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 fh 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;
215 sysopen( $fh, $self->root->{file}, $flags )
217 $self->root->{fh} = $fh;
218 }; if ($@ ) { $self->_throw_error( "Received error: $@\n" ); }
219 if (! defined($self->fh)) {
220 return $self->_throw_error("Cannot sysopen file: " . $self->root->{file} . ": $!");
225 #XXX Can we remove this by using the right sysopen() flags?
226 # Maybe ... q.v. above
227 binmode $fh; # for win32
229 if ($self->root->{autoflush}) {
230 my $old = select $fh;
236 seek($fh, 0, SEEK_SET);
239 my $bytes_read = read( $fh, $signature, length(SIG_FILE));
242 # File is empty -- write signature and master index
245 seek($fh, 0, SEEK_SET);
247 $self->_create_tag($self->base_offset, $self->type, chr(0) x $INDEX_SIZE);
249 my $plain_key = "[base]";
250 print($fh pack($DATA_LENGTH_PACK, length($plain_key)) . $plain_key );
252 # Flush the filehandle
253 my $old_fh = select $fh;
259 my @stats = stat($fh);
260 $self->root->{inode} = $stats[1];
261 $self->root->{end} = $stats[7];
267 # Check signature was valid
269 unless ($signature eq SIG_FILE) {
271 return $self->_throw_error("Signature not found -- file is not a Deep DB");
274 my @stats = stat($fh);
275 $self->root->{inode} = $stats[1];
276 $self->root->{end} = $stats[7];
279 # Get our type from master index signature
281 my $tag = $self->_load_tag($self->base_offset);
283 #XXX We probably also want to store the hash algorithm name and not assume anything
284 #XXX The cool thing would be to allow a different hashing algorithm at every level
287 return $self->_throw_error("Corrupted file, no master index record");
289 if ($self->{type} ne $tag->{signature}) {
290 return $self->_throw_error("File type mismatch");
300 my $self = $_[0]->_get_self;
301 close $self->root->{fh} if $self->root->{fh};
302 $self->root->{fh} = undef;
307 # Given offset, signature and content, create tag and write to disk
309 my ($self, $offset, $sig, $content) = @_;
310 my $size = length($content);
314 seek($fh, $offset, SEEK_SET);
315 print($fh $sig . pack($DATA_LENGTH_PACK, $size) . $content );
317 if ($offset == $self->root->{end}) {
318 $self->root->{end} += SIG_SIZE + $DATA_LENGTH_SIZE + $size;
324 offset => $offset + SIG_SIZE + $DATA_LENGTH_SIZE,
331 # Given offset, load single tag and return signature, size and data
338 seek($fh, $offset, SEEK_SET);
339 if (eof $fh) { return undef; }
342 read( $fh, $sig, SIG_SIZE);
345 read( $fh, $size, $DATA_LENGTH_SIZE);
346 $size = unpack($DATA_LENGTH_PACK, $size);
349 read( $fh, $buffer, $size);
354 offset => $offset + SIG_SIZE + $DATA_LENGTH_SIZE,
361 # Given index tag, lookup single entry in index and return .
364 my ($tag, $index) = @_;
366 my $location = unpack($LONG_PACK, substr($tag->{content}, $index * $LONG_SIZE, $LONG_SIZE) );
367 if (!$location) { return; }
369 return $self->_load_tag( $location );
374 # Adds one key/value pair to bucket list, given offset, MD5 digest of key,
375 # plain (undigested) key and value.
378 my ($tag, $md5, $plain_key, $value) = @_;
379 my $keys = $tag->{content};
383 # added ref() check first to avoid eval and runtime exception for every
384 # scalar value being stored. performance tweak.
385 my $is_dbm_deep = ref($value) && eval { $value->isa( 'DBM::Deep' ) };
387 my $internal_ref = $is_dbm_deep && ($value->root eq $self->root);
392 # Iterate through buckets, seeing if this is a new entry or a replace.
394 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
395 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
396 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
399 # Found empty bucket (end of list). Populate and exit loop.
403 $location = $internal_ref
404 ? $value->base_offset
405 : $self->root->{end};
407 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE), SEEK_SET);
408 print($fh $md5 . pack($LONG_PACK, $location) );
411 elsif ($md5 eq $key) {
413 # Found existing bucket with same key. Replace with new value.
418 $location = $value->base_offset;
419 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE), SEEK_SET);
420 print($fh $md5 . pack($LONG_PACK, $location) );
423 seek($fh, $subloc + SIG_SIZE, SEEK_SET);
425 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
428 # If value is a hash, array, or raw value with equal or less size, we can
429 # reuse the same content area of the database. Otherwise, we have to create
430 # a new content area at the EOF.
433 my $r = Scalar::Util::reftype( $value ) || '';
434 if ( $r eq 'HASH' || $r eq 'ARRAY' ) {
435 $actual_length = $INDEX_SIZE;
437 # if autobless is enabled, must also take into consideration
438 # the class name, as it is stored along with key/value.
439 if ( $self->root->{autobless} ) {
440 my $value_class = Scalar::Util::blessed($value);
441 if ( defined $value_class && $value_class ne 'DBM::Deep' ) {
442 $actual_length += length($value_class);
446 else { $actual_length = length($value); }
448 if ($actual_length <= $size) {
452 $location = $self->root->{end};
453 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $HASH_SIZE, SEEK_SET);
454 print($fh pack($LONG_PACK, $location) );
462 # If this is an internal reference, return now.
463 # No need to write value or plain key
470 # If bucket didn't fit into list, split into a new index level
473 seek($fh, $tag->{ref_loc}, SEEK_SET);
474 print($fh pack($LONG_PACK, $self->root->{end}) );
476 my $index_tag = $self->_create_tag($self->root->{end}, SIG_INDEX, chr(0) x $INDEX_SIZE);
479 $keys .= $md5 . pack($LONG_PACK, 0);
481 for (my $i=0; $i<=$MAX_BUCKETS; $i++) {
482 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
484 my $old_subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
485 my $num = ord(substr($key, $tag->{ch} + 1, 1));
487 if ($offsets[$num]) {
488 my $offset = $offsets[$num] + SIG_SIZE + $DATA_LENGTH_SIZE;
489 seek($fh, $offset, SEEK_SET);
491 read( $fh, $subkeys, $BUCKET_LIST_SIZE);
493 for (my $k=0; $k<$MAX_BUCKETS; $k++) {
494 my $subloc = unpack($LONG_PACK, substr($subkeys, ($k * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
496 seek($fh, $offset + ($k * $BUCKET_SIZE), SEEK_SET);
497 print($fh $key . pack($LONG_PACK, $old_subloc || $self->root->{end}) );
503 $offsets[$num] = $self->root->{end};
504 seek($fh, $index_tag->{offset} + ($num * $LONG_SIZE), SEEK_SET);
505 print($fh pack($LONG_PACK, $self->root->{end}) );
507 my $blist_tag = $self->_create_tag($self->root->{end}, SIG_BLIST, chr(0) x $BUCKET_LIST_SIZE);
509 seek($fh, $blist_tag->{offset}, SEEK_SET);
510 print($fh $key . pack($LONG_PACK, $old_subloc || $self->root->{end}) );
515 $location ||= $self->root->{end};
516 } # re-index bucket list
519 # Seek to content area and store signature, value and plaintext key
523 seek($fh, $location, SEEK_SET);
526 # Write signature based on content type, set content length and write actual value.
528 my $r = Scalar::Util::reftype($value) || '';
530 print($fh TYPE_HASH );
531 print($fh pack($DATA_LENGTH_PACK, $INDEX_SIZE) . chr(0) x $INDEX_SIZE );
532 $content_length = $INDEX_SIZE;
534 elsif ($r eq 'ARRAY') {
535 print($fh TYPE_ARRAY );
536 print($fh pack($DATA_LENGTH_PACK, $INDEX_SIZE) . chr(0) x $INDEX_SIZE );
537 $content_length = $INDEX_SIZE;
539 elsif (!defined($value)) {
540 print($fh SIG_NULL );
541 print($fh pack($DATA_LENGTH_PACK, 0) );
545 print($fh SIG_DATA );
546 print($fh pack($DATA_LENGTH_PACK, length($value)) . $value );
547 $content_length = length($value);
551 # Plain key is stored AFTER value, as keys are typically fetched less often.
553 print($fh pack($DATA_LENGTH_PACK, length($plain_key)) . $plain_key );
556 # If value is blessed, preserve class name
558 if ( $self->root->{autobless} ) {
559 my $value_class = Scalar::Util::blessed($value);
560 if ( defined $value_class && $value_class ne 'DBM::Deep' ) {
562 # Blessed ref -- will restore later
565 print($fh pack($DATA_LENGTH_PACK, length($value_class)) . $value_class );
566 $content_length += 1;
567 $content_length += $DATA_LENGTH_SIZE + length($value_class);
571 $content_length += 1;
576 # If this is a new content area, advance EOF counter
578 if ($location == $self->root->{end}) {
579 $self->root->{end} += SIG_SIZE;
580 $self->root->{end} += $DATA_LENGTH_SIZE + $content_length;
581 $self->root->{end} += $DATA_LENGTH_SIZE + length($plain_key);
585 # If content is a hash or array, create new child DeepDB object and
586 # pass each key or element to it.
589 my $branch = DBM::Deep->new(
591 base_offset => $location,
594 foreach my $key (keys %{$value}) {
595 #$branch->{$key} = $value->{$key};
596 $branch->STORE( $key, $value->{$key} );
599 elsif ($r eq 'ARRAY') {
600 my $branch = DBM::Deep->new(
602 base_offset => $location,
606 foreach my $element (@{$value}) {
607 #$branch->[$index] = $element;
608 $branch->STORE( $index, $element );
616 return $self->_throw_error("Fatal error: indexing failed -- possibly due to corruption in file");
619 sub _get_bucket_value {
621 # Fetch single value given tag and MD5 digested key.
624 my ($tag, $md5) = @_;
625 my $keys = $tag->{content};
630 # Iterate through buckets, looking for a key match
633 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
634 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
635 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
639 # Hit end of list, no match
644 if ( $md5 ne $key ) {
649 # Found match -- seek to offset and read signature
652 seek($fh, $subloc, SEEK_SET);
653 read( $fh, $signature, SIG_SIZE);
656 # If value is a hash or array, return new DeepDB object with correct offset
658 if (($signature eq TYPE_HASH) || ($signature eq TYPE_ARRAY)) {
659 my $obj = DBM::Deep->new(
661 base_offset => $subloc,
665 if ($self->root->{autobless}) {
667 # Skip over value and plain key to see if object needs
670 seek($fh, $DATA_LENGTH_SIZE + $INDEX_SIZE, SEEK_CUR);
673 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
674 if ($size) { seek($fh, $size, SEEK_CUR); }
677 read( $fh, $bless_bit, 1);
678 if (ord($bless_bit)) {
680 # Yes, object needs to be re-blessed
683 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
684 if ($size) { read( $fh, $class_name, $size); }
685 if ($class_name) { $obj = bless( $obj, $class_name ); }
693 # Otherwise return actual value
695 elsif ($signature eq SIG_DATA) {
698 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
699 if ($size) { read( $fh, $value, $size); }
704 # Key exists, but content is null
714 # Delete single key/value pair given tag and MD5 digested key.
717 my ($tag, $md5) = @_;
718 my $keys = $tag->{content};
723 # Iterate through buckets, looking for a key match
726 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
727 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
728 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
732 # Hit end of list, no match
737 if ( $md5 ne $key ) {
742 # Matched key -- delete bucket and return
744 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE), SEEK_SET);
745 print($fh substr($keys, ($i+1) * $BUCKET_SIZE ) );
746 print($fh chr(0) x $BUCKET_SIZE );
756 # Check existence of single key given tag and MD5 digested key.
759 my ($tag, $md5) = @_;
760 my $keys = $tag->{content};
763 # Iterate through buckets, looking for a key match
766 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
767 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
768 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
772 # Hit end of list, no match
777 if ( $md5 ne $key ) {
782 # Matched key -- return true
790 sub _find_bucket_list {
792 # Locate offset for bucket list, given digested key
798 # Locate offset for bucket list using digest index system
801 my $tag = $self->_load_tag($self->base_offset);
802 if (!$tag) { return; }
804 while ($tag->{signature} ne SIG_BLIST) {
805 $tag = $self->_index_lookup($tag, ord(substr($md5, $ch, 1)));
806 if (!$tag) { return; }
813 sub _traverse_index {
815 # Scan index and recursively step into deeper levels, looking for next key.
817 my ($self, $offset, $ch, $force_return_next) = @_;
818 $force_return_next = undef unless $force_return_next;
820 my $tag = $self->_load_tag( $offset );
824 if ($tag->{signature} ne SIG_BLIST) {
825 my $content = $tag->{content};
827 if ($self->{return_next}) { $start = 0; }
828 else { $start = ord(substr($self->{prev_md5}, $ch, 1)); }
830 for (my $index = $start; $index < 256; $index++) {
831 my $subloc = unpack($LONG_PACK, substr($content, $index * $LONG_SIZE, $LONG_SIZE) );
833 my $result = $self->_traverse_index( $subloc, $ch + 1, $force_return_next );
834 if (defined($result)) { return $result; }
838 $self->{return_next} = 1;
841 elsif ($tag->{signature} eq SIG_BLIST) {
842 my $keys = $tag->{content};
843 if ($force_return_next) { $self->{return_next} = 1; }
846 # Iterate through buckets, looking for a key match
848 for (my $i=0; $i<$MAX_BUCKETS; $i++) {
849 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
850 my $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
854 # End of bucket list -- return to outer loop
856 $self->{return_next} = 1;
859 elsif ($key eq $self->{prev_md5}) {
861 # Located previous key -- return next one found
863 $self->{return_next} = 1;
866 elsif ($self->{return_next}) {
868 # Seek to bucket location and skip over signature
870 seek($fh, $subloc + SIG_SIZE, SEEK_SET);
873 # Skip over value to get to plain key
876 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
877 if ($size) { seek($fh, $size, SEEK_CUR); }
880 # Read in plain key and return as scalar
883 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
884 if ($size) { read( $fh, $plain_key, $size); }
890 $self->{return_next} = 1;
891 } # tag is a bucket list
898 # Locate next key, given digested previous one
900 my $self = $_[0]->_get_self;
902 $self->{prev_md5} = $_[1] ? $_[1] : undef;
903 $self->{return_next} = 0;
906 # If the previous key was not specifed, start at the top and
907 # return the first one found.
909 if (!$self->{prev_md5}) {
910 $self->{prev_md5} = chr(0) x $HASH_SIZE;
911 $self->{return_next} = 1;
914 return $self->_traverse_index( $self->base_offset, 0 );
919 # If db locking is set, flock() the db file. If called multiple
920 # times before unlock(), then the same number of unlocks() must
921 # be called before the lock is released.
923 my $self = $_[0]->_get_self;
925 $type = LOCK_EX unless defined $type;
927 if (!defined($self->fh)) { return; }
929 if ($self->root->{locking}) {
930 if (!$self->root->{locked}) {
931 flock($self->fh, $type);
933 # double-check file inode, in case another process
934 # has optimize()d our file while we were waiting.
935 if ((stat($self->root->{file}))[1] != $self->root->{inode}) {
936 $self->_open(); # re-open
937 flock($self->fh, $type); # re-lock
940 $self->root->{locked}++;
950 # If db locking is set, unlock the db file. See note in lock()
951 # regarding calling lock() multiple times.
953 my $self = $_[0]->_get_self;
955 if (!defined($self->fh)) { return; }
957 if ($self->root->{locking} && $self->root->{locked} > 0) {
958 $self->root->{locked}--;
959 if (!$self->root->{locked}) { flock($self->fh, LOCK_UN); }
967 #XXX These uses of ref() need verified
970 # Copy single level of keys or elements to new DB handle.
971 # Recurse for nested structures
973 my $self = $_[0]->_get_self;
976 if ($self->type eq TYPE_HASH) {
977 my $key = $self->first_key();
979 my $value = $self->get($key);
980 #XXX This doesn't work with autobless
981 if (!ref($value)) { $db_temp->{$key} = $value; }
983 my $type = $value->type;
984 if ($type eq TYPE_HASH) { $db_temp->{$key} = {}; }
985 else { $db_temp->{$key} = []; }
986 $value->_copy_node( $db_temp->{$key} );
988 $key = $self->next_key($key);
992 my $length = $self->length();
993 for (my $index = 0; $index < $length; $index++) {
994 my $value = $self->get($index);
995 if (!ref($value)) { $db_temp->[$index] = $value; }
996 #XXX NO tests for this code
998 my $type = $value->type;
999 if ($type eq TYPE_HASH) { $db_temp->[$index] = {}; }
1000 else { $db_temp->[$index] = []; }
1001 $value->_copy_node( $db_temp->[$index] );
1009 # Recursively export into standard Perl hashes and arrays.
1011 my $self = $_[0]->_get_self;
1014 if ($self->type eq TYPE_HASH) { $temp = {}; }
1015 elsif ($self->type eq TYPE_ARRAY) { $temp = []; }
1018 $self->_copy_node( $temp );
1026 # Recursively import Perl hash/array structure
1028 #XXX This use of ref() seems to be ok
1029 if (!ref($_[0])) { return; } # Perl calls import() on use -- ignore
1031 my $self = $_[0]->_get_self;
1034 #XXX This use of ref() seems to be ok
1035 if (!ref($struct)) {
1037 # struct is not a reference, so just import based on our type
1041 if ($self->type eq TYPE_HASH) { $struct = {@_}; }
1042 elsif ($self->type eq TYPE_ARRAY) { $struct = [@_]; }
1045 my $r = Scalar::Util::reftype($struct) || '';
1046 if ($r eq "HASH" && $self->type eq TYPE_HASH) {
1047 foreach my $key (keys %$struct) { $self->put($key, $struct->{$key}); }
1049 elsif ($r eq "ARRAY" && $self->type eq TYPE_ARRAY) {
1050 $self->push( @$struct );
1053 return $self->_throw_error("Cannot import: type mismatch");
1061 # Rebuild entire database into new file, then move
1062 # it back on top of original.
1064 my $self = $_[0]->_get_self;
1066 #XXX Need to create a new test for this
1067 # if ($self->root->{links} > 1) {
1068 # return $self->_throw_error("Cannot optimize: reference count is greater than 1");
1071 my $db_temp = DBM::Deep->new(
1072 file => $self->root->{file} . '.tmp',
1076 return $self->_throw_error("Cannot optimize: failed to open temp file: $!");
1080 $self->_copy_node( $db_temp );
1084 # Attempt to copy user, group and permissions over to new file
1086 my @stats = stat($self->fh);
1087 my $perms = $stats[2] & 07777;
1088 my $uid = $stats[4];
1089 my $gid = $stats[5];
1090 chown( $uid, $gid, $self->root->{file} . '.tmp' );
1091 chmod( $perms, $self->root->{file} . '.tmp' );
1093 # q.v. perlport for more information on this variable
1094 if ( $^O eq 'MSWin32' || $^O eq 'cygwin' ) {
1096 # Potential race condition when optmizing on Win32 with locking.
1097 # The Windows filesystem requires that the filehandle be closed
1098 # before it is overwritten with rename(). This could be redone
1105 if (!rename $self->root->{file} . '.tmp', $self->root->{file}) {
1106 unlink $self->root->{file} . '.tmp';
1108 return $self->_throw_error("Optimize failed: Cannot copy temp file over original: $!");
1120 # Make copy of object and return
1122 my $self = $_[0]->_get_self;
1124 return DBM::Deep->new(
1125 type => $self->type,
1126 base_offset => $self->base_offset,
1132 my %is_legal_filter = map {
1135 store_key store_value
1136 fetch_key fetch_value
1141 # Setup filter function for storing or fetching the key or value
1143 my $self = $_[0]->_get_self;
1144 my $type = lc $_[1];
1145 my $func = $_[2] ? $_[2] : undef;
1147 if ( $is_legal_filter{$type} ) {
1148 $self->root->{"filter_$type"} = $func;
1162 # Get access to the root structure
1164 my $self = $_[0]->_get_self;
1165 return $self->{root};
1170 # Get access to the raw fh
1172 #XXX It will be useful, though, when we split out HASH and ARRAY
1173 my $self = $_[0]->_get_self;
1174 return $self->root->{fh};
1179 # Get type of current node (TYPE_HASH or TYPE_ARRAY)
1181 my $self = $_[0]->_get_self;
1182 return $self->{type};
1187 # Get base_offset of current node (TYPE_HASH or TYPE_ARRAY)
1189 my $self = $_[0]->_get_self;
1190 return $self->{base_offset};
1195 # Get last error string, or undef if no error
1198 #? ( _get_self($_[0])->{root}->{error} or undef )
1199 ? ( $_[0]->_get_self->{root}->{error} or undef )
1209 # Store error string in self
1211 my $self = $_[0]->_get_self;
1212 my $error_text = $_[1];
1214 if ( Scalar::Util::blessed $self ) {
1215 $self->root->{error} = $error_text;
1217 unless ($self->root->{debug}) {
1218 die "DBM::Deep: $error_text\n";
1221 warn "DBM::Deep: $error_text\n";
1225 die "DBM::Deep: $error_text\n";
1233 my $self = $_[0]->_get_self;
1235 undef $self->root->{error};
1240 # Precalculate index, bucket and bucket list sizes
1243 #XXX I don't like this ...
1244 set_pack() unless defined $LONG_SIZE;
1246 $INDEX_SIZE = 256 * $LONG_SIZE;
1247 $BUCKET_SIZE = $HASH_SIZE + $LONG_SIZE;
1248 $BUCKET_LIST_SIZE = $MAX_BUCKETS * $BUCKET_SIZE;
1253 # Set pack/unpack modes (see file header for more)
1255 my ($long_s, $long_p, $data_s, $data_p) = @_;
1257 $LONG_SIZE = $long_s ? $long_s : 4;
1258 $LONG_PACK = $long_p ? $long_p : 'N';
1260 $DATA_LENGTH_SIZE = $data_s ? $data_s : 4;
1261 $DATA_LENGTH_PACK = $data_p ? $data_p : 'N';
1268 # Set key digest function (default is MD5)
1270 my ($digest_func, $hash_size) = @_;
1272 $DIGEST_FUNC = $digest_func ? $digest_func : \&Digest::MD5::md5;
1273 $HASH_SIZE = $hash_size ? $hash_size : 16;
1279 # tie() methods (hashes and arrays)
1284 # Store single hash key/value or array element in database.
1286 my $self = $_[0]->_get_self;
1289 # User may be storing a hash, in which case we do not want it run
1290 # through the filtering system
1291 my $value = ($self->root->{filter_store_value} && !ref($_[2]))
1292 ? $self->root->{filter_store_value}->($_[2])
1295 my $md5 = $DIGEST_FUNC->($key);
1298 # Make sure file is open
1300 if (!defined($self->fh) && !$self->_open()) {
1306 # Request exclusive lock for writing
1308 $self->lock( LOCK_EX );
1313 # If locking is enabled, set 'end' parameter again, in case another
1314 # DB instance appended to our file while we were unlocked.
1316 if ($self->root->{locking} || $self->root->{volatile}) {
1317 $self->root->{end} = (stat($fh))[7];
1321 # Locate offset for bucket list using digest index system
1323 my $tag = $self->_load_tag($self->base_offset);
1325 $tag = $self->_create_tag($self->base_offset, SIG_INDEX, chr(0) x $INDEX_SIZE);
1329 while ($tag->{signature} ne SIG_BLIST) {
1330 my $num = ord(substr($md5, $ch, 1));
1331 my $new_tag = $self->_index_lookup($tag, $num);
1333 my $ref_loc = $tag->{offset} + ($num * $LONG_SIZE);
1334 seek($fh, $ref_loc, SEEK_SET);
1335 print($fh pack($LONG_PACK, $self->root->{end}) );
1337 $tag = $self->_create_tag($self->root->{end}, SIG_BLIST, chr(0) x $BUCKET_LIST_SIZE);
1338 $tag->{ref_loc} = $ref_loc;
1343 my $ref_loc = $tag->{offset} + ($num * $LONG_SIZE);
1345 $tag->{ref_loc} = $ref_loc;
1352 # Add key/value to bucket list
1354 my $result = $self->_add_bucket( $tag, $md5, $key, $value );
1363 # Fetch single value or element given plain key or array index
1365 my $self = shift->_get_self;
1369 # Make sure file is open
1371 if (!defined($self->fh)) { $self->_open(); }
1373 my $md5 = $DIGEST_FUNC->($key);
1376 # Request shared lock for reading
1378 $self->lock( LOCK_SH );
1380 my $tag = $self->_find_bucket_list( $md5 );
1387 # Get value from bucket list
1389 my $result = $self->_get_bucket_value( $tag, $md5 );
1393 #XXX What is ref() checking here?
1394 #YYY Filters only apply on scalar values, so the ref check is making
1395 #YYY sure the fetched bucket is a scalar, not a child hash or array.
1396 return ($result && !ref($result) && $self->root->{filter_fetch_value})
1397 ? $self->root->{filter_fetch_value}->($result)
1403 # Delete single key/value pair or element given plain key or array index
1405 my $self = $_[0]->_get_self;
1408 my $md5 = $DIGEST_FUNC->($key);
1411 # Make sure file is open
1413 if (!defined($self->fh)) { $self->_open(); }
1416 # Request exclusive lock for writing
1418 $self->lock( LOCK_EX );
1420 my $tag = $self->_find_bucket_list( $md5 );
1429 my $value = $self->_get_bucket_value( $tag, $md5 );
1430 if ($value && !ref($value) && $self->root->{filter_fetch_value}) {
1431 $value = $self->root->{filter_fetch_value}->($value);
1434 my $result = $self->_delete_bucket( $tag, $md5 );
1437 # If this object is an array and the key deleted was on the end of the stack,
1438 # decrement the length variable.
1448 # Check if a single key or element exists given plain key or array index
1450 my $self = $_[0]->_get_self;
1453 my $md5 = $DIGEST_FUNC->($key);
1456 # Make sure file is open
1458 if (!defined($self->fh)) { $self->_open(); }
1461 # Request shared lock for reading
1463 $self->lock( LOCK_SH );
1465 my $tag = $self->_find_bucket_list( $md5 );
1468 # For some reason, the built-in exists() function returns '' for false
1476 # Check if bucket exists and return 1 or ''
1478 my $result = $self->_bucket_exists( $tag, $md5 ) || '';
1487 # Clear all keys from hash, or all elements from array.
1489 my $self = $_[0]->_get_self;
1492 # Make sure file is open
1494 if (!defined($self->fh)) { $self->_open(); }
1497 # Request exclusive lock for writing
1499 $self->lock( LOCK_EX );
1503 seek($fh, $self->base_offset, SEEK_SET);
1509 $self->_create_tag($self->base_offset, $self->type, chr(0) x $INDEX_SIZE);
1517 # Public method aliases
1519 sub put { (shift)->STORE( @_ ) }
1520 sub store { (shift)->STORE( @_ ) }
1521 sub get { (shift)->FETCH( @_ ) }
1522 sub fetch { (shift)->FETCH( @_ ) }
1523 sub delete { (shift)->DELETE( @_ ) }
1524 sub exists { (shift)->EXISTS( @_ ) }
1525 sub clear { (shift)->CLEAR( @_ ) }
1527 package DBM::Deep::_::Root;
1541 filter_store_key => undef,
1542 filter_store_value => undef,
1543 filter_fetch_key => undef,
1544 filter_fetch_value => undef,
1555 return unless $self;
1557 close $self->{fh} if $self->{fh};
1568 DBM::Deep - A pure perl multi-level hash/array DBM
1573 my $db = DBM::Deep->new( "foo.db" );
1575 $db->{key} = 'value'; # tie() style
1578 $db->put('key', 'value'); # OO style
1579 print $db->get('key');
1581 # true multi-level support
1582 $db->{my_complex} = [
1583 'hello', { perl => 'rules' },
1589 A unique flat-file database module, written in pure perl. True
1590 multi-level hash/array support (unlike MLDBM, which is faked), hybrid
1591 OO / tie() interface, cross-platform FTPable files, and quite fast. Can
1592 handle millions of keys and unlimited hash levels without significant
1593 slow-down. Written from the ground-up in pure perl -- this is NOT a
1594 wrapper around a C-based DBM. Out-of-the-box compatibility with Unix,
1595 Mac OS X and Windows.
1599 Hopefully you are using Perl's excellent CPAN module, which will download
1600 and install the module for you. If not, get the tarball, and run these
1612 Construction can be done OO-style (which is the recommended way), or using
1613 Perl's tie() function. Both are examined here.
1615 =head2 OO CONSTRUCTION
1617 The recommended way to construct a DBM::Deep object is to use the new()
1618 method, which gets you a blessed, tied hash or array reference.
1620 my $db = DBM::Deep->new( "foo.db" );
1622 This opens a new database handle, mapped to the file "foo.db". If this
1623 file does not exist, it will automatically be created. DB files are
1624 opened in "r+" (read/write) mode, and the type of object returned is a
1625 hash, unless otherwise specified (see L<OPTIONS> below).
1627 You can pass a number of options to the constructor to specify things like
1628 locking, autoflush, etc. This is done by passing an inline hash:
1630 my $db = DBM::Deep->new(
1636 Notice that the filename is now specified I<inside> the hash with
1637 the "file" parameter, as opposed to being the sole argument to the
1638 constructor. This is required if any options are specified.
1639 See L<OPTIONS> below for the complete list.
1643 You can also start with an array instead of a hash. For this, you must
1644 specify the C<type> parameter:
1646 my $db = DBM::Deep->new(
1648 type => DBM::Deep->TYPE_ARRAY
1651 B<Note:> Specifing the C<type> parameter only takes effect when beginning
1652 a new DB file. If you create a DBM::Deep object with an existing file, the
1653 C<type> will be loaded from the file header, and an error will be thrown if
1654 the wrong type is passed in.
1656 =head2 TIE CONSTRUCTION
1658 Alternately, you can create a DBM::Deep handle by using Perl's built-in
1659 tie() function. The object returned from tie() can be used to call methods,
1660 such as lock() and unlock(), but cannot be used to assign to the DBM::Deep
1661 file (as expected with most tie'd objects).
1664 my $db = tie %hash, "DBM::Deep", "foo.db";
1667 my $db = tie @array, "DBM::Deep", "bar.db";
1669 As with the OO constructor, you can replace the DB filename parameter with
1670 a hash containing one or more options (see L<OPTIONS> just below for the
1673 tie %hash, "DBM::Deep", {
1681 There are a number of options that can be passed in when constructing your
1682 DBM::Deep objects. These apply to both the OO- and tie- based approaches.
1688 Filename of the DB file to link the handle to. You can pass a full absolute
1689 filesystem path, partial path, or a plain filename if the file is in the
1690 current working directory. This is a required parameter.
1694 This parameter specifies what type of object to create, a hash or array. Use
1695 one of these two constants: C<DBM::Deep-E<gt>TYPE_HASH> or C<DBM::Deep-E<gt>TYPE_ARRAY>.
1696 This only takes effect when beginning a new file. This is an optional
1697 parameter, and defaults to C<DBM::Deep-E<gt>TYPE_HASH>.
1701 Specifies whether locking is to be enabled. DBM::Deep uses Perl's Fnctl flock()
1702 function to lock the database in exclusive mode for writes, and shared mode for
1703 reads. Pass any true value to enable. This affects the base DB handle I<and
1704 any child hashes or arrays> that use the same DB file. This is an optional
1705 parameter, and defaults to 0 (disabled). See L<LOCKING> below for more.
1709 Specifies whether autoflush is to be enabled on the underlying filehandle.
1710 This obviously slows down write operations, but is required if you may have
1711 multiple processes accessing the same DB file (also consider enable I<locking>
1712 or at least I<volatile>). Pass any true value to enable. This is an optional
1713 parameter, and defaults to 0 (disabled).
1717 If I<volatile> mode is enabled, DBM::Deep will stat() the DB file before each
1718 STORE() operation. This is required if an outside force may change the size of
1719 the file between transactions. Locking also implicitly enables volatile. This
1720 is useful if you want to use a different locking system or write your own. Pass
1721 any true value to enable. This is an optional parameter, and defaults to 0
1726 If I<autobless> mode is enabled, DBM::Deep will preserve blessed hashes, and
1727 restore them when fetched. This is an B<experimental> feature, and does have
1728 side-effects. Basically, when hashes are re-blessed into their original
1729 classes, they are no longer blessed into the DBM::Deep class! So you won't be
1730 able to call any DBM::Deep methods on them. You have been warned.
1731 This is an optional parameter, and defaults to 0 (disabled).
1735 See L<FILTERS> below.
1739 Setting I<debug> mode will make all errors non-fatal, dump them out to
1740 STDERR, and continue on. This is for debugging purposes only, and probably
1741 not what you want. This is an optional parameter, and defaults to 0 (disabled).
1745 Instead of passing a file path, you can instead pass a handle to an pre-opened
1746 filehandle. Note: Beware of using the magick *DATA handle, as this actually
1747 contains your entire Perl script, as well as the data following the __DATA__
1748 marker. This will not work, because DBM::Deep uses absolute seek()s into the
1749 file. Instead, consider reading *DATA into an IO::Scalar handle, then passing
1750 in that. Also please note optimize() will NOT work when passing in only a
1751 handle. Pass in a real filename in order to use optimize().
1755 =head1 TIE INTERFACE
1757 With DBM::Deep you can access your databases using Perl's standard hash/array
1758 syntax. Because all DBM::Deep objects are I<tied> to hashes or arrays, you can
1759 treat them as such. DBM::Deep will intercept all reads/writes and direct them
1760 to the right place -- the DB file. This has nothing to do with the
1761 L<TIE CONSTRUCTION> section above. This simply tells you how to use DBM::Deep
1762 using regular hashes and arrays, rather than calling functions like C<get()>
1763 and C<put()> (although those work too). It is entirely up to you how to want
1764 to access your databases.
1768 You can treat any DBM::Deep object like a normal Perl hash reference. Add keys,
1769 or even nested hashes (or arrays) using standard Perl syntax:
1771 my $db = DBM::Deep->new( "foo.db" );
1773 $db->{mykey} = "myvalue";
1775 $db->{myhash}->{subkey} = "subvalue";
1777 print $db->{myhash}->{subkey} . "\n";
1779 You can even step through hash keys using the normal Perl C<keys()> function:
1781 foreach my $key (keys %$db) {
1782 print "$key: " . $db->{$key} . "\n";
1785 Remember that Perl's C<keys()> function extracts I<every> key from the hash and
1786 pushes them onto an array, all before the loop even begins. If you have an
1787 extra large hash, this may exhaust Perl's memory. Instead, consider using
1788 Perl's C<each()> function, which pulls keys/values one at a time, using very
1791 while (my ($key, $value) = each %$db) {
1792 print "$key: $value\n";
1795 Please note that when using C<each()>, you should always pass a direct
1796 hash reference, not a lookup. Meaning, you should B<never> do this:
1799 while (my ($key, $value) = each %{$db->{foo}}) { # BAD
1801 This causes an infinite loop, because for each iteration, Perl is calling
1802 FETCH() on the $db handle, resulting in a "new" hash for foo every time, so
1803 it effectively keeps returning the first key over and over again. Instead,
1804 assign a temporary variable to C<$db->{foo}>, then pass that to each().
1808 As with hashes, you can treat any DBM::Deep object like a normal Perl array
1809 reference. This includes inserting, removing and manipulating elements,
1810 and the C<push()>, C<pop()>, C<shift()>, C<unshift()> and C<splice()> functions.
1811 The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>,
1812 or simply be a nested array reference inside a hash. Example:
1814 my $db = DBM::Deep->new(
1815 file => "foo-array.db",
1816 type => DBM::Deep->TYPE_ARRAY
1820 push @$db, "bar", "baz";
1821 unshift @$db, "bah";
1823 my $last_elem = pop @$db; # baz
1824 my $first_elem = shift @$db; # bah
1825 my $second_elem = $db->[1]; # bar
1827 my $num_elements = scalar @$db;
1831 In addition to the I<tie()> interface, you can also use a standard OO interface
1832 to manipulate all aspects of DBM::Deep databases. Each type of object (hash or
1833 array) has its own methods, but both types share the following common methods:
1834 C<put()>, C<get()>, C<exists()>, C<delete()> and C<clear()>.
1838 =item * put() / store()
1840 Stores a new hash key/value pair, or sets an array element value. Takes two
1841 arguments, the hash key or array index, and the new value. The value can be
1842 a scalar, hash ref or array ref. Returns true on success, false on failure.
1844 $db->put("foo", "bar"); # for hashes
1845 $db->put(1, "bar"); # for arrays
1847 =item * get() / fetch()
1849 Fetches the value of a hash key or array element. Takes one argument: the hash
1850 key or array index. Returns a scalar, hash ref or array ref, depending on the
1853 my $value = $db->get("foo"); # for hashes
1854 my $value = $db->get(1); # for arrays
1858 Checks if a hash key or array index exists. Takes one argument: the hash key
1859 or array index. Returns true if it exists, false if not.
1861 if ($db->exists("foo")) { print "yay!\n"; } # for hashes
1862 if ($db->exists(1)) { print "yay!\n"; } # for arrays
1866 Deletes one hash key/value pair or array element. Takes one argument: the hash
1867 key or array index. Returns true on success, false if not found. For arrays,
1868 the remaining elements located after the deleted element are NOT moved over.
1869 The deleted element is essentially just undefined, which is exactly how Perl's
1870 internal arrays work. Please note that the space occupied by the deleted
1871 key/value or element is B<not> reused again -- see L<UNUSED SPACE RECOVERY>
1872 below for details and workarounds.
1874 $db->delete("foo"); # for hashes
1875 $db->delete(1); # for arrays
1879 Deletes B<all> hash keys or array elements. Takes no arguments. No return
1880 value. Please note that the space occupied by the deleted keys/values or
1881 elements is B<not> reused again -- see L<UNUSED SPACE RECOVERY> below for
1882 details and workarounds.
1884 $db->clear(); # hashes or arrays
1890 For hashes, DBM::Deep supports all the common methods described above, and the
1891 following additional methods: C<first_key()> and C<next_key()>.
1897 Returns the "first" key in the hash. As with built-in Perl hashes, keys are
1898 fetched in an undefined order (which appears random). Takes no arguments,
1899 returns the key as a scalar value.
1901 my $key = $db->first_key();
1905 Returns the "next" key in the hash, given the previous one as the sole argument.
1906 Returns undef if there are no more keys to be fetched.
1908 $key = $db->next_key($key);
1912 Here are some examples of using hashes:
1914 my $db = DBM::Deep->new( "foo.db" );
1916 $db->put("foo", "bar");
1917 print "foo: " . $db->get("foo") . "\n";
1919 $db->put("baz", {}); # new child hash ref
1920 $db->get("baz")->put("buz", "biz");
1921 print "buz: " . $db->get("baz")->get("buz") . "\n";
1923 my $key = $db->first_key();
1925 print "$key: " . $db->get($key) . "\n";
1926 $key = $db->next_key($key);
1929 if ($db->exists("foo")) { $db->delete("foo"); }
1933 For arrays, DBM::Deep supports all the common methods described above, and the
1934 following additional methods: C<length()>, C<push()>, C<pop()>, C<shift()>,
1935 C<unshift()> and C<splice()>.
1941 Returns the number of elements in the array. Takes no arguments.
1943 my $len = $db->length();
1947 Adds one or more elements onto the end of the array. Accepts scalars, hash
1948 refs or array refs. No return value.
1950 $db->push("foo", "bar", {});
1954 Fetches the last element in the array, and deletes it. Takes no arguments.
1955 Returns undef if array is empty. Returns the element value.
1957 my $elem = $db->pop();
1961 Fetches the first element in the array, deletes it, then shifts all the
1962 remaining elements over to take up the space. Returns the element value. This
1963 method is not recommended with large arrays -- see L<LARGE ARRAYS> below for
1966 my $elem = $db->shift();
1970 Inserts one or more elements onto the beginning of the array, shifting all
1971 existing elements over to make room. Accepts scalars, hash refs or array refs.
1972 No return value. This method is not recommended with large arrays -- see
1973 <LARGE ARRAYS> below for details.
1975 $db->unshift("foo", "bar", {});
1979 Performs exactly like Perl's built-in function of the same name. See L<perldoc
1980 -f splice> for usage -- it is too complicated to document here. This method is
1981 not recommended with large arrays -- see L<LARGE ARRAYS> below for details.
1985 Here are some examples of using arrays:
1987 my $db = DBM::Deep->new(
1989 type => DBM::Deep->TYPE_ARRAY
1992 $db->push("bar", "baz");
1993 $db->unshift("foo");
1996 my $len = $db->length();
1997 print "length: $len\n"; # 4
1999 for (my $k=0; $k<$len; $k++) {
2000 print "$k: " . $db->get($k) . "\n";
2003 $db->splice(1, 2, "biz", "baf");
2005 while (my $elem = shift @$db) {
2006 print "shifted: $elem\n";
2011 Enable automatic file locking by passing a true value to the C<locking>
2012 parameter when constructing your DBM::Deep object (see L<SETUP> above).
2014 my $db = DBM::Deep->new(
2019 This causes DBM::Deep to C<flock()> the underlying filehandle with exclusive
2020 mode for writes, and shared mode for reads. This is required if you have
2021 multiple processes accessing the same database file, to avoid file corruption.
2022 Please note that C<flock()> does NOT work for files over NFS. See L<DB OVER
2023 NFS> below for more.
2025 =head2 EXPLICIT LOCKING
2027 You can explicitly lock a database, so it remains locked for multiple
2028 transactions. This is done by calling the C<lock()> method, and passing an
2029 optional lock mode argument (defaults to exclusive mode). This is particularly
2030 useful for things like counters, where the current value needs to be fetched,
2031 then incremented, then stored again.
2034 my $counter = $db->get("counter");
2036 $db->put("counter", $counter);
2045 You can pass C<lock()> an optional argument, which specifies which mode to use
2046 (exclusive or shared). Use one of these two constants: C<DBM::Deep-E<gt>LOCK_EX>
2047 or C<DBM::Deep-E<gt>LOCK_SH>. These are passed directly to C<flock()>, and are the
2048 same as the constants defined in Perl's C<Fcntl> module.
2050 $db->lock( DBM::Deep->LOCK_SH );
2054 If you want to implement your own file locking scheme, be sure to create your
2055 DBM::Deep objects setting the C<volatile> option to true. This hints to DBM::Deep
2056 that the DB file may change between transactions. See L<LOW-LEVEL ACCESS>
2059 =head1 IMPORTING/EXPORTING
2061 You can import existing complex structures by calling the C<import()> method,
2062 and export an entire database into an in-memory structure using the C<export()>
2063 method. Both are examined here.
2067 Say you have an existing hash with nested hashes/arrays inside it. Instead of
2068 walking the structure and adding keys/elements to the database as you go,
2069 simply pass a reference to the C<import()> method. This recursively adds
2070 everything to an existing DBM::Deep object for you. Here is an example:
2075 array1 => [ "elem0", "elem1", "elem2" ],
2077 subkey1 => "subvalue1",
2078 subkey2 => "subvalue2"
2082 my $db = DBM::Deep->new( "foo.db" );
2083 $db->import( $struct );
2085 print $db->{key1} . "\n"; # prints "value1"
2087 This recursively imports the entire C<$struct> object into C<$db>, including
2088 all nested hashes and arrays. If the DBM::Deep object contains exsiting data,
2089 keys are merged with the existing ones, replacing if they already exist.
2090 The C<import()> method can be called on any database level (not just the base
2091 level), and works with both hash and array DB types.
2093 B<Note:> Make sure your existing structure has no circular references in it.
2094 These will cause an infinite loop when importing.
2098 Calling the C<export()> method on an existing DBM::Deep object will return
2099 a reference to a new in-memory copy of the database. The export is done
2100 recursively, so all nested hashes/arrays are all exported to standard Perl
2101 objects. Here is an example:
2103 my $db = DBM::Deep->new( "foo.db" );
2105 $db->{key1} = "value1";
2106 $db->{key2} = "value2";
2108 $db->{hash1}->{subkey1} = "subvalue1";
2109 $db->{hash1}->{subkey2} = "subvalue2";
2111 my $struct = $db->export();
2113 print $struct->{key1} . "\n"; # prints "value1"
2115 This makes a complete copy of the database in memory, and returns a reference
2116 to it. The C<export()> method can be called on any database level (not just
2117 the base level), and works with both hash and array DB types. Be careful of
2118 large databases -- you can store a lot more data in a DBM::Deep object than an
2119 in-memory Perl structure.
2121 B<Note:> Make sure your database has no circular references in it.
2122 These will cause an infinite loop when exporting.
2126 DBM::Deep has a number of hooks where you can specify your own Perl function
2127 to perform filtering on incoming or outgoing data. This is a perfect
2128 way to extend the engine, and implement things like real-time compression or
2129 encryption. Filtering applies to the base DB level, and all child hashes /
2130 arrays. Filter hooks can be specified when your DBM::Deep object is first
2131 constructed, or by calling the C<set_filter()> method at any time. There are
2132 four available filter hooks, described below:
2136 =item * filter_store_key
2138 This filter is called whenever a hash key is stored. It
2139 is passed the incoming key, and expected to return a transformed key.
2141 =item * filter_store_value
2143 This filter is called whenever a hash key or array element is stored. It
2144 is passed the incoming value, and expected to return a transformed value.
2146 =item * filter_fetch_key
2148 This filter is called whenever a hash key is fetched (i.e. via
2149 C<first_key()> or C<next_key()>). It is passed the transformed key,
2150 and expected to return the plain key.
2152 =item * filter_fetch_value
2154 This filter is called whenever a hash key or array element is fetched.
2155 It is passed the transformed value, and expected to return the plain value.
2159 Here are the two ways to setup a filter hook:
2161 my $db = DBM::Deep->new(
2163 filter_store_value => \&my_filter_store,
2164 filter_fetch_value => \&my_filter_fetch
2169 $db->set_filter( "filter_store_value", \&my_filter_store );
2170 $db->set_filter( "filter_fetch_value", \&my_filter_fetch );
2172 Your filter function will be called only when dealing with SCALAR keys or
2173 values. When nested hashes and arrays are being stored/fetched, filtering
2174 is bypassed. Filters are called as static functions, passed a single SCALAR
2175 argument, and expected to return a single SCALAR value. If you want to
2176 remove a filter, set the function reference to C<undef>:
2178 $db->set_filter( "filter_store_value", undef );
2180 =head2 REAL-TIME ENCRYPTION EXAMPLE
2182 Here is a working example that uses the I<Crypt::Blowfish> module to
2183 do real-time encryption / decryption of keys & values with DBM::Deep Filters.
2184 Please visit L<http://search.cpan.org/search?module=Crypt::Blowfish> for more
2185 on I<Crypt::Blowfish>. You'll also need the I<Crypt::CBC> module.
2188 use Crypt::Blowfish;
2191 my $cipher = Crypt::CBC->new({
2192 'key' => 'my secret key',
2193 'cipher' => 'Blowfish',
2195 'regenerate_key' => 0,
2196 'padding' => 'space',
2200 my $db = DBM::Deep->new(
2201 file => "foo-encrypt.db",
2202 filter_store_key => \&my_encrypt,
2203 filter_store_value => \&my_encrypt,
2204 filter_fetch_key => \&my_decrypt,
2205 filter_fetch_value => \&my_decrypt,
2208 $db->{key1} = "value1";
2209 $db->{key2} = "value2";
2210 print "key1: " . $db->{key1} . "\n";
2211 print "key2: " . $db->{key2} . "\n";
2217 return $cipher->encrypt( $_[0] );
2220 return $cipher->decrypt( $_[0] );
2223 =head2 REAL-TIME COMPRESSION EXAMPLE
2225 Here is a working example that uses the I<Compress::Zlib> module to do real-time
2226 compression / decompression of keys & values with DBM::Deep Filters.
2227 Please visit L<http://search.cpan.org/search?module=Compress::Zlib> for
2228 more on I<Compress::Zlib>.
2233 my $db = DBM::Deep->new(
2234 file => "foo-compress.db",
2235 filter_store_key => \&my_compress,
2236 filter_store_value => \&my_compress,
2237 filter_fetch_key => \&my_decompress,
2238 filter_fetch_value => \&my_decompress,
2241 $db->{key1} = "value1";
2242 $db->{key2} = "value2";
2243 print "key1: " . $db->{key1} . "\n";
2244 print "key2: " . $db->{key2} . "\n";
2250 return Compress::Zlib::memGzip( $_[0] ) ;
2253 return Compress::Zlib::memGunzip( $_[0] ) ;
2256 B<Note:> Filtering of keys only applies to hashes. Array "keys" are
2257 actually numerical index numbers, and are not filtered.
2259 =head1 ERROR HANDLING
2261 Most DBM::Deep methods return a true value for success, and call die() on
2262 failure. You can wrap calls in an eval block to catch the die. Also, the
2263 actual error message is stored in an internal scalar, which can be fetched by
2264 calling the C<error()> method.
2266 my $db = DBM::Deep->new( "foo.db" ); # create hash
2267 eval { $db->push("foo"); }; # ILLEGAL -- push is array-only call
2269 print $@; # prints error message
2270 print $db->error(); # prints error message
2272 You can then call C<clear_error()> to clear the current error state.
2276 If you set the C<debug> option to true when creating your DBM::Deep object,
2277 all errors are considered NON-FATAL, and dumped to STDERR. This should only
2278 be used for debugging purposes and not production work. DBM::Deep expects errors
2279 to be thrown, not propagated back up the stack.
2281 =head1 LARGEFILE SUPPORT
2283 If you have a 64-bit system, and your Perl is compiled with both LARGEFILE
2284 and 64-bit support, you I<may> be able to create databases larger than 2 GB.
2285 DBM::Deep by default uses 32-bit file offset tags, but these can be changed
2286 by calling the static C<set_pack()> method before you do anything else.
2288 DBM::Deep::set_pack(8, 'Q');
2290 This tells DBM::Deep to pack all file offsets with 8-byte (64-bit) quad words
2291 instead of 32-bit longs. After setting these values your DB files have a
2292 theoretical maximum size of 16 XB (exabytes).
2294 B<Note:> Changing these values will B<NOT> work for existing database files.
2295 Only change this for new files, and make sure it stays set consistently
2296 throughout the file's life. If you do set these values, you can no longer
2297 access 32-bit DB files. You can, however, call C<set_pack(4, 'N')> to change
2298 back to 32-bit mode.
2300 B<Note:> I have not personally tested files > 2 GB -- all my systems have
2301 only a 32-bit Perl. However, I have received user reports that this does
2304 =head1 LOW-LEVEL ACCESS
2306 If you require low-level access to the underlying filehandle that DBM::Deep uses,
2307 you can call the C<fh()> method, which returns the handle:
2311 This method can be called on the root level of the datbase, or any child
2312 hashes or arrays. All levels share a I<root> structure, which contains things
2313 like the filehandle, a reference counter, and all the options specified
2314 when you created the object. You can get access to this root structure by
2315 calling the C<root()> method.
2317 my $root = $db->root();
2319 This is useful for changing options after the object has already been created,
2320 such as enabling/disabling locking, volatile or debug modes. You can also
2321 store your own temporary user data in this structure (be wary of name
2322 collision), which is then accessible from any child hash or array.
2324 =head1 CUSTOM DIGEST ALGORITHM
2326 DBM::Deep by default uses the I<Message Digest 5> (MD5) algorithm for hashing
2327 keys. However you can override this, and use another algorithm (such as SHA-256)
2328 or even write your own. But please note that DBM::Deep currently expects zero
2329 collisions, so your algorithm has to be I<perfect>, so to speak.
2330 Collision detection may be introduced in a later version.
2334 You can specify a custom digest algorithm by calling the static C<set_digest()>
2335 function, passing a reference to a subroutine, and the length of the algorithm's
2336 hashes (in bytes). This is a global static function, which affects ALL DBM::Deep
2337 objects. Here is a working example that uses a 256-bit hash from the
2338 I<Digest::SHA256> module. Please see
2339 L<http://search.cpan.org/search?module=Digest::SHA256> for more.
2344 my $context = Digest::SHA256::new(256);
2346 DBM::Deep::set_digest( \&my_digest, 32 );
2348 my $db = DBM::Deep->new( "foo-sha.db" );
2350 $db->{key1} = "value1";
2351 $db->{key2} = "value2";
2352 print "key1: " . $db->{key1} . "\n";
2353 print "key2: " . $db->{key2} . "\n";
2359 return substr( $context->hash($_[0]), 0, 32 );
2362 B<Note:> Your returned digest strings must be B<EXACTLY> the number
2363 of bytes you specify in the C<set_digest()> function (in this case 32).
2365 =head1 CIRCULAR REFERENCES
2367 DBM::Deep has B<experimental> support for circular references. Meaning you
2368 can have a nested hash key or array element that points to a parent object.
2369 This relationship is stored in the DB file, and is preserved between sessions.
2372 my $db = DBM::Deep->new( "foo.db" );
2375 $db->{circle} = $db; # ref to self
2377 print $db->{foo} . "\n"; # prints "foo"
2378 print $db->{circle}->{foo} . "\n"; # prints "foo" again
2380 One catch is, passing the object to a function that recursively walks the
2381 object tree (such as I<Data::Dumper> or even the built-in C<optimize()> or
2382 C<export()> methods) will result in an infinite loop. The other catch is,
2383 if you fetch the I<key> of a circular reference (i.e. using the C<first_key()>
2384 or C<next_key()> methods), you will get the I<target object's key>, not the
2385 ref's key. This gets even more interesting with the above example, where
2386 the I<circle> key points to the base DB object, which technically doesn't
2387 have a key. So I made DBM::Deep return "[base]" as the key name in that
2390 =head1 CAVEATS / ISSUES / BUGS
2392 This section describes all the known issues with DBM::Deep. It you have found
2393 something that is not listed here, please send e-mail to L<jhuckaby@cpan.org>.
2395 =head2 UNUSED SPACE RECOVERY
2397 One major caveat with DBM::Deep is that space occupied by existing keys and
2398 values is not recovered when they are deleted. Meaning if you keep deleting
2399 and adding new keys, your file will continuously grow. I am working on this,
2400 but in the meantime you can call the built-in C<optimize()> method from time to
2401 time (perhaps in a crontab or something) to recover all your unused space.
2403 $db->optimize(); # returns true on success
2405 This rebuilds the ENTIRE database into a new file, then moves it on top of
2406 the original. The new file will have no unused space, thus it will take up as
2407 little disk space as possible. Please note that this operation can take
2408 a long time for large files, and you need enough disk space to temporarily hold
2409 2 copies of your DB file. The temporary file is created in the same directory
2410 as the original, named with a ".tmp" extension, and is deleted when the
2411 operation completes. Oh, and if locking is enabled, the DB is automatically
2412 locked for the entire duration of the copy.
2416 B<WARNING:> Only call optimize() on the top-level node of the database, and
2417 make sure there are no child references lying around. DBM::Deep keeps a reference
2418 counter, and if it is greater than 1, optimize() will abort and return undef.
2420 =head2 AUTOVIVIFICATION
2422 Unfortunately, autovivification doesn't work with tied hashes. This appears to
2423 be a bug in Perl's tie() system, as I<Jakob Schmidt> encountered the very same
2424 issue with his I<DWH_FIle> module (see L<http://search.cpan.org/search?module=DWH_File>),
2425 and it is also mentioned in the BUGS section for the I<MLDBM> module <see
2426 L<http://search.cpan.org/search?module=MLDBM>). Basically, on a new db file,
2429 $db->{foo}->{bar} = "hello";
2431 Since "foo" doesn't exist, you cannot add "bar" to it. You end up with "foo"
2432 being an empty hash. Try this instead, which works fine:
2434 $db->{foo} = { bar => "hello" };
2436 As of Perl 5.8.7, this bug still exists. I have walked very carefully through
2437 the execution path, and Perl indeed passes an empty hash to the STORE() method.
2438 Probably a bug in Perl.
2440 =head2 FILE CORRUPTION
2442 The current level of error handling in DBM::Deep is minimal. Files I<are> checked
2443 for a 32-bit signature when opened, but other corruption in files can cause
2444 segmentation faults. DBM::Deep may try to seek() past the end of a file, or get
2445 stuck in an infinite loop depending on the level of corruption. File write
2446 operations are not checked for failure (for speed), so if you happen to run
2447 out of disk space, DBM::Deep will probably fail in a bad way. These things will
2448 be addressed in a later version of DBM::Deep.
2452 Beware of using DB files over NFS. DBM::Deep uses flock(), which works well on local
2453 filesystems, but will NOT protect you from file corruption over NFS. I've heard
2454 about setting up your NFS server with a locking daemon, then using lockf() to
2455 lock your files, but your mileage may vary there as well. From what I
2456 understand, there is no real way to do it. However, if you need access to the
2457 underlying filehandle in DBM::Deep for using some other kind of locking scheme like
2458 lockf(), see the L<LOW-LEVEL ACCESS> section above.
2460 =head2 COPYING OBJECTS
2462 Beware of copying tied objects in Perl. Very strange things can happen.
2463 Instead, use DBM::Deep's C<clone()> method which safely copies the object and
2464 returns a new, blessed, tied hash or array to the same level in the DB.
2466 my $copy = $db->clone();
2468 B<Note>: Since clone() here is cloning the object, not the database location, any
2469 modifications to either $db or $copy will be visible in both.
2473 Beware of using C<shift()>, C<unshift()> or C<splice()> with large arrays.
2474 These functions cause every element in the array to move, which can be murder
2475 on DBM::Deep, as every element has to be fetched from disk, then stored again in
2476 a different location. This will be addressed in the forthcoming version 1.00.
2480 This section discusses DBM::Deep's speed and memory usage.
2484 Obviously, DBM::Deep isn't going to be as fast as some C-based DBMs, such as
2485 the almighty I<BerkeleyDB>. But it makes up for it in features like true
2486 multi-level hash/array support, and cross-platform FTPable files. Even so,
2487 DBM::Deep is still pretty fast, and the speed stays fairly consistent, even
2488 with huge databases. Here is some test data:
2490 Adding 1,000,000 keys to new DB file...
2492 At 100 keys, avg. speed is 2,703 keys/sec
2493 At 200 keys, avg. speed is 2,642 keys/sec
2494 At 300 keys, avg. speed is 2,598 keys/sec
2495 At 400 keys, avg. speed is 2,578 keys/sec
2496 At 500 keys, avg. speed is 2,722 keys/sec
2497 At 600 keys, avg. speed is 2,628 keys/sec
2498 At 700 keys, avg. speed is 2,700 keys/sec
2499 At 800 keys, avg. speed is 2,607 keys/sec
2500 At 900 keys, avg. speed is 2,190 keys/sec
2501 At 1,000 keys, avg. speed is 2,570 keys/sec
2502 At 2,000 keys, avg. speed is 2,417 keys/sec
2503 At 3,000 keys, avg. speed is 1,982 keys/sec
2504 At 4,000 keys, avg. speed is 1,568 keys/sec
2505 At 5,000 keys, avg. speed is 1,533 keys/sec
2506 At 6,000 keys, avg. speed is 1,787 keys/sec
2507 At 7,000 keys, avg. speed is 1,977 keys/sec
2508 At 8,000 keys, avg. speed is 2,028 keys/sec
2509 At 9,000 keys, avg. speed is 2,077 keys/sec
2510 At 10,000 keys, avg. speed is 2,031 keys/sec
2511 At 20,000 keys, avg. speed is 1,970 keys/sec
2512 At 30,000 keys, avg. speed is 2,050 keys/sec
2513 At 40,000 keys, avg. speed is 2,073 keys/sec
2514 At 50,000 keys, avg. speed is 1,973 keys/sec
2515 At 60,000 keys, avg. speed is 1,914 keys/sec
2516 At 70,000 keys, avg. speed is 2,091 keys/sec
2517 At 80,000 keys, avg. speed is 2,103 keys/sec
2518 At 90,000 keys, avg. speed is 1,886 keys/sec
2519 At 100,000 keys, avg. speed is 1,970 keys/sec
2520 At 200,000 keys, avg. speed is 2,053 keys/sec
2521 At 300,000 keys, avg. speed is 1,697 keys/sec
2522 At 400,000 keys, avg. speed is 1,838 keys/sec
2523 At 500,000 keys, avg. speed is 1,941 keys/sec
2524 At 600,000 keys, avg. speed is 1,930 keys/sec
2525 At 700,000 keys, avg. speed is 1,735 keys/sec
2526 At 800,000 keys, avg. speed is 1,795 keys/sec
2527 At 900,000 keys, avg. speed is 1,221 keys/sec
2528 At 1,000,000 keys, avg. speed is 1,077 keys/sec
2530 This test was performed on a PowerMac G4 1gHz running Mac OS X 10.3.2 & Perl
2531 5.8.1, with an 80GB Ultra ATA/100 HD spinning at 7200RPM. The hash keys and
2532 values were between 6 - 12 chars in length. The DB file ended up at 210MB.
2533 Run time was 12 min 3 sec.
2537 One of the great things about DBM::Deep is that it uses very little memory.
2538 Even with huge databases (1,000,000+ keys) you will not see much increased
2539 memory on your process. DBM::Deep relies solely on the filesystem for storing
2540 and fetching data. Here is output from I</usr/bin/top> before even opening a
2543 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
2544 22831 root 11 0 2716 2716 1296 R 0.0 0.2 0:07 perl
2546 Basically the process is taking 2,716K of memory. And here is the same
2547 process after storing and fetching 1,000,000 keys:
2549 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
2550 22831 root 14 0 2772 2772 1328 R 0.0 0.2 13:32 perl
2552 Notice the memory usage increased by only 56K. Test was performed on a 700mHz
2553 x86 box running Linux RedHat 7.2 & Perl 5.6.1.
2555 =head1 DB FILE FORMAT
2557 In case you were interested in the underlying DB file format, it is documented
2558 here in this section. You don't need to know this to use the module, it's just
2559 included for reference.
2563 DBM::Deep files always start with a 32-bit signature to identify the file type.
2564 This is at offset 0. The signature is "DPDB" in network byte order. This is
2565 checked for when the file is opened and an error will be thrown if it's not found.
2569 The DBM::Deep file is in a I<tagged format>, meaning each section of the file
2570 has a standard header containing the type of data, the length of data, and then
2571 the data itself. The type is a single character (1 byte), the length is a
2572 32-bit unsigned long in network byte order, and the data is, well, the data.
2573 Here is how it unfolds:
2577 Immediately after the 32-bit file signature is the I<Master Index> record.
2578 This is a standard tag header followed by 1024 bytes (in 32-bit mode) or 2048
2579 bytes (in 64-bit mode) of data. The type is I<H> for hash or I<A> for array,
2580 depending on how the DBM::Deep object was constructed.
2582 The index works by looking at a I<MD5 Hash> of the hash key (or array index
2583 number). The first 8-bit char of the MD5 signature is the offset into the
2584 index, multipled by 4 in 32-bit mode, or 8 in 64-bit mode. The value of the
2585 index element is a file offset of the next tag for the key/element in question,
2586 which is usually a I<Bucket List> tag (see below).
2588 The next tag I<could> be another index, depending on how many keys/elements
2589 exist. See L<RE-INDEXING> below for details.
2593 A I<Bucket List> is a collection of 16 MD5 hashes for keys/elements, plus
2594 file offsets to where the actual data is stored. It starts with a standard
2595 tag header, with type I<B>, and a data size of 320 bytes in 32-bit mode, or
2596 384 bytes in 64-bit mode. Each MD5 hash is stored in full (16 bytes), plus
2597 the 32-bit or 64-bit file offset for the I<Bucket> containing the actual data.
2598 When the list fills up, a I<Re-Index> operation is performed (See
2599 L<RE-INDEXING> below).
2603 A I<Bucket> is a tag containing a key/value pair (in hash mode), or a
2604 index/value pair (in array mode). It starts with a standard tag header with
2605 type I<D> for scalar data (string, binary, etc.), or it could be a nested
2606 hash (type I<H>) or array (type I<A>). The value comes just after the tag
2607 header. The size reported in the tag header is only for the value, but then,
2608 just after the value is another size (32-bit unsigned long) and then the plain
2609 key itself. Since the value is likely to be fetched more often than the plain
2610 key, I figured it would be I<slightly> faster to store the value first.
2612 If the type is I<H> (hash) or I<A> (array), the value is another I<Master Index>
2613 record for the nested structure, where the process begins all over again.
2617 After a I<Bucket List> grows to 16 records, its allocated space in the file is
2618 exhausted. Then, when another key/element comes in, the list is converted to a
2619 new index record. However, this index will look at the next char in the MD5
2620 hash, and arrange new Bucket List pointers accordingly. This process is called
2621 I<Re-Indexing>. Basically, a new index tag is created at the file EOF, and all
2622 17 (16 + new one) keys/elements are removed from the old Bucket List and
2623 inserted into the new index. Several new Bucket Lists are created in the
2624 process, as a new MD5 char from the key is being examined (it is unlikely that
2625 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 run 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.
2662 Fetching the plain key occurs when calling the I<first_key()> and I<next_key()>
2663 methods. In this process the indexes are walked systematically, and each key
2664 fetched in increasing MD5 order (which is why it appears random). Once the
2665 I<Bucket> is found, the value is skipped the plain key returned instead.
2666 B<Note:> Do not count on keys being fetched as if the MD5 hashes were
2667 alphabetically sorted. This only happens on an index-level -- as soon as the
2668 I<Bucket Lists> are hit, the keys will come out in the order they went in --
2669 so it's pretty much undefined how the keys will come out -- just like Perl's
2672 =head1 CODE COVERAGE
2674 We use B<Devel::Cover> to test the code coverage of my tests, below is the
2675 B<Devel::Cover> report on this module's test suite.
2677 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2678 File stmt bran cond sub pod time total
2679 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2680 blib/lib/DBM/Deep.pm 93.7 82.5 71.9 96.5 25.9 82.8 87.9
2681 blib/lib/DBM/Deep/Array.pm 98.8 88.0 90.9 100.0 n/a 12.8 96.3
2682 blib/lib/DBM/Deep/Hash.pm 95.2 80.0 100.0 100.0 n/a 4.4 92.3
2683 Total 94.8 83.2 76.5 97.6 25.9 100.0 89.7
2684 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2688 Joseph Huckaby, L<jhuckaby@cpan.org>
2689 Rob Kinyon, L<rkinyon@cpan.org>
2691 Special thanks to Adam Sah and Rich Gaushell! You know why :-)
2695 perltie(1), Tie::Hash(3), Digest::MD5(3), Fcntl(3), flock(2), lockf(3), nfs(5),
2696 Digest::SHA256(3), Crypt::Blowfish(3), Compress::Zlib(3)
2700 Copyright (c) 2002-2006 Joseph Huckaby. All Rights Reserved.
2701 This is free software, you may use it and distribute it under the
2702 same terms as Perl itself.