Commit | Line | Data |
ffed8b01 |
1 | package DBM::Deep; |
2 | |
3 | ## |
4 | # DBM::Deep |
5 | # |
6 | # Description: |
d0b74c17 |
7 | # Multi-level database module for storing hash trees, arrays and simple |
8 | # key/value pairs into FTP-able, cross-platform binary database files. |
ffed8b01 |
9 | # |
d0b74c17 |
10 | # Type `perldoc DBM::Deep` for complete documentation. |
ffed8b01 |
11 | # |
12 | # Usage Examples: |
d0b74c17 |
13 | # my %db; |
14 | # tie %db, 'DBM::Deep', 'my_database.db'; # standard tie() method |
ffed8b01 |
15 | # |
d0b74c17 |
16 | # my $db = new DBM::Deep( 'my_database.db' ); # preferred OO method |
17 | # |
18 | # $db->{my_scalar} = 'hello world'; |
19 | # $db->{my_hash} = { larry => 'genius', hashes => 'fast' }; |
20 | # $db->{my_array} = [ 1, 2, 3, time() ]; |
21 | # $db->{my_complex} = [ 'hello', { perl => 'rules' }, 42, 99 ]; |
22 | # push @{$db->{my_array}}, 'another value'; |
23 | # my @key_list = keys %{$db->{my_hash}}; |
24 | # print "This module " . $db->{my_complex}->[1]->{perl} . "!\n"; |
ffed8b01 |
25 | # |
26 | # Copyright: |
d0b74c17 |
27 | # (c) 2002-2006 Joseph Huckaby. All Rights Reserved. |
28 | # This program is free software; you can redistribute it and/or |
29 | # modify it under the same terms as Perl itself. |
ffed8b01 |
30 | ## |
31 | |
32 | use strict; |
8b957036 |
33 | |
596e9574 |
34 | use Fcntl qw( :DEFAULT :flock :seek ); |
ffed8b01 |
35 | use Digest::MD5 (); |
36 | use Scalar::Util (); |
ffed8b01 |
37 | |
95967a5e |
38 | use DBM::Deep::Engine; |
39 | |
596e9574 |
40 | use vars qw( $VERSION ); |
3a7a0dce |
41 | $VERSION = q(0.99_01); |
ffed8b01 |
42 | |
ffed8b01 |
43 | ## |
44 | # Setup constants for users to pass to new() |
45 | ## |
e06824f8 |
46 | sub TYPE_HASH () { DBM::Deep::Engine->SIG_HASH } |
47 | sub TYPE_ARRAY () { DBM::Deep::Engine->SIG_ARRAY } |
ffed8b01 |
48 | |
0ca7ea98 |
49 | sub _get_args { |
50 | my $proto = shift; |
51 | |
52 | my $args; |
53 | if (scalar(@_) > 1) { |
54 | if ( @_ % 2 ) { |
55 | $proto->_throw_error( "Odd number of parameters to " . (caller(1))[2] ); |
56 | } |
57 | $args = {@_}; |
58 | } |
d0b74c17 |
59 | elsif ( ref $_[0] ) { |
4d35d856 |
60 | unless ( eval { local $SIG{'__DIE__'}; %{$_[0]} || 1 } ) { |
0ca7ea98 |
61 | $proto->_throw_error( "Not a hashref in args to " . (caller(1))[2] ); |
62 | } |
63 | $args = $_[0]; |
64 | } |
d0b74c17 |
65 | else { |
0ca7ea98 |
66 | $args = { file => shift }; |
67 | } |
68 | |
69 | return $args; |
70 | } |
71 | |
ffed8b01 |
72 | sub new { |
d0b74c17 |
73 | ## |
74 | # Class constructor method for Perl OO interface. |
75 | # Calls tie() and returns blessed reference to tied hash or array, |
76 | # providing a hybrid OO/tie interface. |
77 | ## |
78 | my $class = shift; |
79 | my $args = $class->_get_args( @_ ); |
80 | |
81 | ## |
82 | # Check if we want a tied hash or array. |
83 | ## |
84 | my $self; |
85 | if (defined($args->{type}) && $args->{type} eq TYPE_ARRAY) { |
6fe26b29 |
86 | $class = 'DBM::Deep::Array'; |
87 | require DBM::Deep::Array; |
d0b74c17 |
88 | tie @$self, $class, %$args; |
89 | } |
90 | else { |
6fe26b29 |
91 | $class = 'DBM::Deep::Hash'; |
92 | require DBM::Deep::Hash; |
d0b74c17 |
93 | tie %$self, $class, %$args; |
94 | } |
ffed8b01 |
95 | |
d0b74c17 |
96 | return bless $self, $class; |
ffed8b01 |
97 | } |
98 | |
0795f290 |
99 | sub _init { |
100 | ## |
101 | # Setup $self and bless into this class. |
102 | ## |
103 | my $class = shift; |
994ccd8e |
104 | my ($args) = @_; |
0795f290 |
105 | |
106 | # These are the defaults to be optionally overridden below |
107 | my $self = bless { |
95967a5e |
108 | type => TYPE_HASH, |
612969fb |
109 | engine => DBM::Deep::Engine->new, |
e06824f8 |
110 | base_offset => undef, |
0795f290 |
111 | }, $class; |
8db25060 |
112 | |
0795f290 |
113 | foreach my $param ( keys %$self ) { |
114 | next unless exists $args->{$param}; |
115 | $self->{$param} = delete $args->{$param} |
ffed8b01 |
116 | } |
d0b74c17 |
117 | |
37c5bcf0 |
118 | # locking implicitly enables autoflush |
119 | if ($args->{locking}) { $args->{autoflush} = 1; } |
d0b74c17 |
120 | |
0795f290 |
121 | $self->{root} = exists $args->{root} |
122 | ? $args->{root} |
123 | : DBM::Deep::_::Root->new( $args ); |
124 | |
70b55428 |
125 | $self->{engine}->setup_fh( $self ); |
0795f290 |
126 | |
127 | return $self; |
ffed8b01 |
128 | } |
129 | |
ffed8b01 |
130 | sub TIEHASH { |
6fe26b29 |
131 | shift; |
132 | require DBM::Deep::Hash; |
133 | return DBM::Deep::Hash->TIEHASH( @_ ); |
ffed8b01 |
134 | } |
135 | |
136 | sub TIEARRAY { |
6fe26b29 |
137 | shift; |
138 | require DBM::Deep::Array; |
139 | return DBM::Deep::Array->TIEARRAY( @_ ); |
ffed8b01 |
140 | } |
141 | |
cc4bef86 |
142 | #XXX Unneeded now ... |
143 | #sub DESTROY { |
144 | #} |
ffed8b01 |
145 | |
ffed8b01 |
146 | sub lock { |
d0b74c17 |
147 | ## |
148 | # If db locking is set, flock() the db file. If called multiple |
149 | # times before unlock(), then the same number of unlocks() must |
150 | # be called before the lock is released. |
151 | ## |
994ccd8e |
152 | my $self = shift->_get_self; |
153 | my ($type) = @_; |
ffed8b01 |
154 | $type = LOCK_EX unless defined $type; |
d0b74c17 |
155 | |
156 | if (!defined($self->_fh)) { return; } |
157 | |
158 | if ($self->_root->{locking}) { |
159 | if (!$self->_root->{locked}) { |
160 | flock($self->_fh, $type); |
161 | |
162 | # refresh end counter in case file has changed size |
118ba343 |
163 | my @stats = stat($self->_fh); |
d0b74c17 |
164 | $self->_root->{end} = $stats[7]; |
165 | |
166 | # double-check file inode, in case another process |
167 | # has optimize()d our file while we were waiting. |
168 | if ($stats[1] != $self->_root->{inode}) { |
3d1b8be9 |
169 | $self->{engine}->close_fh( $self ); |
70b55428 |
170 | $self->{engine}->setup_fh( $self ); |
d0b74c17 |
171 | flock($self->_fh, $type); # re-lock |
70b55428 |
172 | |
173 | # This may not be necessary after re-opening |
d0b74c17 |
174 | $self->_root->{end} = (stat($self->_fh))[7]; # re-end |
175 | } |
176 | } |
177 | $self->_root->{locked}++; |
b4522594 |
178 | |
179 | return 1; |
d0b74c17 |
180 | } |
b4522594 |
181 | |
182 | return; |
ffed8b01 |
183 | } |
184 | |
185 | sub unlock { |
d0b74c17 |
186 | ## |
187 | # If db locking is set, unlock the db file. See note in lock() |
188 | # regarding calling lock() multiple times. |
189 | ## |
994ccd8e |
190 | my $self = shift->_get_self; |
7f441181 |
191 | |
d0b74c17 |
192 | if (!defined($self->_fh)) { return; } |
193 | |
194 | if ($self->_root->{locking} && $self->_root->{locked} > 0) { |
195 | $self->_root->{locked}--; |
196 | if (!$self->_root->{locked}) { flock($self->_fh, LOCK_UN); } |
b4522594 |
197 | |
198 | return 1; |
d0b74c17 |
199 | } |
b4522594 |
200 | |
201 | return; |
ffed8b01 |
202 | } |
203 | |
906c8e01 |
204 | sub _copy_value { |
205 | my $self = shift->_get_self; |
206 | my ($spot, $value) = @_; |
207 | |
208 | if ( !ref $value ) { |
209 | ${$spot} = $value; |
210 | } |
211 | elsif ( eval { local $SIG{__DIE__}; $value->isa( 'DBM::Deep' ) } ) { |
212 | my $type = $value->_type; |
213 | ${$spot} = $type eq TYPE_HASH ? {} : []; |
214 | $value->_copy_node( ${$spot} ); |
215 | } |
216 | else { |
217 | my $r = Scalar::Util::reftype( $value ); |
218 | my $c = Scalar::Util::blessed( $value ); |
219 | if ( $r eq 'ARRAY' ) { |
220 | ${$spot} = [ @{$value} ]; |
221 | } |
222 | else { |
223 | ${$spot} = { %{$value} }; |
224 | } |
95bbd935 |
225 | ${$spot} = bless ${$spot}, $c |
906c8e01 |
226 | if defined $c; |
227 | } |
228 | |
229 | return 1; |
230 | } |
231 | |
261d1296 |
232 | sub _copy_node { |
d0b74c17 |
233 | ## |
234 | # Copy single level of keys or elements to new DB handle. |
235 | # Recurse for nested structures |
236 | ## |
906c8e01 |
237 | my $self = shift->_get_self; |
d0b74c17 |
238 | my ($db_temp) = @_; |
b8b48a59 |
239 | |
d0b74c17 |
240 | if ($self->_type eq TYPE_HASH) { |
241 | my $key = $self->first_key(); |
242 | while ($key) { |
243 | my $value = $self->get($key); |
906c8e01 |
244 | $self->_copy_value( \$db_temp->{$key}, $value ); |
d0b74c17 |
245 | $key = $self->next_key($key); |
246 | } |
247 | } |
248 | else { |
249 | my $length = $self->length(); |
250 | for (my $index = 0; $index < $length; $index++) { |
251 | my $value = $self->get($index); |
906c8e01 |
252 | $self->_copy_value( \$db_temp->[$index], $value ); |
d0b74c17 |
253 | } |
254 | } |
906c8e01 |
255 | |
256 | return 1; |
ffed8b01 |
257 | } |
258 | |
259 | sub export { |
d0b74c17 |
260 | ## |
261 | # Recursively export into standard Perl hashes and arrays. |
262 | ## |
994ccd8e |
263 | my $self = shift->_get_self; |
d0b74c17 |
264 | |
265 | my $temp; |
266 | if ($self->_type eq TYPE_HASH) { $temp = {}; } |
267 | elsif ($self->_type eq TYPE_ARRAY) { $temp = []; } |
268 | |
269 | $self->lock(); |
270 | $self->_copy_node( $temp ); |
271 | $self->unlock(); |
272 | |
273 | return $temp; |
ffed8b01 |
274 | } |
275 | |
276 | sub import { |
d0b74c17 |
277 | ## |
278 | # Recursively import Perl hash/array structure |
279 | ## |
d0b74c17 |
280 | if (!ref($_[0])) { return; } # Perl calls import() on use -- ignore |
281 | |
994ccd8e |
282 | my $self = shift->_get_self; |
283 | my ($struct) = @_; |
d0b74c17 |
284 | |
c9cec40e |
285 | # struct is not a reference, so just import based on our type |
d0b74c17 |
286 | if (!ref($struct)) { |
d0b74c17 |
287 | if ($self->_type eq TYPE_HASH) { $struct = {@_}; } |
288 | elsif ($self->_type eq TYPE_ARRAY) { $struct = [@_]; } |
289 | } |
290 | |
ffed8b01 |
291 | my $r = Scalar::Util::reftype($struct) || ''; |
d0b74c17 |
292 | if ($r eq "HASH" && $self->_type eq TYPE_HASH) { |
293 | foreach my $key (keys %$struct) { $self->put($key, $struct->{$key}); } |
294 | } |
295 | elsif ($r eq "ARRAY" && $self->_type eq TYPE_ARRAY) { |
296 | $self->push( @$struct ); |
297 | } |
298 | else { |
1400a48e |
299 | $self->_throw_error("Cannot import: type mismatch"); |
d0b74c17 |
300 | } |
301 | |
302 | return 1; |
ffed8b01 |
303 | } |
304 | |
305 | sub optimize { |
d0b74c17 |
306 | ## |
307 | # Rebuild entire database into new file, then move |
308 | # it back on top of original. |
309 | ## |
994ccd8e |
310 | my $self = shift->_get_self; |
cc4bef86 |
311 | |
312 | #XXX Need to create a new test for this |
d0b74c17 |
313 | # if ($self->_root->{links} > 1) { |
1400a48e |
314 | # $self->_throw_error("Cannot optimize: reference count is greater than 1"); |
d0b74c17 |
315 | # } |
316 | |
317 | my $db_temp = DBM::Deep->new( |
318 | file => $self->_root->{file} . '.tmp', |
319 | type => $self->_type |
320 | ); |
d0b74c17 |
321 | |
322 | $self->lock(); |
323 | $self->_copy_node( $db_temp ); |
324 | undef $db_temp; |
325 | |
326 | ## |
327 | # Attempt to copy user, group and permissions over to new file |
328 | ## |
329 | my @stats = stat($self->_fh); |
330 | my $perms = $stats[2] & 07777; |
331 | my $uid = $stats[4]; |
332 | my $gid = $stats[5]; |
333 | chown( $uid, $gid, $self->_root->{file} . '.tmp' ); |
334 | chmod( $perms, $self->_root->{file} . '.tmp' ); |
335 | |
ffed8b01 |
336 | # q.v. perlport for more information on this variable |
90f93b43 |
337 | if ( $^O eq 'MSWin32' || $^O eq 'cygwin' ) { |
d0b74c17 |
338 | ## |
339 | # Potential race condition when optmizing on Win32 with locking. |
340 | # The Windows filesystem requires that the filehandle be closed |
341 | # before it is overwritten with rename(). This could be redone |
342 | # with a soft copy. |
343 | ## |
344 | $self->unlock(); |
345 | $self->{engine}->close_fh( $self ); |
346 | } |
347 | |
348 | if (!rename $self->_root->{file} . '.tmp', $self->_root->{file}) { |
349 | unlink $self->_root->{file} . '.tmp'; |
350 | $self->unlock(); |
1400a48e |
351 | $self->_throw_error("Optimize failed: Cannot copy temp file over original: $!"); |
d0b74c17 |
352 | } |
353 | |
354 | $self->unlock(); |
355 | $self->{engine}->close_fh( $self ); |
70b55428 |
356 | $self->{engine}->setup_fh( $self ); |
357 | |
d0b74c17 |
358 | return 1; |
ffed8b01 |
359 | } |
360 | |
361 | sub clone { |
d0b74c17 |
362 | ## |
363 | # Make copy of object and return |
364 | ## |
994ccd8e |
365 | my $self = shift->_get_self; |
d0b74c17 |
366 | |
367 | return DBM::Deep->new( |
368 | type => $self->_type, |
369 | base_offset => $self->_base_offset, |
370 | root => $self->_root |
371 | ); |
ffed8b01 |
372 | } |
373 | |
374 | { |
375 | my %is_legal_filter = map { |
376 | $_ => ~~1, |
377 | } qw( |
378 | store_key store_value |
379 | fetch_key fetch_value |
380 | ); |
381 | |
382 | sub set_filter { |
383 | ## |
384 | # Setup filter function for storing or fetching the key or value |
385 | ## |
994ccd8e |
386 | my $self = shift->_get_self; |
387 | my $type = lc shift; |
388 | my $func = shift; |
d0b74c17 |
389 | |
ffed8b01 |
390 | if ( $is_legal_filter{$type} ) { |
4d35d856 |
391 | $self->_root->{"filter_$type"} = $func; |
ffed8b01 |
392 | return 1; |
393 | } |
394 | |
395 | return; |
396 | } |
397 | } |
398 | |
399 | ## |
400 | # Accessor methods |
401 | ## |
402 | |
4d35d856 |
403 | sub _root { |
d0b74c17 |
404 | ## |
405 | # Get access to the root structure |
406 | ## |
2ac02042 |
407 | my $self = $_[0]->_get_self; |
d0b74c17 |
408 | return $self->{root}; |
ffed8b01 |
409 | } |
410 | |
4d35d856 |
411 | sub _type { |
d0b74c17 |
412 | ## |
413 | # Get type of current node (TYPE_HASH or TYPE_ARRAY) |
414 | ## |
2ac02042 |
415 | my $self = $_[0]->_get_self; |
d0b74c17 |
416 | return $self->{type}; |
ffed8b01 |
417 | } |
418 | |
4d35d856 |
419 | sub _base_offset { |
d0b74c17 |
420 | ## |
421 | # Get base_offset of current node (TYPE_HASH or TYPE_ARRAY) |
422 | ## |
2ac02042 |
423 | my $self = $_[0]->_get_self; |
d0b74c17 |
424 | return $self->{base_offset}; |
ffed8b01 |
425 | } |
426 | |
994ccd8e |
427 | sub _fh { |
428 | ## |
429 | # Get access to the raw fh |
430 | ## |
431 | my $self = $_[0]->_get_self; |
432 | return $self->_root->{fh}; |
433 | } |
434 | |
ffed8b01 |
435 | ## |
436 | # Utility methods |
437 | ## |
438 | |
261d1296 |
439 | sub _throw_error { |
95967a5e |
440 | die "DBM::Deep: $_[1]\n"; |
ffed8b01 |
441 | } |
442 | |
acd4faf2 |
443 | sub _is_writable { |
444 | my $fh = shift; |
445 | (O_WRONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0); |
446 | } |
447 | |
9be51a89 |
448 | #sub _is_readable { |
449 | # my $fh = shift; |
450 | # (O_RDONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0); |
451 | #} |
acd4faf2 |
452 | |
ffed8b01 |
453 | sub STORE { |
d0b74c17 |
454 | ## |
455 | # Store single hash key/value or array element in database. |
456 | ## |
457 | my $self = shift->_get_self; |
458 | my ($key, $value) = @_; |
81d3d316 |
459 | |
acd4faf2 |
460 | unless ( _is_writable( $self->_fh ) ) { |
461 | $self->_throw_error( 'Cannot write to a readonly filehandle' ); |
462 | } |
d0b74c17 |
463 | |
464 | ## |
465 | # Request exclusive lock for writing |
466 | ## |
467 | $self->lock( LOCK_EX ); |
468 | |
469 | my $md5 = $self->{engine}{digest}->($key); |
470 | |
471 | my $tag = $self->{engine}->find_bucket_list( $self, $md5, { create => 1 } ); |
472 | |
473 | # User may be storing a hash, in which case we do not want it run |
474 | # through the filtering system |
475 | if ( !ref($value) && $self->_root->{filter_store_value} ) { |
476 | $value = $self->_root->{filter_store_value}->( $value ); |
477 | } |
478 | |
479 | ## |
480 | # Add key/value to bucket list |
481 | ## |
482 | my $result = $self->{engine}->add_bucket( $self, $tag, $md5, $key, $value ); |
483 | |
484 | $self->unlock(); |
485 | |
486 | return $result; |
ffed8b01 |
487 | } |
488 | |
489 | sub FETCH { |
d0b74c17 |
490 | ## |
491 | # Fetch single value or element given plain key or array index |
492 | ## |
cb79ec85 |
493 | my $self = shift->_get_self; |
e06824f8 |
494 | my ($key) = @_; |
ffed8b01 |
495 | |
d0b74c17 |
496 | my $md5 = $self->{engine}{digest}->($key); |
497 | |
498 | ## |
499 | # Request shared lock for reading |
500 | ## |
501 | $self->lock( LOCK_SH ); |
502 | |
503 | my $tag = $self->{engine}->find_bucket_list( $self, $md5 ); |
504 | if (!$tag) { |
505 | $self->unlock(); |
506 | return; |
507 | } |
508 | |
509 | ## |
510 | # Get value from bucket list |
511 | ## |
512 | my $result = $self->{engine}->get_bucket_value( $self, $tag, $md5 ); |
513 | |
514 | $self->unlock(); |
515 | |
a86430bd |
516 | # Filters only apply to scalar values, so the ref check is making |
517 | # sure the fetched bucket is a scalar, not a child hash or array. |
d0b74c17 |
518 | return ($result && !ref($result) && $self->_root->{filter_fetch_value}) |
4d35d856 |
519 | ? $self->_root->{filter_fetch_value}->($result) |
cb79ec85 |
520 | : $result; |
ffed8b01 |
521 | } |
522 | |
523 | sub DELETE { |
d0b74c17 |
524 | ## |
525 | # Delete single key/value pair or element given plain key or array index |
526 | ## |
2ac02042 |
527 | my $self = $_[0]->_get_self; |
d0b74c17 |
528 | my $key = $_[1]; |
529 | |
a86430bd |
530 | unless ( _is_writable( $self->_fh ) ) { |
531 | $self->_throw_error( 'Cannot write to a readonly filehandle' ); |
532 | } |
d0b74c17 |
533 | |
534 | ## |
535 | # Request exclusive lock for writing |
536 | ## |
537 | $self->lock( LOCK_EX ); |
538 | |
a86430bd |
539 | my $md5 = $self->{engine}{digest}->($key); |
540 | |
d0b74c17 |
541 | my $tag = $self->{engine}->find_bucket_list( $self, $md5 ); |
542 | if (!$tag) { |
543 | $self->unlock(); |
544 | return; |
545 | } |
546 | |
547 | ## |
548 | # Delete bucket |
549 | ## |
9020ee8c |
550 | my $value = $self->{engine}->get_bucket_value($self, $tag, $md5 ); |
a86430bd |
551 | |
552 | if (defined $value && !ref($value) && $self->_root->{filter_fetch_value}) { |
4d35d856 |
553 | $value = $self->_root->{filter_fetch_value}->($value); |
3b6a5056 |
554 | } |
555 | |
d0b74c17 |
556 | my $result = $self->{engine}->delete_bucket( $self, $tag, $md5 ); |
557 | |
558 | ## |
559 | # If this object is an array and the key deleted was on the end of the stack, |
560 | # decrement the length variable. |
561 | ## |
562 | |
563 | $self->unlock(); |
564 | |
565 | return $value; |
ffed8b01 |
566 | } |
567 | |
568 | sub EXISTS { |
d0b74c17 |
569 | ## |
570 | # Check if a single key or element exists given plain key or array index |
571 | ## |
2ac02042 |
572 | my $self = $_[0]->_get_self; |
d0b74c17 |
573 | my $key = $_[1]; |
574 | |
575 | my $md5 = $self->{engine}{digest}->($key); |
576 | |
577 | ## |
578 | # Request shared lock for reading |
579 | ## |
580 | $self->lock( LOCK_SH ); |
581 | |
582 | my $tag = $self->{engine}->find_bucket_list( $self, $md5 ); |
583 | if (!$tag) { |
584 | $self->unlock(); |
585 | |
586 | ## |
587 | # For some reason, the built-in exists() function returns '' for false |
588 | ## |
589 | return ''; |
590 | } |
591 | |
592 | ## |
593 | # Check if bucket exists and return 1 or '' |
594 | ## |
595 | my $result = $self->{engine}->bucket_exists( $self, $tag, $md5 ) || ''; |
596 | |
597 | $self->unlock(); |
598 | |
599 | return $result; |
ffed8b01 |
600 | } |
601 | |
602 | sub CLEAR { |
d0b74c17 |
603 | ## |
604 | # Clear all keys from hash, or all elements from array. |
605 | ## |
2ac02042 |
606 | my $self = $_[0]->_get_self; |
ffed8b01 |
607 | |
a86430bd |
608 | unless ( _is_writable( $self->_fh ) ) { |
609 | $self->_throw_error( 'Cannot write to a readonly filehandle' ); |
610 | } |
611 | |
d0b74c17 |
612 | ## |
613 | # Request exclusive lock for writing |
614 | ## |
615 | $self->lock( LOCK_EX ); |
616 | |
4d35d856 |
617 | my $fh = $self->_fh; |
629df3a3 |
618 | |
d0b74c17 |
619 | seek($fh, $self->_base_offset + $self->_root->{file_offset}, SEEK_SET); |
620 | if (eof $fh) { |
621 | $self->unlock(); |
622 | return; |
623 | } |
624 | |
625 | $self->{engine}->create_tag($self, $self->_base_offset, $self->_type, chr(0) x $self->{engine}{index_size}); |
626 | |
627 | $self->unlock(); |
628 | |
629 | return 1; |
ffed8b01 |
630 | } |
631 | |
ffed8b01 |
632 | ## |
633 | # Public method aliases |
634 | ## |
7f441181 |
635 | sub put { (shift)->STORE( @_ ) } |
636 | sub store { (shift)->STORE( @_ ) } |
637 | sub get { (shift)->FETCH( @_ ) } |
638 | sub fetch { (shift)->FETCH( @_ ) } |
baa27ab6 |
639 | sub delete { (shift)->DELETE( @_ ) } |
640 | sub exists { (shift)->EXISTS( @_ ) } |
641 | sub clear { (shift)->CLEAR( @_ ) } |
ffed8b01 |
642 | |
cc4bef86 |
643 | package DBM::Deep::_::Root; |
644 | |
645 | sub new { |
646 | my $class = shift; |
647 | my ($args) = @_; |
648 | |
649 | my $self = bless { |
a86430bd |
650 | autobless => undef, |
651 | autoflush => undef, |
c9ec091a |
652 | end => 0, |
f5be9b03 |
653 | fh => undef, |
a86430bd |
654 | file => undef, |
f5be9b03 |
655 | file_offset => 0, |
f5be9b03 |
656 | locking => undef, |
657 | locked => 0, |
658 | filter_store_key => undef, |
cc4bef86 |
659 | filter_store_value => undef, |
f5be9b03 |
660 | filter_fetch_key => undef, |
cc4bef86 |
661 | filter_fetch_value => undef, |
cc4bef86 |
662 | %$args, |
663 | }, $class; |
664 | |
714618f0 |
665 | if ( $self->{fh} && !$self->{file_offset} ) { |
666 | $self->{file_offset} = tell( $self->{fh} ); |
667 | } |
668 | |
cc4bef86 |
669 | return $self; |
670 | } |
671 | |
672 | sub DESTROY { |
673 | my $self = shift; |
674 | return unless $self; |
675 | |
676 | close $self->{fh} if $self->{fh}; |
677 | |
678 | return; |
679 | } |
680 | |
ffed8b01 |
681 | 1; |
ffed8b01 |
682 | __END__ |
683 | |
684 | =head1 NAME |
685 | |
686 | DBM::Deep - A pure perl multi-level hash/array DBM |
687 | |
688 | =head1 SYNOPSIS |
689 | |
690 | use DBM::Deep; |
691 | my $db = DBM::Deep->new( "foo.db" ); |
d0b74c17 |
692 | |
ffed8b01 |
693 | $db->{key} = 'value'; # tie() style |
694 | print $db->{key}; |
d0b74c17 |
695 | |
cbaa107d |
696 | $db->put('key' => 'value'); # OO style |
ffed8b01 |
697 | print $db->get('key'); |
d0b74c17 |
698 | |
ffed8b01 |
699 | # true multi-level support |
700 | $db->{my_complex} = [ |
d0b74c17 |
701 | 'hello', { perl => 'rules' }, |
702 | 42, 99, |
90f93b43 |
703 | ]; |
ffed8b01 |
704 | |
705 | =head1 DESCRIPTION |
706 | |
d0b74c17 |
707 | A unique flat-file database module, written in pure perl. True |
708 | multi-level hash/array support (unlike MLDBM, which is faked), hybrid |
709 | OO / tie() interface, cross-platform FTPable files, and quite fast. Can |
710 | handle millions of keys and unlimited hash levels without significant |
711 | slow-down. Written from the ground-up in pure perl -- this is NOT a |
712 | wrapper around a C-based DBM. Out-of-the-box compatibility with Unix, |
ffed8b01 |
713 | Mac OS X and Windows. |
714 | |
8db25060 |
715 | =head1 VERSION DIFFERENCES |
716 | |
717 | B<NOTE>: 0.99_01 and above have significant file format differences from 0.98 and |
718 | before. While attempts have been made to be backwards compatible, no guarantees. |
719 | |
ffed8b01 |
720 | =head1 INSTALLATION |
721 | |
90f93b43 |
722 | Hopefully you are using Perl's excellent CPAN module, which will download |
d0b74c17 |
723 | and install the module for you. If not, get the tarball, and run these |
ffed8b01 |
724 | commands: |
725 | |
d0b74c17 |
726 | tar zxf DBM-Deep-* |
727 | cd DBM-Deep-* |
728 | perl Makefile.PL |
729 | make |
730 | make test |
731 | make install |
ffed8b01 |
732 | |
733 | =head1 SETUP |
734 | |
d0b74c17 |
735 | Construction can be done OO-style (which is the recommended way), or using |
ffed8b01 |
736 | Perl's tie() function. Both are examined here. |
737 | |
738 | =head2 OO CONSTRUCTION |
739 | |
740 | The recommended way to construct a DBM::Deep object is to use the new() |
741 | method, which gets you a blessed, tied hash or array reference. |
742 | |
d0b74c17 |
743 | my $db = DBM::Deep->new( "foo.db" ); |
ffed8b01 |
744 | |
745 | This opens a new database handle, mapped to the file "foo.db". If this |
d0b74c17 |
746 | file does not exist, it will automatically be created. DB files are |
ffed8b01 |
747 | opened in "r+" (read/write) mode, and the type of object returned is a |
748 | hash, unless otherwise specified (see L<OPTIONS> below). |
749 | |
ffed8b01 |
750 | You can pass a number of options to the constructor to specify things like |
751 | locking, autoflush, etc. This is done by passing an inline hash: |
752 | |
d0b74c17 |
753 | my $db = DBM::Deep->new( |
754 | file => "foo.db", |
755 | locking => 1, |
756 | autoflush => 1 |
757 | ); |
ffed8b01 |
758 | |
759 | Notice that the filename is now specified I<inside> the hash with |
d0b74c17 |
760 | the "file" parameter, as opposed to being the sole argument to the |
ffed8b01 |
761 | constructor. This is required if any options are specified. |
762 | See L<OPTIONS> below for the complete list. |
763 | |
764 | |
765 | |
766 | You can also start with an array instead of a hash. For this, you must |
767 | specify the C<type> parameter: |
768 | |
d0b74c17 |
769 | my $db = DBM::Deep->new( |
770 | file => "foo.db", |
771 | type => DBM::Deep->TYPE_ARRAY |
772 | ); |
ffed8b01 |
773 | |
774 | B<Note:> Specifing the C<type> parameter only takes effect when beginning |
775 | a new DB file. If you create a DBM::Deep object with an existing file, the |
90f93b43 |
776 | C<type> will be loaded from the file header, and an error will be thrown if |
777 | the wrong type is passed in. |
ffed8b01 |
778 | |
779 | =head2 TIE CONSTRUCTION |
780 | |
90f93b43 |
781 | Alternately, you can create a DBM::Deep handle by using Perl's built-in |
782 | tie() function. The object returned from tie() can be used to call methods, |
783 | such as lock() and unlock(), but cannot be used to assign to the DBM::Deep |
784 | file (as expected with most tie'd objects). |
ffed8b01 |
785 | |
d0b74c17 |
786 | my %hash; |
787 | my $db = tie %hash, "DBM::Deep", "foo.db"; |
788 | |
789 | my @array; |
790 | my $db = tie @array, "DBM::Deep", "bar.db"; |
ffed8b01 |
791 | |
792 | As with the OO constructor, you can replace the DB filename parameter with |
793 | a hash containing one or more options (see L<OPTIONS> just below for the |
794 | complete list). |
795 | |
d0b74c17 |
796 | tie %hash, "DBM::Deep", { |
797 | file => "foo.db", |
798 | locking => 1, |
799 | autoflush => 1 |
800 | }; |
ffed8b01 |
801 | |
802 | =head2 OPTIONS |
803 | |
804 | There are a number of options that can be passed in when constructing your |
805 | DBM::Deep objects. These apply to both the OO- and tie- based approaches. |
806 | |
807 | =over |
808 | |
809 | =item * file |
810 | |
811 | Filename of the DB file to link the handle to. You can pass a full absolute |
d0b74c17 |
812 | filesystem path, partial path, or a plain filename if the file is in the |
714618f0 |
813 | current working directory. This is a required parameter (though q.v. fh). |
814 | |
815 | =item * fh |
816 | |
817 | If you want, you can pass in the fh instead of the file. This is most useful for doing |
818 | something like: |
819 | |
820 | my $db = DBM::Deep->new( { fh => \*DATA } ); |
821 | |
822 | You are responsible for making sure that the fh has been opened appropriately for your |
823 | needs. If you open it read-only and attempt to write, an exception will be thrown. If you |
824 | open it write-only or append-only, an exception will be thrown immediately as DBM::Deep |
825 | needs to read from the fh. |
826 | |
827 | =item * file_offset |
828 | |
829 | This is the offset within the file that the DBM::Deep db starts. Most of the time, you will |
830 | not need to set this. However, it's there if you want it. |
831 | |
832 | If you pass in fh and do not set this, it will be set appropriately. |
ffed8b01 |
833 | |
ffed8b01 |
834 | =item * type |
835 | |
836 | This parameter specifies what type of object to create, a hash or array. Use |
837 | one of these two constants: C<DBM::Deep-E<gt>TYPE_HASH> or C<DBM::Deep-E<gt>TYPE_ARRAY>. |
d0b74c17 |
838 | This only takes effect when beginning a new file. This is an optional |
ffed8b01 |
839 | parameter, and defaults to C<DBM::Deep-E<gt>TYPE_HASH>. |
840 | |
841 | =item * locking |
842 | |
843 | Specifies whether locking is to be enabled. DBM::Deep uses Perl's Fnctl flock() |
844 | function to lock the database in exclusive mode for writes, and shared mode for |
d0b74c17 |
845 | reads. Pass any true value to enable. This affects the base DB handle I<and |
846 | any child hashes or arrays> that use the same DB file. This is an optional |
ffed8b01 |
847 | parameter, and defaults to 0 (disabled). See L<LOCKING> below for more. |
848 | |
849 | =item * autoflush |
850 | |
d0b74c17 |
851 | Specifies whether autoflush is to be enabled on the underlying filehandle. |
852 | This obviously slows down write operations, but is required if you may have |
853 | multiple processes accessing the same DB file (also consider enable I<locking>). |
854 | Pass any true value to enable. This is an optional parameter, and defaults to 0 |
ffed8b01 |
855 | (disabled). |
856 | |
857 | =item * autobless |
858 | |
859 | If I<autobless> mode is enabled, DBM::Deep will preserve blessed hashes, and |
860 | restore them when fetched. This is an B<experimental> feature, and does have |
861 | side-effects. Basically, when hashes are re-blessed into their original |
862 | classes, they are no longer blessed into the DBM::Deep class! So you won't be |
863 | able to call any DBM::Deep methods on them. You have been warned. |
864 | This is an optional parameter, and defaults to 0 (disabled). |
865 | |
866 | =item * filter_* |
867 | |
868 | See L<FILTERS> below. |
869 | |
ffed8b01 |
870 | =back |
871 | |
872 | =head1 TIE INTERFACE |
873 | |
874 | With DBM::Deep you can access your databases using Perl's standard hash/array |
90f93b43 |
875 | syntax. Because all DBM::Deep objects are I<tied> to hashes or arrays, you can |
876 | treat them as such. DBM::Deep will intercept all reads/writes and direct them |
877 | to the right place -- the DB file. This has nothing to do with the |
878 | L<TIE CONSTRUCTION> section above. This simply tells you how to use DBM::Deep |
879 | using regular hashes and arrays, rather than calling functions like C<get()> |
880 | and C<put()> (although those work too). It is entirely up to you how to want |
881 | to access your databases. |
ffed8b01 |
882 | |
883 | =head2 HASHES |
884 | |
885 | You can treat any DBM::Deep object like a normal Perl hash reference. Add keys, |
886 | or even nested hashes (or arrays) using standard Perl syntax: |
887 | |
d0b74c17 |
888 | my $db = DBM::Deep->new( "foo.db" ); |
889 | |
890 | $db->{mykey} = "myvalue"; |
891 | $db->{myhash} = {}; |
892 | $db->{myhash}->{subkey} = "subvalue"; |
ffed8b01 |
893 | |
d0b74c17 |
894 | print $db->{myhash}->{subkey} . "\n"; |
ffed8b01 |
895 | |
896 | You can even step through hash keys using the normal Perl C<keys()> function: |
897 | |
d0b74c17 |
898 | foreach my $key (keys %$db) { |
899 | print "$key: " . $db->{$key} . "\n"; |
900 | } |
ffed8b01 |
901 | |
902 | Remember that Perl's C<keys()> function extracts I<every> key from the hash and |
d0b74c17 |
903 | pushes them onto an array, all before the loop even begins. If you have an |
904 | extra large hash, this may exhaust Perl's memory. Instead, consider using |
905 | Perl's C<each()> function, which pulls keys/values one at a time, using very |
ffed8b01 |
906 | little memory: |
907 | |
d0b74c17 |
908 | while (my ($key, $value) = each %$db) { |
909 | print "$key: $value\n"; |
910 | } |
ffed8b01 |
911 | |
912 | Please note that when using C<each()>, you should always pass a direct |
913 | hash reference, not a lookup. Meaning, you should B<never> do this: |
914 | |
d0b74c17 |
915 | # NEVER DO THIS |
916 | while (my ($key, $value) = each %{$db->{foo}}) { # BAD |
ffed8b01 |
917 | |
918 | This causes an infinite loop, because for each iteration, Perl is calling |
919 | FETCH() on the $db handle, resulting in a "new" hash for foo every time, so |
d0b74c17 |
920 | it effectively keeps returning the first key over and over again. Instead, |
ffed8b01 |
921 | assign a temporary variable to C<$db->{foo}>, then pass that to each(). |
922 | |
923 | =head2 ARRAYS |
924 | |
925 | As with hashes, you can treat any DBM::Deep object like a normal Perl array |
d0b74c17 |
926 | reference. This includes inserting, removing and manipulating elements, |
ffed8b01 |
927 | and the C<push()>, C<pop()>, C<shift()>, C<unshift()> and C<splice()> functions. |
d0b74c17 |
928 | The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>, |
ffed8b01 |
929 | or simply be a nested array reference inside a hash. Example: |
930 | |
d0b74c17 |
931 | my $db = DBM::Deep->new( |
932 | file => "foo-array.db", |
933 | type => DBM::Deep->TYPE_ARRAY |
934 | ); |
935 | |
936 | $db->[0] = "foo"; |
937 | push @$db, "bar", "baz"; |
938 | unshift @$db, "bah"; |
939 | |
940 | my $last_elem = pop @$db; # baz |
941 | my $first_elem = shift @$db; # bah |
942 | my $second_elem = $db->[1]; # bar |
943 | |
944 | my $num_elements = scalar @$db; |
ffed8b01 |
945 | |
946 | =head1 OO INTERFACE |
947 | |
948 | In addition to the I<tie()> interface, you can also use a standard OO interface |
949 | to manipulate all aspects of DBM::Deep databases. Each type of object (hash or |
d0b74c17 |
950 | array) has its own methods, but both types share the following common methods: |
ffed8b01 |
951 | C<put()>, C<get()>, C<exists()>, C<delete()> and C<clear()>. |
952 | |
953 | =over |
954 | |
4d35d856 |
955 | =item * new() / clone() |
956 | |
957 | These are the constructor and copy-functions. |
958 | |
90f93b43 |
959 | =item * put() / store() |
ffed8b01 |
960 | |
961 | Stores a new hash key/value pair, or sets an array element value. Takes two |
962 | arguments, the hash key or array index, and the new value. The value can be |
963 | a scalar, hash ref or array ref. Returns true on success, false on failure. |
964 | |
d0b74c17 |
965 | $db->put("foo", "bar"); # for hashes |
966 | $db->put(1, "bar"); # for arrays |
ffed8b01 |
967 | |
90f93b43 |
968 | =item * get() / fetch() |
ffed8b01 |
969 | |
970 | Fetches the value of a hash key or array element. Takes one argument: the hash |
d0b74c17 |
971 | key or array index. Returns a scalar, hash ref or array ref, depending on the |
ffed8b01 |
972 | data type stored. |
973 | |
d0b74c17 |
974 | my $value = $db->get("foo"); # for hashes |
975 | my $value = $db->get(1); # for arrays |
ffed8b01 |
976 | |
977 | =item * exists() |
978 | |
d0b74c17 |
979 | Checks if a hash key or array index exists. Takes one argument: the hash key |
ffed8b01 |
980 | or array index. Returns true if it exists, false if not. |
981 | |
d0b74c17 |
982 | if ($db->exists("foo")) { print "yay!\n"; } # for hashes |
983 | if ($db->exists(1)) { print "yay!\n"; } # for arrays |
ffed8b01 |
984 | |
985 | =item * delete() |
986 | |
987 | Deletes one hash key/value pair or array element. Takes one argument: the hash |
988 | key or array index. Returns true on success, false if not found. For arrays, |
989 | the remaining elements located after the deleted element are NOT moved over. |
990 | The deleted element is essentially just undefined, which is exactly how Perl's |
d0b74c17 |
991 | internal arrays work. Please note that the space occupied by the deleted |
992 | key/value or element is B<not> reused again -- see L<UNUSED SPACE RECOVERY> |
ffed8b01 |
993 | below for details and workarounds. |
994 | |
d0b74c17 |
995 | $db->delete("foo"); # for hashes |
996 | $db->delete(1); # for arrays |
ffed8b01 |
997 | |
998 | =item * clear() |
999 | |
d0b74c17 |
1000 | Deletes B<all> hash keys or array elements. Takes no arguments. No return |
1001 | value. Please note that the space occupied by the deleted keys/values or |
1002 | elements is B<not> reused again -- see L<UNUSED SPACE RECOVERY> below for |
ffed8b01 |
1003 | details and workarounds. |
1004 | |
d0b74c17 |
1005 | $db->clear(); # hashes or arrays |
ffed8b01 |
1006 | |
4d35d856 |
1007 | =item * lock() / unlock() |
1008 | |
1009 | q.v. Locking. |
1010 | |
1011 | =item * optimize() |
1012 | |
1013 | Recover lost disk space. |
1014 | |
1015 | =item * import() / export() |
1016 | |
1017 | Data going in and out. |
1018 | |
1019 | =item * set_digest() / set_pack() / set_filter() |
1020 | |
1021 | q.v. adjusting the interal parameters. |
1022 | |
ffed8b01 |
1023 | =back |
1024 | |
1025 | =head2 HASHES |
1026 | |
d0b74c17 |
1027 | For hashes, DBM::Deep supports all the common methods described above, and the |
ffed8b01 |
1028 | following additional methods: C<first_key()> and C<next_key()>. |
1029 | |
1030 | =over |
1031 | |
1032 | =item * first_key() |
1033 | |
d0b74c17 |
1034 | Returns the "first" key in the hash. As with built-in Perl hashes, keys are |
1035 | fetched in an undefined order (which appears random). Takes no arguments, |
ffed8b01 |
1036 | returns the key as a scalar value. |
1037 | |
d0b74c17 |
1038 | my $key = $db->first_key(); |
ffed8b01 |
1039 | |
1040 | =item * next_key() |
1041 | |
1042 | Returns the "next" key in the hash, given the previous one as the sole argument. |
1043 | Returns undef if there are no more keys to be fetched. |
1044 | |
d0b74c17 |
1045 | $key = $db->next_key($key); |
ffed8b01 |
1046 | |
1047 | =back |
1048 | |
1049 | Here are some examples of using hashes: |
1050 | |
d0b74c17 |
1051 | my $db = DBM::Deep->new( "foo.db" ); |
1052 | |
1053 | $db->put("foo", "bar"); |
1054 | print "foo: " . $db->get("foo") . "\n"; |
1055 | |
1056 | $db->put("baz", {}); # new child hash ref |
1057 | $db->get("baz")->put("buz", "biz"); |
1058 | print "buz: " . $db->get("baz")->get("buz") . "\n"; |
1059 | |
1060 | my $key = $db->first_key(); |
1061 | while ($key) { |
1062 | print "$key: " . $db->get($key) . "\n"; |
1063 | $key = $db->next_key($key); |
1064 | } |
1065 | |
1066 | if ($db->exists("foo")) { $db->delete("foo"); } |
ffed8b01 |
1067 | |
1068 | =head2 ARRAYS |
1069 | |
d0b74c17 |
1070 | For arrays, DBM::Deep supports all the common methods described above, and the |
1071 | following additional methods: C<length()>, C<push()>, C<pop()>, C<shift()>, |
ffed8b01 |
1072 | C<unshift()> and C<splice()>. |
1073 | |
1074 | =over |
1075 | |
1076 | =item * length() |
1077 | |
1078 | Returns the number of elements in the array. Takes no arguments. |
1079 | |
d0b74c17 |
1080 | my $len = $db->length(); |
ffed8b01 |
1081 | |
1082 | =item * push() |
1083 | |
d0b74c17 |
1084 | Adds one or more elements onto the end of the array. Accepts scalars, hash |
ffed8b01 |
1085 | refs or array refs. No return value. |
1086 | |
d0b74c17 |
1087 | $db->push("foo", "bar", {}); |
ffed8b01 |
1088 | |
1089 | =item * pop() |
1090 | |
1091 | Fetches the last element in the array, and deletes it. Takes no arguments. |
1092 | Returns undef if array is empty. Returns the element value. |
1093 | |
d0b74c17 |
1094 | my $elem = $db->pop(); |
ffed8b01 |
1095 | |
1096 | =item * shift() |
1097 | |
d0b74c17 |
1098 | Fetches the first element in the array, deletes it, then shifts all the |
1099 | remaining elements over to take up the space. Returns the element value. This |
1100 | method is not recommended with large arrays -- see L<LARGE ARRAYS> below for |
ffed8b01 |
1101 | details. |
1102 | |
d0b74c17 |
1103 | my $elem = $db->shift(); |
ffed8b01 |
1104 | |
1105 | =item * unshift() |
1106 | |
d0b74c17 |
1107 | Inserts one or more elements onto the beginning of the array, shifting all |
1108 | existing elements over to make room. Accepts scalars, hash refs or array refs. |
1109 | No return value. This method is not recommended with large arrays -- see |
ffed8b01 |
1110 | <LARGE ARRAYS> below for details. |
1111 | |
d0b74c17 |
1112 | $db->unshift("foo", "bar", {}); |
ffed8b01 |
1113 | |
1114 | =item * splice() |
1115 | |
d0b74c17 |
1116 | Performs exactly like Perl's built-in function of the same name. See L<perldoc |
ffed8b01 |
1117 | -f splice> for usage -- it is too complicated to document here. This method is |
1118 | not recommended with large arrays -- see L<LARGE ARRAYS> below for details. |
1119 | |
1120 | =back |
1121 | |
1122 | Here are some examples of using arrays: |
1123 | |
d0b74c17 |
1124 | my $db = DBM::Deep->new( |
1125 | file => "foo.db", |
1126 | type => DBM::Deep->TYPE_ARRAY |
1127 | ); |
1128 | |
1129 | $db->push("bar", "baz"); |
1130 | $db->unshift("foo"); |
1131 | $db->put(3, "buz"); |
1132 | |
1133 | my $len = $db->length(); |
1134 | print "length: $len\n"; # 4 |
1135 | |
1136 | for (my $k=0; $k<$len; $k++) { |
1137 | print "$k: " . $db->get($k) . "\n"; |
1138 | } |
1139 | |
1140 | $db->splice(1, 2, "biz", "baf"); |
1141 | |
1142 | while (my $elem = shift @$db) { |
1143 | print "shifted: $elem\n"; |
1144 | } |
ffed8b01 |
1145 | |
1146 | =head1 LOCKING |
1147 | |
d0b74c17 |
1148 | Enable automatic file locking by passing a true value to the C<locking> |
ffed8b01 |
1149 | parameter when constructing your DBM::Deep object (see L<SETUP> above). |
1150 | |
d0b74c17 |
1151 | my $db = DBM::Deep->new( |
1152 | file => "foo.db", |
1153 | locking => 1 |
1154 | ); |
ffed8b01 |
1155 | |
d0b74c17 |
1156 | This causes DBM::Deep to C<flock()> the underlying filehandle with exclusive |
1157 | mode for writes, and shared mode for reads. This is required if you have |
1158 | multiple processes accessing the same database file, to avoid file corruption. |
1159 | Please note that C<flock()> does NOT work for files over NFS. See L<DB OVER |
ffed8b01 |
1160 | NFS> below for more. |
1161 | |
1162 | =head2 EXPLICIT LOCKING |
1163 | |
d0b74c17 |
1164 | You can explicitly lock a database, so it remains locked for multiple |
1165 | transactions. This is done by calling the C<lock()> method, and passing an |
90f93b43 |
1166 | optional lock mode argument (defaults to exclusive mode). This is particularly |
d0b74c17 |
1167 | useful for things like counters, where the current value needs to be fetched, |
ffed8b01 |
1168 | then incremented, then stored again. |
1169 | |
d0b74c17 |
1170 | $db->lock(); |
1171 | my $counter = $db->get("counter"); |
1172 | $counter++; |
1173 | $db->put("counter", $counter); |
1174 | $db->unlock(); |
1175 | |
1176 | # or... |
ffed8b01 |
1177 | |
d0b74c17 |
1178 | $db->lock(); |
1179 | $db->{counter}++; |
1180 | $db->unlock(); |
ffed8b01 |
1181 | |
1182 | You can pass C<lock()> an optional argument, which specifies which mode to use |
d0b74c17 |
1183 | (exclusive or shared). Use one of these two constants: C<DBM::Deep-E<gt>LOCK_EX> |
1184 | or C<DBM::Deep-E<gt>LOCK_SH>. These are passed directly to C<flock()>, and are the |
ffed8b01 |
1185 | same as the constants defined in Perl's C<Fcntl> module. |
1186 | |
d0b74c17 |
1187 | $db->lock( DBM::Deep->LOCK_SH ); |
1188 | # something here |
1189 | $db->unlock(); |
ffed8b01 |
1190 | |
ffed8b01 |
1191 | =head1 IMPORTING/EXPORTING |
1192 | |
1193 | You can import existing complex structures by calling the C<import()> method, |
1194 | and export an entire database into an in-memory structure using the C<export()> |
1195 | method. Both are examined here. |
1196 | |
1197 | =head2 IMPORTING |
1198 | |
1199 | Say you have an existing hash with nested hashes/arrays inside it. Instead of |
d0b74c17 |
1200 | walking the structure and adding keys/elements to the database as you go, |
1201 | simply pass a reference to the C<import()> method. This recursively adds |
ffed8b01 |
1202 | everything to an existing DBM::Deep object for you. Here is an example: |
1203 | |
d0b74c17 |
1204 | my $struct = { |
1205 | key1 => "value1", |
1206 | key2 => "value2", |
1207 | array1 => [ "elem0", "elem1", "elem2" ], |
1208 | hash1 => { |
1209 | subkey1 => "subvalue1", |
1210 | subkey2 => "subvalue2" |
1211 | } |
1212 | }; |
1213 | |
1214 | my $db = DBM::Deep->new( "foo.db" ); |
1215 | $db->import( $struct ); |
1216 | |
1217 | print $db->{key1} . "\n"; # prints "value1" |
1218 | |
1219 | This recursively imports the entire C<$struct> object into C<$db>, including |
ffed8b01 |
1220 | all nested hashes and arrays. If the DBM::Deep object contains exsiting data, |
d0b74c17 |
1221 | keys are merged with the existing ones, replacing if they already exist. |
1222 | The C<import()> method can be called on any database level (not just the base |
ffed8b01 |
1223 | level), and works with both hash and array DB types. |
1224 | |
ffed8b01 |
1225 | B<Note:> Make sure your existing structure has no circular references in it. |
1226 | These will cause an infinite loop when importing. |
1227 | |
1228 | =head2 EXPORTING |
1229 | |
d0b74c17 |
1230 | Calling the C<export()> method on an existing DBM::Deep object will return |
1231 | a reference to a new in-memory copy of the database. The export is done |
ffed8b01 |
1232 | recursively, so all nested hashes/arrays are all exported to standard Perl |
1233 | objects. Here is an example: |
1234 | |
d0b74c17 |
1235 | my $db = DBM::Deep->new( "foo.db" ); |
1236 | |
1237 | $db->{key1} = "value1"; |
1238 | $db->{key2} = "value2"; |
1239 | $db->{hash1} = {}; |
1240 | $db->{hash1}->{subkey1} = "subvalue1"; |
1241 | $db->{hash1}->{subkey2} = "subvalue2"; |
1242 | |
1243 | my $struct = $db->export(); |
1244 | |
1245 | print $struct->{key1} . "\n"; # prints "value1" |
ffed8b01 |
1246 | |
1247 | This makes a complete copy of the database in memory, and returns a reference |
d0b74c17 |
1248 | to it. The C<export()> method can be called on any database level (not just |
1249 | the base level), and works with both hash and array DB types. Be careful of |
1250 | large databases -- you can store a lot more data in a DBM::Deep object than an |
ffed8b01 |
1251 | in-memory Perl structure. |
1252 | |
ffed8b01 |
1253 | B<Note:> Make sure your database has no circular references in it. |
1254 | These will cause an infinite loop when exporting. |
1255 | |
1256 | =head1 FILTERS |
1257 | |
1258 | DBM::Deep has a number of hooks where you can specify your own Perl function |
1259 | to perform filtering on incoming or outgoing data. This is a perfect |
1260 | way to extend the engine, and implement things like real-time compression or |
d0b74c17 |
1261 | encryption. Filtering applies to the base DB level, and all child hashes / |
1262 | arrays. Filter hooks can be specified when your DBM::Deep object is first |
1263 | constructed, or by calling the C<set_filter()> method at any time. There are |
ffed8b01 |
1264 | four available filter hooks, described below: |
1265 | |
1266 | =over |
1267 | |
1268 | =item * filter_store_key |
1269 | |
d0b74c17 |
1270 | This filter is called whenever a hash key is stored. It |
ffed8b01 |
1271 | is passed the incoming key, and expected to return a transformed key. |
1272 | |
1273 | =item * filter_store_value |
1274 | |
d0b74c17 |
1275 | This filter is called whenever a hash key or array element is stored. It |
ffed8b01 |
1276 | is passed the incoming value, and expected to return a transformed value. |
1277 | |
1278 | =item * filter_fetch_key |
1279 | |
d0b74c17 |
1280 | This filter is called whenever a hash key is fetched (i.e. via |
ffed8b01 |
1281 | C<first_key()> or C<next_key()>). It is passed the transformed key, |
1282 | and expected to return the plain key. |
1283 | |
1284 | =item * filter_fetch_value |
1285 | |
d0b74c17 |
1286 | This filter is called whenever a hash key or array element is fetched. |
ffed8b01 |
1287 | It is passed the transformed value, and expected to return the plain value. |
1288 | |
1289 | =back |
1290 | |
1291 | Here are the two ways to setup a filter hook: |
1292 | |
d0b74c17 |
1293 | my $db = DBM::Deep->new( |
1294 | file => "foo.db", |
1295 | filter_store_value => \&my_filter_store, |
1296 | filter_fetch_value => \&my_filter_fetch |
1297 | ); |
1298 | |
1299 | # or... |
1300 | |
1301 | $db->set_filter( "filter_store_value", \&my_filter_store ); |
1302 | $db->set_filter( "filter_fetch_value", \&my_filter_fetch ); |
ffed8b01 |
1303 | |
1304 | Your filter function will be called only when dealing with SCALAR keys or |
1305 | values. When nested hashes and arrays are being stored/fetched, filtering |
d0b74c17 |
1306 | is bypassed. Filters are called as static functions, passed a single SCALAR |
ffed8b01 |
1307 | argument, and expected to return a single SCALAR value. If you want to |
1308 | remove a filter, set the function reference to C<undef>: |
1309 | |
d0b74c17 |
1310 | $db->set_filter( "filter_store_value", undef ); |
ffed8b01 |
1311 | |
1312 | =head2 REAL-TIME ENCRYPTION EXAMPLE |
1313 | |
d0b74c17 |
1314 | Here is a working example that uses the I<Crypt::Blowfish> module to |
ffed8b01 |
1315 | do real-time encryption / decryption of keys & values with DBM::Deep Filters. |
d0b74c17 |
1316 | Please visit L<http://search.cpan.org/search?module=Crypt::Blowfish> for more |
ffed8b01 |
1317 | on I<Crypt::Blowfish>. You'll also need the I<Crypt::CBC> module. |
1318 | |
d0b74c17 |
1319 | use DBM::Deep; |
1320 | use Crypt::Blowfish; |
1321 | use Crypt::CBC; |
1322 | |
1323 | my $cipher = Crypt::CBC->new({ |
1324 | 'key' => 'my secret key', |
1325 | 'cipher' => 'Blowfish', |
1326 | 'iv' => '$KJh#(}q', |
1327 | 'regenerate_key' => 0, |
1328 | 'padding' => 'space', |
1329 | 'prepend_iv' => 0 |
1330 | }); |
1331 | |
1332 | my $db = DBM::Deep->new( |
1333 | file => "foo-encrypt.db", |
1334 | filter_store_key => \&my_encrypt, |
1335 | filter_store_value => \&my_encrypt, |
1336 | filter_fetch_key => \&my_decrypt, |
1337 | filter_fetch_value => \&my_decrypt, |
1338 | ); |
1339 | |
1340 | $db->{key1} = "value1"; |
1341 | $db->{key2} = "value2"; |
1342 | print "key1: " . $db->{key1} . "\n"; |
1343 | print "key2: " . $db->{key2} . "\n"; |
1344 | |
1345 | undef $db; |
1346 | exit; |
1347 | |
1348 | sub my_encrypt { |
1349 | return $cipher->encrypt( $_[0] ); |
1350 | } |
1351 | sub my_decrypt { |
1352 | return $cipher->decrypt( $_[0] ); |
1353 | } |
ffed8b01 |
1354 | |
1355 | =head2 REAL-TIME COMPRESSION EXAMPLE |
1356 | |
1357 | Here is a working example that uses the I<Compress::Zlib> module to do real-time |
1358 | compression / decompression of keys & values with DBM::Deep Filters. |
d0b74c17 |
1359 | Please visit L<http://search.cpan.org/search?module=Compress::Zlib> for |
ffed8b01 |
1360 | more on I<Compress::Zlib>. |
1361 | |
d0b74c17 |
1362 | use DBM::Deep; |
1363 | use Compress::Zlib; |
1364 | |
1365 | my $db = DBM::Deep->new( |
1366 | file => "foo-compress.db", |
1367 | filter_store_key => \&my_compress, |
1368 | filter_store_value => \&my_compress, |
1369 | filter_fetch_key => \&my_decompress, |
1370 | filter_fetch_value => \&my_decompress, |
1371 | ); |
1372 | |
1373 | $db->{key1} = "value1"; |
1374 | $db->{key2} = "value2"; |
1375 | print "key1: " . $db->{key1} . "\n"; |
1376 | print "key2: " . $db->{key2} . "\n"; |
1377 | |
1378 | undef $db; |
1379 | exit; |
1380 | |
1381 | sub my_compress { |
1382 | return Compress::Zlib::memGzip( $_[0] ) ; |
1383 | } |
1384 | sub my_decompress { |
1385 | return Compress::Zlib::memGunzip( $_[0] ) ; |
1386 | } |
ffed8b01 |
1387 | |
1388 | B<Note:> Filtering of keys only applies to hashes. Array "keys" are |
1389 | actually numerical index numbers, and are not filtered. |
1390 | |
1391 | =head1 ERROR HANDLING |
1392 | |
1393 | Most DBM::Deep methods return a true value for success, and call die() on |
95967a5e |
1394 | failure. You can wrap calls in an eval block to catch the die. |
ffed8b01 |
1395 | |
d0b74c17 |
1396 | my $db = DBM::Deep->new( "foo.db" ); # create hash |
1397 | eval { $db->push("foo"); }; # ILLEGAL -- push is array-only call |
1398 | |
90f93b43 |
1399 | print $@; # prints error message |
429e4192 |
1400 | |
ffed8b01 |
1401 | =head1 LARGEFILE SUPPORT |
1402 | |
1403 | If you have a 64-bit system, and your Perl is compiled with both LARGEFILE |
1404 | and 64-bit support, you I<may> be able to create databases larger than 2 GB. |
1405 | DBM::Deep by default uses 32-bit file offset tags, but these can be changed |
1406 | by calling the static C<set_pack()> method before you do anything else. |
1407 | |
d0b74c17 |
1408 | DBM::Deep::set_pack(8, 'Q'); |
ffed8b01 |
1409 | |
d0b74c17 |
1410 | This tells DBM::Deep to pack all file offsets with 8-byte (64-bit) quad words |
1411 | instead of 32-bit longs. After setting these values your DB files have a |
ffed8b01 |
1412 | theoretical maximum size of 16 XB (exabytes). |
1413 | |
ffed8b01 |
1414 | B<Note:> Changing these values will B<NOT> work for existing database files. |
d0b74c17 |
1415 | Only change this for new files, and make sure it stays set consistently |
1416 | throughout the file's life. If you do set these values, you can no longer |
1417 | access 32-bit DB files. You can, however, call C<set_pack(4, 'N')> to change |
ffed8b01 |
1418 | back to 32-bit mode. |
1419 | |
d0b74c17 |
1420 | B<Note:> I have not personally tested files > 2 GB -- all my systems have |
1421 | only a 32-bit Perl. However, I have received user reports that this does |
ffed8b01 |
1422 | indeed work! |
1423 | |
1424 | =head1 LOW-LEVEL ACCESS |
1425 | |
90f93b43 |
1426 | If you require low-level access to the underlying filehandle that DBM::Deep uses, |
4d35d856 |
1427 | you can call the C<_fh()> method, which returns the handle: |
ffed8b01 |
1428 | |
d0b74c17 |
1429 | my $fh = $db->_fh(); |
ffed8b01 |
1430 | |
1431 | This method can be called on the root level of the datbase, or any child |
1432 | hashes or arrays. All levels share a I<root> structure, which contains things |
90f93b43 |
1433 | like the filehandle, a reference counter, and all the options specified |
d0b74c17 |
1434 | when you created the object. You can get access to this root structure by |
ffed8b01 |
1435 | calling the C<root()> method. |
1436 | |
d0b74c17 |
1437 | my $root = $db->_root(); |
ffed8b01 |
1438 | |
1439 | This is useful for changing options after the object has already been created, |
f5be9b03 |
1440 | such as enabling/disabling locking. You can also store your own temporary user |
1441 | data in this structure (be wary of name collision), which is then accessible from |
1442 | any child hash or array. |
ffed8b01 |
1443 | |
1444 | =head1 CUSTOM DIGEST ALGORITHM |
1445 | |
1446 | DBM::Deep by default uses the I<Message Digest 5> (MD5) algorithm for hashing |
1447 | keys. However you can override this, and use another algorithm (such as SHA-256) |
d0b74c17 |
1448 | or even write your own. But please note that DBM::Deep currently expects zero |
ffed8b01 |
1449 | collisions, so your algorithm has to be I<perfect>, so to speak. |
1450 | Collision detection may be introduced in a later version. |
1451 | |
1452 | |
1453 | |
d0b74c17 |
1454 | You can specify a custom digest algorithm by calling the static C<set_digest()> |
1455 | function, passing a reference to a subroutine, and the length of the algorithm's |
1456 | hashes (in bytes). This is a global static function, which affects ALL DBM::Deep |
1457 | objects. Here is a working example that uses a 256-bit hash from the |
1458 | I<Digest::SHA256> module. Please see |
ffed8b01 |
1459 | L<http://search.cpan.org/search?module=Digest::SHA256> for more. |
1460 | |
d0b74c17 |
1461 | use DBM::Deep; |
1462 | use Digest::SHA256; |
1463 | |
1464 | my $context = Digest::SHA256::new(256); |
1465 | |
1466 | DBM::Deep::set_digest( \&my_digest, 32 ); |
1467 | |
1468 | my $db = DBM::Deep->new( "foo-sha.db" ); |
1469 | |
1470 | $db->{key1} = "value1"; |
1471 | $db->{key2} = "value2"; |
1472 | print "key1: " . $db->{key1} . "\n"; |
1473 | print "key2: " . $db->{key2} . "\n"; |
1474 | |
1475 | undef $db; |
1476 | exit; |
1477 | |
1478 | sub my_digest { |
1479 | return substr( $context->hash($_[0]), 0, 32 ); |
1480 | } |
ffed8b01 |
1481 | |
1482 | B<Note:> Your returned digest strings must be B<EXACTLY> the number |
1483 | of bytes you specify in the C<set_digest()> function (in this case 32). |
1484 | |
1485 | =head1 CIRCULAR REFERENCES |
1486 | |
1487 | DBM::Deep has B<experimental> support for circular references. Meaning you |
1488 | can have a nested hash key or array element that points to a parent object. |
1489 | This relationship is stored in the DB file, and is preserved between sessions. |
1490 | Here is an example: |
1491 | |
d0b74c17 |
1492 | my $db = DBM::Deep->new( "foo.db" ); |
1493 | |
1494 | $db->{foo} = "bar"; |
1495 | $db->{circle} = $db; # ref to self |
1496 | |
1497 | print $db->{foo} . "\n"; # prints "foo" |
1498 | print $db->{circle}->{foo} . "\n"; # prints "foo" again |
ffed8b01 |
1499 | |
69c94980 |
1500 | B<Note>: Passing the object to a function that recursively walks the |
ffed8b01 |
1501 | object tree (such as I<Data::Dumper> or even the built-in C<optimize()> or |
69c94980 |
1502 | C<export()> methods) will result in an infinite loop. This will be fixed in |
1503 | a future release. |
ffed8b01 |
1504 | |
1505 | =head1 CAVEATS / ISSUES / BUGS |
1506 | |
1507 | This section describes all the known issues with DBM::Deep. It you have found |
1508 | something that is not listed here, please send e-mail to L<jhuckaby@cpan.org>. |
1509 | |
1510 | =head2 UNUSED SPACE RECOVERY |
1511 | |
14a3acb6 |
1512 | One major caveat with DBM::Deep is that space occupied by existing keys and |
ffed8b01 |
1513 | values is not recovered when they are deleted. Meaning if you keep deleting |
1514 | and adding new keys, your file will continuously grow. I am working on this, |
d0b74c17 |
1515 | but in the meantime you can call the built-in C<optimize()> method from time to |
ffed8b01 |
1516 | time (perhaps in a crontab or something) to recover all your unused space. |
1517 | |
d0b74c17 |
1518 | $db->optimize(); # returns true on success |
ffed8b01 |
1519 | |
1520 | This rebuilds the ENTIRE database into a new file, then moves it on top of |
1521 | the original. The new file will have no unused space, thus it will take up as |
d0b74c17 |
1522 | little disk space as possible. Please note that this operation can take |
1523 | a long time for large files, and you need enough disk space to temporarily hold |
1524 | 2 copies of your DB file. The temporary file is created in the same directory |
1525 | as the original, named with a ".tmp" extension, and is deleted when the |
1526 | operation completes. Oh, and if locking is enabled, the DB is automatically |
ffed8b01 |
1527 | locked for the entire duration of the copy. |
1528 | |
d0b74c17 |
1529 | B<WARNING:> Only call optimize() on the top-level node of the database, and |
1530 | make sure there are no child references lying around. DBM::Deep keeps a reference |
ffed8b01 |
1531 | counter, and if it is greater than 1, optimize() will abort and return undef. |
1532 | |
1533 | =head2 AUTOVIVIFICATION |
1534 | |
d0b74c17 |
1535 | Unfortunately, autovivification doesn't work with tied hashes. This appears to |
1536 | be a bug in Perl's tie() system, as I<Jakob Schmidt> encountered the very same |
ffed8b01 |
1537 | issue with his I<DWH_FIle> module (see L<http://search.cpan.org/search?module=DWH_File>), |
d0b74c17 |
1538 | and it is also mentioned in the BUGS section for the I<MLDBM> module <see |
ffed8b01 |
1539 | L<http://search.cpan.org/search?module=MLDBM>). Basically, on a new db file, |
1540 | this does not work: |
1541 | |
d0b74c17 |
1542 | $db->{foo}->{bar} = "hello"; |
ffed8b01 |
1543 | |
1544 | Since "foo" doesn't exist, you cannot add "bar" to it. You end up with "foo" |
1545 | being an empty hash. Try this instead, which works fine: |
1546 | |
d0b74c17 |
1547 | $db->{foo} = { bar => "hello" }; |
ffed8b01 |
1548 | |
1549 | As of Perl 5.8.7, this bug still exists. I have walked very carefully through |
1550 | the execution path, and Perl indeed passes an empty hash to the STORE() method. |
1551 | Probably a bug in Perl. |
1552 | |
eea0d863 |
1553 | =head2 REFERENCES |
1554 | |
1555 | (The reasons given assume a high level of Perl understanding, specifically of |
1556 | references. You can safely skip this section.) |
1557 | |
1558 | Currently, the only references supported are HASH and ARRAY. The other reference |
1559 | types (SCALAR, CODE, GLOB, and REF) cannot be supported for various reasons. |
1560 | |
1561 | =over 4 |
1562 | |
1563 | =item * GLOB |
1564 | |
1565 | These are things like filehandles and other sockets. They can't be supported |
1566 | because it's completely unclear how DBM::Deep should serialize them. |
1567 | |
1568 | =item * SCALAR / REF |
1569 | |
1570 | The discussion here refers to the following type of example: |
1571 | |
1572 | my $x = 25; |
1573 | $db->{key1} = \$x; |
1574 | |
1575 | $x = 50; |
1576 | |
1577 | # In some other process ... |
1578 | |
1579 | my $val = ${ $db->{key1} }; |
1580 | |
1581 | is( $val, 50, "What actually gets stored in the DB file?" ); |
1582 | |
1583 | The problem is one of synchronization. When the variable being referred to |
1584 | changes value, the reference isn't notified. This means that the new value won't |
1585 | be stored in the datafile for other processes to read. There is no TIEREF. |
1586 | |
1587 | It is theoretically possible to store references to values already within a |
1588 | DBM::Deep object because everything already is synchronized, but the change to |
1589 | the internals would be quite large. Specifically, DBM::Deep would have to tie |
1590 | every single value that is stored. This would bloat the RAM footprint of |
1591 | DBM::Deep at least twofold (if not more) and be a significant performance drain, |
1592 | all to support a feature that has never been requested. |
1593 | |
1594 | =item * CODE |
1595 | |
1596 | L<http://search.cpan.org/search?module=Data::Dump::Streamer> provides a |
1597 | mechanism for serializing coderefs, including saving off all closure state. |
1598 | However, just as for SCALAR and REF, that closure state may change without |
1599 | notifying the DBM::Deep object storing the reference. |
1600 | |
1601 | =back |
1602 | |
ffed8b01 |
1603 | =head2 FILE CORRUPTION |
1604 | |
14a3acb6 |
1605 | The current level of error handling in DBM::Deep is minimal. Files I<are> checked |
1606 | for a 32-bit signature when opened, but other corruption in files can cause |
1607 | segmentation faults. DBM::Deep may try to seek() past the end of a file, or get |
ffed8b01 |
1608 | stuck in an infinite loop depending on the level of corruption. File write |
1609 | operations are not checked for failure (for speed), so if you happen to run |
d0b74c17 |
1610 | out of disk space, DBM::Deep will probably fail in a bad way. These things will |
ffed8b01 |
1611 | be addressed in a later version of DBM::Deep. |
1612 | |
1613 | =head2 DB OVER NFS |
1614 | |
14a3acb6 |
1615 | Beware of using DB files over NFS. DBM::Deep uses flock(), which works well on local |
d0b74c17 |
1616 | filesystems, but will NOT protect you from file corruption over NFS. I've heard |
1617 | about setting up your NFS server with a locking daemon, then using lockf() to |
1618 | lock your files, but your mileage may vary there as well. From what I |
1619 | understand, there is no real way to do it. However, if you need access to the |
1620 | underlying filehandle in DBM::Deep for using some other kind of locking scheme like |
ffed8b01 |
1621 | lockf(), see the L<LOW-LEVEL ACCESS> section above. |
1622 | |
1623 | =head2 COPYING OBJECTS |
1624 | |
d0b74c17 |
1625 | Beware of copying tied objects in Perl. Very strange things can happen. |
1626 | Instead, use DBM::Deep's C<clone()> method which safely copies the object and |
ffed8b01 |
1627 | returns a new, blessed, tied hash or array to the same level in the DB. |
1628 | |
d0b74c17 |
1629 | my $copy = $db->clone(); |
ffed8b01 |
1630 | |
90f93b43 |
1631 | B<Note>: Since clone() here is cloning the object, not the database location, any |
1632 | modifications to either $db or $copy will be visible in both. |
1633 | |
ffed8b01 |
1634 | =head2 LARGE ARRAYS |
1635 | |
1636 | Beware of using C<shift()>, C<unshift()> or C<splice()> with large arrays. |
1637 | These functions cause every element in the array to move, which can be murder |
1638 | on DBM::Deep, as every element has to be fetched from disk, then stored again in |
90f93b43 |
1639 | a different location. This will be addressed in the forthcoming version 1.00. |
ffed8b01 |
1640 | |
9be51a89 |
1641 | =head2 WRITEONLY FILES |
1642 | |
1643 | If you pass in a filehandle to new(), you may have opened it in either a readonly or |
1644 | writeonly mode. STORE will verify that the filehandle is writable. However, there |
1645 | doesn't seem to be a good way to determine if a filehandle is readable. And, if the |
1646 | filehandle isn't readable, it's not clear what will happen. So, don't do that. |
1647 | |
ffed8b01 |
1648 | =head1 PERFORMANCE |
1649 | |
1650 | This section discusses DBM::Deep's speed and memory usage. |
1651 | |
1652 | =head2 SPEED |
1653 | |
d0b74c17 |
1654 | Obviously, DBM::Deep isn't going to be as fast as some C-based DBMs, such as |
ffed8b01 |
1655 | the almighty I<BerkeleyDB>. But it makes up for it in features like true |
1656 | multi-level hash/array support, and cross-platform FTPable files. Even so, |
1657 | DBM::Deep is still pretty fast, and the speed stays fairly consistent, even |
1658 | with huge databases. Here is some test data: |
d0b74c17 |
1659 | |
1660 | Adding 1,000,000 keys to new DB file... |
1661 | |
1662 | At 100 keys, avg. speed is 2,703 keys/sec |
1663 | At 200 keys, avg. speed is 2,642 keys/sec |
1664 | At 300 keys, avg. speed is 2,598 keys/sec |
1665 | At 400 keys, avg. speed is 2,578 keys/sec |
1666 | At 500 keys, avg. speed is 2,722 keys/sec |
1667 | At 600 keys, avg. speed is 2,628 keys/sec |
1668 | At 700 keys, avg. speed is 2,700 keys/sec |
1669 | At 800 keys, avg. speed is 2,607 keys/sec |
1670 | At 900 keys, avg. speed is 2,190 keys/sec |
1671 | At 1,000 keys, avg. speed is 2,570 keys/sec |
1672 | At 2,000 keys, avg. speed is 2,417 keys/sec |
1673 | At 3,000 keys, avg. speed is 1,982 keys/sec |
1674 | At 4,000 keys, avg. speed is 1,568 keys/sec |
1675 | At 5,000 keys, avg. speed is 1,533 keys/sec |
1676 | At 6,000 keys, avg. speed is 1,787 keys/sec |
1677 | At 7,000 keys, avg. speed is 1,977 keys/sec |
1678 | At 8,000 keys, avg. speed is 2,028 keys/sec |
1679 | At 9,000 keys, avg. speed is 2,077 keys/sec |
1680 | At 10,000 keys, avg. speed is 2,031 keys/sec |
1681 | At 20,000 keys, avg. speed is 1,970 keys/sec |
1682 | At 30,000 keys, avg. speed is 2,050 keys/sec |
1683 | At 40,000 keys, avg. speed is 2,073 keys/sec |
1684 | At 50,000 keys, avg. speed is 1,973 keys/sec |
1685 | At 60,000 keys, avg. speed is 1,914 keys/sec |
1686 | At 70,000 keys, avg. speed is 2,091 keys/sec |
1687 | At 80,000 keys, avg. speed is 2,103 keys/sec |
1688 | At 90,000 keys, avg. speed is 1,886 keys/sec |
1689 | At 100,000 keys, avg. speed is 1,970 keys/sec |
1690 | At 200,000 keys, avg. speed is 2,053 keys/sec |
1691 | At 300,000 keys, avg. speed is 1,697 keys/sec |
1692 | At 400,000 keys, avg. speed is 1,838 keys/sec |
1693 | At 500,000 keys, avg. speed is 1,941 keys/sec |
1694 | At 600,000 keys, avg. speed is 1,930 keys/sec |
1695 | At 700,000 keys, avg. speed is 1,735 keys/sec |
1696 | At 800,000 keys, avg. speed is 1,795 keys/sec |
1697 | At 900,000 keys, avg. speed is 1,221 keys/sec |
1698 | At 1,000,000 keys, avg. speed is 1,077 keys/sec |
1699 | |
1700 | This test was performed on a PowerMac G4 1gHz running Mac OS X 10.3.2 & Perl |
1701 | 5.8.1, with an 80GB Ultra ATA/100 HD spinning at 7200RPM. The hash keys and |
1702 | values were between 6 - 12 chars in length. The DB file ended up at 210MB. |
ffed8b01 |
1703 | Run time was 12 min 3 sec. |
1704 | |
1705 | =head2 MEMORY USAGE |
1706 | |
1707 | One of the great things about DBM::Deep is that it uses very little memory. |
1708 | Even with huge databases (1,000,000+ keys) you will not see much increased |
14a3acb6 |
1709 | memory on your process. DBM::Deep relies solely on the filesystem for storing |
ffed8b01 |
1710 | and fetching data. Here is output from I</usr/bin/top> before even opening a |
1711 | database handle: |
1712 | |
d0b74c17 |
1713 | PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND |
1714 | 22831 root 11 0 2716 2716 1296 R 0.0 0.2 0:07 perl |
ffed8b01 |
1715 | |
d0b74c17 |
1716 | Basically the process is taking 2,716K of memory. And here is the same |
ffed8b01 |
1717 | process after storing and fetching 1,000,000 keys: |
1718 | |
d0b74c17 |
1719 | PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND |
1720 | 22831 root 14 0 2772 2772 1328 R 0.0 0.2 13:32 perl |
ffed8b01 |
1721 | |
d0b74c17 |
1722 | Notice the memory usage increased by only 56K. Test was performed on a 700mHz |
ffed8b01 |
1723 | x86 box running Linux RedHat 7.2 & Perl 5.6.1. |
1724 | |
1725 | =head1 DB FILE FORMAT |
1726 | |
1727 | In case you were interested in the underlying DB file format, it is documented |
d0b74c17 |
1728 | here in this section. You don't need to know this to use the module, it's just |
ffed8b01 |
1729 | included for reference. |
1730 | |
1731 | =head2 SIGNATURE |
1732 | |
1733 | DBM::Deep files always start with a 32-bit signature to identify the file type. |
1734 | This is at offset 0. The signature is "DPDB" in network byte order. This is |
90f93b43 |
1735 | checked for when the file is opened and an error will be thrown if it's not found. |
ffed8b01 |
1736 | |
1737 | =head2 TAG |
1738 | |
1739 | The DBM::Deep file is in a I<tagged format>, meaning each section of the file |
d0b74c17 |
1740 | has a standard header containing the type of data, the length of data, and then |
1741 | the data itself. The type is a single character (1 byte), the length is a |
ffed8b01 |
1742 | 32-bit unsigned long in network byte order, and the data is, well, the data. |
1743 | Here is how it unfolds: |
1744 | |
1745 | =head2 MASTER INDEX |
1746 | |
d0b74c17 |
1747 | Immediately after the 32-bit file signature is the I<Master Index> record. |
1748 | This is a standard tag header followed by 1024 bytes (in 32-bit mode) or 2048 |
1749 | bytes (in 64-bit mode) of data. The type is I<H> for hash or I<A> for array, |
ffed8b01 |
1750 | depending on how the DBM::Deep object was constructed. |
1751 | |
d0b74c17 |
1752 | The index works by looking at a I<MD5 Hash> of the hash key (or array index |
1753 | number). The first 8-bit char of the MD5 signature is the offset into the |
1754 | index, multipled by 4 in 32-bit mode, or 8 in 64-bit mode. The value of the |
ffed8b01 |
1755 | index element is a file offset of the next tag for the key/element in question, |
1756 | which is usually a I<Bucket List> tag (see below). |
1757 | |
ffed8b01 |
1758 | The next tag I<could> be another index, depending on how many keys/elements |
1759 | exist. See L<RE-INDEXING> below for details. |
1760 | |
1761 | =head2 BUCKET LIST |
1762 | |
d0b74c17 |
1763 | A I<Bucket List> is a collection of 16 MD5 hashes for keys/elements, plus |
1764 | file offsets to where the actual data is stored. It starts with a standard |
1765 | tag header, with type I<B>, and a data size of 320 bytes in 32-bit mode, or |
ffed8b01 |
1766 | 384 bytes in 64-bit mode. Each MD5 hash is stored in full (16 bytes), plus |
1767 | the 32-bit or 64-bit file offset for the I<Bucket> containing the actual data. |
d0b74c17 |
1768 | When the list fills up, a I<Re-Index> operation is performed (See |
ffed8b01 |
1769 | L<RE-INDEXING> below). |
1770 | |
1771 | =head2 BUCKET |
1772 | |
1773 | A I<Bucket> is a tag containing a key/value pair (in hash mode), or a |
1774 | index/value pair (in array mode). It starts with a standard tag header with |
1775 | type I<D> for scalar data (string, binary, etc.), or it could be a nested |
1776 | hash (type I<H>) or array (type I<A>). The value comes just after the tag |
1777 | header. The size reported in the tag header is only for the value, but then, |
d0b74c17 |
1778 | just after the value is another size (32-bit unsigned long) and then the plain |
1779 | key itself. Since the value is likely to be fetched more often than the plain |
ffed8b01 |
1780 | key, I figured it would be I<slightly> faster to store the value first. |
1781 | |
ffed8b01 |
1782 | If the type is I<H> (hash) or I<A> (array), the value is another I<Master Index> |
1783 | record for the nested structure, where the process begins all over again. |
1784 | |
1785 | =head2 RE-INDEXING |
1786 | |
1787 | After a I<Bucket List> grows to 16 records, its allocated space in the file is |
d0b74c17 |
1788 | exhausted. Then, when another key/element comes in, the list is converted to a |
1789 | new index record. However, this index will look at the next char in the MD5 |
1790 | hash, and arrange new Bucket List pointers accordingly. This process is called |
1791 | I<Re-Indexing>. Basically, a new index tag is created at the file EOF, and all |
1792 | 17 (16 + new one) keys/elements are removed from the old Bucket List and |
1793 | inserted into the new index. Several new Bucket Lists are created in the |
1794 | process, as a new MD5 char from the key is being examined (it is unlikely that |
ffed8b01 |
1795 | the keys will all share the same next char of their MD5s). |
1796 | |
ffed8b01 |
1797 | Because of the way the I<MD5> algorithm works, it is impossible to tell exactly |
d0b74c17 |
1798 | when the Bucket Lists will turn into indexes, but the first round tends to |
1799 | happen right around 4,000 keys. You will see a I<slight> decrease in |
1800 | performance here, but it picks back up pretty quick (see L<SPEED> above). Then |
1801 | it takes B<a lot> more keys to exhaust the next level of Bucket Lists. It's |
1802 | right around 900,000 keys. This process can continue nearly indefinitely -- |
1803 | right up until the point the I<MD5> signatures start colliding with each other, |
1804 | and this is B<EXTREMELY> rare -- like winning the lottery 5 times in a row AND |
1805 | getting struck by lightning while you are walking to cash in your tickets. |
1806 | Theoretically, since I<MD5> hashes are 128-bit values, you I<could> have up to |
1807 | 340,282,366,921,000,000,000,000,000,000,000,000,000 keys/elements (I believe |
ffed8b01 |
1808 | this is 340 unodecillion, but don't quote me). |
1809 | |
1810 | =head2 STORING |
1811 | |
d0b74c17 |
1812 | When a new key/element is stored, the key (or index number) is first run through |
1813 | I<Digest::MD5> to get a 128-bit signature (example, in hex: |
ffed8b01 |
1814 | b05783b0773d894396d475ced9d2f4f6). Then, the I<Master Index> record is checked |
37c5bcf0 |
1815 | for the first char of the signature (in this case I<b0>). If it does not exist, |
d0b74c17 |
1816 | a new I<Bucket List> is created for our key (and the next 15 future keys that |
1817 | happen to also have I<b> as their first MD5 char). The entire MD5 is written |
ffed8b01 |
1818 | to the I<Bucket List> along with the offset of the new I<Bucket> record (EOF at |
d0b74c17 |
1819 | this point, unless we are replacing an existing I<Bucket>), where the actual |
ffed8b01 |
1820 | data will be stored. |
1821 | |
1822 | =head2 FETCHING |
1823 | |
d0b74c17 |
1824 | Fetching an existing key/element involves getting a I<Digest::MD5> of the key |
1825 | (or index number), then walking along the indexes. If there are enough |
1826 | keys/elements in this DB level, there might be nested indexes, each linked to |
1827 | a particular char of the MD5. Finally, a I<Bucket List> is pointed to, which |
1828 | contains up to 16 full MD5 hashes. Each is checked for equality to the key in |
1829 | question. If we found a match, the I<Bucket> tag is loaded, where the value and |
ffed8b01 |
1830 | plain key are stored. |
1831 | |
ffed8b01 |
1832 | Fetching the plain key occurs when calling the I<first_key()> and I<next_key()> |
1833 | methods. In this process the indexes are walked systematically, and each key |
1834 | fetched in increasing MD5 order (which is why it appears random). Once the |
d0b74c17 |
1835 | I<Bucket> is found, the value is skipped and the plain key returned instead. |
1836 | B<Note:> Do not count on keys being fetched as if the MD5 hashes were |
1837 | alphabetically sorted. This only happens on an index-level -- as soon as the |
1838 | I<Bucket Lists> are hit, the keys will come out in the order they went in -- |
1839 | so it's pretty much undefined how the keys will come out -- just like Perl's |
ffed8b01 |
1840 | built-in hashes. |
1841 | |
261d1296 |
1842 | =head1 CODE COVERAGE |
1843 | |
37c5bcf0 |
1844 | We use B<Devel::Cover> to test the code coverage of our tests, below is the |
90f93b43 |
1845 | B<Devel::Cover> report on this module's test suite. |
7910cf68 |
1846 | |
386bab6c |
1847 | ----------------------------------- ------ ------ ------ ------ ------ ------ |
1848 | File stmt bran cond sub time total |
1849 | ----------------------------------- ------ ------ ------ ------ ------ ------ |
1850 | blib/lib/DBM/Deep.pm 94.9 80.6 73.0 100.0 37.9 90.4 |
1851 | blib/lib/DBM/Deep/Array.pm 100.0 91.1 100.0 100.0 18.2 98.1 |
1852 | blib/lib/DBM/Deep/Engine.pm 98.9 87.3 80.0 100.0 34.2 95.2 |
1853 | blib/lib/DBM/Deep/Hash.pm 100.0 87.5 100.0 100.0 9.7 97.3 |
1854 | Total 97.9 85.9 79.7 100.0 100.0 94.3 |
1855 | ----------------------------------- ------ ------ ------ ------ ------ ------ |
37c5bcf0 |
1856 | |
1857 | =head1 MORE INFORMATION |
1858 | |
1859 | Check out the DBM::Deep Google Group at L<http://groups.google.com/group/DBM-Deep> |
1860 | or send email to L<DBM-Deep@googlegroups.com>. |
261d1296 |
1861 | |
aeeb5497 |
1862 | =head1 AUTHORS |
ffed8b01 |
1863 | |
1864 | Joseph Huckaby, L<jhuckaby@cpan.org> |
37c5bcf0 |
1865 | |
aeeb5497 |
1866 | Rob Kinyon, L<rkinyon@cpan.org> |
ffed8b01 |
1867 | |
1868 | Special thanks to Adam Sah and Rich Gaushell! You know why :-) |
1869 | |
1870 | =head1 SEE ALSO |
1871 | |
1872 | perltie(1), Tie::Hash(3), Digest::MD5(3), Fcntl(3), flock(2), lockf(3), nfs(5), |
1873 | Digest::SHA256(3), Crypt::Blowfish(3), Compress::Zlib(3) |
1874 | |
1875 | =head1 LICENSE |
1876 | |
aeeb5497 |
1877 | Copyright (c) 2002-2006 Joseph Huckaby. All Rights Reserved. |
ffed8b01 |
1878 | This is free software, you may use it and distribute it under the |
1879 | same terms as Perl itself. |
1880 | |
1881 | =cut |