1 # DB_File.pm -- Perl 5 interface to Berkeley DB
3 # written by Paul Marquess (Paul.Marquess@btinternet.com)
4 # last modified 6th June 1999
7 # Copyright (c) 1995-1999 Paul Marquess. All rights reserved.
8 # This program is free software; you can redistribute it and/or
9 # modify it under the same terms as Perl itself.
12 package DB_File::HASHINFO ;
19 @DB_File::HASHINFO::ISA = qw(Tie::Hash);
34 bless { VALID => { map {$_, 1}
35 qw( bsize ffactor nelem cachesize hash lorder)
47 return $self->{GOT}{$key} if exists $self->{VALID}{$key} ;
50 croak "${pkg}::FETCH - Unknown element '$key'" ;
60 if ( exists $self->{VALID}{$key} )
62 $self->{GOT}{$key} = $value ;
67 croak "${pkg}::STORE - Unknown element '$key'" ;
75 if ( exists $self->{VALID}{$key} )
77 delete $self->{GOT}{$key} ;
82 croak "DB_File::HASHINFO::DELETE - Unknown element '$key'" ;
90 exists $self->{VALID}{$key} ;
98 croak ref($self) . " does not define the method ${method}" ;
101 sub FIRSTKEY { my $self = shift ; $self->NotHere("FIRSTKEY") }
102 sub NEXTKEY { my $self = shift ; $self->NotHere("NEXTKEY") }
103 sub CLEAR { my $self = shift ; $self->NotHere("CLEAR") }
105 package DB_File::RECNOINFO ;
109 @DB_File::RECNOINFO::ISA = qw(DB_File::HASHINFO) ;
115 bless { VALID => { map {$_, 1}
116 qw( bval cachesize psize flags lorder reclen bfname )
122 package DB_File::BTREEINFO ;
126 @DB_File::BTREEINFO::ISA = qw(DB_File::HASHINFO) ;
132 bless { VALID => { map {$_, 1}
133 qw( flags cachesize maxkeypage minkeypage psize
134 compare prefix lorder )
144 use vars qw($VERSION @ISA @EXPORT $AUTOLOAD $DB_BTREE $DB_HASH $DB_RECNO $db_version) ;
150 #typedef enum { DB_BTREE, DB_HASH, DB_RECNO } DBTYPE;
151 $DB_BTREE = new DB_File::BTREEINFO ;
152 $DB_HASH = new DB_File::HASHINFO ;
153 $DB_RECNO = new DB_File::RECNOINFO ;
159 @ISA = qw(Tie::Hash Exporter DynaLoader);
161 $DB_BTREE $DB_HASH $DB_RECNO
196 ($constname = $AUTOLOAD) =~ s/.*:://;
197 my $val = constant($constname, @_ ? $_[0] : 0);
199 if ($! =~ /Invalid/) {
200 $AutoLoader::AUTOLOAD = $AUTOLOAD;
201 goto &AutoLoader::AUTOLOAD;
204 my($pack,$file,$line) = caller;
205 croak "Your vendor has not defined DB macro $constname, used at $file line $line.
209 eval "sub $AUTOLOAD { $val }";
215 # Make all Fcntl O_XXX constants available for importing
217 my @O = grep /^O_/, @Fcntl::EXPORT;
218 Fcntl->import(@O); # first we import what we want to export
222 ## import borrowed from IO::File
223 ## exports Fcntl constants if available.
226 # my $callpkg = caller;
227 # Exporter::export $pkg, $callpkg, @_;
230 # Exporter::export 'Fcntl', $callpkg, '/^O_/';
234 bootstrap DB_File $VERSION;
236 # Preloaded methods go here. Autoload methods go after __END__, and are
237 # processed by the autosplit program.
239 sub tie_hash_or_array
242 my $tieHASH = ( (caller(1))[3] =~ /TIEHASH/ ) ;
244 $arg[4] = tied %{ $arg[4] }
245 if @arg >= 5 && ref $arg[4] && $arg[4] =~ /=HASH/ && tied %{ $arg[4] } ;
247 # make recno in Berkeley DB version 2 work like recno in version 1.
248 if ($db_version > 1 and defined $arg[4] and $arg[4] =~ /RECNO/ and
249 $arg[1] and ! -e $arg[1]) {
250 open(FH, ">$arg[1]") or return undef ;
252 chmod $arg[3] ? $arg[3] : 0666 , $arg[1] ;
255 DoTie_($tieHASH, @arg) ;
260 tie_hash_or_array(@_) ;
265 tie_hash_or_array(@_) ;
273 my $status = $self->seq($key, $value, R_FIRST());
276 while ($status == 0) {
278 $status = $self->seq($key, $value, R_NEXT());
280 foreach $key (reverse @keys) {
281 my $s = $self->del($key);
291 my $current_length = $self->length() ;
293 if ($length < $current_length) {
295 for ($key = $current_length - 1 ; $key >= $length ; -- $key)
298 elsif ($length > $current_length) {
299 $self->put($length-1, "") ;
305 croak "Usage: \$db->find_dup(key,value)\n"
309 my ($origkey, $value_wanted) = @_ ;
310 my ($key, $value) = ($origkey, 0);
313 for ($status = $db->seq($key, $value, R_CURSOR() ) ;
315 $status = $db->seq($key, $value, R_NEXT() ) ) {
317 return 0 if $key eq $origkey and $value eq $value_wanted ;
325 croak "Usage: \$db->del_dup(key,value)\n"
329 my ($key, $value) = @_ ;
330 my ($status) = $db->find_dup($key, $value) ;
331 return $status if $status != 0 ;
333 $status = $db->del($key, R_CURSOR() ) ;
339 croak "Usage: \$db->get_dup(key [,flag])\n"
340 unless @_ == 2 or @_ == 3 ;
347 my $wantarray = wantarray ;
353 # iterate through the database until either EOF ($status == 0)
354 # or a different key is encountered ($key ne $origkey).
355 for ($status = $db->seq($key, $value, R_CURSOR()) ;
356 $status == 0 and $key eq $origkey ;
357 $status = $db->seq($key, $value, R_NEXT()) ) {
359 # save the value or count number of matches
362 { ++ $values{$value} }
364 { push (@values, $value) }
371 return ($wantarray ? ($flag ? %values : @values) : $counter) ;
380 DB_File - Perl5 access to Berkeley DB version 1.x
386 [$X =] tie %hash, 'DB_File', [$filename, $flags, $mode, $DB_HASH] ;
387 [$X =] tie %hash, 'DB_File', $filename, $flags, $mode, $DB_BTREE ;
388 [$X =] tie @array, 'DB_File', $filename, $flags, $mode, $DB_RECNO ;
390 $status = $X->del($key [, $flags]) ;
391 $status = $X->put($key, $value [, $flags]) ;
392 $status = $X->get($key, $value [, $flags]) ;
393 $status = $X->seq($key, $value, $flags) ;
394 $status = $X->sync([$flags]) ;
398 $count = $X->get_dup($key) ;
399 @list = $X->get_dup($key) ;
400 %list = $X->get_dup($key, 1) ;
401 $status = $X->find_dup($key, $value) ;
402 $status = $X->del_dup($key, $value) ;
412 $old_filter = $db->filter_store_key ( sub { ... } ) ;
413 $old_filter = $db->filter_store_value( sub { ... } ) ;
414 $old_filter = $db->filter_fetch_key ( sub { ... } ) ;
415 $old_filter = $db->filter_fetch_value( sub { ... } ) ;
422 B<DB_File> is a module which allows Perl programs to make use of the
423 facilities provided by Berkeley DB version 1.x (if you have a newer
424 version of DB, see L<Using DB_File with Berkeley DB version 2>). It is
425 assumed that you have a copy of the Berkeley DB manual pages at hand
426 when reading this documentation. The interface defined here mirrors the
427 Berkeley DB interface closely.
429 Berkeley DB is a C library which provides a consistent interface to a
430 number of database formats. B<DB_File> provides an interface to all
431 three of the database types currently supported by Berkeley DB.
439 This database type allows arbitrary key/value pairs to be stored in data
440 files. This is equivalent to the functionality provided by other
441 hashing packages like DBM, NDBM, ODBM, GDBM, and SDBM. Remember though,
442 the files created using DB_HASH are not compatible with any of the
443 other packages mentioned.
445 A default hashing algorithm, which will be adequate for most
446 applications, is built into Berkeley DB. If you do need to use your own
447 hashing algorithm it is possible to write your own in Perl and have
448 B<DB_File> use it instead.
452 The btree format allows arbitrary key/value pairs to be stored in a
453 sorted, balanced binary tree.
455 As with the DB_HASH format, it is possible to provide a user defined
456 Perl routine to perform the comparison of keys. By default, though, the
457 keys are stored in lexical order.
461 DB_RECNO allows both fixed-length and variable-length flat text files
462 to be manipulated using the same key/value pair interface as in DB_HASH
463 and DB_BTREE. In this case the key will consist of a record (line)
468 =head2 Using DB_File with Berkeley DB version 2
470 Although B<DB_File> is intended to be used with Berkeley DB version 1,
471 it can also be used with version 2. In this case the interface is
472 limited to the functionality provided by Berkeley DB 1.x. Anywhere the
473 version 2 interface differs, B<DB_File> arranges for it to work like
474 version 1. This feature allows B<DB_File> scripts that were built with
475 version 1 to be migrated to version 2 without any changes.
477 If you want to make use of the new features available in Berkeley DB
478 2.x, use the Perl module B<BerkeleyDB> instead.
480 At the time of writing this document the B<BerkeleyDB> module is still
481 alpha quality (the version number is < 1.0), and so unsuitable for use
482 in any serious development work. Once its version number is >= 1.0, it
483 is considered stable enough for real work.
485 B<Note:> The database file format has changed in Berkeley DB version 2.
486 If you cannot recreate your databases, you must dump any existing
487 databases with the C<db_dump185> utility that comes with Berkeley DB.
488 Once you have rebuilt DB_File to use Berkeley DB version 2, your
489 databases can be recreated using C<db_load>. Refer to the Berkeley DB
490 documentation for further details.
492 Please read L<"COPYRIGHT"> before using version 2.x of Berkeley DB with
495 =head2 Interface to Berkeley DB
497 B<DB_File> allows access to Berkeley DB files using the tie() mechanism
498 in Perl 5 (for full details, see L<perlfunc/tie()>). This facility
499 allows B<DB_File> to access Berkeley DB files using either an
500 associative array (for DB_HASH & DB_BTREE file types) or an ordinary
501 array (for the DB_RECNO file type).
503 In addition to the tie() interface, it is also possible to access most
504 of the functions provided in the Berkeley DB API directly.
505 See L<THE API INTERFACE>.
507 =head2 Opening a Berkeley DB Database File
509 Berkeley DB uses the function dbopen() to open or create a database.
510 Here is the C prototype for dbopen():
513 dbopen (const char * file, int flags, int mode,
514 DBTYPE type, const void * openinfo)
516 The parameter C<type> is an enumeration which specifies which of the 3
517 interface methods (DB_HASH, DB_BTREE or DB_RECNO) is to be used.
518 Depending on which of these is actually chosen, the final parameter,
519 I<openinfo> points to a data structure which allows tailoring of the
520 specific interface method.
522 This interface is handled slightly differently in B<DB_File>. Here is
523 an equivalent call using B<DB_File>:
525 tie %array, 'DB_File', $filename, $flags, $mode, $DB_HASH ;
527 The C<filename>, C<flags> and C<mode> parameters are the direct
528 equivalent of their dbopen() counterparts. The final parameter $DB_HASH
529 performs the function of both the C<type> and C<openinfo> parameters in
532 In the example above $DB_HASH is actually a pre-defined reference to a
533 hash object. B<DB_File> has three of these pre-defined references.
534 Apart from $DB_HASH, there is also $DB_BTREE and $DB_RECNO.
536 The keys allowed in each of these pre-defined references is limited to
537 the names used in the equivalent C structure. So, for example, the
538 $DB_HASH reference will only allow keys called C<bsize>, C<cachesize>,
539 C<ffactor>, C<hash>, C<lorder> and C<nelem>.
541 To change one of these elements, just assign to it like this:
543 $DB_HASH->{'cachesize'} = 10000 ;
545 The three predefined variables $DB_HASH, $DB_BTREE and $DB_RECNO are
546 usually adequate for most applications. If you do need to create extra
547 instances of these objects, constructors are available for each file
550 Here are examples of the constructors and the valid options available
551 for DB_HASH, DB_BTREE and DB_RECNO respectively.
553 $a = new DB_File::HASHINFO ;
561 $b = new DB_File::BTREEINFO ;
571 $c = new DB_File::RECNOINFO ;
580 The values stored in the hashes above are mostly the direct equivalent
581 of their C counterpart. Like their C counterparts, all are set to a
582 default values - that means you don't have to set I<all> of the
583 values when you only want to change one. Here is an example:
585 $a = new DB_File::HASHINFO ;
586 $a->{'cachesize'} = 12345 ;
587 tie %y, 'DB_File', "filename", $flags, 0777, $a ;
589 A few of the options need extra discussion here. When used, the C
590 equivalent of the keys C<hash>, C<compare> and C<prefix> store pointers
591 to C functions. In B<DB_File> these keys are used to store references
592 to Perl subs. Below are templates for each of the subs:
598 # return the hash value for $data
604 my ($key, $key2) = @_ ;
606 # return 0 if $key1 eq $key2
607 # -1 if $key1 lt $key2
608 # 1 if $key1 gt $key2
609 return (-1 , 0 or 1) ;
614 my ($key, $key2) = @_ ;
616 # return number of bytes of $key2 which are
617 # necessary to determine that it is greater than $key1
621 See L<Changing the BTREE sort order> for an example of using the
624 If you are using the DB_RECNO interface and you intend making use of
625 C<bval>, you should check out L<The 'bval' Option>.
627 =head2 Default Parameters
629 It is possible to omit some or all of the final 4 parameters in the
630 call to C<tie> and let them take default values. As DB_HASH is the most
631 common file format used, the call:
633 tie %A, "DB_File", "filename" ;
637 tie %A, "DB_File", "filename", O_CREAT|O_RDWR, 0666, $DB_HASH ;
639 It is also possible to omit the filename parameter as well, so the
646 tie %A, "DB_File", undef, O_CREAT|O_RDWR, 0666, $DB_HASH ;
648 See L<In Memory Databases> for a discussion on the use of C<undef>
649 in place of a filename.
651 =head2 In Memory Databases
653 Berkeley DB allows the creation of in-memory databases by using NULL
654 (that is, a C<(char *)0> in C) in place of the filename. B<DB_File>
655 uses C<undef> instead of NULL to provide this functionality.
659 The DB_HASH file format is probably the most commonly used of the three
660 file formats that B<DB_File> supports. It is also very straightforward
663 =head2 A Simple Example
665 This example shows how to create a database, add key/value pairs to the
666 database, delete keys/value pairs and finally how to enumerate the
667 contents of the database.
671 use vars qw( %h $k $v ) ;
673 tie %h, "DB_File", "fruit", O_RDWR|O_CREAT, 0640, $DB_HASH
674 or die "Cannot open file 'fruit': $!\n";
676 # Add a few key/value pairs to the file
677 $h{"apple"} = "red" ;
678 $h{"orange"} = "orange" ;
679 $h{"banana"} = "yellow" ;
680 $h{"tomato"} = "red" ;
682 # Check for existence of a key
683 print "Banana Exists\n\n" if $h{"banana"} ;
685 # Delete a key/value pair.
688 # print the contents of the file
689 while (($k, $v) = each %h)
690 { print "$k -> $v\n" }
702 Note that the like ordinary associative arrays, the order of the keys
703 retrieved is in an apparently random order.
707 The DB_BTREE format is useful when you want to store data in a given
708 order. By default the keys will be stored in lexical order, but as you
709 will see from the example shown in the next section, it is very easy to
710 define your own sorting function.
712 =head2 Changing the BTREE sort order
714 This script shows how to override the default sorting algorithm that
715 BTREE uses. Instead of using the normal lexical ordering, a case
716 insensitive compare function will be used.
725 my ($key1, $key2) = @_ ;
726 "\L$key1" cmp "\L$key2" ;
729 # specify the Perl sub that will do the comparison
730 $DB_BTREE->{'compare'} = \&Compare ;
732 tie %h, "DB_File", "tree", O_RDWR|O_CREAT, 0640, $DB_BTREE
733 or die "Cannot open file 'tree': $!\n" ;
735 # Add a key/value pair to the file
736 $h{'Wall'} = 'Larry' ;
737 $h{'Smith'} = 'John' ;
738 $h{'mouse'} = 'mickey' ;
739 $h{'duck'} = 'donald' ;
744 # Cycle through the keys printing them in order.
745 # Note it is not necessary to sort the keys as
746 # the btree will have kept them in order automatically.
752 Here is the output from the code above.
758 There are a few point to bear in mind if you want to change the
759 ordering in a BTREE database:
765 The new compare function must be specified when you create the database.
769 You cannot change the ordering once the database has been created. Thus
770 you must use the same compare function every time you access the
775 =head2 Handling Duplicate Keys
777 The BTREE file type optionally allows a single key to be associated
778 with an arbitrary number of values. This option is enabled by setting
779 the flags element of C<$DB_BTREE> to R_DUP when creating the database.
781 There are some difficulties in using the tied hash interface if you
782 want to manipulate a BTREE database with duplicate keys. Consider this
788 use vars qw($filename %h ) ;
793 # Enable duplicate records
794 $DB_BTREE->{'flags'} = R_DUP ;
796 tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
797 or die "Cannot open $filename: $!\n";
799 # Add some key/value pairs to the file
800 $h{'Wall'} = 'Larry' ;
801 $h{'Wall'} = 'Brick' ; # Note the duplicate key
802 $h{'Wall'} = 'Brick' ; # Note the duplicate key and value
803 $h{'Smith'} = 'John' ;
804 $h{'mouse'} = 'mickey' ;
806 # iterate through the associative array
807 # and print each key/value pair.
809 { print "$_ -> $h{$_}\n" }
821 As you can see 3 records have been successfully created with key C<Wall>
822 - the only thing is, when they are retrieved from the database they
823 I<seem> to have the same value, namely C<Larry>. The problem is caused
824 by the way that the associative array interface works. Basically, when
825 the associative array interface is used to fetch the value associated
826 with a given key, it will only ever retrieve the first value.
828 Although it may not be immediately obvious from the code above, the
829 associative array interface can be used to write values with duplicate
830 keys, but it cannot be used to read them back from the database.
832 The way to get around this problem is to use the Berkeley DB API method
833 called C<seq>. This method allows sequential access to key/value
834 pairs. See L<THE API INTERFACE> for details of both the C<seq> method
835 and the API in general.
837 Here is the script above rewritten using the C<seq> API method.
842 use vars qw($filename $x %h $status $key $value) ;
847 # Enable duplicate records
848 $DB_BTREE->{'flags'} = R_DUP ;
850 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
851 or die "Cannot open $filename: $!\n";
853 # Add some key/value pairs to the file
854 $h{'Wall'} = 'Larry' ;
855 $h{'Wall'} = 'Brick' ; # Note the duplicate key
856 $h{'Wall'} = 'Brick' ; # Note the duplicate key and value
857 $h{'Smith'} = 'John' ;
858 $h{'mouse'} = 'mickey' ;
860 # iterate through the btree using seq
861 # and print each key/value pair.
863 for ($status = $x->seq($key, $value, R_FIRST) ;
865 $status = $x->seq($key, $value, R_NEXT) )
866 { print "$key -> $value\n" }
879 This time we have got all the key/value pairs, including the multiple
880 values associated with the key C<Wall>.
882 To make life easier when dealing with duplicate keys, B<DB_File> comes with
883 a few utility methods.
885 =head2 The get_dup() Method
887 The C<get_dup> method assists in
888 reading duplicate values from BTREE databases. The method can take the
891 $count = $x->get_dup($key) ;
892 @list = $x->get_dup($key) ;
893 %list = $x->get_dup($key, 1) ;
895 In a scalar context the method returns the number of values associated
896 with the key, C<$key>.
898 In list context, it returns all the values which match C<$key>. Note
899 that the values will be returned in an apparently random order.
901 In list context, if the second parameter is present and evaluates
902 TRUE, the method returns an associative array. The keys of the
903 associative array correspond to the values that matched in the BTREE
904 and the values of the array are a count of the number of times that
905 particular value occurred in the BTREE.
907 So assuming the database created above, we can use C<get_dup> like
910 my $cnt = $x->get_dup("Wall") ;
911 print "Wall occurred $cnt times\n" ;
913 my %hash = $x->get_dup("Wall", 1) ;
914 print "Larry is there\n" if $hash{'Larry'} ;
915 print "There are $hash{'Brick'} Brick Walls\n" ;
917 my @list = $x->get_dup("Wall") ;
918 print "Wall => [@list]\n" ;
920 @list = $x->get_dup("Smith") ;
921 print "Smith => [@list]\n" ;
923 @list = $x->get_dup("Dog") ;
924 print "Dog => [@list]\n" ;
929 Wall occurred 3 times
931 There are 2 Brick Walls
932 Wall => [Brick Brick Larry]
936 =head2 The find_dup() Method
938 $status = $X->find_dup($key, $value) ;
940 This method checks for the existance of a specific key/value pair. If the
941 pair exists, the cursor is left pointing to the pair and the method
942 returns 0. Otherwise the method returns a non-zero value.
944 Assuming the database from the previous example:
949 use vars qw($filename $x %h $found) ;
951 my $filename = "tree" ;
953 # Enable duplicate records
954 $DB_BTREE->{'flags'} = R_DUP ;
956 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
957 or die "Cannot open $filename: $!\n";
959 $found = ( $x->find_dup("Wall", "Larry") == 0 ? "" : "not") ;
960 print "Larry Wall is $found there\n" ;
962 $found = ( $x->find_dup("Wall", "Harry") == 0 ? "" : "not") ;
963 print "Harry Wall is $found there\n" ;
971 Harry Wall is not there
974 =head2 The del_dup() Method
976 $status = $X->del_dup($key, $value) ;
978 This method deletes a specific key/value pair. It returns
979 0 if they exist and have been deleted successfully.
980 Otherwise the method returns a non-zero value.
982 Again assuming the existance of the C<tree> database
987 use vars qw($filename $x %h $found) ;
989 my $filename = "tree" ;
991 # Enable duplicate records
992 $DB_BTREE->{'flags'} = R_DUP ;
994 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
995 or die "Cannot open $filename: $!\n";
997 $x->del_dup("Wall", "Larry") ;
999 $found = ( $x->find_dup("Wall", "Larry") == 0 ? "" : "not") ;
1000 print "Larry Wall is $found there\n" ;
1007 Larry Wall is not there
1009 =head2 Matching Partial Keys
1011 The BTREE interface has a feature which allows partial keys to be
1012 matched. This functionality is I<only> available when the C<seq> method
1013 is used along with the R_CURSOR flag.
1015 $x->seq($key, $value, R_CURSOR) ;
1017 Here is the relevant quote from the dbopen man page where it defines
1018 the use of the R_CURSOR flag with seq:
1020 Note, for the DB_BTREE access method, the returned key is not
1021 necessarily an exact match for the specified key. The returned key
1022 is the smallest key greater than or equal to the specified key,
1023 permitting partial key matches and range searches.
1025 In the example script below, the C<match> sub uses this feature to find
1026 and print the first matching key/value pair given a partial key.
1032 use vars qw($filename $x %h $st $key $value) ;
1038 my $orig_key = $key ;
1039 $x->seq($key, $value, R_CURSOR) ;
1040 print "$orig_key\t-> $key\t-> $value\n" ;
1043 $filename = "tree" ;
1046 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
1047 or die "Cannot open $filename: $!\n";
1049 # Add some key/value pairs to the file
1050 $h{'mouse'} = 'mickey' ;
1051 $h{'Wall'} = 'Larry' ;
1052 $h{'Walls'} = 'Brick' ;
1053 $h{'Smith'} = 'John' ;
1057 print "IN ORDER\n" ;
1058 for ($st = $x->seq($key, $value, R_FIRST) ;
1060 $st = $x->seq($key, $value, R_NEXT) )
1062 { print "$key -> $value\n" }
1064 print "\nPARTIAL MATCH\n" ;
1084 a -> mouse -> mickey
1088 DB_RECNO provides an interface to flat text files. Both variable and
1089 fixed length records are supported.
1091 In order to make RECNO more compatible with Perl, the array offset for
1092 all RECNO arrays begins at 0 rather than 1 as in Berkeley DB.
1094 As with normal Perl arrays, a RECNO array can be accessed using
1095 negative indexes. The index -1 refers to the last element of the array,
1096 -2 the second last, and so on. Attempting to access an element before
1097 the start of the array will raise a fatal run-time error.
1099 =head2 The 'bval' Option
1101 The operation of the bval option warrants some discussion. Here is the
1102 definition of bval from the Berkeley DB 1.85 recno manual page:
1104 The delimiting byte to be used to mark the end of a
1105 record for variable-length records, and the pad charac-
1106 ter for fixed-length records. If no value is speci-
1107 fied, newlines (``\n'') are used to mark the end of
1108 variable-length records and fixed-length records are
1111 The second sentence is wrong. In actual fact bval will only default to
1112 C<"\n"> when the openinfo parameter in dbopen is NULL. If a non-NULL
1113 openinfo parameter is used at all, the value that happens to be in bval
1114 will be used. That means you always have to specify bval when making
1115 use of any of the options in the openinfo parameter. This documentation
1116 error will be fixed in the next release of Berkeley DB.
1118 That clarifies the situation with regards Berkeley DB itself. What
1119 about B<DB_File>? Well, the behavior defined in the quote above is
1120 quite useful, so B<DB_File> conforms to it.
1122 That means that you can specify other options (e.g. cachesize) and
1123 still have bval default to C<"\n"> for variable length records, and
1124 space for fixed length records.
1126 =head2 A Simple Example
1128 Here is a simple example that uses RECNO (if you are using a version
1129 of Perl earlier than 5.004_57 this example won't work -- see
1130 L<Extra RECNO Methods> for a workaround).
1136 tie @h, "DB_File", "text", O_RDWR|O_CREAT, 0640, $DB_RECNO
1137 or die "Cannot open file 'text': $!\n" ;
1139 # Add a few key/value pairs to the file
1144 push @h, "green", "black" ;
1146 my $elements = scalar @h ;
1147 print "The array contains $elements entries\n" ;
1150 print "popped $last\n" ;
1152 unshift @h, "white" ;
1153 my $first = shift @h ;
1154 print "shifted $first\n" ;
1156 # Check for existence of a key
1157 print "Element 1 Exists with value $h[1]\n" if $h[1] ;
1159 # use a negative index
1160 print "The last element is $h[-1]\n" ;
1161 print "The 2nd last element is $h[-2]\n" ;
1165 Here is the output from the script:
1167 The array contains 5 entries
1170 Element 1 Exists with value blue
1171 The last element is green
1172 The 2nd last element is yellow
1174 =head2 Extra RECNO Methods
1176 If you are using a version of Perl earlier than 5.004_57, the tied
1177 array interface is quite limited. In the example script above
1178 C<push>, C<pop>, C<shift>, C<unshift>
1179 or determining the array length will not work with a tied array.
1181 To make the interface more useful for older versions of Perl, a number
1182 of methods are supplied with B<DB_File> to simulate the missing array
1183 operations. All these methods are accessed via the object returned from
1186 Here are the methods:
1190 =item B<$X-E<gt>push(list) ;>
1192 Pushes the elements of C<list> to the end of the array.
1194 =item B<$value = $X-E<gt>pop ;>
1196 Removes and returns the last element of the array.
1198 =item B<$X-E<gt>shift>
1200 Removes and returns the first element of the array.
1202 =item B<$X-E<gt>unshift(list) ;>
1204 Pushes the elements of C<list> to the start of the array.
1206 =item B<$X-E<gt>length>
1208 Returns the number of elements in the array.
1212 =head2 Another Example
1214 Here is a more complete example that makes use of some of the methods
1215 described above. It also makes use of the API interface directly (see
1216 L<THE API INTERFACE>).
1219 use vars qw(@h $H $file $i) ;
1227 $H = tie @h, "DB_File", $file, O_RDWR|O_CREAT, 0640, $DB_RECNO
1228 or die "Cannot open file $file: $!\n" ;
1230 # first create a text file to play with
1238 # Print the records in order.
1240 # The length method is needed here because evaluating a tied
1241 # array in a scalar context does not return the number of
1242 # elements in the array.
1244 print "\nORIGINAL\n" ;
1245 foreach $i (0 .. $H->length - 1) {
1246 print "$i: $h[$i]\n" ;
1249 # use the push & pop methods
1252 print "\nThe last record was [$a]\n" ;
1254 # and the shift & unshift methods
1256 $H->unshift("first") ;
1257 print "The first record was [$a]\n" ;
1259 # Use the API to add a new record after record 2.
1261 $H->put($i, "Newbie", R_IAFTER) ;
1263 # and a new record before record 1.
1265 $H->put($i, "New One", R_IBEFORE) ;
1270 # now print the records in reverse order
1271 print "\nREVERSE\n" ;
1272 for ($i = $H->length - 1 ; $i >= 0 ; -- $i)
1273 { print "$i: $h[$i]\n" }
1275 # same again, but use the API functions instead
1276 print "\nREVERSE again\n" ;
1277 my ($s, $k, $v) = (0, 0, 0) ;
1278 for ($s = $H->seq($k, $v, R_LAST) ;
1280 $s = $H->seq($k, $v, R_PREV))
1281 { print "$k: $v\n" }
1286 and this is what it outputs:
1295 The last record was [four]
1296 The first record was [zero]
1320 Rather than iterating through the array, C<@h> like this:
1324 it is necessary to use either this:
1326 foreach $i (0 .. $H->length - 1)
1330 for ($a = $H->get($k, $v, R_FIRST) ;
1332 $a = $H->get($k, $v, R_NEXT) )
1336 Notice that both times the C<put> method was used the record index was
1337 specified using a variable, C<$i>, rather than the literal value
1338 itself. This is because C<put> will return the record number of the
1339 inserted line via that parameter.
1343 =head1 THE API INTERFACE
1345 As well as accessing Berkeley DB using a tied hash or array, it is also
1346 possible to make direct use of most of the API functions defined in the
1347 Berkeley DB documentation.
1349 To do this you need to store a copy of the object returned from the tie.
1351 $db = tie %hash, "DB_File", "filename" ;
1353 Once you have done that, you can access the Berkeley DB API functions
1354 as B<DB_File> methods directly like this:
1356 $db->put($key, $value, R_NOOVERWRITE) ;
1358 B<Important:> If you have saved a copy of the object returned from
1359 C<tie>, the underlying database file will I<not> be closed until both
1360 the tied variable is untied and all copies of the saved object are
1364 $db = tie %hash, "DB_File", "filename"
1365 or die "Cannot tie filename: $!" ;
1370 See L<The untie() Gotcha> for more details.
1372 All the functions defined in L<dbopen> are available except for
1373 close() and dbopen() itself. The B<DB_File> method interface to the
1374 supported functions have been implemented to mirror the way Berkeley DB
1375 works whenever possible. In particular note that:
1381 The methods return a status value. All return 0 on success.
1382 All return -1 to signify an error and set C<$!> to the exact
1383 error code. The return code 1 generally (but not always) means that the
1384 key specified did not exist in the database.
1386 Other return codes are defined. See below and in the Berkeley DB
1387 documentation for details. The Berkeley DB documentation should be used
1388 as the definitive source.
1392 Whenever a Berkeley DB function returns data via one of its parameters,
1393 the equivalent B<DB_File> method does exactly the same.
1397 If you are careful, it is possible to mix API calls with the tied
1398 hash/array interface in the same piece of code. Although only a few of
1399 the methods used to implement the tied interface currently make use of
1400 the cursor, you should always assume that the cursor has been changed
1401 any time the tied hash/array interface is used. As an example, this
1402 code will probably not do what you expect:
1404 $X = tie %x, 'DB_File', $filename, O_RDWR|O_CREAT, 0777, $DB_BTREE
1405 or die "Cannot tie $filename: $!" ;
1407 # Get the first key/value pair and set the cursor
1408 $X->seq($key, $value, R_FIRST) ;
1410 # this line will modify the cursor
1411 $count = scalar keys %x ;
1413 # Get the second key/value pair.
1414 # oops, it didn't, it got the last key/value pair!
1415 $X->seq($key, $value, R_NEXT) ;
1417 The code above can be rearranged to get around the problem, like this:
1419 $X = tie %x, 'DB_File', $filename, O_RDWR|O_CREAT, 0777, $DB_BTREE
1420 or die "Cannot tie $filename: $!" ;
1422 # this line will modify the cursor
1423 $count = scalar keys %x ;
1425 # Get the first key/value pair and set the cursor
1426 $X->seq($key, $value, R_FIRST) ;
1428 # Get the second key/value pair.
1430 $X->seq($key, $value, R_NEXT) ;
1434 All the constants defined in L<dbopen> for use in the flags parameters
1435 in the methods defined below are also available. Refer to the Berkeley
1436 DB documentation for the precise meaning of the flags values.
1438 Below is a list of the methods available.
1442 =item B<$status = $X-E<gt>get($key, $value [, $flags]) ;>
1444 Given a key (C<$key>) this method reads the value associated with it
1445 from the database. The value read from the database is returned in the
1446 C<$value> parameter.
1448 If the key does not exist the method returns 1.
1450 No flags are currently defined for this method.
1452 =item B<$status = $X-E<gt>put($key, $value [, $flags]) ;>
1454 Stores the key/value pair in the database.
1456 If you use either the R_IAFTER or R_IBEFORE flags, the C<$key> parameter
1457 will have the record number of the inserted key/value pair set.
1459 Valid flags are R_CURSOR, R_IAFTER, R_IBEFORE, R_NOOVERWRITE and
1462 =item B<$status = $X-E<gt>del($key [, $flags]) ;>
1464 Removes all key/value pairs with key C<$key> from the database.
1466 A return code of 1 means that the requested key was not in the
1469 R_CURSOR is the only valid flag at present.
1471 =item B<$status = $X-E<gt>fd ;>
1473 Returns the file descriptor for the underlying database.
1475 See L<Locking Databases> for an example of how to make use of the
1476 C<fd> method to lock your database.
1478 =item B<$status = $X-E<gt>seq($key, $value, $flags) ;>
1480 This interface allows sequential retrieval from the database. See
1481 L<dbopen> for full details.
1483 Both the C<$key> and C<$value> parameters will be set to the key/value
1484 pair read from the database.
1486 The flags parameter is mandatory. The valid flag values are R_CURSOR,
1487 R_FIRST, R_LAST, R_NEXT and R_PREV.
1489 =item B<$status = $X-E<gt>sync([$flags]) ;>
1491 Flushes any cached buffers to disk.
1493 R_RECNOSYNC is the only valid flag at present.
1499 A DBM Filter is a piece of code that is be used when you I<always>
1500 want to make the same transformation to all keys and/or values in a
1503 There are four methods associated with DBM Filters. All work identically,
1504 and each is used to install (or uninstall) a single DBM Filter. Each
1505 expects a single parameter, namely a reference to a sub. The only
1506 difference between them is the place that the filter is installed.
1512 =item B<filter_store_key>
1514 If a filter has been installed with this method, it will be invoked
1515 every time you write a key to a DBM database.
1517 =item B<filter_store_value>
1519 If a filter has been installed with this method, it will be invoked
1520 every time you write a value to a DBM database.
1523 =item B<filter_fetch_key>
1525 If a filter has been installed with this method, it will be invoked
1526 every time you read a key from a DBM database.
1528 =item B<filter_fetch_value>
1530 If a filter has been installed with this method, it will be invoked
1531 every time you read a value from a DBM database.
1535 You can use any combination of the methods, from none, to all four.
1537 All filter methods return the existing filter, if present, or C<undef>
1540 To delete a filter pass C<undef> to it.
1544 When each filter is called by Perl, a local copy of C<$_> will contain
1545 the key or value to be filtered. Filtering is achieved by modifying
1546 the contents of C<$_>. The return code from the filter is ignored.
1548 =head2 An Example -- the NULL termination problem.
1550 Consider the following scenario. You have a DBM database
1551 that you need to share with a third-party C application. The C application
1552 assumes that I<all> keys and values are NULL terminated. Unfortunately
1553 when Perl writes to DBM databases it doesn't use NULL termination, so
1554 your Perl application will have to manage NULL termination itself. When
1555 you write to the database you will have to use something like this:
1557 $hash{"$key\0"} = "$value\0" ;
1559 Similarly the NULL needs to be taken into account when you are considering
1560 the length of existing keys/values.
1562 It would be much better if you could ignore the NULL terminations issue
1563 in the main application code and have a mechanism that automatically
1564 added the terminating NULL to all keys and values whenever you write to
1565 the database and have them removed when you read from the database. As I'm
1566 sure you have already guessed, this is a problem that DBM Filters can
1573 my $filename = "/tmp/filt" ;
1576 my $db = tie %hash, 'DB_File', $filename, O_CREAT|O_RDWR, 0666, $DB_HASH
1577 or die "Cannot open $filename: $!\n" ;
1579 # Install DBM Filters
1580 $db->filter_fetch_key ( sub { s/\0$// } ) ;
1581 $db->filter_store_key ( sub { $_ .= "\0" } ) ;
1582 $db->filter_fetch_value( sub { s/\0$// } ) ;
1583 $db->filter_store_value( sub { $_ .= "\0" } ) ;
1585 $hash{"abc"} = "def" ;
1586 my $a = $hash{"ABC"} ;
1591 Hopefully the contents of each of the filters should be
1592 self-explanatory. Both "fetch" filters remove the terminating NULL,
1593 and both "store" filters add a terminating NULL.
1596 =head2 Another Example -- Key is a C int.
1598 Here is another real-life example. By default, whenever Perl writes to
1599 a DBM database it always writes the key and value as strings. So when
1602 $hash{12345} = "soemthing" ;
1604 the key 12345 will get stored in the DBM database as the 5 byte string
1605 "12345". If you actually want the key to be stored in the DBM database
1606 as a C int, you will have to use C<pack> when writing, and C<unpack>
1609 Here is a DBM Filter that does it:
1614 my $filename = "/tmp/filt" ;
1618 my $db = tie %hash, 'DB_File', $filename, O_CREAT|O_RDWR, 0666, $DB_HASH
1619 or die "Cannot open $filename: $!\n" ;
1621 $db->filter_fetch_key ( sub { $_ = unpack("i", $_) } ) ;
1622 $db->filter_store_key ( sub { $_ = pack ("i", $_) } ) ;
1623 $hash{123} = "def" ;
1628 This time only two filters have been used -- we only need to manipulate
1629 the contents of the key, so it wasn't necessary to install any value
1632 =head1 HINTS AND TIPS
1635 =head2 Locking Databases
1637 Concurrent access of a read-write database by several parties requires
1638 them all to use some kind of locking. Here's an example of Tom's that
1639 uses the I<fd> method to get the file descriptor, and then a careful
1640 open() to give something Perl will flock() for you. Run this repeatedly
1641 in the background to watch the locks granted in proper order.
1652 my($oldval, $fd, $db, %db, $value, $key);
1654 $key = shift || 'default';
1655 $value = shift || 'magic';
1659 $db = tie(%db, 'DB_File', '/tmp/foo.db', O_CREAT|O_RDWR, 0644)
1660 || die "dbcreat /tmp/foo.db $!";
1662 print "$$: db fd is $fd\n";
1663 open(DB_FH, "+<&=$fd") || die "dup $!";
1666 unless (flock (DB_FH, LOCK_SH | LOCK_NB)) {
1667 print "$$: CONTENTION; can't read during write update!
1668 Waiting for read lock ($!) ....";
1669 unless (flock (DB_FH, LOCK_SH)) { die "flock: $!" }
1671 print "$$: Read lock granted\n";
1673 $oldval = $db{$key};
1674 print "$$: Old value was $oldval\n";
1675 flock(DB_FH, LOCK_UN);
1677 unless (flock (DB_FH, LOCK_EX | LOCK_NB)) {
1678 print "$$: CONTENTION; must have exclusive lock!
1679 Waiting for write lock ($!) ....";
1680 unless (flock (DB_FH, LOCK_EX)) { die "flock: $!" }
1683 print "$$: Write lock granted\n";
1685 $db->sync; # to flush
1688 flock(DB_FH, LOCK_UN);
1692 print "$$: Updated db to $key=$value\n";
1694 =head2 Sharing Databases With C Applications
1696 There is no technical reason why a Berkeley DB database cannot be
1697 shared by both a Perl and a C application.
1699 The vast majority of problems that are reported in this area boil down
1700 to the fact that C strings are NULL terminated, whilst Perl strings are
1701 not. See L<DBM FILTERS> for a generic way to work around this problem.
1703 Here is a real example. Netscape 2.0 keeps a record of the locations you
1704 visit along with the time you last visited them in a DB_HASH database.
1705 This is usually stored in the file F<~/.netscape/history.db>. The key
1706 field in the database is the location string and the value field is the
1707 time the location was last visited stored as a 4 byte binary value.
1709 If you haven't already guessed, the location string is stored with a
1710 terminating NULL. This means you need to be careful when accessing the
1713 Here is a snippet of code that is loosely based on Tom Christiansen's
1714 I<ggh> script (available from your nearest CPAN archive in
1715 F<authors/id/TOMC/scripts/nshist.gz>).
1721 use vars qw( $dotdir $HISTORY %hist_db $href $binary_time $date ) ;
1722 $dotdir = $ENV{HOME} || $ENV{LOGNAME};
1724 $HISTORY = "$dotdir/.netscape/history.db";
1726 tie %hist_db, 'DB_File', $HISTORY
1727 or die "Cannot open $HISTORY: $!\n" ;;
1729 # Dump the complete database
1730 while ( ($href, $binary_time) = each %hist_db ) {
1732 # remove the terminating NULL
1733 $href =~ s/\x00$// ;
1735 # convert the binary time into a user friendly string
1736 $date = localtime unpack("V", $binary_time);
1737 print "$date $href\n" ;
1740 # check for the existence of a specific key
1741 # remember to add the NULL
1742 if ( $binary_time = $hist_db{"http://mox.perl.com/\x00"} ) {
1743 $date = localtime unpack("V", $binary_time) ;
1744 print "Last visited mox.perl.com on $date\n" ;
1747 print "Never visited mox.perl.com\n"
1752 =head2 The untie() Gotcha
1754 If you make use of the Berkeley DB API, it is I<very> strongly
1755 recommended that you read L<perltie/The untie Gotcha>.
1757 Even if you don't currently make use of the API interface, it is still
1760 Here is an example which illustrates the problem from a B<DB_File>
1769 $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_TRUNC
1770 or die "Cannot tie first time: $!" ;
1776 tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT
1777 or die "Cannot tie second time: $!" ;
1781 When run, the script will produce this error message:
1783 Cannot tie second time: Invalid argument at bad.file line 14.
1785 Although the error message above refers to the second tie() statement
1786 in the script, the source of the problem is really with the untie()
1787 statement that precedes it.
1789 Having read L<perltie> you will probably have already guessed that the
1790 error is caused by the extra copy of the tied object stored in C<$X>.
1791 If you haven't, then the problem boils down to the fact that the
1792 B<DB_File> destructor, DESTROY, will not be called until I<all>
1793 references to the tied object are destroyed. Both the tied variable,
1794 C<%x>, and C<$X> above hold a reference to the object. The call to
1795 untie() will destroy the first, but C<$X> still holds a valid
1796 reference, so the destructor will not get called and the database file
1797 F<tst.fil> will remain open. The fact that Berkeley DB then reports the
1798 attempt to open a database that is alreday open via the catch-all
1799 "Invalid argument" doesn't help.
1801 If you run the script with the C<-w> flag the error message becomes:
1803 untie attempted while 1 inner references still exist at bad.file line 12.
1804 Cannot tie second time: Invalid argument at bad.file line 14.
1806 which pinpoints the real problem. Finally the script can now be
1807 modified to fix the original problem by destroying the API object
1816 $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT
1820 =head1 COMMON QUESTIONS
1822 =head2 Why is there Perl source in my database?
1824 If you look at the contents of a database file created by DB_File,
1825 there can sometimes be part of a Perl script included in it.
1827 This happens because Berkeley DB uses dynamic memory to allocate
1828 buffers which will subsequently be written to the database file. Being
1829 dynamic, the memory could have been used for anything before DB
1830 malloced it. As Berkeley DB doesn't clear the memory once it has been
1831 allocated, the unused portions will contain random junk. In the case
1832 where a Perl script gets written to the database, the random junk will
1833 correspond to an area of dynamic memory that happened to be used during
1834 the compilation of the script.
1836 Unless you don't like the possibility of there being part of your Perl
1837 scripts embedded in a database file, this is nothing to worry about.
1839 =head2 How do I store complex data structures with DB_File?
1841 Although B<DB_File> cannot do this directly, there is a module which
1842 can layer transparently over B<DB_File> to accomplish this feat.
1844 Check out the MLDBM module, available on CPAN in the directory
1845 F<modules/by-module/MLDBM>.
1847 =head2 What does "Invalid Argument" mean?
1849 You will get this error message when one of the parameters in the
1850 C<tie> call is wrong. Unfortunately there are quite a few parameters to
1851 get wrong, so it can be difficult to figure out which one it is.
1853 Here are a couple of possibilities:
1859 Attempting to reopen a database without closing it.
1863 Using the O_WRONLY flag.
1867 =head2 What does "Bareword 'DB_File' not allowed" mean?
1869 You will encounter this particular error message when you have the
1870 C<strict 'subs'> pragma (or the full strict pragma) in your script.
1871 Consider this script:
1876 tie %x, DB_File, "filename" ;
1878 Running it produces the error in question:
1880 Bareword "DB_File" not allowed while "strict subs" in use
1882 To get around the error, place the word C<DB_File> in either single or
1883 double quotes, like this:
1885 tie %x, "DB_File", "filename" ;
1887 Although it might seem like a real pain, it is really worth the effort
1888 of having a C<use strict> in all your scripts.
1892 Articles that are either about B<DB_File> or make use of it.
1898 I<Full-Text Searching in Perl>, Tim Kientzle (tkientzle@ddj.com),
1899 Dr. Dobb's Journal, Issue 295, January 1999, pp 34-41
1905 Moved to the Changes file.
1909 Some older versions of Berkeley DB had problems with fixed length
1910 records using the RECNO file format. This problem has been fixed since
1911 version 1.85 of Berkeley DB.
1913 I am sure there are bugs in the code. If you do find any, or can
1914 suggest any enhancements, I would welcome your comments.
1918 B<DB_File> comes with the standard Perl source distribution. Look in
1919 the directory F<ext/DB_File>. Given the amount of time between releases
1920 of Perl the version that ships with Perl is quite likely to be out of
1921 date, so the most recent version can always be found on CPAN (see
1922 L<perlmod/CPAN> for details), in the directory
1923 F<modules/by-module/DB_File>.
1925 This version of B<DB_File> will work with either version 1.x or 2.x of
1926 Berkeley DB, but is limited to the functionality provided by version 1.
1928 The official web site for Berkeley DB is F<http://www.sleepycat.com>.
1929 Both versions 1 and 2 of Berkeley DB are available there.
1931 Alternatively, Berkeley DB version 1 is available at your nearest CPAN
1932 archive in F<src/misc/db.1.85.tar.gz>.
1934 If you are running IRIX, then get Berkeley DB version 1 from
1935 F<http://reality.sgi.com/ariel>. It has the patches necessary to
1936 compile properly on IRIX 5.3.
1940 Copyright (c) 1995-1999 Paul Marquess. All rights reserved. This program
1941 is free software; you can redistribute it and/or modify it under the
1942 same terms as Perl itself.
1944 Although B<DB_File> is covered by the Perl license, the library it
1945 makes use of, namely Berkeley DB, is not. Berkeley DB has its own
1946 copyright and its own license. Please take the time to read it.
1948 Here are are few words taken from the Berkeley DB FAQ (at
1949 http://www.sleepycat.com) regarding the license:
1951 Do I have to license DB to use it in Perl scripts?
1953 No. The Berkeley DB license requires that software that uses
1954 Berkeley DB be freely redistributable. In the case of Perl, that
1955 software is Perl, and not your scripts. Any Perl scripts that you
1956 write are your property, including scripts that make use of
1957 Berkeley DB. Neither the Perl license nor the Berkeley DB license
1958 place any restriction on what you may do with them.
1960 If you are in any doubt about the license situation, contact either the
1961 Berkeley DB authors or the author of DB_File. See L<"AUTHOR"> for details.
1966 L<perl(1)>, L<dbopen(3)>, L<hash(3)>, L<recno(3)>, L<btree(3)>,
1971 The DB_File interface was written by Paul Marquess
1972 E<lt>Paul.Marquess@btinternet.comE<gt>.
1973 Questions about the DB system itself may be addressed to
1974 E<lt>db@sleepycat.com<gt>.