7 # Multi-level database module for storing hash trees, arrays and simple
8 # key/value pairs into FTP-able, cross-platform binary database files.
10 # Type `perldoc DBM::Deep` for complete documentation.
14 # tie %db, 'DBM::Deep', 'my_database.db'; # standard tie() method
16 # my $db = new DBM::Deep( 'my_database.db' ); # preferred OO method
18 # $db->{my_scalar} = 'hello world';
19 # $db->{my_hash} = { larry => 'genius', hashes => 'fast' };
20 # $db->{my_array} = [ 1, 2, 3, time() ];
21 # $db->{my_complex} = [ 'hello', { perl => 'rules' }, 42, 99 ];
22 # push @{$db->{my_array}}, 'another value';
23 # my @key_list = keys %{$db->{my_hash}};
24 # print "This module " . $db->{my_complex}->[1]->{perl} . "!\n";
27 # (c) 2002-2006 Joseph Huckaby. All Rights Reserved.
28 # This program is free software; you can redistribute it and/or
29 # modify it under the same terms as Perl itself.
34 use Fcntl qw( :DEFAULT :flock :seek );
38 use DBM::Deep::Engine;
40 use vars qw( $VERSION );
41 $VERSION = q(0.99_01);
44 # Set to 4 and 'N' for 32-bit offset tags (default). Theoretical limit of 4 GB per file.
45 # (Perl must be compiled with largefile support for files > 2 GB)
47 # Set to 8 and 'Q' for 64-bit offsets. Theoretical limit of 16 XB per file.
48 # (Perl must be compiled with largefile and 64-bit long support)
54 # Set to 4 and 'N' for 32-bit data length prefixes. Limit of 4 GB for each key/value.
55 # Upgrading this is possible (see above) but probably not necessary. If you need
56 # more than 4 GB for a single key or value, this module is really not for you :-)
58 #my $DATA_LENGTH_SIZE = 4;
59 #my $DATA_LENGTH_PACK = 'N';
60 our ($LONG_SIZE, $LONG_PACK, $DATA_LENGTH_SIZE, $DATA_LENGTH_PACK);
63 # Maximum number of buckets per list before another level of indexing is done.
64 # Increase this value for slightly greater speed, but larger database files.
65 # DO NOT decrease this value below 16, due to risk of recursive reindex overrun.
70 # Better not adjust anything below here, unless you're me :-)
74 # Setup digest function for keys
76 our ($DIGEST_FUNC, $HASH_SIZE);
77 #my $DIGEST_FUNC = \&Digest::MD5::md5;
80 # Precalculate index and bucket sizes based on values above.
83 my ($INDEX_SIZE, $BUCKET_SIZE, $BUCKET_LIST_SIZE);
90 # Setup file and tag signatures. These should never change.
92 sub SIG_FILE () { 'DPDB' }
93 sub SIG_HASH () { 'H' }
94 sub SIG_ARRAY () { 'A' }
95 sub SIG_SCALAR () { 'S' }
96 sub SIG_NULL () { 'N' }
97 sub SIG_DATA () { 'D' }
98 sub SIG_INDEX () { 'I' }
99 sub SIG_BLIST () { 'B' }
100 sub SIG_SIZE () { 1 }
103 # Setup constants for users to pass to new()
105 sub TYPE_HASH () { SIG_HASH }
106 sub TYPE_ARRAY () { SIG_ARRAY }
107 sub TYPE_SCALAR () { SIG_SCALAR }
113 if (scalar(@_) > 1) {
115 $proto->_throw_error( "Odd number of parameters to " . (caller(1))[2] );
119 elsif ( ref $_[0] ) {
120 unless ( eval { local $SIG{'__DIE__'}; %{$_[0]} || 1 } ) {
121 $proto->_throw_error( "Not a hashref in args to " . (caller(1))[2] );
126 $args = { file => shift };
134 # Class constructor method for Perl OO interface.
135 # Calls tie() and returns blessed reference to tied hash or array,
136 # providing a hybrid OO/tie interface.
139 my $args = $class->_get_args( @_ );
142 # Check if we want a tied hash or array.
145 if (defined($args->{type}) && $args->{type} eq TYPE_ARRAY) {
146 $class = 'DBM::Deep::Array';
147 require DBM::Deep::Array;
148 tie @$self, $class, %$args;
151 $class = 'DBM::Deep::Hash';
152 require DBM::Deep::Hash;
153 tie %$self, $class, %$args;
156 return bless $self, $class;
161 # Setup $self and bless into this class.
166 # These are the defaults to be optionally overridden below
169 base_offset => length(SIG_FILE),
170 engine => 'DBM::Deep::Engine',
173 foreach my $param ( keys %$self ) {
174 next unless exists $args->{$param};
175 $self->{$param} = delete $args->{$param}
178 # locking implicitly enables autoflush
179 if ($args->{locking}) { $args->{autoflush} = 1; }
181 $self->{root} = exists $args->{root}
183 : DBM::Deep::_::Root->new( $args );
185 if (!defined($self->_fh)) { $self->_open(); }
192 require DBM::Deep::Hash;
193 return DBM::Deep::Hash->TIEHASH( @_ );
198 require DBM::Deep::Array;
199 return DBM::Deep::Array->TIEARRAY( @_ );
202 #XXX Unneeded now ...
208 # Open a fh to the database, create if nonexistent.
209 # Make sure file signature matches DBM::Deep spec.
211 my $self = $_[0]->_get_self;
213 if (defined($self->_fh)) { $self->_close(); }
216 local $SIG{'__DIE__'};
217 # Theoretically, adding O_BINARY should remove the need for the binmode
218 # Of course, testing it is going to be ... interesting.
219 my $flags = O_RDWR | O_CREAT | O_BINARY;
222 sysopen( $fh, $self->_root->{file}, $flags )
224 $self->_root->{fh} = $fh;
225 }; if ($@ ) { $self->_throw_error( "Received error: $@\n" ); }
226 if (! defined($self->_fh)) {
227 return $self->_throw_error("Cannot sysopen file: " . $self->_root->{file} . ": $!");
232 #XXX Can we remove this by using the right sysopen() flags?
233 # Maybe ... q.v. above
234 binmode $fh; # for win32
236 if ($self->_root->{autoflush}) {
237 my $old = select $fh;
242 seek($fh, 0 + $self->_root->{file_offset}, SEEK_SET);
245 my $bytes_read = read( $fh, $signature, length(SIG_FILE));
248 # File is empty -- write signature and master index
251 seek($fh, 0 + $self->_root->{file_offset}, SEEK_SET);
252 print( $fh SIG_FILE);
253 $self->_create_tag($self->_base_offset, $self->_type, chr(0) x $INDEX_SIZE);
255 my $plain_key = "[base]";
256 print( $fh pack($DATA_LENGTH_PACK, length($plain_key)) . $plain_key );
258 # Flush the filehandle
259 my $old_fh = select $fh;
260 my $old_af = $|; $| = 1; $| = $old_af;
263 my @stats = stat($fh);
264 $self->_root->{inode} = $stats[1];
265 $self->_root->{end} = $stats[7];
271 # Check signature was valid
273 unless ($signature eq SIG_FILE) {
275 return $self->_throw_error("Signature not found -- file is not a Deep DB");
278 my @stats = stat($fh);
279 $self->_root->{inode} = $stats[1];
280 $self->_root->{end} = $stats[7];
283 # Get our type from master index signature
285 my $tag = $self->_load_tag($self->_base_offset);
287 #XXX We probably also want to store the hash algorithm name and not assume anything
288 #XXX The cool thing would be to allow a different hashing algorithm at every level
291 return $self->_throw_error("Corrupted file, no master index record");
293 if ($self->{type} ne $tag->{signature}) {
294 return $self->_throw_error("File type mismatch");
304 my $self = $_[0]->_get_self;
305 close $self->_root->{fh} if $self->_root->{fh};
306 $self->_root->{fh} = undef;
311 # Given offset, signature and content, create tag and write to disk
313 my ($self, $offset, $sig, $content) = @_;
314 my $size = length($content);
318 seek($fh, $offset + $self->_root->{file_offset}, SEEK_SET);
319 print( $fh $sig . pack($DATA_LENGTH_PACK, $size) . $content );
321 if ($offset == $self->_root->{end}) {
322 $self->_root->{end} += SIG_SIZE + $DATA_LENGTH_SIZE + $size;
328 offset => $offset + SIG_SIZE + $DATA_LENGTH_SIZE,
335 # Given offset, load single tag and return signature, size and data
342 seek($fh, $offset + $self->_root->{file_offset}, SEEK_SET);
343 if (eof $fh) { return undef; }
346 read( $fh, $b, SIG_SIZE + $DATA_LENGTH_SIZE );
347 my ($sig, $size) = unpack( "A $DATA_LENGTH_PACK", $b );
350 read( $fh, $buffer, $size);
355 offset => $offset + SIG_SIZE + $DATA_LENGTH_SIZE,
362 # Given index tag, lookup single entry in index and return .
365 my ($tag, $index) = @_;
367 my $location = unpack($LONG_PACK, substr($tag->{content}, $index * $LONG_SIZE, $LONG_SIZE) );
368 if (!$location) { return; }
370 return $self->_load_tag( $location );
375 # Adds one key/value pair to bucket list, given offset, MD5 digest of key,
376 # plain (undigested) key and value.
379 my ($tag, $md5, $plain_key, $value) = @_;
380 my $keys = $tag->{content};
384 my $root = $self->_root;
386 my $is_dbm_deep = eval { local $SIG{'__DIE__'}; $value->isa( 'DBM::Deep' ) };
387 my $internal_ref = $is_dbm_deep && ($value->_root eq $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 $subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
398 # Found empty bucket (end of list). Populate and exit loop.
402 $location = $internal_ref
403 ? $value->_base_offset
406 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $root->{file_offset}, SEEK_SET);
407 print( $fh $md5 . pack($LONG_PACK, $location) );
411 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
414 # Found existing bucket with same key. Replace with new value.
419 $location = $value->_base_offset;
420 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $root->{file_offset}, SEEK_SET);
421 print( $fh $md5 . pack($LONG_PACK, $location) );
425 seek($fh, $subloc + SIG_SIZE + $root->{file_offset}, SEEK_SET);
427 read( $fh, $size, $DATA_LENGTH_SIZE); $size = unpack($DATA_LENGTH_PACK, $size);
430 # If value is a hash, array, or raw value with equal or less size, we can
431 # reuse the same content area of the database. Otherwise, we have to create
432 # a new content area at the EOF.
435 my $r = Scalar::Util::reftype( $value ) || '';
436 if ( $r eq 'HASH' || $r eq 'ARRAY' ) {
437 $actual_length = $INDEX_SIZE;
439 # if autobless is enabled, must also take into consideration
440 # the class name, as it is stored along with key/value.
441 if ( $root->{autobless} ) {
442 my $value_class = Scalar::Util::blessed($value);
443 if ( defined $value_class && !$value->isa('DBM::Deep') ) {
444 $actual_length += length($value_class);
448 else { $actual_length = length($value); }
450 if ($actual_length <= $size) {
454 $location = $root->{end};
455 seek($fh, $tag->{offset} + ($i * $BUCKET_SIZE) + $HASH_SIZE + $root->{file_offset}, SEEK_SET);
456 print( $fh pack($LONG_PACK, $location) );
464 # If this is an internal reference, return now.
465 # No need to write value or plain key
472 # If bucket didn't fit into list, split into a new index level
475 seek($fh, $tag->{ref_loc} + $root->{file_offset}, SEEK_SET);
476 print( $fh pack($LONG_PACK, $root->{end}) );
478 my $index_tag = $self->_create_tag($root->{end}, SIG_INDEX, chr(0) x $INDEX_SIZE);
481 $keys .= $md5 . pack($LONG_PACK, 0);
483 for (my $i=0; $i<=$MAX_BUCKETS; $i++) {
484 my $key = substr($keys, $i * $BUCKET_SIZE, $HASH_SIZE);
486 my $old_subloc = unpack($LONG_PACK, substr($keys, ($i * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
487 my $num = ord(substr($key, $tag->{ch} + 1, 1));
489 if ($offsets[$num]) {
490 my $offset = $offsets[$num] + SIG_SIZE + $DATA_LENGTH_SIZE;
491 seek($fh, $offset + $root->{file_offset}, SEEK_SET);
493 read( $fh, $subkeys, $BUCKET_LIST_SIZE);
495 for (my $k=0; $k<$MAX_BUCKETS; $k++) {
496 my $subloc = unpack($LONG_PACK, substr($subkeys, ($k * $BUCKET_SIZE) + $HASH_SIZE, $LONG_SIZE));
498 seek($fh, $offset + ($k * $BUCKET_SIZE) + $root->{file_offset}, SEEK_SET);
499 print( $fh $key . pack($LONG_PACK, $old_subloc || $root->{end}) );
505 $offsets[$num] = $root->{end};
506 seek($fh, $index_tag->{offset} + ($num * $LONG_SIZE) + $root->{file_offset}, SEEK_SET);
507 print( $fh pack($LONG_PACK, $root->{end}) );
509 my $blist_tag = $self->_create_tag($root->{end}, SIG_BLIST, chr(0) x $BUCKET_LIST_SIZE);
511 seek($fh, $blist_tag->{offset} + $root->{file_offset}, SEEK_SET);
512 print( $fh $key . pack($LONG_PACK, $old_subloc || $root->{end}) );
517 $location ||= $root->{end};
518 } # re-index bucket list
521 # Seek to content area and store signature, value and plaintext key
525 seek($fh, $location + $root->{file_offset}, SEEK_SET);
528 # Write signature based on content type, set content length and write actual value.
530 my $r = Scalar::Util::reftype($value) || '';
532 print( $fh TYPE_HASH );
533 print( $fh pack($DATA_LENGTH_PACK, $INDEX_SIZE) . chr(0) x $INDEX_SIZE );
534 $content_length = $INDEX_SIZE;
536 elsif ($r eq 'ARRAY') {
537 print( $fh TYPE_ARRAY );
538 print( $fh pack($DATA_LENGTH_PACK, $INDEX_SIZE) . chr(0) x $INDEX_SIZE );
539 $content_length = $INDEX_SIZE;
541 elsif (!defined($value)) {
542 print( $fh SIG_NULL );
543 print( $fh pack($DATA_LENGTH_PACK, 0) );
547 print( $fh SIG_DATA );
548 print( $fh pack($DATA_LENGTH_PACK, length($value)) . $value );
549 $content_length = length($value);
553 # Plain key is stored AFTER value, as keys are typically fetched less often.
555 print( $fh pack($DATA_LENGTH_PACK, length($plain_key)) . $plain_key );
558 # If value is blessed, preserve class name
560 if ( $root->{autobless} ) {
561 my $value_class = Scalar::Util::blessed($value);
562 if ( defined $value_class && $value_class ne 'DBM::Deep' ) {
564 # Blessed ref -- will restore later
567 print( $fh pack($DATA_LENGTH_PACK, length($value_class)) . $value_class );
568 $content_length += 1;
569 $content_length += $DATA_LENGTH_SIZE + length($value_class);
573 $content_length += 1;
578 # If this is a new content area, advance EOF counter
580 if ($location == $root->{end}) {
581 $root->{end} += SIG_SIZE;
582 $root->{end} += $DATA_LENGTH_SIZE + $content_length;
583 $root->{end} += $DATA_LENGTH_SIZE + length($plain_key);
587 # If content is a hash or array, create new child DBM::Deep object and
588 # pass each key or element to it.
591 my $branch = DBM::Deep->new(
593 base_offset => $location,
596 foreach my $key (keys %{$value}) {
597 $branch->STORE( $key, $value->{$key} );
600 elsif ($r eq 'ARRAY') {
601 my $branch = DBM::Deep->new(
603 base_offset => $location,
607 foreach my $element (@{$value}) {
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 + $self->_root->{file_offset}, SEEK_SET);
653 read( $fh, $signature, SIG_SIZE);
656 # If value is a hash or array, return new DBM::Deep object with correct offset
658 if (($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) + $self->_root->{file_offset}, 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 + $self->_root->{file_offset}, 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, $type);
933 # refresh end counter in case file has changed size
934 my @stats = stat($self->_root->{file});
935 $self->_root->{end} = $stats[7];
937 # double-check file inode, in case another process
938 # has optimize()d our file while we were waiting.
939 if ($stats[1] != $self->_root->{inode}) {
940 $self->_open(); # re-open
941 flock($self->_fh, $type); # re-lock
942 $self->_root->{end} = (stat($self->_fh))[7]; # re-end
945 $self->_root->{locked}++;
955 # If db locking is set, unlock the db file. See note in lock()
956 # regarding calling lock() multiple times.
958 my $self = $_[0]->_get_self;
960 if (!defined($self->_fh)) { return; }
962 if ($self->_root->{locking} && $self->_root->{locked} > 0) {
963 $self->_root->{locked}--;
964 if (!$self->_root->{locked}) { flock($self->_fh, LOCK_UN); }
973 my $self = shift->_get_self;
974 my ($spot, $value) = @_;
979 elsif ( eval { local $SIG{__DIE__}; $value->isa( 'DBM::Deep' ) } ) {
980 my $type = $value->_type;
981 ${$spot} = $type eq TYPE_HASH ? {} : [];
982 $value->_copy_node( ${$spot} );
985 my $r = Scalar::Util::reftype( $value );
986 my $c = Scalar::Util::blessed( $value );
987 if ( $r eq 'ARRAY' ) {
988 ${$spot} = [ @{$value} ];
991 ${$spot} = { %{$value} };
993 ${$spot} = bless ${$spot}, $c
1002 # Copy single level of keys or elements to new DB handle.
1003 # Recurse for nested structures
1005 my $self = shift->_get_self;
1008 if ($self->_type eq TYPE_HASH) {
1009 my $key = $self->first_key();
1011 my $value = $self->get($key);
1012 $self->_copy_value( \$db_temp->{$key}, $value );
1013 $key = $self->next_key($key);
1017 my $length = $self->length();
1018 for (my $index = 0; $index < $length; $index++) {
1019 my $value = $self->get($index);
1020 $self->_copy_value( \$db_temp->[$index], $value );
1029 # Recursively export into standard Perl hashes and arrays.
1031 my $self = $_[0]->_get_self;
1034 if ($self->_type eq TYPE_HASH) { $temp = {}; }
1035 elsif ($self->_type eq TYPE_ARRAY) { $temp = []; }
1038 $self->_copy_node( $temp );
1046 # Recursively import Perl hash/array structure
1048 #XXX This use of ref() seems to be ok
1049 if (!ref($_[0])) { return; } # Perl calls import() on use -- ignore
1051 my $self = $_[0]->_get_self;
1054 #XXX This use of ref() seems to be ok
1055 if (!ref($struct)) {
1057 # struct is not a reference, so just import based on our type
1061 if ($self->_type eq TYPE_HASH) { $struct = {@_}; }
1062 elsif ($self->_type eq TYPE_ARRAY) { $struct = [@_]; }
1065 my $r = Scalar::Util::reftype($struct) || '';
1066 if ($r eq "HASH" && $self->_type eq TYPE_HASH) {
1067 foreach my $key (keys %$struct) { $self->put($key, $struct->{$key}); }
1069 elsif ($r eq "ARRAY" && $self->_type eq TYPE_ARRAY) {
1070 $self->push( @$struct );
1073 return $self->_throw_error("Cannot import: type mismatch");
1081 # Rebuild entire database into new file, then move
1082 # it back on top of original.
1084 my $self = $_[0]->_get_self;
1086 #XXX Need to create a new test for this
1087 # if ($self->_root->{links} > 1) {
1088 # return $self->_throw_error("Cannot optimize: reference count is greater than 1");
1091 my $db_temp = DBM::Deep->new(
1092 file => $self->_root->{file} . '.tmp',
1093 type => $self->_type
1096 return $self->_throw_error("Cannot optimize: failed to open temp file: $!");
1100 $self->_copy_node( $db_temp );
1104 # Attempt to copy user, group and permissions over to new file
1106 my @stats = stat($self->_fh);
1107 my $perms = $stats[2] & 07777;
1108 my $uid = $stats[4];
1109 my $gid = $stats[5];
1110 chown( $uid, $gid, $self->_root->{file} . '.tmp' );
1111 chmod( $perms, $self->_root->{file} . '.tmp' );
1113 # q.v. perlport for more information on this variable
1114 if ( $^O eq 'MSWin32' || $^O eq 'cygwin' ) {
1116 # Potential race condition when optmizing on Win32 with locking.
1117 # The Windows filesystem requires that the filehandle be closed
1118 # before it is overwritten with rename(). This could be redone
1125 if (!rename $self->_root->{file} . '.tmp', $self->_root->{file}) {
1126 unlink $self->_root->{file} . '.tmp';
1128 return $self->_throw_error("Optimize failed: Cannot copy temp file over original: $!");
1140 # Make copy of object and return
1142 my $self = $_[0]->_get_self;
1144 return DBM::Deep->new(
1145 type => $self->_type,
1146 base_offset => $self->_base_offset,
1147 root => $self->_root
1152 my %is_legal_filter = map {
1155 store_key store_value
1156 fetch_key fetch_value
1161 # Setup filter function for storing or fetching the key or value
1163 my $self = $_[0]->_get_self;
1164 my $type = lc $_[1];
1165 my $func = $_[2] ? $_[2] : undef;
1167 if ( $is_legal_filter{$type} ) {
1168 $self->_root->{"filter_$type"} = $func;
1182 # Get access to the root structure
1184 my $self = $_[0]->_get_self;
1185 return $self->{root};
1190 # Get access to the raw fh
1192 #XXX It will be useful, though, when we split out HASH and ARRAY
1193 my $self = $_[0]->_get_self;
1194 return $self->_root->{fh};
1199 # Get type of current node (TYPE_HASH or TYPE_ARRAY)
1201 my $self = $_[0]->_get_self;
1202 return $self->{type};
1207 # Get base_offset of current node (TYPE_HASH or TYPE_ARRAY)
1209 my $self = $_[0]->_get_self;
1210 return $self->{base_offset};
1218 die "DBM::Deep: $_[1]\n";
1221 sub _precalc_sizes {
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;
1263 (O_WRONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0);
1268 # (O_RDONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0);
1272 # tie() methods (hashes and arrays)
1277 # Store single hash key/value or array element in database.
1279 my $self = $_[0]->_get_self;
1282 # User may be storing a hash, in which case we do not want it run
1283 # through the filtering system
1284 my $value = ($self->_root->{filter_store_value} && !ref($_[2]))
1285 ? $self->_root->{filter_store_value}->($_[2])
1288 my $md5 = $DIGEST_FUNC->($key);
1290 unless ( _is_writable( $self->_fh ) ) {
1291 $self->_throw_error( 'Cannot write to a readonly filehandle' );
1295 # Request exclusive lock for writing
1297 $self->lock( LOCK_EX );
1299 my $fh = $self->_fh;
1302 # Locate offset for bucket list using digest index system
1304 my $tag = $self->_load_tag($self->_base_offset);
1306 $tag = $self->_create_tag($self->_base_offset, SIG_INDEX, chr(0) x $INDEX_SIZE);
1310 while ($tag->{signature} ne SIG_BLIST) {
1311 my $num = ord(substr($md5, $ch, 1));
1313 my $ref_loc = $tag->{offset} + ($num * $LONG_SIZE);
1314 my $new_tag = $self->_index_lookup($tag, $num);
1317 seek($fh, $ref_loc + $self->_root->{file_offset}, SEEK_SET);
1318 print( $fh pack($LONG_PACK, $self->_root->{end}) );
1320 $tag = $self->_create_tag($self->_root->{end}, SIG_BLIST, chr(0) x $BUCKET_LIST_SIZE);
1322 $tag->{ref_loc} = $ref_loc;
1330 $tag->{ref_loc} = $ref_loc;
1337 # Add key/value to bucket list
1339 my $result = $self->_add_bucket( $tag, $md5, $key, $value );
1348 # Fetch single value or element given plain key or array index
1350 my $self = shift->_get_self;
1353 my $md5 = $DIGEST_FUNC->($key);
1356 # Request shared lock for reading
1358 $self->lock( LOCK_SH );
1360 my $tag = $self->_find_bucket_list( $md5 );
1367 # Get value from bucket list
1369 my $result = $self->_get_bucket_value( $tag, $md5 );
1373 #XXX What is ref() checking here?
1374 #YYY Filters only apply on scalar values, so the ref check is making
1375 #YYY sure the fetched bucket is a scalar, not a child hash or array.
1376 return ($result && !ref($result) && $self->_root->{filter_fetch_value})
1377 ? $self->_root->{filter_fetch_value}->($result)
1383 # Delete single key/value pair or element given plain key or array index
1385 my $self = $_[0]->_get_self;
1388 my $md5 = $DIGEST_FUNC->($key);
1391 # Request exclusive lock for writing
1393 $self->lock( LOCK_EX );
1395 my $tag = $self->_find_bucket_list( $md5 );
1404 my $value = $self->_get_bucket_value( $tag, $md5 );
1405 if ($value && !ref($value) && $self->_root->{filter_fetch_value}) {
1406 $value = $self->_root->{filter_fetch_value}->($value);
1409 my $result = $self->_delete_bucket( $tag, $md5 );
1412 # If this object is an array and the key deleted was on the end of the stack,
1413 # decrement the length variable.
1423 # Check if a single key or element exists given plain key or array index
1425 my $self = $_[0]->_get_self;
1428 my $md5 = $DIGEST_FUNC->($key);
1431 # Request shared lock for reading
1433 $self->lock( LOCK_SH );
1435 my $tag = $self->_find_bucket_list( $md5 );
1438 # For some reason, the built-in exists() function returns '' for false
1446 # Check if bucket exists and return 1 or ''
1448 my $result = $self->_bucket_exists( $tag, $md5 ) || '';
1457 # Clear all keys from hash, or all elements from array.
1459 my $self = $_[0]->_get_self;
1462 # Request exclusive lock for writing
1464 $self->lock( LOCK_EX );
1466 my $fh = $self->_fh;
1468 seek($fh, $self->_base_offset + $self->_root->{file_offset}, SEEK_SET);
1474 $self->_create_tag($self->_base_offset, $self->_type, chr(0) x $INDEX_SIZE);
1482 # Public method aliases
1484 sub put { (shift)->STORE( @_ ) }
1485 sub store { (shift)->STORE( @_ ) }
1486 sub get { (shift)->FETCH( @_ ) }
1487 sub fetch { (shift)->FETCH( @_ ) }
1488 sub delete { (shift)->DELETE( @_ ) }
1489 sub exists { (shift)->EXISTS( @_ ) }
1490 sub clear { (shift)->CLEAR( @_ ) }
1492 package DBM::Deep::_::Root;
1506 filter_store_key => undef,
1507 filter_store_value => undef,
1508 filter_fetch_key => undef,
1509 filter_fetch_value => undef,
1515 if ( $self->{fh} && !$self->{file_offset} ) {
1516 $self->{file_offset} = tell( $self->{fh} );
1524 return unless $self;
1526 close $self->{fh} if $self->{fh};
1537 DBM::Deep - A pure perl multi-level hash/array DBM
1542 my $db = DBM::Deep->new( "foo.db" );
1544 $db->{key} = 'value'; # tie() style
1547 $db->put('key' => 'value'); # OO style
1548 print $db->get('key');
1550 # true multi-level support
1551 $db->{my_complex} = [
1552 'hello', { perl => 'rules' },
1558 A unique flat-file database module, written in pure perl. True
1559 multi-level hash/array support (unlike MLDBM, which is faked), hybrid
1560 OO / tie() interface, cross-platform FTPable files, and quite fast. Can
1561 handle millions of keys and unlimited hash levels without significant
1562 slow-down. Written from the ground-up in pure perl -- this is NOT a
1563 wrapper around a C-based DBM. Out-of-the-box compatibility with Unix,
1564 Mac OS X and Windows.
1568 Hopefully you are using Perl's excellent CPAN module, which will download
1569 and install the module for you. If not, get the tarball, and run these
1581 Construction can be done OO-style (which is the recommended way), or using
1582 Perl's tie() function. Both are examined here.
1584 =head2 OO CONSTRUCTION
1586 The recommended way to construct a DBM::Deep object is to use the new()
1587 method, which gets you a blessed, tied hash or array reference.
1589 my $db = DBM::Deep->new( "foo.db" );
1591 This opens a new database handle, mapped to the file "foo.db". If this
1592 file does not exist, it will automatically be created. DB files are
1593 opened in "r+" (read/write) mode, and the type of object returned is a
1594 hash, unless otherwise specified (see L<OPTIONS> below).
1596 You can pass a number of options to the constructor to specify things like
1597 locking, autoflush, etc. This is done by passing an inline hash:
1599 my $db = DBM::Deep->new(
1605 Notice that the filename is now specified I<inside> the hash with
1606 the "file" parameter, as opposed to being the sole argument to the
1607 constructor. This is required if any options are specified.
1608 See L<OPTIONS> below for the complete list.
1612 You can also start with an array instead of a hash. For this, you must
1613 specify the C<type> parameter:
1615 my $db = DBM::Deep->new(
1617 type => DBM::Deep->TYPE_ARRAY
1620 B<Note:> Specifing the C<type> parameter only takes effect when beginning
1621 a new DB file. If you create a DBM::Deep object with an existing file, the
1622 C<type> will be loaded from the file header, and an error will be thrown if
1623 the wrong type is passed in.
1625 =head2 TIE CONSTRUCTION
1627 Alternately, you can create a DBM::Deep handle by using Perl's built-in
1628 tie() function. The object returned from tie() can be used to call methods,
1629 such as lock() and unlock(), but cannot be used to assign to the DBM::Deep
1630 file (as expected with most tie'd objects).
1633 my $db = tie %hash, "DBM::Deep", "foo.db";
1636 my $db = tie @array, "DBM::Deep", "bar.db";
1638 As with the OO constructor, you can replace the DB filename parameter with
1639 a hash containing one or more options (see L<OPTIONS> just below for the
1642 tie %hash, "DBM::Deep", {
1650 There are a number of options that can be passed in when constructing your
1651 DBM::Deep objects. These apply to both the OO- and tie- based approaches.
1657 Filename of the DB file to link the handle to. You can pass a full absolute
1658 filesystem path, partial path, or a plain filename if the file is in the
1659 current working directory. This is a required parameter (though q.v. fh).
1663 If you want, you can pass in the fh instead of the file. This is most useful for doing
1666 my $db = DBM::Deep->new( { fh => \*DATA } );
1668 You are responsible for making sure that the fh has been opened appropriately for your
1669 needs. If you open it read-only and attempt to write, an exception will be thrown. If you
1670 open it write-only or append-only, an exception will be thrown immediately as DBM::Deep
1671 needs to read from the fh.
1675 This is the offset within the file that the DBM::Deep db starts. Most of the time, you will
1676 not need to set this. However, it's there if you want it.
1678 If you pass in fh and do not set this, it will be set appropriately.
1682 This parameter specifies what type of object to create, a hash or array. Use
1683 one of these two constants: C<DBM::Deep-E<gt>TYPE_HASH> or C<DBM::Deep-E<gt>TYPE_ARRAY>.
1684 This only takes effect when beginning a new file. This is an optional
1685 parameter, and defaults to C<DBM::Deep-E<gt>TYPE_HASH>.
1689 Specifies whether locking is to be enabled. DBM::Deep uses Perl's Fnctl flock()
1690 function to lock the database in exclusive mode for writes, and shared mode for
1691 reads. Pass any true value to enable. This affects the base DB handle I<and
1692 any child hashes or arrays> that use the same DB file. This is an optional
1693 parameter, and defaults to 0 (disabled). See L<LOCKING> below for more.
1697 Specifies whether autoflush is to be enabled on the underlying filehandle.
1698 This obviously slows down write operations, but is required if you may have
1699 multiple processes accessing the same DB file (also consider enable I<locking>).
1700 Pass any true value to enable. This is an optional parameter, and defaults to 0
1705 If I<autobless> mode is enabled, DBM::Deep will preserve blessed hashes, and
1706 restore them when fetched. This is an B<experimental> feature, and does have
1707 side-effects. Basically, when hashes are re-blessed into their original
1708 classes, they are no longer blessed into the DBM::Deep class! So you won't be
1709 able to call any DBM::Deep methods on them. You have been warned.
1710 This is an optional parameter, and defaults to 0 (disabled).
1714 See L<FILTERS> below.
1718 Setting I<debug> mode will make all errors non-fatal, dump them out to
1719 STDERR, and continue on. This is for debugging purposes only, and probably
1720 not what you want. This is an optional parameter, and defaults to 0 (disabled).
1722 B<NOTE>: This parameter is considered deprecated and should not be used anymore.
1726 =head1 TIE INTERFACE
1728 With DBM::Deep you can access your databases using Perl's standard hash/array
1729 syntax. Because all DBM::Deep objects are I<tied> to hashes or arrays, you can
1730 treat them as such. DBM::Deep will intercept all reads/writes and direct them
1731 to the right place -- the DB file. This has nothing to do with the
1732 L<TIE CONSTRUCTION> section above. This simply tells you how to use DBM::Deep
1733 using regular hashes and arrays, rather than calling functions like C<get()>
1734 and C<put()> (although those work too). It is entirely up to you how to want
1735 to access your databases.
1739 You can treat any DBM::Deep object like a normal Perl hash reference. Add keys,
1740 or even nested hashes (or arrays) using standard Perl syntax:
1742 my $db = DBM::Deep->new( "foo.db" );
1744 $db->{mykey} = "myvalue";
1746 $db->{myhash}->{subkey} = "subvalue";
1748 print $db->{myhash}->{subkey} . "\n";
1750 You can even step through hash keys using the normal Perl C<keys()> function:
1752 foreach my $key (keys %$db) {
1753 print "$key: " . $db->{$key} . "\n";
1756 Remember that Perl's C<keys()> function extracts I<every> key from the hash and
1757 pushes them onto an array, all before the loop even begins. If you have an
1758 extra large hash, this may exhaust Perl's memory. Instead, consider using
1759 Perl's C<each()> function, which pulls keys/values one at a time, using very
1762 while (my ($key, $value) = each %$db) {
1763 print "$key: $value\n";
1766 Please note that when using C<each()>, you should always pass a direct
1767 hash reference, not a lookup. Meaning, you should B<never> do this:
1770 while (my ($key, $value) = each %{$db->{foo}}) { # BAD
1772 This causes an infinite loop, because for each iteration, Perl is calling
1773 FETCH() on the $db handle, resulting in a "new" hash for foo every time, so
1774 it effectively keeps returning the first key over and over again. Instead,
1775 assign a temporary variable to C<$db->{foo}>, then pass that to each().
1779 As with hashes, you can treat any DBM::Deep object like a normal Perl array
1780 reference. This includes inserting, removing and manipulating elements,
1781 and the C<push()>, C<pop()>, C<shift()>, C<unshift()> and C<splice()> functions.
1782 The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>,
1783 or simply be a nested array reference inside a hash. Example:
1785 my $db = DBM::Deep->new(
1786 file => "foo-array.db",
1787 type => DBM::Deep->TYPE_ARRAY
1791 push @$db, "bar", "baz";
1792 unshift @$db, "bah";
1794 my $last_elem = pop @$db; # baz
1795 my $first_elem = shift @$db; # bah
1796 my $second_elem = $db->[1]; # bar
1798 my $num_elements = scalar @$db;
1802 In addition to the I<tie()> interface, you can also use a standard OO interface
1803 to manipulate all aspects of DBM::Deep databases. Each type of object (hash or
1804 array) has its own methods, but both types share the following common methods:
1805 C<put()>, C<get()>, C<exists()>, C<delete()> and C<clear()>.
1809 =item * new() / clone()
1811 These are the constructor and copy-functions.
1813 =item * put() / store()
1815 Stores a new hash key/value pair, or sets an array element value. Takes two
1816 arguments, the hash key or array index, and the new value. The value can be
1817 a scalar, hash ref or array ref. Returns true on success, false on failure.
1819 $db->put("foo", "bar"); # for hashes
1820 $db->put(1, "bar"); # for arrays
1822 =item * get() / fetch()
1824 Fetches the value of a hash key or array element. Takes one argument: the hash
1825 key or array index. Returns a scalar, hash ref or array ref, depending on the
1828 my $value = $db->get("foo"); # for hashes
1829 my $value = $db->get(1); # for arrays
1833 Checks if a hash key or array index exists. Takes one argument: the hash key
1834 or array index. Returns true if it exists, false if not.
1836 if ($db->exists("foo")) { print "yay!\n"; } # for hashes
1837 if ($db->exists(1)) { print "yay!\n"; } # for arrays
1841 Deletes one hash key/value pair or array element. Takes one argument: the hash
1842 key or array index. Returns true on success, false if not found. For arrays,
1843 the remaining elements located after the deleted element are NOT moved over.
1844 The deleted element is essentially just undefined, which is exactly how Perl's
1845 internal arrays work. Please note that the space occupied by the deleted
1846 key/value or element is B<not> reused again -- see L<UNUSED SPACE RECOVERY>
1847 below for details and workarounds.
1849 $db->delete("foo"); # for hashes
1850 $db->delete(1); # for arrays
1854 Deletes B<all> hash keys or array elements. Takes no arguments. No return
1855 value. Please note that the space occupied by the deleted keys/values or
1856 elements is B<not> reused again -- see L<UNUSED SPACE RECOVERY> below for
1857 details and workarounds.
1859 $db->clear(); # hashes or arrays
1861 =item * lock() / unlock()
1867 Recover lost disk space.
1869 =item * import() / export()
1871 Data going in and out.
1873 =item * set_digest() / set_pack() / set_filter()
1875 q.v. adjusting the interal parameters.
1881 For hashes, DBM::Deep supports all the common methods described above, and the
1882 following additional methods: C<first_key()> and C<next_key()>.
1888 Returns the "first" key in the hash. As with built-in Perl hashes, keys are
1889 fetched in an undefined order (which appears random). Takes no arguments,
1890 returns the key as a scalar value.
1892 my $key = $db->first_key();
1896 Returns the "next" key in the hash, given the previous one as the sole argument.
1897 Returns undef if there are no more keys to be fetched.
1899 $key = $db->next_key($key);
1903 Here are some examples of using hashes:
1905 my $db = DBM::Deep->new( "foo.db" );
1907 $db->put("foo", "bar");
1908 print "foo: " . $db->get("foo") . "\n";
1910 $db->put("baz", {}); # new child hash ref
1911 $db->get("baz")->put("buz", "biz");
1912 print "buz: " . $db->get("baz")->get("buz") . "\n";
1914 my $key = $db->first_key();
1916 print "$key: " . $db->get($key) . "\n";
1917 $key = $db->next_key($key);
1920 if ($db->exists("foo")) { $db->delete("foo"); }
1924 For arrays, DBM::Deep supports all the common methods described above, and the
1925 following additional methods: C<length()>, C<push()>, C<pop()>, C<shift()>,
1926 C<unshift()> and C<splice()>.
1932 Returns the number of elements in the array. Takes no arguments.
1934 my $len = $db->length();
1938 Adds one or more elements onto the end of the array. Accepts scalars, hash
1939 refs or array refs. No return value.
1941 $db->push("foo", "bar", {});
1945 Fetches the last element in the array, and deletes it. Takes no arguments.
1946 Returns undef if array is empty. Returns the element value.
1948 my $elem = $db->pop();
1952 Fetches the first element in the array, deletes it, then shifts all the
1953 remaining elements over to take up the space. Returns the element value. This
1954 method is not recommended with large arrays -- see L<LARGE ARRAYS> below for
1957 my $elem = $db->shift();
1961 Inserts one or more elements onto the beginning of the array, shifting all
1962 existing elements over to make room. Accepts scalars, hash refs or array refs.
1963 No return value. This method is not recommended with large arrays -- see
1964 <LARGE ARRAYS> below for details.
1966 $db->unshift("foo", "bar", {});
1970 Performs exactly like Perl's built-in function of the same name. See L<perldoc
1971 -f splice> for usage -- it is too complicated to document here. This method is
1972 not recommended with large arrays -- see L<LARGE ARRAYS> below for details.
1976 Here are some examples of using arrays:
1978 my $db = DBM::Deep->new(
1980 type => DBM::Deep->TYPE_ARRAY
1983 $db->push("bar", "baz");
1984 $db->unshift("foo");
1987 my $len = $db->length();
1988 print "length: $len\n"; # 4
1990 for (my $k=0; $k<$len; $k++) {
1991 print "$k: " . $db->get($k) . "\n";
1994 $db->splice(1, 2, "biz", "baf");
1996 while (my $elem = shift @$db) {
1997 print "shifted: $elem\n";
2002 Enable automatic file locking by passing a true value to the C<locking>
2003 parameter when constructing your DBM::Deep object (see L<SETUP> above).
2005 my $db = DBM::Deep->new(
2010 This causes DBM::Deep to C<flock()> the underlying filehandle with exclusive
2011 mode for writes, and shared mode for reads. This is required if you have
2012 multiple processes accessing the same database file, to avoid file corruption.
2013 Please note that C<flock()> does NOT work for files over NFS. See L<DB OVER
2014 NFS> below for more.
2016 =head2 EXPLICIT LOCKING
2018 You can explicitly lock a database, so it remains locked for multiple
2019 transactions. This is done by calling the C<lock()> method, and passing an
2020 optional lock mode argument (defaults to exclusive mode). This is particularly
2021 useful for things like counters, where the current value needs to be fetched,
2022 then incremented, then stored again.
2025 my $counter = $db->get("counter");
2027 $db->put("counter", $counter);
2036 You can pass C<lock()> an optional argument, which specifies which mode to use
2037 (exclusive or shared). Use one of these two constants: C<DBM::Deep-E<gt>LOCK_EX>
2038 or C<DBM::Deep-E<gt>LOCK_SH>. These are passed directly to C<flock()>, and are the
2039 same as the constants defined in Perl's C<Fcntl> module.
2041 $db->lock( DBM::Deep->LOCK_SH );
2045 =head1 IMPORTING/EXPORTING
2047 You can import existing complex structures by calling the C<import()> method,
2048 and export an entire database into an in-memory structure using the C<export()>
2049 method. Both are examined here.
2053 Say you have an existing hash with nested hashes/arrays inside it. Instead of
2054 walking the structure and adding keys/elements to the database as you go,
2055 simply pass a reference to the C<import()> method. This recursively adds
2056 everything to an existing DBM::Deep object for you. Here is an example:
2061 array1 => [ "elem0", "elem1", "elem2" ],
2063 subkey1 => "subvalue1",
2064 subkey2 => "subvalue2"
2068 my $db = DBM::Deep->new( "foo.db" );
2069 $db->import( $struct );
2071 print $db->{key1} . "\n"; # prints "value1"
2073 This recursively imports the entire C<$struct> object into C<$db>, including
2074 all nested hashes and arrays. If the DBM::Deep object contains exsiting data,
2075 keys are merged with the existing ones, replacing if they already exist.
2076 The C<import()> method can be called on any database level (not just the base
2077 level), and works with both hash and array DB types.
2079 B<Note:> Make sure your existing structure has no circular references in it.
2080 These will cause an infinite loop when importing.
2084 Calling the C<export()> method on an existing DBM::Deep object will return
2085 a reference to a new in-memory copy of the database. The export is done
2086 recursively, so all nested hashes/arrays are all exported to standard Perl
2087 objects. Here is an example:
2089 my $db = DBM::Deep->new( "foo.db" );
2091 $db->{key1} = "value1";
2092 $db->{key2} = "value2";
2094 $db->{hash1}->{subkey1} = "subvalue1";
2095 $db->{hash1}->{subkey2} = "subvalue2";
2097 my $struct = $db->export();
2099 print $struct->{key1} . "\n"; # prints "value1"
2101 This makes a complete copy of the database in memory, and returns a reference
2102 to it. The C<export()> method can be called on any database level (not just
2103 the base level), and works with both hash and array DB types. Be careful of
2104 large databases -- you can store a lot more data in a DBM::Deep object than an
2105 in-memory Perl structure.
2107 B<Note:> Make sure your database has no circular references in it.
2108 These will cause an infinite loop when exporting.
2112 DBM::Deep has a number of hooks where you can specify your own Perl function
2113 to perform filtering on incoming or outgoing data. This is a perfect
2114 way to extend the engine, and implement things like real-time compression or
2115 encryption. Filtering applies to the base DB level, and all child hashes /
2116 arrays. Filter hooks can be specified when your DBM::Deep object is first
2117 constructed, or by calling the C<set_filter()> method at any time. There are
2118 four available filter hooks, described below:
2122 =item * filter_store_key
2124 This filter is called whenever a hash key is stored. It
2125 is passed the incoming key, and expected to return a transformed key.
2127 =item * filter_store_value
2129 This filter is called whenever a hash key or array element is stored. It
2130 is passed the incoming value, and expected to return a transformed value.
2132 =item * filter_fetch_key
2134 This filter is called whenever a hash key is fetched (i.e. via
2135 C<first_key()> or C<next_key()>). It is passed the transformed key,
2136 and expected to return the plain key.
2138 =item * filter_fetch_value
2140 This filter is called whenever a hash key or array element is fetched.
2141 It is passed the transformed value, and expected to return the plain value.
2145 Here are the two ways to setup a filter hook:
2147 my $db = DBM::Deep->new(
2149 filter_store_value => \&my_filter_store,
2150 filter_fetch_value => \&my_filter_fetch
2155 $db->set_filter( "filter_store_value", \&my_filter_store );
2156 $db->set_filter( "filter_fetch_value", \&my_filter_fetch );
2158 Your filter function will be called only when dealing with SCALAR keys or
2159 values. When nested hashes and arrays are being stored/fetched, filtering
2160 is bypassed. Filters are called as static functions, passed a single SCALAR
2161 argument, and expected to return a single SCALAR value. If you want to
2162 remove a filter, set the function reference to C<undef>:
2164 $db->set_filter( "filter_store_value", undef );
2166 =head2 REAL-TIME ENCRYPTION EXAMPLE
2168 Here is a working example that uses the I<Crypt::Blowfish> module to
2169 do real-time encryption / decryption of keys & values with DBM::Deep Filters.
2170 Please visit L<http://search.cpan.org/search?module=Crypt::Blowfish> for more
2171 on I<Crypt::Blowfish>. You'll also need the I<Crypt::CBC> module.
2174 use Crypt::Blowfish;
2177 my $cipher = Crypt::CBC->new({
2178 'key' => 'my secret key',
2179 'cipher' => 'Blowfish',
2181 'regenerate_key' => 0,
2182 'padding' => 'space',
2186 my $db = DBM::Deep->new(
2187 file => "foo-encrypt.db",
2188 filter_store_key => \&my_encrypt,
2189 filter_store_value => \&my_encrypt,
2190 filter_fetch_key => \&my_decrypt,
2191 filter_fetch_value => \&my_decrypt,
2194 $db->{key1} = "value1";
2195 $db->{key2} = "value2";
2196 print "key1: " . $db->{key1} . "\n";
2197 print "key2: " . $db->{key2} . "\n";
2203 return $cipher->encrypt( $_[0] );
2206 return $cipher->decrypt( $_[0] );
2209 =head2 REAL-TIME COMPRESSION EXAMPLE
2211 Here is a working example that uses the I<Compress::Zlib> module to do real-time
2212 compression / decompression of keys & values with DBM::Deep Filters.
2213 Please visit L<http://search.cpan.org/search?module=Compress::Zlib> for
2214 more on I<Compress::Zlib>.
2219 my $db = DBM::Deep->new(
2220 file => "foo-compress.db",
2221 filter_store_key => \&my_compress,
2222 filter_store_value => \&my_compress,
2223 filter_fetch_key => \&my_decompress,
2224 filter_fetch_value => \&my_decompress,
2227 $db->{key1} = "value1";
2228 $db->{key2} = "value2";
2229 print "key1: " . $db->{key1} . "\n";
2230 print "key2: " . $db->{key2} . "\n";
2236 return Compress::Zlib::memGzip( $_[0] ) ;
2239 return Compress::Zlib::memGunzip( $_[0] ) ;
2242 B<Note:> Filtering of keys only applies to hashes. Array "keys" are
2243 actually numerical index numbers, and are not filtered.
2245 =head1 ERROR HANDLING
2247 Most DBM::Deep methods return a true value for success, and call die() on
2248 failure. You can wrap calls in an eval block to catch the die.
2250 my $db = DBM::Deep->new( "foo.db" ); # create hash
2251 eval { $db->push("foo"); }; # ILLEGAL -- push is array-only call
2253 print $@; # prints error message
2255 =head1 LARGEFILE SUPPORT
2257 If you have a 64-bit system, and your Perl is compiled with both LARGEFILE
2258 and 64-bit support, you I<may> be able to create databases larger than 2 GB.
2259 DBM::Deep by default uses 32-bit file offset tags, but these can be changed
2260 by calling the static C<set_pack()> method before you do anything else.
2262 DBM::Deep::set_pack(8, 'Q');
2264 This tells DBM::Deep to pack all file offsets with 8-byte (64-bit) quad words
2265 instead of 32-bit longs. After setting these values your DB files have a
2266 theoretical maximum size of 16 XB (exabytes).
2268 B<Note:> Changing these values will B<NOT> work for existing database files.
2269 Only change this for new files, and make sure it stays set consistently
2270 throughout the file's life. If you do set these values, you can no longer
2271 access 32-bit DB files. You can, however, call C<set_pack(4, 'N')> to change
2272 back to 32-bit mode.
2274 B<Note:> I have not personally tested files > 2 GB -- all my systems have
2275 only a 32-bit Perl. However, I have received user reports that this does
2278 =head1 LOW-LEVEL ACCESS
2280 If you require low-level access to the underlying filehandle that DBM::Deep uses,
2281 you can call the C<_fh()> method, which returns the handle:
2283 my $fh = $db->_fh();
2285 This method can be called on the root level of the datbase, or any child
2286 hashes or arrays. All levels share a I<root> structure, which contains things
2287 like the filehandle, a reference counter, and all the options specified
2288 when you created the object. You can get access to this root structure by
2289 calling the C<root()> method.
2291 my $root = $db->_root();
2293 This is useful for changing options after the object has already been created,
2294 such as enabling/disabling locking, or debug modes. You can also
2295 store your own temporary user data in this structure (be wary of name
2296 collision), which is then accessible from any child hash or array.
2298 =head1 CUSTOM DIGEST ALGORITHM
2300 DBM::Deep by default uses the I<Message Digest 5> (MD5) algorithm for hashing
2301 keys. However you can override this, and use another algorithm (such as SHA-256)
2302 or even write your own. But please note that DBM::Deep currently expects zero
2303 collisions, so your algorithm has to be I<perfect>, so to speak.
2304 Collision detection may be introduced in a later version.
2308 You can specify a custom digest algorithm by calling the static C<set_digest()>
2309 function, passing a reference to a subroutine, and the length of the algorithm's
2310 hashes (in bytes). This is a global static function, which affects ALL DBM::Deep
2311 objects. Here is a working example that uses a 256-bit hash from the
2312 I<Digest::SHA256> module. Please see
2313 L<http://search.cpan.org/search?module=Digest::SHA256> for more.
2318 my $context = Digest::SHA256::new(256);
2320 DBM::Deep::set_digest( \&my_digest, 32 );
2322 my $db = DBM::Deep->new( "foo-sha.db" );
2324 $db->{key1} = "value1";
2325 $db->{key2} = "value2";
2326 print "key1: " . $db->{key1} . "\n";
2327 print "key2: " . $db->{key2} . "\n";
2333 return substr( $context->hash($_[0]), 0, 32 );
2336 B<Note:> Your returned digest strings must be B<EXACTLY> the number
2337 of bytes you specify in the C<set_digest()> function (in this case 32).
2339 =head1 CIRCULAR REFERENCES
2341 DBM::Deep has B<experimental> support for circular references. Meaning you
2342 can have a nested hash key or array element that points to a parent object.
2343 This relationship is stored in the DB file, and is preserved between sessions.
2346 my $db = DBM::Deep->new( "foo.db" );
2349 $db->{circle} = $db; # ref to self
2351 print $db->{foo} . "\n"; # prints "foo"
2352 print $db->{circle}->{foo} . "\n"; # prints "foo" again
2354 One catch is, passing the object to a function that recursively walks the
2355 object tree (such as I<Data::Dumper> or even the built-in C<optimize()> or
2356 C<export()> methods) will result in an infinite loop. The other catch is,
2357 if you fetch the I<key> of a circular reference (i.e. using the C<first_key()>
2358 or C<next_key()> methods), you will get the I<target object's key>, not the
2359 ref's key. This gets even more interesting with the above example, where
2360 the I<circle> key points to the base DB object, which technically doesn't
2361 have a key. So I made DBM::Deep return "[base]" as the key name in that
2364 =head1 CAVEATS / ISSUES / BUGS
2366 This section describes all the known issues with DBM::Deep. It you have found
2367 something that is not listed here, please send e-mail to L<jhuckaby@cpan.org>.
2369 =head2 UNUSED SPACE RECOVERY
2371 One major caveat with DBM::Deep is that space occupied by existing keys and
2372 values is not recovered when they are deleted. Meaning if you keep deleting
2373 and adding new keys, your file will continuously grow. I am working on this,
2374 but in the meantime you can call the built-in C<optimize()> method from time to
2375 time (perhaps in a crontab or something) to recover all your unused space.
2377 $db->optimize(); # returns true on success
2379 This rebuilds the ENTIRE database into a new file, then moves it on top of
2380 the original. The new file will have no unused space, thus it will take up as
2381 little disk space as possible. Please note that this operation can take
2382 a long time for large files, and you need enough disk space to temporarily hold
2383 2 copies of your DB file. The temporary file is created in the same directory
2384 as the original, named with a ".tmp" extension, and is deleted when the
2385 operation completes. Oh, and if locking is enabled, the DB is automatically
2386 locked for the entire duration of the copy.
2388 B<WARNING:> Only call optimize() on the top-level node of the database, and
2389 make sure there are no child references lying around. DBM::Deep keeps a reference
2390 counter, and if it is greater than 1, optimize() will abort and return undef.
2392 =head2 AUTOVIVIFICATION
2394 Unfortunately, autovivification doesn't work with tied hashes. This appears to
2395 be a bug in Perl's tie() system, as I<Jakob Schmidt> encountered the very same
2396 issue with his I<DWH_FIle> module (see L<http://search.cpan.org/search?module=DWH_File>),
2397 and it is also mentioned in the BUGS section for the I<MLDBM> module <see
2398 L<http://search.cpan.org/search?module=MLDBM>). Basically, on a new db file,
2401 $db->{foo}->{bar} = "hello";
2403 Since "foo" doesn't exist, you cannot add "bar" to it. You end up with "foo"
2404 being an empty hash. Try this instead, which works fine:
2406 $db->{foo} = { bar => "hello" };
2408 As of Perl 5.8.7, this bug still exists. I have walked very carefully through
2409 the execution path, and Perl indeed passes an empty hash to the STORE() method.
2410 Probably a bug in Perl.
2412 =head2 FILE CORRUPTION
2414 The current level of error handling in DBM::Deep is minimal. Files I<are> checked
2415 for a 32-bit signature when opened, but other corruption in files can cause
2416 segmentation faults. DBM::Deep may try to seek() past the end of a file, or get
2417 stuck in an infinite loop depending on the level of corruption. File write
2418 operations are not checked for failure (for speed), so if you happen to run
2419 out of disk space, DBM::Deep will probably fail in a bad way. These things will
2420 be addressed in a later version of DBM::Deep.
2424 Beware of using DB files over NFS. DBM::Deep uses flock(), which works well on local
2425 filesystems, but will NOT protect you from file corruption over NFS. I've heard
2426 about setting up your NFS server with a locking daemon, then using lockf() to
2427 lock your files, but your mileage may vary there as well. From what I
2428 understand, there is no real way to do it. However, if you need access to the
2429 underlying filehandle in DBM::Deep for using some other kind of locking scheme like
2430 lockf(), see the L<LOW-LEVEL ACCESS> section above.
2432 =head2 COPYING OBJECTS
2434 Beware of copying tied objects in Perl. Very strange things can happen.
2435 Instead, use DBM::Deep's C<clone()> method which safely copies the object and
2436 returns a new, blessed, tied hash or array to the same level in the DB.
2438 my $copy = $db->clone();
2440 B<Note>: Since clone() here is cloning the object, not the database location, any
2441 modifications to either $db or $copy will be visible in both.
2445 Beware of using C<shift()>, C<unshift()> or C<splice()> with large arrays.
2446 These functions cause every element in the array to move, which can be murder
2447 on DBM::Deep, as every element has to be fetched from disk, then stored again in
2448 a different location. This will be addressed in the forthcoming version 1.00.
2450 =head2 WRITEONLY FILES
2452 If you pass in a filehandle to new(), you may have opened it in either a readonly or
2453 writeonly mode. STORE will verify that the filehandle is writable. However, there
2454 doesn't seem to be a good way to determine if a filehandle is readable. And, if the
2455 filehandle isn't readable, it's not clear what will happen. So, don't do that.
2459 This section discusses DBM::Deep's speed and memory usage.
2463 Obviously, DBM::Deep isn't going to be as fast as some C-based DBMs, such as
2464 the almighty I<BerkeleyDB>. But it makes up for it in features like true
2465 multi-level hash/array support, and cross-platform FTPable files. Even so,
2466 DBM::Deep is still pretty fast, and the speed stays fairly consistent, even
2467 with huge databases. Here is some test data:
2469 Adding 1,000,000 keys to new DB file...
2471 At 100 keys, avg. speed is 2,703 keys/sec
2472 At 200 keys, avg. speed is 2,642 keys/sec
2473 At 300 keys, avg. speed is 2,598 keys/sec
2474 At 400 keys, avg. speed is 2,578 keys/sec
2475 At 500 keys, avg. speed is 2,722 keys/sec
2476 At 600 keys, avg. speed is 2,628 keys/sec
2477 At 700 keys, avg. speed is 2,700 keys/sec
2478 At 800 keys, avg. speed is 2,607 keys/sec
2479 At 900 keys, avg. speed is 2,190 keys/sec
2480 At 1,000 keys, avg. speed is 2,570 keys/sec
2481 At 2,000 keys, avg. speed is 2,417 keys/sec
2482 At 3,000 keys, avg. speed is 1,982 keys/sec
2483 At 4,000 keys, avg. speed is 1,568 keys/sec
2484 At 5,000 keys, avg. speed is 1,533 keys/sec
2485 At 6,000 keys, avg. speed is 1,787 keys/sec
2486 At 7,000 keys, avg. speed is 1,977 keys/sec
2487 At 8,000 keys, avg. speed is 2,028 keys/sec
2488 At 9,000 keys, avg. speed is 2,077 keys/sec
2489 At 10,000 keys, avg. speed is 2,031 keys/sec
2490 At 20,000 keys, avg. speed is 1,970 keys/sec
2491 At 30,000 keys, avg. speed is 2,050 keys/sec
2492 At 40,000 keys, avg. speed is 2,073 keys/sec
2493 At 50,000 keys, avg. speed is 1,973 keys/sec
2494 At 60,000 keys, avg. speed is 1,914 keys/sec
2495 At 70,000 keys, avg. speed is 2,091 keys/sec
2496 At 80,000 keys, avg. speed is 2,103 keys/sec
2497 At 90,000 keys, avg. speed is 1,886 keys/sec
2498 At 100,000 keys, avg. speed is 1,970 keys/sec
2499 At 200,000 keys, avg. speed is 2,053 keys/sec
2500 At 300,000 keys, avg. speed is 1,697 keys/sec
2501 At 400,000 keys, avg. speed is 1,838 keys/sec
2502 At 500,000 keys, avg. speed is 1,941 keys/sec
2503 At 600,000 keys, avg. speed is 1,930 keys/sec
2504 At 700,000 keys, avg. speed is 1,735 keys/sec
2505 At 800,000 keys, avg. speed is 1,795 keys/sec
2506 At 900,000 keys, avg. speed is 1,221 keys/sec
2507 At 1,000,000 keys, avg. speed is 1,077 keys/sec
2509 This test was performed on a PowerMac G4 1gHz running Mac OS X 10.3.2 & Perl
2510 5.8.1, with an 80GB Ultra ATA/100 HD spinning at 7200RPM. The hash keys and
2511 values were between 6 - 12 chars in length. The DB file ended up at 210MB.
2512 Run time was 12 min 3 sec.
2516 One of the great things about DBM::Deep is that it uses very little memory.
2517 Even with huge databases (1,000,000+ keys) you will not see much increased
2518 memory on your process. DBM::Deep relies solely on the filesystem for storing
2519 and fetching data. Here is output from I</usr/bin/top> before even opening a
2522 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
2523 22831 root 11 0 2716 2716 1296 R 0.0 0.2 0:07 perl
2525 Basically the process is taking 2,716K of memory. And here is the same
2526 process after storing and fetching 1,000,000 keys:
2528 PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
2529 22831 root 14 0 2772 2772 1328 R 0.0 0.2 13:32 perl
2531 Notice the memory usage increased by only 56K. Test was performed on a 700mHz
2532 x86 box running Linux RedHat 7.2 & Perl 5.6.1.
2534 =head1 DB FILE FORMAT
2536 In case you were interested in the underlying DB file format, it is documented
2537 here in this section. You don't need to know this to use the module, it's just
2538 included for reference.
2542 DBM::Deep files always start with a 32-bit signature to identify the file type.
2543 This is at offset 0. The signature is "DPDB" in network byte order. This is
2544 checked for when the file is opened and an error will be thrown if it's not found.
2548 The DBM::Deep file is in a I<tagged format>, meaning each section of the file
2549 has a standard header containing the type of data, the length of data, and then
2550 the data itself. The type is a single character (1 byte), the length is a
2551 32-bit unsigned long in network byte order, and the data is, well, the data.
2552 Here is how it unfolds:
2556 Immediately after the 32-bit file signature is the I<Master Index> record.
2557 This is a standard tag header followed by 1024 bytes (in 32-bit mode) or 2048
2558 bytes (in 64-bit mode) of data. The type is I<H> for hash or I<A> for array,
2559 depending on how the DBM::Deep object was constructed.
2561 The index works by looking at a I<MD5 Hash> of the hash key (or array index
2562 number). The first 8-bit char of the MD5 signature is the offset into the
2563 index, multipled by 4 in 32-bit mode, or 8 in 64-bit mode. The value of the
2564 index element is a file offset of the next tag for the key/element in question,
2565 which is usually a I<Bucket List> tag (see below).
2567 The next tag I<could> be another index, depending on how many keys/elements
2568 exist. See L<RE-INDEXING> below for details.
2572 A I<Bucket List> is a collection of 16 MD5 hashes for keys/elements, plus
2573 file offsets to where the actual data is stored. It starts with a standard
2574 tag header, with type I<B>, and a data size of 320 bytes in 32-bit mode, or
2575 384 bytes in 64-bit mode. Each MD5 hash is stored in full (16 bytes), plus
2576 the 32-bit or 64-bit file offset for the I<Bucket> containing the actual data.
2577 When the list fills up, a I<Re-Index> operation is performed (See
2578 L<RE-INDEXING> below).
2582 A I<Bucket> is a tag containing a key/value pair (in hash mode), or a
2583 index/value pair (in array mode). It starts with a standard tag header with
2584 type I<D> for scalar data (string, binary, etc.), or it could be a nested
2585 hash (type I<H>) or array (type I<A>). The value comes just after the tag
2586 header. The size reported in the tag header is only for the value, but then,
2587 just after the value is another size (32-bit unsigned long) and then the plain
2588 key itself. Since the value is likely to be fetched more often than the plain
2589 key, I figured it would be I<slightly> faster to store the value first.
2591 If the type is I<H> (hash) or I<A> (array), the value is another I<Master Index>
2592 record for the nested structure, where the process begins all over again.
2596 After a I<Bucket List> grows to 16 records, its allocated space in the file is
2597 exhausted. Then, when another key/element comes in, the list is converted to a
2598 new index record. However, this index will look at the next char in the MD5
2599 hash, and arrange new Bucket List pointers accordingly. This process is called
2600 I<Re-Indexing>. Basically, a new index tag is created at the file EOF, and all
2601 17 (16 + new one) keys/elements are removed from the old Bucket List and
2602 inserted into the new index. Several new Bucket Lists are created in the
2603 process, as a new MD5 char from the key is being examined (it is unlikely that
2604 the keys will all share the same next char of their MD5s).
2606 Because of the way the I<MD5> algorithm works, it is impossible to tell exactly
2607 when the Bucket Lists will turn into indexes, but the first round tends to
2608 happen right around 4,000 keys. You will see a I<slight> decrease in
2609 performance here, but it picks back up pretty quick (see L<SPEED> above). Then
2610 it takes B<a lot> more keys to exhaust the next level of Bucket Lists. It's
2611 right around 900,000 keys. This process can continue nearly indefinitely --
2612 right up until the point the I<MD5> signatures start colliding with each other,
2613 and this is B<EXTREMELY> rare -- like winning the lottery 5 times in a row AND
2614 getting struck by lightning while you are walking to cash in your tickets.
2615 Theoretically, since I<MD5> hashes are 128-bit values, you I<could> have up to
2616 340,282,366,921,000,000,000,000,000,000,000,000,000 keys/elements (I believe
2617 this is 340 unodecillion, but don't quote me).
2621 When a new key/element is stored, the key (or index number) is first run through
2622 I<Digest::MD5> to get a 128-bit signature (example, in hex:
2623 b05783b0773d894396d475ced9d2f4f6). Then, the I<Master Index> record is checked
2624 for the first char of the signature (in this case I<b0>). If it does not exist,
2625 a new I<Bucket List> is created for our key (and the next 15 future keys that
2626 happen to also have I<b> as their first MD5 char). The entire MD5 is written
2627 to the I<Bucket List> along with the offset of the new I<Bucket> record (EOF at
2628 this point, unless we are replacing an existing I<Bucket>), where the actual
2629 data will be stored.
2633 Fetching an existing key/element involves getting a I<Digest::MD5> of the key
2634 (or index number), then walking along the indexes. If there are enough
2635 keys/elements in this DB level, there might be nested indexes, each linked to
2636 a particular char of the MD5. Finally, a I<Bucket List> is pointed to, which
2637 contains up to 16 full MD5 hashes. Each is checked for equality to the key in
2638 question. If we found a match, the I<Bucket> tag is loaded, where the value and
2639 plain key are stored.
2641 Fetching the plain key occurs when calling the I<first_key()> and I<next_key()>
2642 methods. In this process the indexes are walked systematically, and each key
2643 fetched in increasing MD5 order (which is why it appears random). Once the
2644 I<Bucket> is found, the value is skipped and the plain key returned instead.
2645 B<Note:> Do not count on keys being fetched as if the MD5 hashes were
2646 alphabetically sorted. This only happens on an index-level -- as soon as the
2647 I<Bucket Lists> are hit, the keys will come out in the order they went in --
2648 so it's pretty much undefined how the keys will come out -- just like Perl's
2651 =head1 CODE COVERAGE
2653 We use B<Devel::Cover> to test the code coverage of our tests, below is the
2654 B<Devel::Cover> report on this module's test suite.
2656 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2657 File stmt bran cond sub pod time total
2658 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2659 blib/lib/DBM/Deep.pm 95.2 83.8 70.0 98.2 100.0 58.0 91.0
2660 blib/lib/DBM/Deep/Array.pm 100.0 91.1 100.0 100.0 n/a 26.7 98.0
2661 blib/lib/DBM/Deep/Hash.pm 95.3 80.0 100.0 100.0 n/a 15.3 92.4
2662 Total 96.2 84.8 74.4 98.8 100.0 100.0 92.4
2663 ---------------------------- ------ ------ ------ ------ ------ ------ ------
2665 =head1 MORE INFORMATION
2667 Check out the DBM::Deep Google Group at L<http://groups.google.com/group/DBM-Deep>
2668 or send email to L<DBM-Deep@googlegroups.com>.
2672 Joseph Huckaby, L<jhuckaby@cpan.org>
2674 Rob Kinyon, L<rkinyon@cpan.org>
2676 Special thanks to Adam Sah and Rich Gaushell! You know why :-)
2680 perltie(1), Tie::Hash(3), Digest::MD5(3), Fcntl(3), flock(2), lockf(3), nfs(5),
2681 Digest::SHA256(3), Crypt::Blowfish(3), Compress::Zlib(3)
2685 Copyright (c) 2002-2006 Joseph Huckaby. All Rights Reserved.
2686 This is free software, you may use it and distribute it under the
2687 same terms as Perl itself.