281 This tells DBM::Deep to pack all file offsets with 8-byte (64-bit) quad words
2282 instead of 32-bit longs. After setting these values your DB files have a
2283 theoretical maximum size of 16 XB (exabytes).
2287 B<Note:> Changing these values will B<NOT> work for existing database files.
2288 Only change this for new files, and make sure it stays set consistently
2289 throughout the file's life. If you do set these values, you can no longer
2290 access 32-bit DB files. You can, however, call C<set_pack(4, 'N')> to change
2291 back to 32-bit mode.
2295 B<Note:> I have not personally tested files > 2 GB -- all my systems have
2296 only a 32-bit Perl. However, I have received user reports that this does
2299 =head1 LOW-LEVEL ACCESS
2301 If you require low-level access to the underlying FileHandle that DBM::Deep uses,
2302 you can call the C<fh()> method, which returns the handle:
2306 This method can be called on the root level of the datbase, or any child
2307 hashes or arrays. All levels share a I<root> structure, which contains things
2308 like the FileHandle, a reference counter, and all your options you specified
2309 when you created the object. You can get access to this root structure by
2310 calling the C<root()> method.
2312 my $root = $db->root();
2314 This is useful for changing options after the object has already been created,
2315 such as enabling/disabling locking, volatile or debug modes. You can also
2316 store your own temporary user data in this structure (be wary of name
2317 collision), which is then accessible from any child hash or array.
2319 =head1 CUSTOM DIGEST ALGORITHM
2321 DBM::Deep by default uses the I<Message Digest 5> (MD5) algorithm for hashing
2322 keys. However you can override this, and use another algorithm (such as SHA-256)
2323 or even write your own. But please note that DBM::Deep currently expects zero
2324 collisions, so your algorithm has to be I<perfect>, so to speak.
2325 Collision detection may be introduced in a later version.
2329 You can specify a custom digest algorithm by calling the static C<set_digest()>
2330 function, passing a reference to a subroutine, and the length of the algorithm's
2331 hashes (in bytes). This is a global static function, which affects ALL DBM::Deep
2332 objects. Here is a working example that uses a 256-bit hash from the
2333 I<Digest::SHA256> module. Please see
2334 L<http://search.cpan.org/search?module=Digest::SHA256> for more.
2339 my $context = Digest::SHA256::new(256);
2341 DBM::Deep::set_digest( \&my_digest, 32 );
2343 my $db = DBM::Deep->new( "foo-sha.db" );
2345 $db->{key1} = "value1";
2346 $db->{key2} = "value2";
2347 print "key1: " . $db->{key1} . "\n";
2348 print "key2: " . $db->{key2} . "\n";
2354 return substr( $context->hash($_[0]), 0, 32 );
2357 B<Note:> Your returned digest strings must be B<EXACTLY> the number
2358 of bytes you specify in the C<set_digest()> function (in this case 32).
2360 =head1 CIRCULAR REFERENCES
2362 DBM::Deep has B<experimental> support for circular references. Meaning you
2363 can have a nested hash key or array element that points to a parent object.
2364 This relationship is stored in the DB file, and is preserved between sessions.
2367 my $db = DBM::Deep->new( "foo.db" );
2370 $db->{circle} = $db; # ref to self
2372 print $db->{foo} . "\n"; # prints "foo"
2373 print $db->{circle}->{foo} . "\n"; # prints "foo" again
2375 One catch is, passing the object to a function that recursively walks the
2376 object tree (such as I<Data::Dumper> or even the built-in C<optimize()> or
2377 C<export()> methods) will result in an infinite loop. The other catch is,
2378 if you fetch the I<key> of a circular reference (i.e. using the C<first_key()>
2379 or C<next_key()> methods), you will get the I<target object's key>, not the
2380 ref's key. This gets even more interesting with the above example, where
2381 the I<circle> key points to the base DB object, which technically doesn't
2382 have a key. So I made DBM::Deep return "[base]" as the key name in that
2385 =head1 CAVEATS / ISSUES / BUGS
2387 This section describes all the known issues with DBM::Deep. It you have found
2388 something that is not listed here, please send e-mail to L<jhuckaby@cpan.org>.
2390 =head2 UNUSED SPACE RECOVERY
2392 One major caveat with DBM::Deep is that space occupied by existing keys and
2393 values is not recovered when they are deleted. Meaning if you keep deleting
2394 and adding new keys, your file will continuously grow. I am working on this,
2395 but in the meantime you can call the built-in C<optimize()> method from time to
2396 time (perhaps in a crontab or something) to recover all your unused space.
2398 $db->optimize(); # returns true on success
2400 This rebuilds the ENTIRE database into a new file, then moves it on top of
2401 the original. The new file will have no unused space, thus it will take up as
2402 little disk space as possible. Please note that this operation can take
2403 a long time for large files, and you need enough disk space to temporarily hold
2404 2 copies of your DB file. The temporary file is created in the same directory
2405 as the original, named with a ".tmp" extension, and is deleted when the
2406 operation completes. Oh, and if locking is enabled, the DB is automatically
2407 locked for the entire duration of the copy.
2411 B<WARNING:> Only call optimize() on the top-level node of the database, and
2412 make sure there are no child references lying around. DBM::Deep keeps a reference
2413 counter, and if it is greater than 1, optimize() will abort and return undef.
2415 =head2 AUTOVIVIFICATION
2417 Unfortunately, autovivification doesn't work with tied hashes. This appears to
2418 be a bug in Perl's tie() system, as I<Jakob Schmidt> encountered the very same
2419 issue with his I<DWH_FIle> module (see L<http://search.cpan.org/search?module=DWH_File>),
2420 and it is also mentioned in the BUGS section for the I<MLDBM> module <see
2421 L<http://search.cpan.org/search?module=MLDBM>). Basically, on a new db file,
2424 $db->{foo}->{bar} = "hello";
2426 Since "foo" doesn't exist, you cannot add "bar" to it. You end up with "foo"
2427 being an empty hash. Try this instead, which works fine:
2429 $db->{foo} = { bar => "hello" };
2431 As of Perl 5.8.7, this bug still exists. I have walked very carefully through
2432 the execution path, and Perl indeed passes an empty hash to the STORE() method.
2433 Probably a bug in Perl.
2435 =head2 FILE CORRUPTION
2437 The current level of error handling in DBM::Deep is minimal. Files I<are> checked
2438 for a 32-bit signature when opened, but other corruption in files can cause
2439 segmentation faults. DBM::Deep may try to seek() past the end of a file, or get
2440 stuck in an infinite loop depending on the level of corruption. File write
2441 operations are not checked for failure (for speed), so if you happen to run
2442 out of disk space, DBM::Deep will probably fail in a bad way. These things will
2443 be addressed in a later version of DBM::Deep.
2447 Beware of using DB files over NFS. DBM::Deep uses flock(), which works well on local
2448 filesystems, but will NOT protect you from file corruption over NFS. I've heard
2449 about setting up your NFS server with a locking daemon, then using lockf() to
2450 lock your files, but your milage may vary there as well. From what I
2451 understand, there is no real way to do it. However, if you need access to the
2452 underlying FileHandle in DBM::Deep for using some other kind of locking scheme like
2453 lockf(), see the L<LOW-LEVEL ACCESS> section above.
2455 =head2 COPYING OBJECTS
2457 Beware of copying tied objects in Perl. Very strange things can happen.
2458 Instead, use DBM::Deep's C<clone()> method which safely copies the object and
2459 returns a new, blessed, tied hash or array to the same level in the DB.
2461 my $copy = $db->clone();
2465 Beware of using C<shift()>, C<unshift()> or C<splice()> with large arrays.
2466 These functions cause every element in the array to move, which can be murder
2467 on DBM::Deep, as every element has to be fetched from disk, then stored again in
2468 a different location. This may be addressed in a later version.
2472 This section discusses DBM::Deep's speed and memory usage.
2476 Obviously, DBM::Deep isn't going to be as fast as some C-based DBMs, such as
2477 the almighty I<BerkeleyDB>. But it makes up for it in features like true
2478 multi-level hash/array support, and cross-platform FTPable files. Even so,
2479 DBM::Deep is still pretty fast, and the speed stays fairly consistent, even
2480 with huge databases. Here is some test data:
2482 Adding 1,000,000 keys to new DB file...
2484 At 100 keys, avg. speed is 2,703 keys/sec
2485 At 200 keys, avg. speed is 2,642 keys/sec
2486 At 300 keys, avg. speed is 2,598 keys/sec
2487 At 400 keys, avg. speed is 2,578 keys/sec
2488 At 500 keys, avg. speed is 2,722 keys/sec
2489 At 600 keys, avg. speed is 2,628 keys/sec
2490 At 700 keys, avg. speed is 2,700 keys/sec
2491 At 800 keys, avg. speed is 2,607 keys/sec
2492 At 900 keys, avg. speed is 2,190 keys/sec
2493 At 1,000 keys, avg. speed is 2,570 keys/sec
2494 At 2,000 keys, avg. speed is 2,417 keys/sec
2495 At 3,000 keys, avg. speed is 1,982 keys/sec
2496 At 4,000 keys, avg. speed is 1,568 keys/sec
2497 At 5,000 keys, avg. speed is 1,533 keys/sec
2498 At 6,000 keys, avg. speed is 1,787 keys/sec
2499 At 7,000 keys, avg. speed is 1,977 keys/sec
2500 At 8,000 keys, avg. speed is 2,028 keys/sec
2501 At 9,000 keys, avg. speed is 2,077 keys/sec
2502 At 10,000 keys, avg. speed is 2,031 keys/sec
2503 At 20,000 keys, avg. speed is 1,970 keys/sec
2504 At 30,000 keys, avg. speed is 2,050 keys/sec
2505 At 40,000 keys, avg. speed is 2,073 keys/sec
2506 At 50,000 keys, avg. speed is 1,973 keys/sec
2507 At 60,000 keys, avg. speed is 1,914 keys/sec
2508 At 70,000 keys, avg. speed is 2,091 keys/sec
2509 At 80,000 keys, avg. speed is 2,103 keys/sec
2510 At 90,000 keys, avg. speed is 1,886 keys/sec
2511 At 100,000 keys, avg. speed is 1,970 keys/sec
2512 At 200,000 keys, avg. speed is 2,053 keys/sec
2513 At 300,000 keys, avg. speed is 1,697 keys/sec
2514 At 400,000 keys, avg. speed is 1,838 keys/sec
2515 At 500,000 keys, avg. speed is 1,941 keys/sec
2516 At 600,000 keys, avg. speed is 1,930 keys/sec
2517 At 700,000 keys, avg. speed is 1,735 keys/sec
2518 At 800,000 keys, avg. speed is 1,795 keys/sec
2519 At 900,000 keys, avg. speed is 1,221 keys/sec
2520 At 1,000,000 keys, avg. speed is 1,077 keys/sec
2522 This test was performed on a PowerMac G4 1gHz running Mac OS X 10.3.2 & Perl
2523 5.8.1, with an 80GB Ultra ATA/100 HD spinning at 7200RPM. The hash keys and
2524 values were between 6 - 12 chars in length. The DB file ended up at 210MB.
2525 Run time was 12 min 3 sec.
2529 One of the great things about DBM::Deep is that it uses very little memory.
2530 Even with huge databases (1,000,000+ keys) you will not see much increased
2531 memory on your process. DBM::Deep relies solely on the filesystem for storing
2532 and fetching data. Here is output from I</usr/bin/top> before even opening a
2535 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
2536 22831 root 11 0 2716 2716 1296 R 0.0 0.2 0:07 perl
2538 Basically the process is taking 2,716K of memory. And here is the same
2539 process after storing and fetching 1,000,000 keys:
2541 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
2542 22831 root 14 0 2772 2772 1328 R 0.0 0.2 13:32 perl
2544 Notice the memory usage increased by only 56K. Test was performed on a 700mHz
2545 x86 box running Linux RedHat 7.2 & Perl 5.6.1.
2547 =head1 DB FILE FORMAT
2549 In case you were interested in the underlying DB file format, it is documented
2550 here in this section. You don't need to know this to use the module, it's just
2551 included for reference.
2555 DBM::Deep files always start with a 32-bit signature to identify the file type.
2556 This is at offset 0. The signature is "DPDB" in network byte order. This is
2557 checked when the file is opened.
2561 The DBM::Deep file is in a I<tagged format>, meaning each section of the file
2562 has a standard header containing the type of data, the length of data, and then
2563 the data itself. The type is a single character (1 byte), the length is a
2564 32-bit unsigned long in network byte order, and the data is, well, the data.
2565 Here is how it unfolds:
2569 Immediately after the 32-bit file signature is the I<Master Index> record.
2570 This is a standard tag header followed by 1024 bytes (in 32-bit mode) or 2048
2571 bytes (in 64-bit mode) of data. The type is I<H> for hash or I<A> for array,
2572 depending on how the DBM::Deep object was constructed.
2576 The index works by looking at a I<MD5 Hash> of the hash key (or array index
2577 number). The first 8-bit char of the MD5 signature is the offset into the
2578 index, multipled by 4 in 32-bit mode, or 8 in 64-bit mode. The value of the
2579 index element is a file offset of the next tag for the key/element in question,
2580 which is usually a I<Bucket List> tag (see below).
2584 The next tag I<could> be another index, depending on how many keys/elements
2585 exist. See L<RE-INDEXING> below for details.
2589 A I<Bucket List> is a collection of 16 MD5 hashes for keys/elements, plus
2590 file offsets to where the actual data is stored. It starts with a standard
2591 tag header, with type I<B>, and a data size of 320 bytes in 32-bit mode, or
2592 384 bytes in 64-bit mode. Each MD5 hash is stored in full (16 bytes), plus
2593 the 32-bit or 64-bit file offset for the I<Bucket> containing the actual data.
2594 When the list fills up, a I<Re-Index> operation is performed (See
2595 L<RE-INDEXING> below).
2599 A I<Bucket> is a tag containing a key/value pair (in hash mode), or a
2600 index/value pair (in array mode). It starts with a standard tag header with
2601 type I<D> for scalar data (string, binary, etc.), or it could be a nested
2602 hash (type I<H>) or array (type I<A>). The value comes just after the tag
2603 header. The size reported in the tag header is only for the value, but then,
2604 just after the value is another size (32-bit unsigned long) and then the plain
2605 key itself. Since the value is likely to be fetched more often than the plain
2606 key, I figured it would be I<slightly> faster to store the value first.
2610 If the type is I<H> (hash) or I<A> (array), the value is another I<Master Index>
2611 record for the nested structure, where the process begins all over again.
2615 After a I<Bucket List> grows to 16 records, its allocated space in the file is
2616 exhausted. Then, when another key/element comes in, the list is converted to a
2617 new index record. However, this index will look at the next char in the MD5
2618 hash, and arrange new Bucket List pointers accordingly. This process is called
2619 I<Re-Indexing>. Basically, a new index tag is created at the file EOF, and all
2620 17 (16 + new one) keys/elements are removed from the old Bucket List and
2621 inserted into the new index. Several new Bucket Lists are created in the
2622 process, as a new MD5 char from the key is being examined (it is unlikely that
2623 the keys will all share the same next char of their MD5s).
2627 Because of the way the I<MD5> algorithm works, it is impossible to tell exactly
2628 when the Bucket Lists will turn into indexes, but the first round tends to
2629 happen right around 4,000 keys. You will see a I<slight> decrease in
2630 performance here, but it picks back up pretty quick (see L<SPEED> above). Then
2631 it takes B<a lot> more keys to exhaust the next level of Bucket Lists. It's
2632 right around 900,000 keys. This process can continue nearly indefinitely --
2633 right up until the point the I<MD5> signatures start colliding with each other,
2634 and this is B<EXTREMELY> rare -- like winning the lottery 5 times in a row AND
2635 getting struck by lightning while you are walking to cash in your tickets.
2636 Theoretically, since I<MD5> hashes are 128-bit values, you I<could> have up to
2637 340,282,366,921,000,000,000,000,000,000,000,000,000 keys/elements (I believe
2638 this is 340 unodecillion, but don't quote me).
2642 When a new key/element is stored, the key (or index number) is first ran through
2643 I<Digest::MD5> to get a 128-bit signature (example, in hex:
2644 b05783b0773d894396d475ced9d2f4f6). Then, the I<Master Index> record is checked
2645 for the first char of the signature (in this case I<b>). If it does not exist,
2646 a new I<Bucket List> is created for our key (and the next 15 future keys that
2647 happen to also have I<b> as their first MD5 char). The entire MD5 is written
2648 to the I<Bucket List> along with the offset of the new I<Bucket> record (EOF at
2649 this point, unless we are replacing an existing I<Bucket>), where the actual
2650 data will be stored.
2654 Fetching an existing key/element involves getting a I<Digest::MD5> of the key
2655 (or index number), then walking along the indexes. If there are enough
2656 keys/elements in this DB level, there might be nested indexes, each linked to
2657 a particular char of the MD5. Finally, a I<Bucket List> is pointed to, which
2658 contains up to 16 full MD5 hashes. Each is checked for equality to the key in
2659 question. If we found a match, the I<Bucket> tag is loaded, where the value and
2660 plain key are stored.
2664 Fetching the plain key occurs when calling the I<first_key()> and I<next_key()>
2665 methods. In this process the indexes are walked systematically, and each key
2666 fetched in increasing MD5 order (which is why it appears random). Once the
2667 I<Bucket> is found, the value is skipped the plain key returned instead.
2668 B<Note:> Do not count on keys being fetched as if the MD5 hashes were
2669 alphabetically sorted. This only happens on an index-level -- as soon as the
2670 I<Bucket Lists> are hit, the keys will come out in the order they went in --
2671 so it's pretty much undefined how the keys will come out -- just like Perl's
2674 =head1 CODE COVERAGE
2676 I use B<Devel::Cover> to test the code coverage of my tests, below is the B<Devel::Cover> report on this
2677 module's test suite.
2679 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2680 File stmt bran cond sub pod time total
2681 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2682 blib/lib/DBM/Deep.pm 93.9 82.4 74.7 97.9 10.5 85.7 88.0
2683 blib/lib/DBM/Deep/Array.pm 97.8 84.6 50.0 100.0 n/a 9.0 94.6
2684 blib/lib/DBM/Deep/Hash.pm 93.9 87.5 100.0 100.0 n/a 5.3 93.4
2685 Total 94.4 82.9 75.8 98.5 10.5 100.0 89.0
2686 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2690 Joseph Huckaby, L<jhuckaby@cpan.org>
2692 Special thanks to Adam Sah and Rich Gaushell! You know why :-)
2696 perltie(1), Tie::Hash(3), Digest::MD5(3), Fcntl(3), flock(2), lockf(3), nfs(5),
2697 Digest::SHA256(3), Crypt::Blowfish(3), Compress::Zlib(3)
2701 Copyright (c) 2002-2005 Joseph Huckaby. All Rights Reserved.
2702 This is free software, you may use it and distribute it under the
2703 same terms as Perl itself.