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a0d0e21e LW |
1 | # DB_File.pm -- Perl 5 interface to Berkeley DB |
2 | # | |
6ca2e664 | 3 | # written by Paul Marquess (Paul.Marquess@btinternet.com) |
c5da4faf PM |
4 | # last modified 26th April 2001 |
5 | # version 1.77 | |
36477c24 | 6 | # |
c5da4faf | 7 | # Copyright (c) 1995-2001 Paul Marquess. All rights reserved. |
36477c24 | 8 | # This program is free software; you can redistribute it and/or |
9 | # modify it under the same terms as Perl itself. | |
10 | ||
8e07c86e AD |
11 | |
12 | package DB_File::HASHINFO ; | |
785da04d | 13 | |
610ab055 PM |
14 | require 5.003 ; |
15 | ||
3245f058 | 16 | use warnings; |
785da04d | 17 | use strict; |
8e07c86e | 18 | use Carp; |
88108326 | 19 | require Tie::Hash; |
20 | @DB_File::HASHINFO::ISA = qw(Tie::Hash); | |
8e07c86e | 21 | |
88108326 | 22 | sub new |
8e07c86e | 23 | { |
88108326 | 24 | my $pkg = shift ; |
25 | my %x ; | |
26 | tie %x, $pkg ; | |
27 | bless \%x, $pkg ; | |
8e07c86e AD |
28 | } |
29 | ||
610ab055 | 30 | |
88108326 | 31 | sub TIEHASH |
32 | { | |
33 | my $pkg = shift ; | |
34 | ||
36477c24 | 35 | bless { VALID => { map {$_, 1} |
36 | qw( bsize ffactor nelem cachesize hash lorder) | |
37 | }, | |
38 | GOT => {} | |
39 | }, $pkg ; | |
88108326 | 40 | } |
8e07c86e | 41 | |
610ab055 | 42 | |
8e07c86e AD |
43 | sub FETCH |
44 | { | |
88108326 | 45 | my $self = shift ; |
46 | my $key = shift ; | |
8e07c86e | 47 | |
36477c24 | 48 | return $self->{GOT}{$key} if exists $self->{VALID}{$key} ; |
88108326 | 49 | |
50 | my $pkg = ref $self ; | |
51 | croak "${pkg}::FETCH - Unknown element '$key'" ; | |
8e07c86e AD |
52 | } |
53 | ||
54 | ||
55 | sub STORE | |
56 | { | |
88108326 | 57 | my $self = shift ; |
58 | my $key = shift ; | |
59 | my $value = shift ; | |
60 | ||
36477c24 | 61 | if ( exists $self->{VALID}{$key} ) |
8e07c86e | 62 | { |
36477c24 | 63 | $self->{GOT}{$key} = $value ; |
8e07c86e AD |
64 | return ; |
65 | } | |
66 | ||
88108326 | 67 | my $pkg = ref $self ; |
68 | croak "${pkg}::STORE - Unknown element '$key'" ; | |
8e07c86e AD |
69 | } |
70 | ||
71 | sub DELETE | |
72 | { | |
88108326 | 73 | my $self = shift ; |
74 | my $key = shift ; | |
75 | ||
36477c24 | 76 | if ( exists $self->{VALID}{$key} ) |
8e07c86e | 77 | { |
36477c24 | 78 | delete $self->{GOT}{$key} ; |
8e07c86e AD |
79 | return ; |
80 | } | |
81 | ||
88108326 | 82 | my $pkg = ref $self ; |
83 | croak "DB_File::HASHINFO::DELETE - Unknown element '$key'" ; | |
8e07c86e AD |
84 | } |
85 | ||
88108326 | 86 | sub EXISTS |
8e07c86e | 87 | { |
88108326 | 88 | my $self = shift ; |
89 | my $key = shift ; | |
8e07c86e | 90 | |
36477c24 | 91 | exists $self->{VALID}{$key} ; |
8e07c86e AD |
92 | } |
93 | ||
88108326 | 94 | sub NotHere |
8e07c86e | 95 | { |
18d2dc8c | 96 | my $self = shift ; |
88108326 | 97 | my $method = shift ; |
8e07c86e | 98 | |
18d2dc8c | 99 | croak ref($self) . " does not define the method ${method}" ; |
8e07c86e AD |
100 | } |
101 | ||
18d2dc8c PM |
102 | sub FIRSTKEY { my $self = shift ; $self->NotHere("FIRSTKEY") } |
103 | sub NEXTKEY { my $self = shift ; $self->NotHere("NEXTKEY") } | |
104 | sub CLEAR { my $self = shift ; $self->NotHere("CLEAR") } | |
8e07c86e AD |
105 | |
106 | package DB_File::RECNOINFO ; | |
785da04d | 107 | |
3245f058 | 108 | use warnings; |
88108326 | 109 | use strict ; |
110 | ||
045291aa | 111 | @DB_File::RECNOINFO::ISA = qw(DB_File::HASHINFO) ; |
8e07c86e AD |
112 | |
113 | sub TIEHASH | |
114 | { | |
88108326 | 115 | my $pkg = shift ; |
116 | ||
36477c24 | 117 | bless { VALID => { map {$_, 1} |
118 | qw( bval cachesize psize flags lorder reclen bfname ) | |
119 | }, | |
120 | GOT => {}, | |
121 | }, $pkg ; | |
8e07c86e AD |
122 | } |
123 | ||
88108326 | 124 | package DB_File::BTREEINFO ; |
8e07c86e | 125 | |
3245f058 | 126 | use warnings; |
88108326 | 127 | use strict ; |
8e07c86e | 128 | |
88108326 | 129 | @DB_File::BTREEINFO::ISA = qw(DB_File::HASHINFO) ; |
8e07c86e | 130 | |
88108326 | 131 | sub TIEHASH |
8e07c86e | 132 | { |
88108326 | 133 | my $pkg = shift ; |
134 | ||
36477c24 | 135 | bless { VALID => { map {$_, 1} |
136 | qw( flags cachesize maxkeypage minkeypage psize | |
137 | compare prefix lorder ) | |
138 | }, | |
139 | GOT => {}, | |
140 | }, $pkg ; | |
8e07c86e AD |
141 | } |
142 | ||
143 | ||
8e07c86e | 144 | package DB_File ; |
785da04d | 145 | |
3245f058 | 146 | use warnings; |
785da04d | 147 | use strict; |
b90e71be GS |
148 | use vars qw($VERSION @ISA @EXPORT $AUTOLOAD $DB_BTREE $DB_HASH $DB_RECNO |
149 | $db_version $use_XSLoader | |
150 | ) ; | |
8e07c86e AD |
151 | use Carp; |
152 | ||
785da04d | 153 | |
c5da4faf | 154 | $VERSION = "1.77" ; |
8e07c86e AD |
155 | |
156 | #typedef enum { DB_BTREE, DB_HASH, DB_RECNO } DBTYPE; | |
88108326 | 157 | $DB_BTREE = new DB_File::BTREEINFO ; |
158 | $DB_HASH = new DB_File::HASHINFO ; | |
159 | $DB_RECNO = new DB_File::RECNOINFO ; | |
8e07c86e | 160 | |
785da04d | 161 | require Tie::Hash; |
8e07c86e AD |
162 | require Exporter; |
163 | use AutoLoader; | |
b90e71be GS |
164 | BEGIN { |
165 | $use_XSLoader = 1 ; | |
166 | eval { require XSLoader } ; | |
167 | ||
168 | if ($@) { | |
169 | $use_XSLoader = 0 ; | |
170 | require DynaLoader; | |
171 | @ISA = qw(DynaLoader); | |
172 | } | |
173 | } | |
174 | ||
175 | push @ISA, qw(Tie::Hash Exporter); | |
8e07c86e AD |
176 | @EXPORT = qw( |
177 | $DB_BTREE $DB_HASH $DB_RECNO | |
88108326 | 178 | |
8e07c86e AD |
179 | BTREEMAGIC |
180 | BTREEVERSION | |
181 | DB_LOCK | |
182 | DB_SHMEM | |
183 | DB_TXN | |
184 | HASHMAGIC | |
185 | HASHVERSION | |
186 | MAX_PAGE_NUMBER | |
187 | MAX_PAGE_OFFSET | |
188 | MAX_REC_NUMBER | |
189 | RET_ERROR | |
190 | RET_SPECIAL | |
191 | RET_SUCCESS | |
192 | R_CURSOR | |
193 | R_DUP | |
194 | R_FIRST | |
195 | R_FIXEDLEN | |
196 | R_IAFTER | |
197 | R_IBEFORE | |
198 | R_LAST | |
199 | R_NEXT | |
200 | R_NOKEY | |
201 | R_NOOVERWRITE | |
202 | R_PREV | |
203 | R_RECNOSYNC | |
204 | R_SETCURSOR | |
205 | R_SNAPSHOT | |
206 | __R_UNUSED | |
88108326 | 207 | |
045291aa | 208 | ); |
8e07c86e AD |
209 | |
210 | sub AUTOLOAD { | |
785da04d | 211 | my($constname); |
8e07c86e | 212 | ($constname = $AUTOLOAD) =~ s/.*:://; |
785da04d | 213 | my $val = constant($constname, @_ ? $_[0] : 0); |
8e07c86e | 214 | if ($! != 0) { |
265f5c4a | 215 | if ($! =~ /Invalid/ || $!{EINVAL}) { |
8e07c86e AD |
216 | $AutoLoader::AUTOLOAD = $AUTOLOAD; |
217 | goto &AutoLoader::AUTOLOAD; | |
218 | } | |
219 | else { | |
785da04d | 220 | my($pack,$file,$line) = caller; |
8e07c86e AD |
221 | croak "Your vendor has not defined DB macro $constname, used at $file line $line. |
222 | "; | |
223 | } | |
224 | } | |
225 | eval "sub $AUTOLOAD { $val }"; | |
226 | goto &$AUTOLOAD; | |
227 | } | |
228 | ||
f6b705ef | 229 | |
a6ed719b | 230 | eval { |
1f70e1ea PM |
231 | # Make all Fcntl O_XXX constants available for importing |
232 | require Fcntl; | |
233 | my @O = grep /^O_/, @Fcntl::EXPORT; | |
234 | Fcntl->import(@O); # first we import what we want to export | |
235 | push(@EXPORT, @O); | |
a6ed719b | 236 | }; |
f6b705ef | 237 | |
b90e71be GS |
238 | if ($use_XSLoader) |
239 | { XSLoader::load("DB_File", $VERSION)} | |
240 | else | |
241 | { bootstrap DB_File $VERSION } | |
8e07c86e AD |
242 | |
243 | # Preloaded methods go here. Autoload methods go after __END__, and are | |
244 | # processed by the autosplit program. | |
245 | ||
05475680 | 246 | sub tie_hash_or_array |
610ab055 PM |
247 | { |
248 | my (@arg) = @_ ; | |
05475680 | 249 | my $tieHASH = ( (caller(1))[3] =~ /TIEHASH/ ) ; |
610ab055 PM |
250 | |
251 | $arg[4] = tied %{ $arg[4] } | |
252 | if @arg >= 5 && ref $arg[4] && $arg[4] =~ /=HASH/ && tied %{ $arg[4] } ; | |
253 | ||
1f70e1ea PM |
254 | # make recno in Berkeley DB version 2 work like recno in version 1. |
255 | if ($db_version > 1 and defined $arg[4] and $arg[4] =~ /RECNO/ and | |
256 | $arg[1] and ! -e $arg[1]) { | |
257 | open(FH, ">$arg[1]") or return undef ; | |
258 | close FH ; | |
259 | chmod $arg[3] ? $arg[3] : 0666 , $arg[1] ; | |
260 | } | |
261 | ||
05475680 | 262 | DoTie_($tieHASH, @arg) ; |
610ab055 PM |
263 | } |
264 | ||
05475680 PM |
265 | sub TIEHASH |
266 | { | |
267 | tie_hash_or_array(@_) ; | |
268 | } | |
269 | ||
270 | sub TIEARRAY | |
271 | { | |
272 | tie_hash_or_array(@_) ; | |
273 | } | |
88108326 | 274 | |
045291aa PM |
275 | sub CLEAR |
276 | { | |
1f70e1ea | 277 | my $self = shift; |
3245f058 | 278 | my $key = 0 ; |
1f70e1ea PM |
279 | my $value = "" ; |
280 | my $status = $self->seq($key, $value, R_FIRST()); | |
281 | my @keys; | |
282 | ||
283 | while ($status == 0) { | |
284 | push @keys, $key; | |
285 | $status = $self->seq($key, $value, R_NEXT()); | |
286 | } | |
287 | foreach $key (reverse @keys) { | |
288 | my $s = $self->del($key); | |
289 | } | |
290 | } | |
291 | ||
045291aa PM |
292 | sub EXTEND { } |
293 | ||
294 | sub STORESIZE | |
295 | { | |
296 | my $self = shift; | |
297 | my $length = shift ; | |
298 | my $current_length = $self->length() ; | |
299 | ||
300 | if ($length < $current_length) { | |
301 | my $key ; | |
302 | for ($key = $current_length - 1 ; $key >= $length ; -- $key) | |
303 | { $self->del($key) } | |
304 | } | |
a9fd575d PM |
305 | elsif ($length > $current_length) { |
306 | $self->put($length-1, "") ; | |
307 | } | |
045291aa PM |
308 | } |
309 | ||
c5da4faf PM |
310 | |
311 | sub SPLICE | |
312 | { | |
313 | my $self = shift; | |
314 | my $offset = shift; | |
315 | if (not defined $offset) { | |
316 | carp 'Use of uninitialized value in splice'; | |
317 | $offset = 0; | |
318 | } | |
319 | ||
320 | my $length = @_ ? shift : 0; | |
321 | # Carping about definedness comes _after_ the OFFSET sanity check. | |
322 | # This is so we get the same error messages as Perl's splice(). | |
323 | # | |
324 | ||
325 | my @list = @_; | |
326 | ||
327 | my $size = $self->FETCHSIZE(); | |
328 | ||
329 | # 'If OFFSET is negative then it start that far from the end of | |
330 | # the array.' | |
331 | # | |
332 | if ($offset < 0) { | |
333 | my $new_offset = $size + $offset; | |
334 | if ($new_offset < 0) { | |
335 | die "Modification of non-creatable array value attempted, " | |
336 | . "subscript $offset"; | |
337 | } | |
338 | $offset = $new_offset; | |
339 | } | |
340 | ||
341 | if ($offset > $size) { | |
342 | $offset = $size; | |
343 | } | |
344 | ||
345 | if (not defined $length) { | |
346 | carp 'Use of uninitialized value in splice'; | |
347 | $length = 0; | |
348 | } | |
349 | ||
350 | # 'If LENGTH is omitted, removes everything from OFFSET onward.' | |
351 | if (not defined $length) { | |
352 | $length = $size - $offset; | |
353 | } | |
354 | ||
355 | # 'If LENGTH is negative, leave that many elements off the end of | |
356 | # the array.' | |
357 | # | |
358 | if ($length < 0) { | |
359 | $length = $size - $offset + $length; | |
360 | ||
361 | if ($length < 0) { | |
362 | # The user must have specified a length bigger than the | |
363 | # length of the array passed in. But perl's splice() | |
364 | # doesn't catch this, it just behaves as for length=0. | |
365 | # | |
366 | $length = 0; | |
367 | } | |
368 | } | |
369 | ||
370 | if ($length > $size - $offset) { | |
371 | $length = $size - $offset; | |
372 | } | |
373 | ||
374 | # $num_elems holds the current number of elements in the database. | |
375 | my $num_elems = $size; | |
376 | ||
377 | # 'Removes the elements designated by OFFSET and LENGTH from an | |
378 | # array,'... | |
379 | # | |
380 | my @removed = (); | |
381 | foreach (0 .. $length - 1) { | |
382 | my $old; | |
383 | my $status = $self->get($offset, $old); | |
384 | if ($status != 0) { | |
385 | my $msg = "error from Berkeley DB on get($offset, \$old)"; | |
386 | if ($status == 1) { | |
387 | $msg .= ' (no such element?)'; | |
388 | } | |
389 | else { | |
390 | $msg .= ": error status $status"; | |
391 | if (defined $! and $! ne '') { | |
392 | $msg .= ", message $!"; | |
393 | } | |
394 | } | |
395 | die $msg; | |
396 | } | |
397 | push @removed, $old; | |
398 | ||
399 | $status = $self->del($offset); | |
400 | if ($status != 0) { | |
401 | my $msg = "error from Berkeley DB on del($offset)"; | |
402 | if ($status == 1) { | |
403 | $msg .= ' (no such element?)'; | |
404 | } | |
405 | else { | |
406 | $msg .= ": error status $status"; | |
407 | if (defined $! and $! ne '') { | |
408 | $msg .= ", message $!"; | |
409 | } | |
410 | } | |
411 | die $msg; | |
412 | } | |
413 | ||
414 | -- $num_elems; | |
415 | } | |
416 | ||
417 | # ...'and replaces them with the elements of LIST, if any.' | |
418 | my $pos = $offset; | |
419 | while (defined (my $elem = shift @list)) { | |
420 | my $old_pos = $pos; | |
421 | my $status; | |
422 | if ($pos >= $num_elems) { | |
423 | $status = $self->put($pos, $elem); | |
424 | } | |
425 | else { | |
426 | $status = $self->put($pos, $elem, $self->R_IBEFORE); | |
427 | } | |
428 | ||
429 | if ($status != 0) { | |
430 | my $msg = "error from Berkeley DB on put($pos, $elem, ...)"; | |
431 | if ($status == 1) { | |
432 | $msg .= ' (no such element?)'; | |
433 | } | |
434 | else { | |
435 | $msg .= ", error status $status"; | |
436 | if (defined $! and $! ne '') { | |
437 | $msg .= ", message $!"; | |
438 | } | |
439 | } | |
440 | die $msg; | |
441 | } | |
442 | ||
443 | die "pos unexpectedly changed from $old_pos to $pos with R_IBEFORE" | |
444 | if $old_pos != $pos; | |
445 | ||
446 | ++ $pos; | |
447 | ++ $num_elems; | |
448 | } | |
449 | ||
450 | if (wantarray) { | |
451 | # 'In list context, returns the elements removed from the | |
452 | # array.' | |
453 | # | |
454 | return @removed; | |
455 | } | |
456 | elsif (defined wantarray and not wantarray) { | |
457 | # 'In scalar context, returns the last element removed, or | |
458 | # undef if no elements are removed.' | |
459 | # | |
460 | if (@removed) { | |
461 | my $last = pop @removed; | |
462 | return "$last"; | |
463 | } | |
464 | else { | |
465 | return undef; | |
466 | } | |
467 | } | |
468 | elsif (not defined wantarray) { | |
469 | # Void context | |
470 | } | |
471 | else { die } | |
472 | } | |
473 | sub ::DB_File::splice { &SPLICE } | |
474 | ||
6ca2e664 PM |
475 | sub find_dup |
476 | { | |
477 | croak "Usage: \$db->find_dup(key,value)\n" | |
478 | unless @_ == 3 ; | |
479 | ||
480 | my $db = shift ; | |
481 | my ($origkey, $value_wanted) = @_ ; | |
482 | my ($key, $value) = ($origkey, 0); | |
483 | my ($status) = 0 ; | |
484 | ||
485 | for ($status = $db->seq($key, $value, R_CURSOR() ) ; | |
486 | $status == 0 ; | |
487 | $status = $db->seq($key, $value, R_NEXT() ) ) { | |
488 | ||
489 | return 0 if $key eq $origkey and $value eq $value_wanted ; | |
490 | } | |
491 | ||
492 | return $status ; | |
493 | } | |
494 | ||
495 | sub del_dup | |
496 | { | |
497 | croak "Usage: \$db->del_dup(key,value)\n" | |
498 | unless @_ == 3 ; | |
499 | ||
500 | my $db = shift ; | |
501 | my ($key, $value) = @_ ; | |
502 | my ($status) = $db->find_dup($key, $value) ; | |
503 | return $status if $status != 0 ; | |
504 | ||
505 | $status = $db->del($key, R_CURSOR() ) ; | |
506 | return $status ; | |
507 | } | |
508 | ||
88108326 | 509 | sub get_dup |
510 | { | |
511 | croak "Usage: \$db->get_dup(key [,flag])\n" | |
512 | unless @_ == 2 or @_ == 3 ; | |
513 | ||
514 | my $db = shift ; | |
515 | my $key = shift ; | |
516 | my $flag = shift ; | |
f6b705ef | 517 | my $value = 0 ; |
88108326 | 518 | my $origkey = $key ; |
519 | my $wantarray = wantarray ; | |
f6b705ef | 520 | my %values = () ; |
88108326 | 521 | my @values = () ; |
522 | my $counter = 0 ; | |
f6b705ef | 523 | my $status = 0 ; |
88108326 | 524 | |
f6b705ef | 525 | # iterate through the database until either EOF ($status == 0) |
526 | # or a different key is encountered ($key ne $origkey). | |
527 | for ($status = $db->seq($key, $value, R_CURSOR()) ; | |
528 | $status == 0 and $key eq $origkey ; | |
529 | $status = $db->seq($key, $value, R_NEXT()) ) { | |
88108326 | 530 | |
f6b705ef | 531 | # save the value or count number of matches |
532 | if ($wantarray) { | |
533 | if ($flag) | |
534 | { ++ $values{$value} } | |
535 | else | |
536 | { push (@values, $value) } | |
537 | } | |
538 | else | |
539 | { ++ $counter } | |
88108326 | 540 | |
88108326 | 541 | } |
542 | ||
f6b705ef | 543 | return ($wantarray ? ($flag ? %values : @values) : $counter) ; |
88108326 | 544 | } |
545 | ||
546 | ||
8e07c86e AD |
547 | 1; |
548 | __END__ | |
549 | ||
3b35bae3 AD |
550 | =head1 NAME |
551 | ||
1f70e1ea | 552 | DB_File - Perl5 access to Berkeley DB version 1.x |
3b35bae3 AD |
553 | |
554 | =head1 SYNOPSIS | |
555 | ||
bbc7dcd2 MS |
556 | use DB_File; |
557 | ||
88108326 | 558 | [$X =] tie %hash, 'DB_File', [$filename, $flags, $mode, $DB_HASH] ; |
559 | [$X =] tie %hash, 'DB_File', $filename, $flags, $mode, $DB_BTREE ; | |
560 | [$X =] tie @array, 'DB_File', $filename, $flags, $mode, $DB_RECNO ; | |
760ac839 | 561 | |
3b35bae3 AD |
562 | $status = $X->del($key [, $flags]) ; |
563 | $status = $X->put($key, $value [, $flags]) ; | |
564 | $status = $X->get($key, $value [, $flags]) ; | |
760ac839 | 565 | $status = $X->seq($key, $value, $flags) ; |
3b35bae3 AD |
566 | $status = $X->sync([$flags]) ; |
567 | $status = $X->fd ; | |
760ac839 | 568 | |
f6b705ef | 569 | # BTREE only |
88108326 | 570 | $count = $X->get_dup($key) ; |
571 | @list = $X->get_dup($key) ; | |
572 | %list = $X->get_dup($key, 1) ; | |
6ca2e664 PM |
573 | $status = $X->find_dup($key, $value) ; |
574 | $status = $X->del_dup($key, $value) ; | |
88108326 | 575 | |
f6b705ef | 576 | # RECNO only |
577 | $a = $X->length; | |
578 | $a = $X->pop ; | |
579 | $X->push(list); | |
580 | $a = $X->shift; | |
581 | $X->unshift(list); | |
c5da4faf | 582 | @r = $X->splice(offset, length, elements); |
f6b705ef | 583 | |
cad2e5aa JH |
584 | # DBM Filters |
585 | $old_filter = $db->filter_store_key ( sub { ... } ) ; | |
586 | $old_filter = $db->filter_store_value( sub { ... } ) ; | |
587 | $old_filter = $db->filter_fetch_key ( sub { ... } ) ; | |
588 | $old_filter = $db->filter_fetch_value( sub { ... } ) ; | |
589 | ||
3b35bae3 AD |
590 | untie %hash ; |
591 | untie @array ; | |
592 | ||
593 | =head1 DESCRIPTION | |
594 | ||
8e07c86e | 595 | B<DB_File> is a module which allows Perl programs to make use of the |
1f70e1ea | 596 | facilities provided by Berkeley DB version 1.x (if you have a newer |
039d031f PM |
597 | version of DB, see L<Using DB_File with Berkeley DB version 2 or 3>). |
598 | It is assumed that you have a copy of the Berkeley DB manual pages at | |
599 | hand when reading this documentation. The interface defined here | |
600 | mirrors the Berkeley DB interface closely. | |
68dc0745 | 601 | |
8e07c86e AD |
602 | Berkeley DB is a C library which provides a consistent interface to a |
603 | number of database formats. B<DB_File> provides an interface to all | |
604 | three of the database types currently supported by Berkeley DB. | |
3b35bae3 AD |
605 | |
606 | The file types are: | |
607 | ||
608 | =over 5 | |
609 | ||
88108326 | 610 | =item B<DB_HASH> |
3b35bae3 | 611 | |
88108326 | 612 | This database type allows arbitrary key/value pairs to be stored in data |
8e07c86e AD |
613 | files. This is equivalent to the functionality provided by other |
614 | hashing packages like DBM, NDBM, ODBM, GDBM, and SDBM. Remember though, | |
615 | the files created using DB_HASH are not compatible with any of the | |
616 | other packages mentioned. | |
3b35bae3 | 617 | |
8e07c86e AD |
618 | A default hashing algorithm, which will be adequate for most |
619 | applications, is built into Berkeley DB. If you do need to use your own | |
620 | hashing algorithm it is possible to write your own in Perl and have | |
621 | B<DB_File> use it instead. | |
3b35bae3 | 622 | |
88108326 | 623 | =item B<DB_BTREE> |
624 | ||
625 | The btree format allows arbitrary key/value pairs to be stored in a | |
8e07c86e | 626 | sorted, balanced binary tree. |
3b35bae3 | 627 | |
8e07c86e AD |
628 | As with the DB_HASH format, it is possible to provide a user defined |
629 | Perl routine to perform the comparison of keys. By default, though, the | |
630 | keys are stored in lexical order. | |
3b35bae3 | 631 | |
88108326 | 632 | =item B<DB_RECNO> |
3b35bae3 | 633 | |
8e07c86e AD |
634 | DB_RECNO allows both fixed-length and variable-length flat text files |
635 | to be manipulated using the same key/value pair interface as in DB_HASH | |
636 | and DB_BTREE. In this case the key will consist of a record (line) | |
637 | number. | |
3b35bae3 AD |
638 | |
639 | =back | |
640 | ||
039d031f | 641 | =head2 Using DB_File with Berkeley DB version 2 or 3 |
1f70e1ea PM |
642 | |
643 | Although B<DB_File> is intended to be used with Berkeley DB version 1, | |
c5da4faf | 644 | it can also be used with version 2 or 3. In this case the interface is |
1f70e1ea | 645 | limited to the functionality provided by Berkeley DB 1.x. Anywhere the |
039d031f PM |
646 | version 2 or 3 interface differs, B<DB_File> arranges for it to work |
647 | like version 1. This feature allows B<DB_File> scripts that were built | |
648 | with version 1 to be migrated to version 2 or 3 without any changes. | |
1f70e1ea PM |
649 | |
650 | If you want to make use of the new features available in Berkeley DB | |
b90e71be | 651 | 2.x or greater, use the Perl module B<BerkeleyDB> instead. |
1f70e1ea | 652 | |
039d031f PM |
653 | B<Note:> The database file format has changed in both Berkeley DB |
654 | version 2 and 3. If you cannot recreate your databases, you must dump | |
c5da4faf PM |
655 | any existing databases with either the C<db_dump> or the C<db_dump185> |
656 | utility that comes with Berkeley DB. | |
039d031f | 657 | Once you have rebuilt DB_File to use Berkeley DB version 2 or 3, your |
1f70e1ea PM |
658 | databases can be recreated using C<db_load>. Refer to the Berkeley DB |
659 | documentation for further details. | |
660 | ||
039d031f PM |
661 | Please read L<"COPYRIGHT"> before using version 2.x or 3.x of Berkeley |
662 | DB with DB_File. | |
1f70e1ea | 663 | |
68dc0745 | 664 | =head2 Interface to Berkeley DB |
3b35bae3 AD |
665 | |
666 | B<DB_File> allows access to Berkeley DB files using the tie() mechanism | |
8e07c86e AD |
667 | in Perl 5 (for full details, see L<perlfunc/tie()>). This facility |
668 | allows B<DB_File> to access Berkeley DB files using either an | |
669 | associative array (for DB_HASH & DB_BTREE file types) or an ordinary | |
670 | array (for the DB_RECNO file type). | |
3b35bae3 | 671 | |
88108326 | 672 | In addition to the tie() interface, it is also possible to access most |
673 | of the functions provided in the Berkeley DB API directly. | |
f6b705ef | 674 | See L<THE API INTERFACE>. |
3b35bae3 | 675 | |
88108326 | 676 | =head2 Opening a Berkeley DB Database File |
3b35bae3 | 677 | |
8e07c86e | 678 | Berkeley DB uses the function dbopen() to open or create a database. |
f6b705ef | 679 | Here is the C prototype for dbopen(): |
3b35bae3 AD |
680 | |
681 | DB* | |
682 | dbopen (const char * file, int flags, int mode, | |
683 | DBTYPE type, const void * openinfo) | |
684 | ||
685 | The parameter C<type> is an enumeration which specifies which of the 3 | |
686 | interface methods (DB_HASH, DB_BTREE or DB_RECNO) is to be used. | |
687 | Depending on which of these is actually chosen, the final parameter, | |
688 | I<openinfo> points to a data structure which allows tailoring of the | |
689 | specific interface method. | |
690 | ||
8e07c86e | 691 | This interface is handled slightly differently in B<DB_File>. Here is |
88108326 | 692 | an equivalent call using B<DB_File>: |
3b35bae3 | 693 | |
88108326 | 694 | tie %array, 'DB_File', $filename, $flags, $mode, $DB_HASH ; |
3b35bae3 | 695 | |
8e07c86e AD |
696 | The C<filename>, C<flags> and C<mode> parameters are the direct |
697 | equivalent of their dbopen() counterparts. The final parameter $DB_HASH | |
698 | performs the function of both the C<type> and C<openinfo> parameters in | |
699 | dbopen(). | |
3b35bae3 | 700 | |
88108326 | 701 | In the example above $DB_HASH is actually a pre-defined reference to a |
702 | hash object. B<DB_File> has three of these pre-defined references. | |
703 | Apart from $DB_HASH, there is also $DB_BTREE and $DB_RECNO. | |
3b35bae3 | 704 | |
8e07c86e AD |
705 | The keys allowed in each of these pre-defined references is limited to |
706 | the names used in the equivalent C structure. So, for example, the | |
707 | $DB_HASH reference will only allow keys called C<bsize>, C<cachesize>, | |
88108326 | 708 | C<ffactor>, C<hash>, C<lorder> and C<nelem>. |
709 | ||
710 | To change one of these elements, just assign to it like this: | |
711 | ||
712 | $DB_HASH->{'cachesize'} = 10000 ; | |
713 | ||
714 | The three predefined variables $DB_HASH, $DB_BTREE and $DB_RECNO are | |
715 | usually adequate for most applications. If you do need to create extra | |
716 | instances of these objects, constructors are available for each file | |
717 | type. | |
718 | ||
719 | Here are examples of the constructors and the valid options available | |
720 | for DB_HASH, DB_BTREE and DB_RECNO respectively. | |
721 | ||
722 | $a = new DB_File::HASHINFO ; | |
723 | $a->{'bsize'} ; | |
724 | $a->{'cachesize'} ; | |
725 | $a->{'ffactor'}; | |
726 | $a->{'hash'} ; | |
727 | $a->{'lorder'} ; | |
728 | $a->{'nelem'} ; | |
729 | ||
730 | $b = new DB_File::BTREEINFO ; | |
731 | $b->{'flags'} ; | |
732 | $b->{'cachesize'} ; | |
733 | $b->{'maxkeypage'} ; | |
734 | $b->{'minkeypage'} ; | |
735 | $b->{'psize'} ; | |
736 | $b->{'compare'} ; | |
737 | $b->{'prefix'} ; | |
738 | $b->{'lorder'} ; | |
739 | ||
740 | $c = new DB_File::RECNOINFO ; | |
741 | $c->{'bval'} ; | |
742 | $c->{'cachesize'} ; | |
743 | $c->{'psize'} ; | |
744 | $c->{'flags'} ; | |
745 | $c->{'lorder'} ; | |
746 | $c->{'reclen'} ; | |
747 | $c->{'bfname'} ; | |
748 | ||
749 | The values stored in the hashes above are mostly the direct equivalent | |
750 | of their C counterpart. Like their C counterparts, all are set to a | |
f6b705ef | 751 | default values - that means you don't have to set I<all> of the |
88108326 | 752 | values when you only want to change one. Here is an example: |
753 | ||
754 | $a = new DB_File::HASHINFO ; | |
755 | $a->{'cachesize'} = 12345 ; | |
756 | tie %y, 'DB_File', "filename", $flags, 0777, $a ; | |
757 | ||
36477c24 | 758 | A few of the options need extra discussion here. When used, the C |
88108326 | 759 | equivalent of the keys C<hash>, C<compare> and C<prefix> store pointers |
760 | to C functions. In B<DB_File> these keys are used to store references | |
761 | to Perl subs. Below are templates for each of the subs: | |
762 | ||
763 | sub hash | |
764 | { | |
765 | my ($data) = @_ ; | |
766 | ... | |
767 | # return the hash value for $data | |
768 | return $hash ; | |
769 | } | |
3b35bae3 | 770 | |
88108326 | 771 | sub compare |
772 | { | |
773 | my ($key, $key2) = @_ ; | |
774 | ... | |
775 | # return 0 if $key1 eq $key2 | |
776 | # -1 if $key1 lt $key2 | |
777 | # 1 if $key1 gt $key2 | |
778 | return (-1 , 0 or 1) ; | |
779 | } | |
3b35bae3 | 780 | |
88108326 | 781 | sub prefix |
782 | { | |
783 | my ($key, $key2) = @_ ; | |
784 | ... | |
785 | # return number of bytes of $key2 which are | |
786 | # necessary to determine that it is greater than $key1 | |
787 | return $bytes ; | |
788 | } | |
3b35bae3 | 789 | |
f6b705ef | 790 | See L<Changing the BTREE sort order> for an example of using the |
791 | C<compare> template. | |
88108326 | 792 | |
36477c24 | 793 | If you are using the DB_RECNO interface and you intend making use of |
9a2c4ce3 | 794 | C<bval>, you should check out L<The 'bval' Option>. |
36477c24 | 795 | |
88108326 | 796 | =head2 Default Parameters |
797 | ||
798 | It is possible to omit some or all of the final 4 parameters in the | |
799 | call to C<tie> and let them take default values. As DB_HASH is the most | |
800 | common file format used, the call: | |
801 | ||
802 | tie %A, "DB_File", "filename" ; | |
803 | ||
804 | is equivalent to: | |
805 | ||
18d2dc8c | 806 | tie %A, "DB_File", "filename", O_CREAT|O_RDWR, 0666, $DB_HASH ; |
88108326 | 807 | |
808 | It is also possible to omit the filename parameter as well, so the | |
809 | call: | |
810 | ||
811 | tie %A, "DB_File" ; | |
812 | ||
813 | is equivalent to: | |
814 | ||
18d2dc8c | 815 | tie %A, "DB_File", undef, O_CREAT|O_RDWR, 0666, $DB_HASH ; |
88108326 | 816 | |
f6b705ef | 817 | See L<In Memory Databases> for a discussion on the use of C<undef> |
88108326 | 818 | in place of a filename. |
819 | ||
f6b705ef | 820 | =head2 In Memory Databases |
821 | ||
822 | Berkeley DB allows the creation of in-memory databases by using NULL | |
823 | (that is, a C<(char *)0> in C) in place of the filename. B<DB_File> | |
824 | uses C<undef> instead of NULL to provide this functionality. | |
825 | ||
826 | =head1 DB_HASH | |
827 | ||
828 | The DB_HASH file format is probably the most commonly used of the three | |
829 | file formats that B<DB_File> supports. It is also very straightforward | |
830 | to use. | |
831 | ||
68dc0745 | 832 | =head2 A Simple Example |
f6b705ef | 833 | |
834 | This example shows how to create a database, add key/value pairs to the | |
835 | database, delete keys/value pairs and finally how to enumerate the | |
836 | contents of the database. | |
837 | ||
3245f058 | 838 | use warnings ; |
610ab055 | 839 | use strict ; |
f6b705ef | 840 | use DB_File ; |
610ab055 | 841 | use vars qw( %h $k $v ) ; |
f6b705ef | 842 | |
2c2d71f5 | 843 | unlink "fruit" ; |
f6b705ef | 844 | tie %h, "DB_File", "fruit", O_RDWR|O_CREAT, 0640, $DB_HASH |
845 | or die "Cannot open file 'fruit': $!\n"; | |
846 | ||
847 | # Add a few key/value pairs to the file | |
848 | $h{"apple"} = "red" ; | |
849 | $h{"orange"} = "orange" ; | |
850 | $h{"banana"} = "yellow" ; | |
851 | $h{"tomato"} = "red" ; | |
852 | ||
853 | # Check for existence of a key | |
854 | print "Banana Exists\n\n" if $h{"banana"} ; | |
855 | ||
856 | # Delete a key/value pair. | |
857 | delete $h{"apple"} ; | |
858 | ||
859 | # print the contents of the file | |
860 | while (($k, $v) = each %h) | |
861 | { print "$k -> $v\n" } | |
862 | ||
863 | untie %h ; | |
864 | ||
865 | here is the output: | |
866 | ||
867 | Banana Exists | |
bbc7dcd2 | 868 | |
f6b705ef | 869 | orange -> orange |
870 | tomato -> red | |
871 | banana -> yellow | |
872 | ||
873 | Note that the like ordinary associative arrays, the order of the keys | |
874 | retrieved is in an apparently random order. | |
875 | ||
876 | =head1 DB_BTREE | |
877 | ||
878 | The DB_BTREE format is useful when you want to store data in a given | |
879 | order. By default the keys will be stored in lexical order, but as you | |
880 | will see from the example shown in the next section, it is very easy to | |
881 | define your own sorting function. | |
882 | ||
883 | =head2 Changing the BTREE sort order | |
884 | ||
885 | This script shows how to override the default sorting algorithm that | |
886 | BTREE uses. Instead of using the normal lexical ordering, a case | |
887 | insensitive compare function will be used. | |
88108326 | 888 | |
3245f058 | 889 | use warnings ; |
610ab055 | 890 | use strict ; |
f6b705ef | 891 | use DB_File ; |
610ab055 PM |
892 | |
893 | my %h ; | |
f6b705ef | 894 | |
895 | sub Compare | |
896 | { | |
897 | my ($key1, $key2) = @_ ; | |
898 | "\L$key1" cmp "\L$key2" ; | |
899 | } | |
900 | ||
901 | # specify the Perl sub that will do the comparison | |
902 | $DB_BTREE->{'compare'} = \&Compare ; | |
903 | ||
2c2d71f5 | 904 | unlink "tree" ; |
f6b705ef | 905 | tie %h, "DB_File", "tree", O_RDWR|O_CREAT, 0640, $DB_BTREE |
906 | or die "Cannot open file 'tree': $!\n" ; | |
907 | ||
908 | # Add a key/value pair to the file | |
909 | $h{'Wall'} = 'Larry' ; | |
910 | $h{'Smith'} = 'John' ; | |
911 | $h{'mouse'} = 'mickey' ; | |
912 | $h{'duck'} = 'donald' ; | |
913 | ||
914 | # Delete | |
915 | delete $h{"duck"} ; | |
916 | ||
917 | # Cycle through the keys printing them in order. | |
918 | # Note it is not necessary to sort the keys as | |
919 | # the btree will have kept them in order automatically. | |
920 | foreach (keys %h) | |
921 | { print "$_\n" } | |
922 | ||
923 | untie %h ; | |
924 | ||
925 | Here is the output from the code above. | |
926 | ||
927 | mouse | |
928 | Smith | |
929 | Wall | |
930 | ||
931 | There are a few point to bear in mind if you want to change the | |
932 | ordering in a BTREE database: | |
933 | ||
934 | =over 5 | |
935 | ||
936 | =item 1. | |
937 | ||
938 | The new compare function must be specified when you create the database. | |
939 | ||
940 | =item 2. | |
941 | ||
942 | You cannot change the ordering once the database has been created. Thus | |
943 | you must use the same compare function every time you access the | |
88108326 | 944 | database. |
945 | ||
f6b705ef | 946 | =back |
947 | ||
68dc0745 | 948 | =head2 Handling Duplicate Keys |
f6b705ef | 949 | |
950 | The BTREE file type optionally allows a single key to be associated | |
951 | with an arbitrary number of values. This option is enabled by setting | |
952 | the flags element of C<$DB_BTREE> to R_DUP when creating the database. | |
953 | ||
88108326 | 954 | There are some difficulties in using the tied hash interface if you |
955 | want to manipulate a BTREE database with duplicate keys. Consider this | |
956 | code: | |
957 | ||
3245f058 | 958 | use warnings ; |
610ab055 | 959 | use strict ; |
88108326 | 960 | use DB_File ; |
610ab055 PM |
961 | |
962 | use vars qw($filename %h ) ; | |
963 | ||
88108326 | 964 | $filename = "tree" ; |
965 | unlink $filename ; | |
bbc7dcd2 | 966 | |
88108326 | 967 | # Enable duplicate records |
968 | $DB_BTREE->{'flags'} = R_DUP ; | |
bbc7dcd2 | 969 | |
88108326 | 970 | tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE |
971 | or die "Cannot open $filename: $!\n"; | |
bbc7dcd2 | 972 | |
88108326 | 973 | # Add some key/value pairs to the file |
974 | $h{'Wall'} = 'Larry' ; | |
975 | $h{'Wall'} = 'Brick' ; # Note the duplicate key | |
f6b705ef | 976 | $h{'Wall'} = 'Brick' ; # Note the duplicate key and value |
88108326 | 977 | $h{'Smith'} = 'John' ; |
978 | $h{'mouse'} = 'mickey' ; | |
979 | ||
980 | # iterate through the associative array | |
981 | # and print each key/value pair. | |
2c2d71f5 | 982 | foreach (sort keys %h) |
88108326 | 983 | { print "$_ -> $h{$_}\n" } |
984 | ||
f6b705ef | 985 | untie %h ; |
986 | ||
88108326 | 987 | Here is the output: |
988 | ||
989 | Smith -> John | |
990 | Wall -> Larry | |
991 | Wall -> Larry | |
f6b705ef | 992 | Wall -> Larry |
88108326 | 993 | mouse -> mickey |
994 | ||
f6b705ef | 995 | As you can see 3 records have been successfully created with key C<Wall> |
88108326 | 996 | - the only thing is, when they are retrieved from the database they |
f6b705ef | 997 | I<seem> to have the same value, namely C<Larry>. The problem is caused |
998 | by the way that the associative array interface works. Basically, when | |
999 | the associative array interface is used to fetch the value associated | |
1000 | with a given key, it will only ever retrieve the first value. | |
88108326 | 1001 | |
1002 | Although it may not be immediately obvious from the code above, the | |
1003 | associative array interface can be used to write values with duplicate | |
1004 | keys, but it cannot be used to read them back from the database. | |
1005 | ||
1006 | The way to get around this problem is to use the Berkeley DB API method | |
1007 | called C<seq>. This method allows sequential access to key/value | |
f6b705ef | 1008 | pairs. See L<THE API INTERFACE> for details of both the C<seq> method |
1009 | and the API in general. | |
88108326 | 1010 | |
1011 | Here is the script above rewritten using the C<seq> API method. | |
1012 | ||
3245f058 | 1013 | use warnings ; |
610ab055 | 1014 | use strict ; |
88108326 | 1015 | use DB_File ; |
bbc7dcd2 | 1016 | |
610ab055 PM |
1017 | use vars qw($filename $x %h $status $key $value) ; |
1018 | ||
88108326 | 1019 | $filename = "tree" ; |
1020 | unlink $filename ; | |
bbc7dcd2 | 1021 | |
88108326 | 1022 | # Enable duplicate records |
1023 | $DB_BTREE->{'flags'} = R_DUP ; | |
bbc7dcd2 | 1024 | |
88108326 | 1025 | $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE |
1026 | or die "Cannot open $filename: $!\n"; | |
bbc7dcd2 | 1027 | |
88108326 | 1028 | # Add some key/value pairs to the file |
1029 | $h{'Wall'} = 'Larry' ; | |
1030 | $h{'Wall'} = 'Brick' ; # Note the duplicate key | |
f6b705ef | 1031 | $h{'Wall'} = 'Brick' ; # Note the duplicate key and value |
88108326 | 1032 | $h{'Smith'} = 'John' ; |
1033 | $h{'mouse'} = 'mickey' ; | |
bbc7dcd2 | 1034 | |
f6b705ef | 1035 | # iterate through the btree using seq |
88108326 | 1036 | # and print each key/value pair. |
610ab055 | 1037 | $key = $value = 0 ; |
f6b705ef | 1038 | for ($status = $x->seq($key, $value, R_FIRST) ; |
1039 | $status == 0 ; | |
1040 | $status = $x->seq($key, $value, R_NEXT) ) | |
88108326 | 1041 | { print "$key -> $value\n" } |
bbc7dcd2 | 1042 | |
88108326 | 1043 | undef $x ; |
1044 | untie %h ; | |
1045 | ||
1046 | that prints: | |
1047 | ||
1048 | Smith -> John | |
1049 | Wall -> Brick | |
f6b705ef | 1050 | Wall -> Brick |
88108326 | 1051 | Wall -> Larry |
1052 | mouse -> mickey | |
1053 | ||
f6b705ef | 1054 | This time we have got all the key/value pairs, including the multiple |
88108326 | 1055 | values associated with the key C<Wall>. |
1056 | ||
6ca2e664 PM |
1057 | To make life easier when dealing with duplicate keys, B<DB_File> comes with |
1058 | a few utility methods. | |
1059 | ||
68dc0745 | 1060 | =head2 The get_dup() Method |
f6b705ef | 1061 | |
6ca2e664 | 1062 | The C<get_dup> method assists in |
88108326 | 1063 | reading duplicate values from BTREE databases. The method can take the |
1064 | following forms: | |
1065 | ||
1066 | $count = $x->get_dup($key) ; | |
1067 | @list = $x->get_dup($key) ; | |
1068 | %list = $x->get_dup($key, 1) ; | |
1069 | ||
1070 | In a scalar context the method returns the number of values associated | |
1071 | with the key, C<$key>. | |
1072 | ||
1073 | In list context, it returns all the values which match C<$key>. Note | |
f6b705ef | 1074 | that the values will be returned in an apparently random order. |
88108326 | 1075 | |
7a2e2cd6 | 1076 | In list context, if the second parameter is present and evaluates |
1077 | TRUE, the method returns an associative array. The keys of the | |
1078 | associative array correspond to the values that matched in the BTREE | |
1079 | and the values of the array are a count of the number of times that | |
1080 | particular value occurred in the BTREE. | |
88108326 | 1081 | |
f6b705ef | 1082 | So assuming the database created above, we can use C<get_dup> like |
88108326 | 1083 | this: |
1084 | ||
3245f058 | 1085 | use warnings ; |
2c2d71f5 JH |
1086 | use strict ; |
1087 | use DB_File ; | |
bbc7dcd2 | 1088 | |
2c2d71f5 JH |
1089 | use vars qw($filename $x %h ) ; |
1090 | ||
1091 | $filename = "tree" ; | |
bbc7dcd2 | 1092 | |
2c2d71f5 JH |
1093 | # Enable duplicate records |
1094 | $DB_BTREE->{'flags'} = R_DUP ; | |
bbc7dcd2 | 1095 | |
2c2d71f5 JH |
1096 | $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE |
1097 | or die "Cannot open $filename: $!\n"; | |
1098 | ||
610ab055 | 1099 | my $cnt = $x->get_dup("Wall") ; |
88108326 | 1100 | print "Wall occurred $cnt times\n" ; |
1101 | ||
610ab055 | 1102 | my %hash = $x->get_dup("Wall", 1) ; |
88108326 | 1103 | print "Larry is there\n" if $hash{'Larry'} ; |
f6b705ef | 1104 | print "There are $hash{'Brick'} Brick Walls\n" ; |
88108326 | 1105 | |
2c2d71f5 | 1106 | my @list = sort $x->get_dup("Wall") ; |
88108326 | 1107 | print "Wall => [@list]\n" ; |
1108 | ||
f6b705ef | 1109 | @list = $x->get_dup("Smith") ; |
88108326 | 1110 | print "Smith => [@list]\n" ; |
bbc7dcd2 | 1111 | |
f6b705ef | 1112 | @list = $x->get_dup("Dog") ; |
88108326 | 1113 | print "Dog => [@list]\n" ; |
1114 | ||
1115 | ||
1116 | and it will print: | |
1117 | ||
f6b705ef | 1118 | Wall occurred 3 times |
88108326 | 1119 | Larry is there |
f6b705ef | 1120 | There are 2 Brick Walls |
1121 | Wall => [Brick Brick Larry] | |
88108326 | 1122 | Smith => [John] |
1123 | Dog => [] | |
3b35bae3 | 1124 | |
6ca2e664 PM |
1125 | =head2 The find_dup() Method |
1126 | ||
1127 | $status = $X->find_dup($key, $value) ; | |
1128 | ||
b90e71be | 1129 | This method checks for the existence of a specific key/value pair. If the |
6ca2e664 PM |
1130 | pair exists, the cursor is left pointing to the pair and the method |
1131 | returns 0. Otherwise the method returns a non-zero value. | |
1132 | ||
1133 | Assuming the database from the previous example: | |
1134 | ||
3245f058 | 1135 | use warnings ; |
6ca2e664 PM |
1136 | use strict ; |
1137 | use DB_File ; | |
bbc7dcd2 | 1138 | |
6ca2e664 PM |
1139 | use vars qw($filename $x %h $found) ; |
1140 | ||
1141 | my $filename = "tree" ; | |
bbc7dcd2 | 1142 | |
6ca2e664 PM |
1143 | # Enable duplicate records |
1144 | $DB_BTREE->{'flags'} = R_DUP ; | |
bbc7dcd2 | 1145 | |
6ca2e664 PM |
1146 | $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE |
1147 | or die "Cannot open $filename: $!\n"; | |
1148 | ||
1149 | $found = ( $x->find_dup("Wall", "Larry") == 0 ? "" : "not") ; | |
1150 | print "Larry Wall is $found there\n" ; | |
bbc7dcd2 | 1151 | |
6ca2e664 PM |
1152 | $found = ( $x->find_dup("Wall", "Harry") == 0 ? "" : "not") ; |
1153 | print "Harry Wall is $found there\n" ; | |
bbc7dcd2 | 1154 | |
6ca2e664 PM |
1155 | undef $x ; |
1156 | untie %h ; | |
1157 | ||
1158 | prints this | |
1159 | ||
2c2d71f5 | 1160 | Larry Wall is there |
6ca2e664 PM |
1161 | Harry Wall is not there |
1162 | ||
1163 | ||
1164 | =head2 The del_dup() Method | |
1165 | ||
1166 | $status = $X->del_dup($key, $value) ; | |
1167 | ||
1168 | This method deletes a specific key/value pair. It returns | |
1169 | 0 if they exist and have been deleted successfully. | |
1170 | Otherwise the method returns a non-zero value. | |
1171 | ||
b90e71be | 1172 | Again assuming the existence of the C<tree> database |
6ca2e664 | 1173 | |
3245f058 | 1174 | use warnings ; |
6ca2e664 PM |
1175 | use strict ; |
1176 | use DB_File ; | |
bbc7dcd2 | 1177 | |
6ca2e664 PM |
1178 | use vars qw($filename $x %h $found) ; |
1179 | ||
1180 | my $filename = "tree" ; | |
bbc7dcd2 | 1181 | |
6ca2e664 PM |
1182 | # Enable duplicate records |
1183 | $DB_BTREE->{'flags'} = R_DUP ; | |
bbc7dcd2 | 1184 | |
6ca2e664 PM |
1185 | $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE |
1186 | or die "Cannot open $filename: $!\n"; | |
1187 | ||
1188 | $x->del_dup("Wall", "Larry") ; | |
1189 | ||
1190 | $found = ( $x->find_dup("Wall", "Larry") == 0 ? "" : "not") ; | |
1191 | print "Larry Wall is $found there\n" ; | |
bbc7dcd2 | 1192 | |
6ca2e664 PM |
1193 | undef $x ; |
1194 | untie %h ; | |
1195 | ||
1196 | prints this | |
1197 | ||
1198 | Larry Wall is not there | |
1199 | ||
f6b705ef | 1200 | =head2 Matching Partial Keys |
1201 | ||
1202 | The BTREE interface has a feature which allows partial keys to be | |
1203 | matched. This functionality is I<only> available when the C<seq> method | |
1204 | is used along with the R_CURSOR flag. | |
1205 | ||
1206 | $x->seq($key, $value, R_CURSOR) ; | |
1207 | ||
1208 | Here is the relevant quote from the dbopen man page where it defines | |
1209 | the use of the R_CURSOR flag with seq: | |
1210 | ||
f6b705ef | 1211 | Note, for the DB_BTREE access method, the returned key is not |
1212 | necessarily an exact match for the specified key. The returned key | |
1213 | is the smallest key greater than or equal to the specified key, | |
1214 | permitting partial key matches and range searches. | |
1215 | ||
f6b705ef | 1216 | In the example script below, the C<match> sub uses this feature to find |
1217 | and print the first matching key/value pair given a partial key. | |
1218 | ||
3245f058 | 1219 | use warnings ; |
610ab055 | 1220 | use strict ; |
f6b705ef | 1221 | use DB_File ; |
1222 | use Fcntl ; | |
610ab055 PM |
1223 | |
1224 | use vars qw($filename $x %h $st $key $value) ; | |
f6b705ef | 1225 | |
1226 | sub match | |
1227 | { | |
1228 | my $key = shift ; | |
610ab055 | 1229 | my $value = 0; |
f6b705ef | 1230 | my $orig_key = $key ; |
1231 | $x->seq($key, $value, R_CURSOR) ; | |
1232 | print "$orig_key\t-> $key\t-> $value\n" ; | |
1233 | } | |
1234 | ||
1235 | $filename = "tree" ; | |
1236 | unlink $filename ; | |
1237 | ||
1238 | $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE | |
1239 | or die "Cannot open $filename: $!\n"; | |
bbc7dcd2 | 1240 | |
f6b705ef | 1241 | # Add some key/value pairs to the file |
1242 | $h{'mouse'} = 'mickey' ; | |
1243 | $h{'Wall'} = 'Larry' ; | |
1244 | $h{'Walls'} = 'Brick' ; | |
1245 | $h{'Smith'} = 'John' ; | |
bbc7dcd2 | 1246 | |
f6b705ef | 1247 | |
610ab055 | 1248 | $key = $value = 0 ; |
f6b705ef | 1249 | print "IN ORDER\n" ; |
1250 | for ($st = $x->seq($key, $value, R_FIRST) ; | |
1251 | $st == 0 ; | |
1252 | $st = $x->seq($key, $value, R_NEXT) ) | |
bbc7dcd2 | 1253 | |
2c2d71f5 | 1254 | { print "$key -> $value\n" } |
bbc7dcd2 | 1255 | |
f6b705ef | 1256 | print "\nPARTIAL MATCH\n" ; |
1257 | ||
1258 | match "Wa" ; | |
1259 | match "A" ; | |
1260 | match "a" ; | |
1261 | ||
1262 | undef $x ; | |
1263 | untie %h ; | |
1264 | ||
1265 | Here is the output: | |
1266 | ||
1267 | IN ORDER | |
1268 | Smith -> John | |
1269 | Wall -> Larry | |
1270 | Walls -> Brick | |
1271 | mouse -> mickey | |
1272 | ||
1273 | PARTIAL MATCH | |
1274 | Wa -> Wall -> Larry | |
1275 | A -> Smith -> John | |
1276 | a -> mouse -> mickey | |
1277 | ||
1278 | =head1 DB_RECNO | |
1279 | ||
1280 | DB_RECNO provides an interface to flat text files. Both variable and | |
1281 | fixed length records are supported. | |
3b35bae3 | 1282 | |
6ca2e664 | 1283 | In order to make RECNO more compatible with Perl, the array offset for |
88108326 | 1284 | all RECNO arrays begins at 0 rather than 1 as in Berkeley DB. |
3b35bae3 | 1285 | |
88108326 | 1286 | As with normal Perl arrays, a RECNO array can be accessed using |
1287 | negative indexes. The index -1 refers to the last element of the array, | |
1288 | -2 the second last, and so on. Attempting to access an element before | |
1289 | the start of the array will raise a fatal run-time error. | |
3b35bae3 | 1290 | |
68dc0745 | 1291 | =head2 The 'bval' Option |
36477c24 | 1292 | |
1293 | The operation of the bval option warrants some discussion. Here is the | |
1294 | definition of bval from the Berkeley DB 1.85 recno manual page: | |
1295 | ||
1296 | The delimiting byte to be used to mark the end of a | |
1297 | record for variable-length records, and the pad charac- | |
1298 | ter for fixed-length records. If no value is speci- | |
1299 | fied, newlines (``\n'') are used to mark the end of | |
1300 | variable-length records and fixed-length records are | |
1301 | padded with spaces. | |
1302 | ||
1303 | The second sentence is wrong. In actual fact bval will only default to | |
1304 | C<"\n"> when the openinfo parameter in dbopen is NULL. If a non-NULL | |
1305 | openinfo parameter is used at all, the value that happens to be in bval | |
1306 | will be used. That means you always have to specify bval when making | |
1307 | use of any of the options in the openinfo parameter. This documentation | |
1308 | error will be fixed in the next release of Berkeley DB. | |
1309 | ||
1310 | That clarifies the situation with regards Berkeley DB itself. What | |
1311 | about B<DB_File>? Well, the behavior defined in the quote above is | |
6ca2e664 | 1312 | quite useful, so B<DB_File> conforms to it. |
36477c24 | 1313 | |
1314 | That means that you can specify other options (e.g. cachesize) and | |
1315 | still have bval default to C<"\n"> for variable length records, and | |
1316 | space for fixed length records. | |
1317 | ||
c5da4faf PM |
1318 | Also note that the bval option only allows you to specify a single byte |
1319 | as a delimeter. | |
1320 | ||
f6b705ef | 1321 | =head2 A Simple Example |
3b35bae3 | 1322 | |
6ca2e664 PM |
1323 | Here is a simple example that uses RECNO (if you are using a version |
1324 | of Perl earlier than 5.004_57 this example won't work -- see | |
1325 | L<Extra RECNO Methods> for a workaround). | |
f6b705ef | 1326 | |
3245f058 | 1327 | use warnings ; |
610ab055 | 1328 | use strict ; |
f6b705ef | 1329 | use DB_File ; |
f6b705ef | 1330 | |
2c2d71f5 JH |
1331 | my $filename = "text" ; |
1332 | unlink $filename ; | |
1333 | ||
610ab055 | 1334 | my @h ; |
2c2d71f5 | 1335 | tie @h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_RECNO |
f6b705ef | 1336 | or die "Cannot open file 'text': $!\n" ; |
1337 | ||
1338 | # Add a few key/value pairs to the file | |
1339 | $h[0] = "orange" ; | |
1340 | $h[1] = "blue" ; | |
1341 | $h[2] = "yellow" ; | |
1342 | ||
6ca2e664 PM |
1343 | push @h, "green", "black" ; |
1344 | ||
1345 | my $elements = scalar @h ; | |
1346 | print "The array contains $elements entries\n" ; | |
1347 | ||
1348 | my $last = pop @h ; | |
1349 | print "popped $last\n" ; | |
1350 | ||
1351 | unshift @h, "white" ; | |
1352 | my $first = shift @h ; | |
1353 | print "shifted $first\n" ; | |
1354 | ||
f6b705ef | 1355 | # Check for existence of a key |
1356 | print "Element 1 Exists with value $h[1]\n" if $h[1] ; | |
1357 | ||
1358 | # use a negative index | |
1359 | print "The last element is $h[-1]\n" ; | |
1360 | print "The 2nd last element is $h[-2]\n" ; | |
1361 | ||
1362 | untie @h ; | |
3b35bae3 | 1363 | |
f6b705ef | 1364 | Here is the output from the script: |
1365 | ||
6ca2e664 PM |
1366 | The array contains 5 entries |
1367 | popped black | |
2c2d71f5 | 1368 | shifted white |
f6b705ef | 1369 | Element 1 Exists with value blue |
6ca2e664 PM |
1370 | The last element is green |
1371 | The 2nd last element is yellow | |
f6b705ef | 1372 | |
6ca2e664 | 1373 | =head2 Extra RECNO Methods |
f6b705ef | 1374 | |
045291aa | 1375 | If you are using a version of Perl earlier than 5.004_57, the tied |
6ca2e664 PM |
1376 | array interface is quite limited. In the example script above |
1377 | C<push>, C<pop>, C<shift>, C<unshift> | |
1378 | or determining the array length will not work with a tied array. | |
045291aa PM |
1379 | |
1380 | To make the interface more useful for older versions of Perl, a number | |
1381 | of methods are supplied with B<DB_File> to simulate the missing array | |
1382 | operations. All these methods are accessed via the object returned from | |
1383 | the tie call. | |
f6b705ef | 1384 | |
1385 | Here are the methods: | |
1386 | ||
1387 | =over 5 | |
3b35bae3 | 1388 | |
f6b705ef | 1389 | =item B<$X-E<gt>push(list) ;> |
1390 | ||
1391 | Pushes the elements of C<list> to the end of the array. | |
1392 | ||
1393 | =item B<$value = $X-E<gt>pop ;> | |
1394 | ||
1395 | Removes and returns the last element of the array. | |
1396 | ||
1397 | =item B<$X-E<gt>shift> | |
1398 | ||
1399 | Removes and returns the first element of the array. | |
1400 | ||
1401 | =item B<$X-E<gt>unshift(list) ;> | |
1402 | ||
1403 | Pushes the elements of C<list> to the start of the array. | |
1404 | ||
1405 | =item B<$X-E<gt>length> | |
1406 | ||
1407 | Returns the number of elements in the array. | |
1408 | ||
c5da4faf PM |
1409 | =item B<$X-E<gt>splice(offset, length, elements);> |
1410 | ||
1411 | Returns a splice of the the array. | |
1412 | ||
f6b705ef | 1413 | =back |
1414 | ||
1415 | =head2 Another Example | |
1416 | ||
1417 | Here is a more complete example that makes use of some of the methods | |
1418 | described above. It also makes use of the API interface directly (see | |
1419 | L<THE API INTERFACE>). | |
1420 | ||
3245f058 | 1421 | use warnings ; |
f6b705ef | 1422 | use strict ; |
1423 | use vars qw(@h $H $file $i) ; | |
1424 | use DB_File ; | |
1425 | use Fcntl ; | |
bbc7dcd2 | 1426 | |
f6b705ef | 1427 | $file = "text" ; |
1428 | ||
1429 | unlink $file ; | |
1430 | ||
1431 | $H = tie @h, "DB_File", $file, O_RDWR|O_CREAT, 0640, $DB_RECNO | |
1432 | or die "Cannot open file $file: $!\n" ; | |
bbc7dcd2 | 1433 | |
f6b705ef | 1434 | # first create a text file to play with |
1435 | $h[0] = "zero" ; | |
1436 | $h[1] = "one" ; | |
1437 | $h[2] = "two" ; | |
1438 | $h[3] = "three" ; | |
1439 | $h[4] = "four" ; | |
1440 | ||
bbc7dcd2 | 1441 | |
f6b705ef | 1442 | # Print the records in order. |
1443 | # | |
1444 | # The length method is needed here because evaluating a tied | |
1445 | # array in a scalar context does not return the number of | |
1446 | # elements in the array. | |
1447 | ||
1448 | print "\nORIGINAL\n" ; | |
1449 | foreach $i (0 .. $H->length - 1) { | |
1450 | print "$i: $h[$i]\n" ; | |
1451 | } | |
1452 | ||
1453 | # use the push & pop methods | |
1454 | $a = $H->pop ; | |
1455 | $H->push("last") ; | |
1456 | print "\nThe last record was [$a]\n" ; | |
1457 | ||
1458 | # and the shift & unshift methods | |
1459 | $a = $H->shift ; | |
1460 | $H->unshift("first") ; | |
1461 | print "The first record was [$a]\n" ; | |
1462 | ||
1463 | # Use the API to add a new record after record 2. | |
1464 | $i = 2 ; | |
1465 | $H->put($i, "Newbie", R_IAFTER) ; | |
1466 | ||
1467 | # and a new record before record 1. | |
1468 | $i = 1 ; | |
1469 | $H->put($i, "New One", R_IBEFORE) ; | |
1470 | ||
1471 | # delete record 3 | |
1472 | $H->del(3) ; | |
1473 | ||
1474 | # now print the records in reverse order | |
1475 | print "\nREVERSE\n" ; | |
1476 | for ($i = $H->length - 1 ; $i >= 0 ; -- $i) | |
1477 | { print "$i: $h[$i]\n" } | |
1478 | ||
1479 | # same again, but use the API functions instead | |
1480 | print "\nREVERSE again\n" ; | |
610ab055 | 1481 | my ($s, $k, $v) = (0, 0, 0) ; |
f6b705ef | 1482 | for ($s = $H->seq($k, $v, R_LAST) ; |
1483 | $s == 0 ; | |
1484 | $s = $H->seq($k, $v, R_PREV)) | |
1485 | { print "$k: $v\n" } | |
1486 | ||
1487 | undef $H ; | |
1488 | untie @h ; | |
1489 | ||
1490 | and this is what it outputs: | |
1491 | ||
1492 | ORIGINAL | |
1493 | 0: zero | |
1494 | 1: one | |
1495 | 2: two | |
1496 | 3: three | |
1497 | 4: four | |
1498 | ||
1499 | The last record was [four] | |
1500 | The first record was [zero] | |
1501 | ||
1502 | REVERSE | |
1503 | 5: last | |
1504 | 4: three | |
1505 | 3: Newbie | |
1506 | 2: one | |
1507 | 1: New One | |
1508 | 0: first | |
1509 | ||
1510 | REVERSE again | |
1511 | 5: last | |
1512 | 4: three | |
1513 | 3: Newbie | |
1514 | 2: one | |
1515 | 1: New One | |
1516 | 0: first | |
1517 | ||
1518 | Notes: | |
1519 | ||
1520 | =over 5 | |
1521 | ||
1522 | =item 1. | |
1523 | ||
1524 | Rather than iterating through the array, C<@h> like this: | |
1525 | ||
1526 | foreach $i (@h) | |
1527 | ||
1528 | it is necessary to use either this: | |
1529 | ||
1530 | foreach $i (0 .. $H->length - 1) | |
1531 | ||
1532 | or this: | |
1533 | ||
1534 | for ($a = $H->get($k, $v, R_FIRST) ; | |
1535 | $a == 0 ; | |
1536 | $a = $H->get($k, $v, R_NEXT) ) | |
1537 | ||
1538 | =item 2. | |
1539 | ||
1540 | Notice that both times the C<put> method was used the record index was | |
1541 | specified using a variable, C<$i>, rather than the literal value | |
1542 | itself. This is because C<put> will return the record number of the | |
1543 | inserted line via that parameter. | |
1544 | ||
1545 | =back | |
1546 | ||
1547 | =head1 THE API INTERFACE | |
3b35bae3 AD |
1548 | |
1549 | As well as accessing Berkeley DB using a tied hash or array, it is also | |
88108326 | 1550 | possible to make direct use of most of the API functions defined in the |
8e07c86e | 1551 | Berkeley DB documentation. |
3b35bae3 | 1552 | |
88108326 | 1553 | To do this you need to store a copy of the object returned from the tie. |
3b35bae3 | 1554 | |
88108326 | 1555 | $db = tie %hash, "DB_File", "filename" ; |
3b35bae3 | 1556 | |
8e07c86e | 1557 | Once you have done that, you can access the Berkeley DB API functions |
88108326 | 1558 | as B<DB_File> methods directly like this: |
3b35bae3 AD |
1559 | |
1560 | $db->put($key, $value, R_NOOVERWRITE) ; | |
1561 | ||
88108326 | 1562 | B<Important:> If you have saved a copy of the object returned from |
1563 | C<tie>, the underlying database file will I<not> be closed until both | |
1564 | the tied variable is untied and all copies of the saved object are | |
610ab055 | 1565 | destroyed. |
88108326 | 1566 | |
1567 | use DB_File ; | |
1568 | $db = tie %hash, "DB_File", "filename" | |
1569 | or die "Cannot tie filename: $!" ; | |
1570 | ... | |
1571 | undef $db ; | |
1572 | untie %hash ; | |
1573 | ||
9a2c4ce3 | 1574 | See L<The untie() Gotcha> for more details. |
778183f3 | 1575 | |
88108326 | 1576 | All the functions defined in L<dbopen> are available except for |
1577 | close() and dbopen() itself. The B<DB_File> method interface to the | |
1578 | supported functions have been implemented to mirror the way Berkeley DB | |
1579 | works whenever possible. In particular note that: | |
1580 | ||
1581 | =over 5 | |
1582 | ||
1583 | =item * | |
1584 | ||
1585 | The methods return a status value. All return 0 on success. | |
1586 | All return -1 to signify an error and set C<$!> to the exact | |
1587 | error code. The return code 1 generally (but not always) means that the | |
1588 | key specified did not exist in the database. | |
1589 | ||
1590 | Other return codes are defined. See below and in the Berkeley DB | |
1591 | documentation for details. The Berkeley DB documentation should be used | |
1592 | as the definitive source. | |
1593 | ||
1594 | =item * | |
3b35bae3 | 1595 | |
88108326 | 1596 | Whenever a Berkeley DB function returns data via one of its parameters, |
1597 | the equivalent B<DB_File> method does exactly the same. | |
3b35bae3 | 1598 | |
88108326 | 1599 | =item * |
1600 | ||
1601 | If you are careful, it is possible to mix API calls with the tied | |
1602 | hash/array interface in the same piece of code. Although only a few of | |
1603 | the methods used to implement the tied interface currently make use of | |
1604 | the cursor, you should always assume that the cursor has been changed | |
1605 | any time the tied hash/array interface is used. As an example, this | |
1606 | code will probably not do what you expect: | |
1607 | ||
1608 | $X = tie %x, 'DB_File', $filename, O_RDWR|O_CREAT, 0777, $DB_BTREE | |
1609 | or die "Cannot tie $filename: $!" ; | |
1610 | ||
1611 | # Get the first key/value pair and set the cursor | |
1612 | $X->seq($key, $value, R_FIRST) ; | |
1613 | ||
1614 | # this line will modify the cursor | |
1615 | $count = scalar keys %x ; | |
1616 | ||
1617 | # Get the second key/value pair. | |
1618 | # oops, it didn't, it got the last key/value pair! | |
1619 | $X->seq($key, $value, R_NEXT) ; | |
1620 | ||
1621 | The code above can be rearranged to get around the problem, like this: | |
1622 | ||
1623 | $X = tie %x, 'DB_File', $filename, O_RDWR|O_CREAT, 0777, $DB_BTREE | |
1624 | or die "Cannot tie $filename: $!" ; | |
1625 | ||
1626 | # this line will modify the cursor | |
1627 | $count = scalar keys %x ; | |
1628 | ||
1629 | # Get the first key/value pair and set the cursor | |
1630 | $X->seq($key, $value, R_FIRST) ; | |
1631 | ||
1632 | # Get the second key/value pair. | |
1633 | # worked this time. | |
1634 | $X->seq($key, $value, R_NEXT) ; | |
1635 | ||
1636 | =back | |
1637 | ||
1638 | All the constants defined in L<dbopen> for use in the flags parameters | |
1639 | in the methods defined below are also available. Refer to the Berkeley | |
1640 | DB documentation for the precise meaning of the flags values. | |
1641 | ||
1642 | Below is a list of the methods available. | |
3b35bae3 AD |
1643 | |
1644 | =over 5 | |
1645 | ||
f6b705ef | 1646 | =item B<$status = $X-E<gt>get($key, $value [, $flags]) ;> |
88108326 | 1647 | |
1648 | Given a key (C<$key>) this method reads the value associated with it | |
1649 | from the database. The value read from the database is returned in the | |
1650 | C<$value> parameter. | |
3b35bae3 | 1651 | |
88108326 | 1652 | If the key does not exist the method returns 1. |
3b35bae3 | 1653 | |
88108326 | 1654 | No flags are currently defined for this method. |
3b35bae3 | 1655 | |
f6b705ef | 1656 | =item B<$status = $X-E<gt>put($key, $value [, $flags]) ;> |
3b35bae3 | 1657 | |
88108326 | 1658 | Stores the key/value pair in the database. |
1659 | ||
1660 | If you use either the R_IAFTER or R_IBEFORE flags, the C<$key> parameter | |
8e07c86e | 1661 | will have the record number of the inserted key/value pair set. |
3b35bae3 | 1662 | |
88108326 | 1663 | Valid flags are R_CURSOR, R_IAFTER, R_IBEFORE, R_NOOVERWRITE and |
1664 | R_SETCURSOR. | |
1665 | ||
f6b705ef | 1666 | =item B<$status = $X-E<gt>del($key [, $flags]) ;> |
3b35bae3 | 1667 | |
88108326 | 1668 | Removes all key/value pairs with key C<$key> from the database. |
3b35bae3 | 1669 | |
88108326 | 1670 | A return code of 1 means that the requested key was not in the |
1671 | database. | |
3b35bae3 | 1672 | |
88108326 | 1673 | R_CURSOR is the only valid flag at present. |
3b35bae3 | 1674 | |
f6b705ef | 1675 | =item B<$status = $X-E<gt>fd ;> |
3b35bae3 | 1676 | |
88108326 | 1677 | Returns the file descriptor for the underlying database. |
3b35bae3 | 1678 | |
b90e71be GS |
1679 | See L<Locking: The Trouble with fd> for an explanation for why you should |
1680 | not use C<fd> to lock your database. | |
3b35bae3 | 1681 | |
f6b705ef | 1682 | =item B<$status = $X-E<gt>seq($key, $value, $flags) ;> |
3b35bae3 | 1683 | |
88108326 | 1684 | This interface allows sequential retrieval from the database. See |
1685 | L<dbopen> for full details. | |
1686 | ||
1687 | Both the C<$key> and C<$value> parameters will be set to the key/value | |
1688 | pair read from the database. | |
1689 | ||
1690 | The flags parameter is mandatory. The valid flag values are R_CURSOR, | |
1691 | R_FIRST, R_LAST, R_NEXT and R_PREV. | |
1692 | ||
f6b705ef | 1693 | =item B<$status = $X-E<gt>sync([$flags]) ;> |
88108326 | 1694 | |
1695 | Flushes any cached buffers to disk. | |
1696 | ||
1697 | R_RECNOSYNC is the only valid flag at present. | |
3b35bae3 AD |
1698 | |
1699 | =back | |
1700 | ||
cad2e5aa JH |
1701 | =head1 DBM FILTERS |
1702 | ||
1703 | A DBM Filter is a piece of code that is be used when you I<always> | |
1704 | want to make the same transformation to all keys and/or values in a | |
1705 | DBM database. | |
1706 | ||
1707 | There are four methods associated with DBM Filters. All work identically, | |
1708 | and each is used to install (or uninstall) a single DBM Filter. Each | |
1709 | expects a single parameter, namely a reference to a sub. The only | |
1710 | difference between them is the place that the filter is installed. | |
1711 | ||
1712 | To summarise: | |
1713 | ||
1714 | =over 5 | |
1715 | ||
1716 | =item B<filter_store_key> | |
1717 | ||
1718 | If a filter has been installed with this method, it will be invoked | |
1719 | every time you write a key to a DBM database. | |
1720 | ||
1721 | =item B<filter_store_value> | |
1722 | ||
1723 | If a filter has been installed with this method, it will be invoked | |
1724 | every time you write a value to a DBM database. | |
1725 | ||
1726 | ||
1727 | =item B<filter_fetch_key> | |
1728 | ||
1729 | If a filter has been installed with this method, it will be invoked | |
1730 | every time you read a key from a DBM database. | |
1731 | ||
1732 | =item B<filter_fetch_value> | |
1733 | ||
1734 | If a filter has been installed with this method, it will be invoked | |
1735 | every time you read a value from a DBM database. | |
1736 | ||
1737 | =back | |
1738 | ||
1739 | You can use any combination of the methods, from none, to all four. | |
1740 | ||
1741 | All filter methods return the existing filter, if present, or C<undef> | |
1742 | in not. | |
1743 | ||
1744 | To delete a filter pass C<undef> to it. | |
1745 | ||
1746 | =head2 The Filter | |
1747 | ||
1748 | When each filter is called by Perl, a local copy of C<$_> will contain | |
1749 | the key or value to be filtered. Filtering is achieved by modifying | |
1750 | the contents of C<$_>. The return code from the filter is ignored. | |
1751 | ||
1752 | =head2 An Example -- the NULL termination problem. | |
1753 | ||
1754 | Consider the following scenario. You have a DBM database | |
1755 | that you need to share with a third-party C application. The C application | |
1756 | assumes that I<all> keys and values are NULL terminated. Unfortunately | |
1757 | when Perl writes to DBM databases it doesn't use NULL termination, so | |
1758 | your Perl application will have to manage NULL termination itself. When | |
1759 | you write to the database you will have to use something like this: | |
1760 | ||
1761 | $hash{"$key\0"} = "$value\0" ; | |
1762 | ||
1763 | Similarly the NULL needs to be taken into account when you are considering | |
1764 | the length of existing keys/values. | |
1765 | ||
1766 | It would be much better if you could ignore the NULL terminations issue | |
1767 | in the main application code and have a mechanism that automatically | |
1768 | added the terminating NULL to all keys and values whenever you write to | |
1769 | the database and have them removed when you read from the database. As I'm | |
1770 | sure you have already guessed, this is a problem that DBM Filters can | |
1771 | fix very easily. | |
1772 | ||
3245f058 | 1773 | use warnings ; |
cad2e5aa JH |
1774 | use strict ; |
1775 | use DB_File ; | |
1776 | ||
1777 | my %hash ; | |
1778 | my $filename = "/tmp/filt" ; | |
1779 | unlink $filename ; | |
1780 | ||
1781 | my $db = tie %hash, 'DB_File', $filename, O_CREAT|O_RDWR, 0666, $DB_HASH | |
1782 | or die "Cannot open $filename: $!\n" ; | |
1783 | ||
1784 | # Install DBM Filters | |
1785 | $db->filter_fetch_key ( sub { s/\0$// } ) ; | |
1786 | $db->filter_store_key ( sub { $_ .= "\0" } ) ; | |
1787 | $db->filter_fetch_value( sub { s/\0$// } ) ; | |
1788 | $db->filter_store_value( sub { $_ .= "\0" } ) ; | |
1789 | ||
1790 | $hash{"abc"} = "def" ; | |
1791 | my $a = $hash{"ABC"} ; | |
1792 | # ... | |
1793 | undef $db ; | |
1794 | untie %hash ; | |
1795 | ||
1796 | Hopefully the contents of each of the filters should be | |
1797 | self-explanatory. Both "fetch" filters remove the terminating NULL, | |
1798 | and both "store" filters add a terminating NULL. | |
1799 | ||
1800 | ||
1801 | =head2 Another Example -- Key is a C int. | |
1802 | ||
1803 | Here is another real-life example. By default, whenever Perl writes to | |
1804 | a DBM database it always writes the key and value as strings. So when | |
1805 | you use this: | |
1806 | ||
1807 | $hash{12345} = "soemthing" ; | |
1808 | ||
1809 | the key 12345 will get stored in the DBM database as the 5 byte string | |
1810 | "12345". If you actually want the key to be stored in the DBM database | |
1811 | as a C int, you will have to use C<pack> when writing, and C<unpack> | |
1812 | when reading. | |
1813 | ||
1814 | Here is a DBM Filter that does it: | |
1815 | ||
3245f058 | 1816 | use warnings ; |
cad2e5aa JH |
1817 | use strict ; |
1818 | use DB_File ; | |
1819 | my %hash ; | |
1820 | my $filename = "/tmp/filt" ; | |
1821 | unlink $filename ; | |
1822 | ||
1823 | ||
1824 | my $db = tie %hash, 'DB_File', $filename, O_CREAT|O_RDWR, 0666, $DB_HASH | |
1825 | or die "Cannot open $filename: $!\n" ; | |
1826 | ||
1827 | $db->filter_fetch_key ( sub { $_ = unpack("i", $_) } ) ; | |
1828 | $db->filter_store_key ( sub { $_ = pack ("i", $_) } ) ; | |
1829 | $hash{123} = "def" ; | |
1830 | # ... | |
1831 | undef $db ; | |
1832 | untie %hash ; | |
1833 | ||
1834 | This time only two filters have been used -- we only need to manipulate | |
1835 | the contents of the key, so it wasn't necessary to install any value | |
1836 | filters. | |
1837 | ||
f6b705ef | 1838 | =head1 HINTS AND TIPS |
3b35bae3 | 1839 | |
3b35bae3 | 1840 | |
b90e71be | 1841 | =head2 Locking: The Trouble with fd |
3b35bae3 | 1842 | |
b90e71be GS |
1843 | Until version 1.72 of this module, the recommended technique for locking |
1844 | B<DB_File> databases was to flock the filehandle returned from the "fd" | |
1845 | function. Unfortunately this technique has been shown to be fundamentally | |
1846 | flawed (Kudos to David Harris for tracking this down). Use it at your own | |
1847 | peril! | |
3b35bae3 | 1848 | |
b90e71be | 1849 | The locking technique went like this. |
cb1a09d0 | 1850 | |
b90e71be GS |
1851 | $db = tie(%db, 'DB_File', '/tmp/foo.db', O_CREAT|O_RDWR, 0644) |
1852 | || die "dbcreat /tmp/foo.db $!"; | |
1853 | $fd = $db->fd; | |
1854 | open(DB_FH, "+<&=$fd") || die "dup $!"; | |
1855 | flock (DB_FH, LOCK_EX) || die "flock: $!"; | |
1856 | ... | |
1857 | $db{"Tom"} = "Jerry" ; | |
1858 | ... | |
1859 | flock(DB_FH, LOCK_UN); | |
1860 | undef $db; | |
1861 | untie %db; | |
1862 | close(DB_FH); | |
cb1a09d0 | 1863 | |
b90e71be | 1864 | In simple terms, this is what happens: |
cb1a09d0 | 1865 | |
b90e71be | 1866 | =over 5 |
cb1a09d0 | 1867 | |
b90e71be | 1868 | =item 1. |
cb1a09d0 | 1869 | |
b90e71be | 1870 | Use "tie" to open the database. |
cb1a09d0 | 1871 | |
b90e71be | 1872 | =item 2. |
cb1a09d0 | 1873 | |
b90e71be | 1874 | Lock the database with fd & flock. |
cb1a09d0 | 1875 | |
b90e71be | 1876 | =item 3. |
cb1a09d0 | 1877 | |
b90e71be | 1878 | Read & Write to the database. |
cb1a09d0 | 1879 | |
b90e71be | 1880 | =item 4. |
cb1a09d0 | 1881 | |
b90e71be | 1882 | Unlock and close the database. |
cb1a09d0 | 1883 | |
b90e71be GS |
1884 | =back |
1885 | ||
1886 | Here is the crux of the problem. A side-effect of opening the B<DB_File> | |
1887 | database in step 2 is that an initial block from the database will get | |
1888 | read from disk and cached in memory. | |
1889 | ||
1890 | To see why this is a problem, consider what can happen when two processes, | |
1891 | say "A" and "B", both want to update the same B<DB_File> database | |
1892 | using the locking steps outlined above. Assume process "A" has already | |
1893 | opened the database and has a write lock, but it hasn't actually updated | |
1894 | the database yet (it has finished step 2, but not started step 3 yet). Now | |
1895 | process "B" tries to open the same database - step 1 will succeed, | |
1896 | but it will block on step 2 until process "A" releases the lock. The | |
1897 | important thing to notice here is that at this point in time both | |
1898 | processes will have cached identical initial blocks from the database. | |
1899 | ||
1900 | Now process "A" updates the database and happens to change some of the | |
1901 | data held in the initial buffer. Process "A" terminates, flushing | |
1902 | all cached data to disk and releasing the database lock. At this point | |
1903 | the database on disk will correctly reflect the changes made by process | |
1904 | "A". | |
1905 | ||
1906 | With the lock released, process "B" can now continue. It also updates the | |
1907 | database and unfortunately it too modifies the data that was in its | |
1908 | initial buffer. Once that data gets flushed to disk it will overwrite | |
1909 | some/all of the changes process "A" made to the database. | |
1910 | ||
1911 | The result of this scenario is at best a database that doesn't contain | |
1912 | what you expect. At worst the database will corrupt. | |
1913 | ||
1914 | The above won't happen every time competing process update the same | |
1915 | B<DB_File> database, but it does illustrate why the technique should | |
1916 | not be used. | |
1917 | ||
1918 | =head2 Safe ways to lock a database | |
1919 | ||
1920 | Starting with version 2.x, Berkeley DB has internal support for locking. | |
1921 | The companion module to this one, B<BerkeleyDB>, provides an interface | |
1922 | to this locking functionality. If you are serious about locking | |
1923 | Berkeley DB databases, I strongly recommend using B<BerkeleyDB>. | |
1924 | ||
1925 | If using B<BerkeleyDB> isn't an option, there are a number of modules | |
1926 | available on CPAN that can be used to implement locking. Each one | |
1927 | implements locking differently and has different goals in mind. It is | |
1928 | therefore worth knowing the difference, so that you can pick the right | |
1929 | one for your application. Here are the three locking wrappers: | |
1930 | ||
1931 | =over 5 | |
1932 | ||
1933 | =item B<Tie::DB_Lock> | |
1934 | ||
1935 | A B<DB_File> wrapper which creates copies of the database file for | |
1936 | read access, so that you have a kind of a multiversioning concurrent read | |
1937 | system. However, updates are still serial. Use for databases where reads | |
1938 | may be lengthy and consistency problems may occur. | |
1939 | ||
1940 | =item B<Tie::DB_LockFile> | |
1941 | ||
1942 | A B<DB_File> wrapper that has the ability to lock and unlock the database | |
1943 | while it is being used. Avoids the tie-before-flock problem by simply | |
1944 | re-tie-ing the database when you get or drop a lock. Because of the | |
1945 | flexibility in dropping and re-acquiring the lock in the middle of a | |
1946 | session, this can be massaged into a system that will work with long | |
1947 | updates and/or reads if the application follows the hints in the POD | |
1948 | documentation. | |
1949 | ||
1950 | =item B<DB_File::Lock> | |
1951 | ||
1952 | An extremely lightweight B<DB_File> wrapper that simply flocks a lockfile | |
1953 | before tie-ing the database and drops the lock after the untie. Allows | |
1954 | one to use the same lockfile for multiple databases to avoid deadlock | |
1955 | problems, if desired. Use for databases where updates are reads are | |
1956 | quick and simple flock locking semantics are enough. | |
1957 | ||
1958 | =back | |
cb1a09d0 | 1959 | |
68dc0745 | 1960 | =head2 Sharing Databases With C Applications |
f6b705ef | 1961 | |
1962 | There is no technical reason why a Berkeley DB database cannot be | |
1963 | shared by both a Perl and a C application. | |
1964 | ||
1965 | The vast majority of problems that are reported in this area boil down | |
1966 | to the fact that C strings are NULL terminated, whilst Perl strings are | |
cad2e5aa | 1967 | not. See L<DBM FILTERS> for a generic way to work around this problem. |
f6b705ef | 1968 | |
1969 | Here is a real example. Netscape 2.0 keeps a record of the locations you | |
1970 | visit along with the time you last visited them in a DB_HASH database. | |
1971 | This is usually stored in the file F<~/.netscape/history.db>. The key | |
1972 | field in the database is the location string and the value field is the | |
1973 | time the location was last visited stored as a 4 byte binary value. | |
1974 | ||
1975 | If you haven't already guessed, the location string is stored with a | |
1976 | terminating NULL. This means you need to be careful when accessing the | |
1977 | database. | |
1978 | ||
1979 | Here is a snippet of code that is loosely based on Tom Christiansen's | |
1980 | I<ggh> script (available from your nearest CPAN archive in | |
1981 | F<authors/id/TOMC/scripts/nshist.gz>). | |
1982 | ||
3245f058 | 1983 | use warnings ; |
610ab055 | 1984 | use strict ; |
f6b705ef | 1985 | use DB_File ; |
1986 | use Fcntl ; | |
f6b705ef | 1987 | |
610ab055 | 1988 | use vars qw( $dotdir $HISTORY %hist_db $href $binary_time $date ) ; |
f6b705ef | 1989 | $dotdir = $ENV{HOME} || $ENV{LOGNAME}; |
1990 | ||
1991 | $HISTORY = "$dotdir/.netscape/history.db"; | |
1992 | ||
1993 | tie %hist_db, 'DB_File', $HISTORY | |
1994 | or die "Cannot open $HISTORY: $!\n" ;; | |
1995 | ||
1996 | # Dump the complete database | |
1997 | while ( ($href, $binary_time) = each %hist_db ) { | |
1998 | ||
1999 | # remove the terminating NULL | |
2000 | $href =~ s/\x00$// ; | |
2001 | ||
2002 | # convert the binary time into a user friendly string | |
2003 | $date = localtime unpack("V", $binary_time); | |
2004 | print "$date $href\n" ; | |
2005 | } | |
2006 | ||
2007 | # check for the existence of a specific key | |
2008 | # remember to add the NULL | |
2009 | if ( $binary_time = $hist_db{"http://mox.perl.com/\x00"} ) { | |
2010 | $date = localtime unpack("V", $binary_time) ; | |
2011 | print "Last visited mox.perl.com on $date\n" ; | |
2012 | } | |
2013 | else { | |
2014 | print "Never visited mox.perl.com\n" | |
2015 | } | |
2016 | ||
2017 | untie %hist_db ; | |
2018 | ||
68dc0745 | 2019 | =head2 The untie() Gotcha |
778183f3 | 2020 | |
7a2e2cd6 | 2021 | If you make use of the Berkeley DB API, it is I<very> strongly |
68dc0745 | 2022 | recommended that you read L<perltie/The untie Gotcha>. |
778183f3 PM |
2023 | |
2024 | Even if you don't currently make use of the API interface, it is still | |
2025 | worth reading it. | |
2026 | ||
2027 | Here is an example which illustrates the problem from a B<DB_File> | |
2028 | perspective: | |
2029 | ||
2030 | use DB_File ; | |
2031 | use Fcntl ; | |
2032 | ||
2033 | my %x ; | |
2034 | my $X ; | |
2035 | ||
2036 | $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_TRUNC | |
2037 | or die "Cannot tie first time: $!" ; | |
2038 | ||
2039 | $x{123} = 456 ; | |
2040 | ||
2041 | untie %x ; | |
2042 | ||
2043 | tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT | |
2044 | or die "Cannot tie second time: $!" ; | |
2045 | ||
2046 | untie %x ; | |
2047 | ||
2048 | When run, the script will produce this error message: | |
2049 | ||
2050 | Cannot tie second time: Invalid argument at bad.file line 14. | |
2051 | ||
2052 | Although the error message above refers to the second tie() statement | |
2053 | in the script, the source of the problem is really with the untie() | |
2054 | statement that precedes it. | |
2055 | ||
2056 | Having read L<perltie> you will probably have already guessed that the | |
2057 | error is caused by the extra copy of the tied object stored in C<$X>. | |
2058 | If you haven't, then the problem boils down to the fact that the | |
2059 | B<DB_File> destructor, DESTROY, will not be called until I<all> | |
2060 | references to the tied object are destroyed. Both the tied variable, | |
2061 | C<%x>, and C<$X> above hold a reference to the object. The call to | |
2062 | untie() will destroy the first, but C<$X> still holds a valid | |
2063 | reference, so the destructor will not get called and the database file | |
2064 | F<tst.fil> will remain open. The fact that Berkeley DB then reports the | |
b90e71be | 2065 | attempt to open a database that is already open via the catch-all |
778183f3 PM |
2066 | "Invalid argument" doesn't help. |
2067 | ||
2068 | If you run the script with the C<-w> flag the error message becomes: | |
2069 | ||
2070 | untie attempted while 1 inner references still exist at bad.file line 12. | |
2071 | Cannot tie second time: Invalid argument at bad.file line 14. | |
2072 | ||
2073 | which pinpoints the real problem. Finally the script can now be | |
2074 | modified to fix the original problem by destroying the API object | |
2075 | before the untie: | |
2076 | ||
2077 | ... | |
2078 | $x{123} = 456 ; | |
2079 | ||
2080 | undef $X ; | |
2081 | untie %x ; | |
2082 | ||
2083 | $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT | |
2084 | ... | |
2085 | ||
f6b705ef | 2086 | |
2087 | =head1 COMMON QUESTIONS | |
2088 | ||
2089 | =head2 Why is there Perl source in my database? | |
2090 | ||
2091 | If you look at the contents of a database file created by DB_File, | |
2092 | there can sometimes be part of a Perl script included in it. | |
2093 | ||
2094 | This happens because Berkeley DB uses dynamic memory to allocate | |
2095 | buffers which will subsequently be written to the database file. Being | |
2096 | dynamic, the memory could have been used for anything before DB | |
2097 | malloced it. As Berkeley DB doesn't clear the memory once it has been | |
2098 | allocated, the unused portions will contain random junk. In the case | |
2099 | where a Perl script gets written to the database, the random junk will | |
2100 | correspond to an area of dynamic memory that happened to be used during | |
2101 | the compilation of the script. | |
2102 | ||
2103 | Unless you don't like the possibility of there being part of your Perl | |
2104 | scripts embedded in a database file, this is nothing to worry about. | |
2105 | ||
2106 | =head2 How do I store complex data structures with DB_File? | |
2107 | ||
2108 | Although B<DB_File> cannot do this directly, there is a module which | |
2109 | can layer transparently over B<DB_File> to accomplish this feat. | |
2110 | ||
2111 | Check out the MLDBM module, available on CPAN in the directory | |
2112 | F<modules/by-module/MLDBM>. | |
2113 | ||
2114 | =head2 What does "Invalid Argument" mean? | |
2115 | ||
2116 | You will get this error message when one of the parameters in the | |
2117 | C<tie> call is wrong. Unfortunately there are quite a few parameters to | |
2118 | get wrong, so it can be difficult to figure out which one it is. | |
2119 | ||
2120 | Here are a couple of possibilities: | |
2121 | ||
2122 | =over 5 | |
2123 | ||
2124 | =item 1. | |
2125 | ||
610ab055 | 2126 | Attempting to reopen a database without closing it. |
f6b705ef | 2127 | |
2128 | =item 2. | |
2129 | ||
2130 | Using the O_WRONLY flag. | |
2131 | ||
2132 | =back | |
2133 | ||
2134 | =head2 What does "Bareword 'DB_File' not allowed" mean? | |
2135 | ||
2136 | You will encounter this particular error message when you have the | |
2137 | C<strict 'subs'> pragma (or the full strict pragma) in your script. | |
2138 | Consider this script: | |
2139 | ||
3245f058 | 2140 | use warnings ; |
f6b705ef | 2141 | use strict ; |
2142 | use DB_File ; | |
2143 | use vars qw(%x) ; | |
2144 | tie %x, DB_File, "filename" ; | |
2145 | ||
2146 | Running it produces the error in question: | |
2147 | ||
2148 | Bareword "DB_File" not allowed while "strict subs" in use | |
2149 | ||
2150 | To get around the error, place the word C<DB_File> in either single or | |
2151 | double quotes, like this: | |
2152 | ||
2153 | tie %x, "DB_File", "filename" ; | |
2154 | ||
2155 | Although it might seem like a real pain, it is really worth the effort | |
2156 | of having a C<use strict> in all your scripts. | |
2157 | ||
cad2e5aa JH |
2158 | =head1 REFERENCES |
2159 | ||
2160 | Articles that are either about B<DB_File> or make use of it. | |
2161 | ||
2162 | =over 5 | |
2163 | ||
2164 | =item 1. | |
2165 | ||
2166 | I<Full-Text Searching in Perl>, Tim Kientzle (tkientzle@ddj.com), | |
2167 | Dr. Dobb's Journal, Issue 295, January 1999, pp 34-41 | |
2168 | ||
2169 | =back | |
2170 | ||
cb1a09d0 AD |
2171 | =head1 HISTORY |
2172 | ||
1f70e1ea | 2173 | Moved to the Changes file. |
610ab055 | 2174 | |
1f70e1ea | 2175 | =head1 BUGS |
05475680 | 2176 | |
1f70e1ea PM |
2177 | Some older versions of Berkeley DB had problems with fixed length |
2178 | records using the RECNO file format. This problem has been fixed since | |
2179 | version 1.85 of Berkeley DB. | |
e858de61 | 2180 | |
1f70e1ea PM |
2181 | I am sure there are bugs in the code. If you do find any, or can |
2182 | suggest any enhancements, I would welcome your comments. | |
a6ed719b | 2183 | |
1f70e1ea | 2184 | =head1 AVAILABILITY |
a6ed719b | 2185 | |
1f70e1ea PM |
2186 | B<DB_File> comes with the standard Perl source distribution. Look in |
2187 | the directory F<ext/DB_File>. Given the amount of time between releases | |
2188 | of Perl the version that ships with Perl is quite likely to be out of | |
2189 | date, so the most recent version can always be found on CPAN (see | |
2190 | L<perlmod/CPAN> for details), in the directory | |
2191 | F<modules/by-module/DB_File>. | |
a6ed719b | 2192 | |
039d031f PM |
2193 | This version of B<DB_File> will work with either version 1.x, 2.x or |
2194 | 3.x of Berkeley DB, but is limited to the functionality provided by | |
2195 | version 1. | |
a6ed719b | 2196 | |
cad2e5aa | 2197 | The official web site for Berkeley DB is F<http://www.sleepycat.com>. |
039d031f | 2198 | All versions of Berkeley DB are available there. |
93af7a87 | 2199 | |
1f70e1ea PM |
2200 | Alternatively, Berkeley DB version 1 is available at your nearest CPAN |
2201 | archive in F<src/misc/db.1.85.tar.gz>. | |
e858de61 | 2202 | |
1f70e1ea PM |
2203 | If you are running IRIX, then get Berkeley DB version 1 from |
2204 | F<http://reality.sgi.com/ariel>. It has the patches necessary to | |
2205 | compile properly on IRIX 5.3. | |
610ab055 | 2206 | |
1f70e1ea | 2207 | =head1 COPYRIGHT |
3b35bae3 | 2208 | |
c5da4faf | 2209 | Copyright (c) 1995-2001 Paul Marquess. All rights reserved. This program |
a9fd575d PM |
2210 | is free software; you can redistribute it and/or modify it under the |
2211 | same terms as Perl itself. | |
3b35bae3 | 2212 | |
1f70e1ea PM |
2213 | Although B<DB_File> is covered by the Perl license, the library it |
2214 | makes use of, namely Berkeley DB, is not. Berkeley DB has its own | |
2215 | copyright and its own license. Please take the time to read it. | |
3b35bae3 | 2216 | |
a9fd575d | 2217 | Here are are few words taken from the Berkeley DB FAQ (at |
b90e71be | 2218 | F<http://www.sleepycat.com>) regarding the license: |
68dc0745 | 2219 | |
a9fd575d | 2220 | Do I have to license DB to use it in Perl scripts? |
3b35bae3 | 2221 | |
a9fd575d PM |
2222 | No. The Berkeley DB license requires that software that uses |
2223 | Berkeley DB be freely redistributable. In the case of Perl, that | |
2224 | software is Perl, and not your scripts. Any Perl scripts that you | |
2225 | write are your property, including scripts that make use of | |
2226 | Berkeley DB. Neither the Perl license nor the Berkeley DB license | |
2227 | place any restriction on what you may do with them. | |
88108326 | 2228 | |
1f70e1ea PM |
2229 | If you are in any doubt about the license situation, contact either the |
2230 | Berkeley DB authors or the author of DB_File. See L<"AUTHOR"> for details. | |
a0b8c8c1 PM |
2231 | |
2232 | ||
3b35bae3 AD |
2233 | =head1 SEE ALSO |
2234 | ||
9fe6733a PM |
2235 | L<perl(1)>, L<dbopen(3)>, L<hash(3)>, L<recno(3)>, L<btree(3)>, |
2236 | L<dbmfilter> | |
3b35bae3 | 2237 | |
3b35bae3 AD |
2238 | =head1 AUTHOR |
2239 | ||
8e07c86e | 2240 | The DB_File interface was written by Paul Marquess |
6ca2e664 | 2241 | E<lt>Paul.Marquess@btinternet.comE<gt>. |
d3ef3b8a PM |
2242 | Questions about the DB system itself may be addressed to |
2243 | E<lt>db@sleepycat.com<gt>. | |
3b35bae3 AD |
2244 | |
2245 | =cut |