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 | |
460b1067 |
32 | use 5.6.0; |
33 | |
ffed8b01 |
34 | use strict; |
460b1067 |
35 | use warnings; |
8b957036 |
36 | |
596e9574 |
37 | use Fcntl qw( :DEFAULT :flock :seek ); |
ffed8b01 |
38 | use Digest::MD5 (); |
39 | use Scalar::Util (); |
ffed8b01 |
40 | |
95967a5e |
41 | use DBM::Deep::Engine; |
460b1067 |
42 | use DBM::Deep::File; |
95967a5e |
43 | |
596e9574 |
44 | use vars qw( $VERSION ); |
3a7a0dce |
45 | $VERSION = q(0.99_01); |
ffed8b01 |
46 | |
ffed8b01 |
47 | ## |
48 | # Setup constants for users to pass to new() |
49 | ## |
e06824f8 |
50 | sub TYPE_HASH () { DBM::Deep::Engine->SIG_HASH } |
51 | sub TYPE_ARRAY () { DBM::Deep::Engine->SIG_ARRAY } |
ffed8b01 |
52 | |
0ca7ea98 |
53 | sub _get_args { |
54 | my $proto = shift; |
55 | |
56 | my $args; |
57 | if (scalar(@_) > 1) { |
58 | if ( @_ % 2 ) { |
59 | $proto->_throw_error( "Odd number of parameters to " . (caller(1))[2] ); |
60 | } |
61 | $args = {@_}; |
62 | } |
d0b74c17 |
63 | elsif ( ref $_[0] ) { |
4d35d856 |
64 | unless ( eval { local $SIG{'__DIE__'}; %{$_[0]} || 1 } ) { |
0ca7ea98 |
65 | $proto->_throw_error( "Not a hashref in args to " . (caller(1))[2] ); |
66 | } |
67 | $args = $_[0]; |
68 | } |
d0b74c17 |
69 | else { |
0ca7ea98 |
70 | $args = { file => shift }; |
71 | } |
72 | |
73 | return $args; |
74 | } |
75 | |
ffed8b01 |
76 | sub new { |
d0b74c17 |
77 | ## |
78 | # Class constructor method for Perl OO interface. |
79 | # Calls tie() and returns blessed reference to tied hash or array, |
80 | # providing a hybrid OO/tie interface. |
81 | ## |
82 | my $class = shift; |
83 | my $args = $class->_get_args( @_ ); |
84 | |
85 | ## |
86 | # Check if we want a tied hash or array. |
87 | ## |
88 | my $self; |
89 | if (defined($args->{type}) && $args->{type} eq TYPE_ARRAY) { |
6fe26b29 |
90 | $class = 'DBM::Deep::Array'; |
91 | require DBM::Deep::Array; |
d0b74c17 |
92 | tie @$self, $class, %$args; |
93 | } |
94 | else { |
6fe26b29 |
95 | $class = 'DBM::Deep::Hash'; |
96 | require DBM::Deep::Hash; |
d0b74c17 |
97 | tie %$self, $class, %$args; |
98 | } |
ffed8b01 |
99 | |
d0b74c17 |
100 | return bless $self, $class; |
ffed8b01 |
101 | } |
102 | |
96041a25 |
103 | # This initializer is called from the various TIE* methods. new() calls tie(), |
104 | # which allows for a single point of entry. |
0795f290 |
105 | sub _init { |
0795f290 |
106 | my $class = shift; |
994ccd8e |
107 | my ($args) = @_; |
0795f290 |
108 | |
460b1067 |
109 | $args->{fileobj} = DBM::Deep::File->new( $args ) |
110 | unless exists $args->{fileobj}; |
111 | |
112 | # locking implicitly enables autoflush |
113 | if ($args->{locking}) { $args->{autoflush} = 1; } |
114 | |
0795f290 |
115 | # These are the defaults to be optionally overridden below |
116 | my $self = bless { |
95967a5e |
117 | type => TYPE_HASH, |
fde3db1a |
118 | engine => DBM::Deep::Engine->new( $args ), |
e06824f8 |
119 | base_offset => undef, |
460b1067 |
120 | fileobj => undef, |
0795f290 |
121 | }, $class; |
8db25060 |
122 | |
fde3db1a |
123 | # Grab the parameters we want to use |
0795f290 |
124 | foreach my $param ( keys %$self ) { |
125 | next unless exists $args->{$param}; |
3e9498a1 |
126 | $self->{$param} = $args->{$param}; |
ffed8b01 |
127 | } |
d0b74c17 |
128 | |
70b55428 |
129 | $self->{engine}->setup_fh( $self ); |
0795f290 |
130 | |
131 | return $self; |
ffed8b01 |
132 | } |
133 | |
ffed8b01 |
134 | sub TIEHASH { |
6fe26b29 |
135 | shift; |
136 | require DBM::Deep::Hash; |
137 | return DBM::Deep::Hash->TIEHASH( @_ ); |
ffed8b01 |
138 | } |
139 | |
140 | sub TIEARRAY { |
6fe26b29 |
141 | shift; |
142 | require DBM::Deep::Array; |
143 | return DBM::Deep::Array->TIEARRAY( @_ ); |
ffed8b01 |
144 | } |
145 | |
cc4bef86 |
146 | #XXX Unneeded now ... |
147 | #sub DESTROY { |
148 | #} |
ffed8b01 |
149 | |
ffed8b01 |
150 | sub lock { |
d0b74c17 |
151 | ## |
152 | # If db locking is set, flock() the db file. If called multiple |
153 | # times before unlock(), then the same number of unlocks() must |
154 | # be called before the lock is released. |
155 | ## |
994ccd8e |
156 | my $self = shift->_get_self; |
157 | my ($type) = @_; |
ffed8b01 |
158 | $type = LOCK_EX unless defined $type; |
d0b74c17 |
159 | |
160 | if (!defined($self->_fh)) { return; } |
161 | |
460b1067 |
162 | if ($self->_fileobj->{locking}) { |
163 | if (!$self->_fileobj->{locked}) { |
d0b74c17 |
164 | flock($self->_fh, $type); |
165 | |
166 | # refresh end counter in case file has changed size |
118ba343 |
167 | my @stats = stat($self->_fh); |
460b1067 |
168 | $self->_fileobj->{end} = $stats[7]; |
d0b74c17 |
169 | |
170 | # double-check file inode, in case another process |
171 | # has optimize()d our file while we were waiting. |
460b1067 |
172 | if ($stats[1] != $self->_fileobj->{inode}) { |
173 | $self->_fileobj->close; |
174 | $self->_fileobj->open; |
70b55428 |
175 | $self->{engine}->setup_fh( $self ); |
d0b74c17 |
176 | flock($self->_fh, $type); # re-lock |
70b55428 |
177 | |
178 | # This may not be necessary after re-opening |
460b1067 |
179 | $self->_fileobj->{end} = (stat($self->_fh))[7]; # re-end |
d0b74c17 |
180 | } |
181 | } |
460b1067 |
182 | $self->_fileobj->{locked}++; |
b4522594 |
183 | |
184 | return 1; |
d0b74c17 |
185 | } |
b4522594 |
186 | |
187 | return; |
ffed8b01 |
188 | } |
189 | |
190 | sub unlock { |
d0b74c17 |
191 | ## |
192 | # If db locking is set, unlock the db file. See note in lock() |
193 | # regarding calling lock() multiple times. |
194 | ## |
994ccd8e |
195 | my $self = shift->_get_self; |
7f441181 |
196 | |
d0b74c17 |
197 | if (!defined($self->_fh)) { return; } |
198 | |
460b1067 |
199 | if ($self->_fileobj->{locking} && $self->_fileobj->{locked} > 0) { |
200 | $self->_fileobj->{locked}--; |
201 | if (!$self->_fileobj->{locked}) { flock($self->_fh, LOCK_UN); } |
b4522594 |
202 | |
203 | return 1; |
d0b74c17 |
204 | } |
b4522594 |
205 | |
206 | return; |
ffed8b01 |
207 | } |
208 | |
906c8e01 |
209 | sub _copy_value { |
210 | my $self = shift->_get_self; |
211 | my ($spot, $value) = @_; |
212 | |
213 | if ( !ref $value ) { |
214 | ${$spot} = $value; |
215 | } |
216 | elsif ( eval { local $SIG{__DIE__}; $value->isa( 'DBM::Deep' ) } ) { |
f9c33187 |
217 | ${$spot} = $value->_repr; |
906c8e01 |
218 | $value->_copy_node( ${$spot} ); |
219 | } |
220 | else { |
221 | my $r = Scalar::Util::reftype( $value ); |
222 | my $c = Scalar::Util::blessed( $value ); |
223 | if ( $r eq 'ARRAY' ) { |
224 | ${$spot} = [ @{$value} ]; |
225 | } |
226 | else { |
227 | ${$spot} = { %{$value} }; |
228 | } |
95bbd935 |
229 | ${$spot} = bless ${$spot}, $c |
906c8e01 |
230 | if defined $c; |
231 | } |
232 | |
233 | return 1; |
234 | } |
235 | |
261d1296 |
236 | sub _copy_node { |
f9c33187 |
237 | die "Must be implemented in a child class\n"; |
238 | } |
906c8e01 |
239 | |
f9c33187 |
240 | sub _repr { |
241 | die "Must be implemented in a child class\n"; |
ffed8b01 |
242 | } |
243 | |
244 | sub export { |
d0b74c17 |
245 | ## |
246 | # Recursively export into standard Perl hashes and arrays. |
247 | ## |
994ccd8e |
248 | my $self = shift->_get_self; |
d0b74c17 |
249 | |
f9c33187 |
250 | my $temp = $self->_repr; |
d0b74c17 |
251 | |
252 | $self->lock(); |
253 | $self->_copy_node( $temp ); |
254 | $self->unlock(); |
255 | |
256 | return $temp; |
ffed8b01 |
257 | } |
258 | |
259 | sub import { |
d0b74c17 |
260 | ## |
261 | # Recursively import Perl hash/array structure |
262 | ## |
d0b74c17 |
263 | if (!ref($_[0])) { return; } # Perl calls import() on use -- ignore |
264 | |
994ccd8e |
265 | my $self = shift->_get_self; |
266 | my ($struct) = @_; |
d0b74c17 |
267 | |
c9cec40e |
268 | # struct is not a reference, so just import based on our type |
d0b74c17 |
269 | if (!ref($struct)) { |
f9c33187 |
270 | $struct = $self->_repr( @_ ); |
d0b74c17 |
271 | } |
272 | |
f9c33187 |
273 | return $self->_import( $struct ); |
ffed8b01 |
274 | } |
275 | |
276 | sub optimize { |
d0b74c17 |
277 | ## |
278 | # Rebuild entire database into new file, then move |
279 | # it back on top of original. |
280 | ## |
994ccd8e |
281 | my $self = shift->_get_self; |
cc4bef86 |
282 | |
283 | #XXX Need to create a new test for this |
460b1067 |
284 | # if ($self->_fileobj->{links} > 1) { |
1400a48e |
285 | # $self->_throw_error("Cannot optimize: reference count is greater than 1"); |
d0b74c17 |
286 | # } |
287 | |
288 | my $db_temp = DBM::Deep->new( |
460b1067 |
289 | file => $self->_fileobj->{file} . '.tmp', |
d0b74c17 |
290 | type => $self->_type |
291 | ); |
d0b74c17 |
292 | |
293 | $self->lock(); |
294 | $self->_copy_node( $db_temp ); |
295 | undef $db_temp; |
296 | |
297 | ## |
298 | # Attempt to copy user, group and permissions over to new file |
299 | ## |
300 | my @stats = stat($self->_fh); |
301 | my $perms = $stats[2] & 07777; |
302 | my $uid = $stats[4]; |
303 | my $gid = $stats[5]; |
460b1067 |
304 | chown( $uid, $gid, $self->_fileobj->{file} . '.tmp' ); |
305 | chmod( $perms, $self->_fileobj->{file} . '.tmp' ); |
d0b74c17 |
306 | |
ffed8b01 |
307 | # q.v. perlport for more information on this variable |
90f93b43 |
308 | if ( $^O eq 'MSWin32' || $^O eq 'cygwin' ) { |
d0b74c17 |
309 | ## |
310 | # Potential race condition when optmizing on Win32 with locking. |
311 | # The Windows filesystem requires that the filehandle be closed |
312 | # before it is overwritten with rename(). This could be redone |
313 | # with a soft copy. |
314 | ## |
315 | $self->unlock(); |
460b1067 |
316 | $self->_fileobj->close; |
d0b74c17 |
317 | } |
318 | |
460b1067 |
319 | if (!rename $self->_fileobj->{file} . '.tmp', $self->_fileobj->{file}) { |
320 | unlink $self->_fileobj->{file} . '.tmp'; |
d0b74c17 |
321 | $self->unlock(); |
1400a48e |
322 | $self->_throw_error("Optimize failed: Cannot copy temp file over original: $!"); |
d0b74c17 |
323 | } |
324 | |
325 | $self->unlock(); |
460b1067 |
326 | $self->_fileobj->close; |
327 | $self->_fileobj->open; |
70b55428 |
328 | $self->{engine}->setup_fh( $self ); |
329 | |
d0b74c17 |
330 | return 1; |
ffed8b01 |
331 | } |
332 | |
333 | sub clone { |
d0b74c17 |
334 | ## |
335 | # Make copy of object and return |
336 | ## |
994ccd8e |
337 | my $self = shift->_get_self; |
d0b74c17 |
338 | |
339 | return DBM::Deep->new( |
340 | type => $self->_type, |
341 | base_offset => $self->_base_offset, |
460b1067 |
342 | fileobj => $self->_fileobj, |
d0b74c17 |
343 | ); |
ffed8b01 |
344 | } |
345 | |
346 | { |
347 | my %is_legal_filter = map { |
348 | $_ => ~~1, |
349 | } qw( |
350 | store_key store_value |
351 | fetch_key fetch_value |
352 | ); |
353 | |
354 | sub set_filter { |
355 | ## |
356 | # Setup filter function for storing or fetching the key or value |
357 | ## |
994ccd8e |
358 | my $self = shift->_get_self; |
359 | my $type = lc shift; |
360 | my $func = shift; |
d0b74c17 |
361 | |
ffed8b01 |
362 | if ( $is_legal_filter{$type} ) { |
460b1067 |
363 | $self->_fileobj->{"filter_$type"} = $func; |
ffed8b01 |
364 | return 1; |
365 | } |
366 | |
367 | return; |
368 | } |
369 | } |
370 | |
fee0243f |
371 | sub begin_work { |
372 | my $self = shift->_get_self; |
28394a1a |
373 | $self->_fileobj->begin_transaction; |
374 | return 1; |
fee0243f |
375 | } |
376 | |
377 | sub rollback { |
378 | my $self = shift->_get_self; |
28394a1a |
379 | $self->_fileobj->end_transaction; |
380 | return 1; |
fee0243f |
381 | } |
382 | |
383 | #sub commit { |
384 | # my $self = shift->_get_self; |
385 | #} |
386 | |
ffed8b01 |
387 | ## |
388 | # Accessor methods |
389 | ## |
390 | |
460b1067 |
391 | sub _fileobj { |
d0b74c17 |
392 | ## |
393 | # Get access to the root structure |
394 | ## |
2ac02042 |
395 | my $self = $_[0]->_get_self; |
460b1067 |
396 | return $self->{fileobj}; |
ffed8b01 |
397 | } |
398 | |
4d35d856 |
399 | sub _type { |
d0b74c17 |
400 | ## |
401 | # Get type of current node (TYPE_HASH or TYPE_ARRAY) |
402 | ## |
2ac02042 |
403 | my $self = $_[0]->_get_self; |
d0b74c17 |
404 | return $self->{type}; |
ffed8b01 |
405 | } |
406 | |
4d35d856 |
407 | sub _base_offset { |
d0b74c17 |
408 | ## |
409 | # Get base_offset of current node (TYPE_HASH or TYPE_ARRAY) |
410 | ## |
2ac02042 |
411 | my $self = $_[0]->_get_self; |
d0b74c17 |
412 | return $self->{base_offset}; |
ffed8b01 |
413 | } |
414 | |
994ccd8e |
415 | sub _fh { |
416 | ## |
417 | # Get access to the raw fh |
418 | ## |
419 | my $self = $_[0]->_get_self; |
460b1067 |
420 | return $self->_fileobj->{fh}; |
994ccd8e |
421 | } |
422 | |
ffed8b01 |
423 | ## |
424 | # Utility methods |
425 | ## |
426 | |
261d1296 |
427 | sub _throw_error { |
95967a5e |
428 | die "DBM::Deep: $_[1]\n"; |
ffed8b01 |
429 | } |
430 | |
acd4faf2 |
431 | sub _is_writable { |
432 | my $fh = shift; |
433 | (O_WRONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0); |
434 | } |
435 | |
9be51a89 |
436 | #sub _is_readable { |
437 | # my $fh = shift; |
438 | # (O_RDONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0); |
439 | #} |
acd4faf2 |
440 | |
ffed8b01 |
441 | sub STORE { |
d0b74c17 |
442 | ## |
443 | # Store single hash key/value or array element in database. |
444 | ## |
445 | my $self = shift->_get_self; |
446 | my ($key, $value) = @_; |
81d3d316 |
447 | |
9e4f83a0 |
448 | if ( $^O ne 'MSWin32' && !_is_writable( $self->_fh ) ) { |
acd4faf2 |
449 | $self->_throw_error( 'Cannot write to a readonly filehandle' ); |
450 | } |
d0b74c17 |
451 | |
452 | ## |
453 | # Request exclusive lock for writing |
454 | ## |
455 | $self->lock( LOCK_EX ); |
456 | |
457 | my $md5 = $self->{engine}{digest}->($key); |
458 | |
e96daec8 |
459 | my $tag = $self->{engine}->find_bucket_list( $self->_base_offset, $md5, { create => 1 } ); |
d0b74c17 |
460 | |
461 | # User may be storing a hash, in which case we do not want it run |
462 | # through the filtering system |
460b1067 |
463 | if ( !ref($value) && $self->_fileobj->{filter_store_value} ) { |
464 | $value = $self->_fileobj->{filter_store_value}->( $value ); |
d0b74c17 |
465 | } |
466 | |
467 | ## |
468 | # Add key/value to bucket list |
469 | ## |
e96daec8 |
470 | my $result = $self->{engine}->add_bucket( $tag, $md5, $key, $value ); |
d0b74c17 |
471 | |
472 | $self->unlock(); |
473 | |
474 | return $result; |
ffed8b01 |
475 | } |
476 | |
477 | sub FETCH { |
d0b74c17 |
478 | ## |
479 | # Fetch single value or element given plain key or array index |
480 | ## |
cb79ec85 |
481 | my $self = shift->_get_self; |
e06824f8 |
482 | my ($key) = @_; |
ffed8b01 |
483 | |
d0b74c17 |
484 | my $md5 = $self->{engine}{digest}->($key); |
485 | |
486 | ## |
487 | # Request shared lock for reading |
488 | ## |
489 | $self->lock( LOCK_SH ); |
490 | |
e96daec8 |
491 | my $tag = $self->{engine}->find_bucket_list( $self->_base_offset, $md5 ); |
d0b74c17 |
492 | if (!$tag) { |
493 | $self->unlock(); |
494 | return; |
495 | } |
496 | |
497 | ## |
498 | # Get value from bucket list |
499 | ## |
e96daec8 |
500 | my $result = $self->{engine}->get_bucket_value( $tag, $md5 ); |
d0b74c17 |
501 | |
502 | $self->unlock(); |
503 | |
a86430bd |
504 | # Filters only apply to scalar values, so the ref check is making |
505 | # sure the fetched bucket is a scalar, not a child hash or array. |
460b1067 |
506 | return ($result && !ref($result) && $self->_fileobj->{filter_fetch_value}) |
507 | ? $self->_fileobj->{filter_fetch_value}->($result) |
cb79ec85 |
508 | : $result; |
ffed8b01 |
509 | } |
510 | |
511 | sub DELETE { |
d0b74c17 |
512 | ## |
513 | # Delete single key/value pair or element given plain key or array index |
514 | ## |
2ac02042 |
515 | my $self = $_[0]->_get_self; |
d0b74c17 |
516 | my $key = $_[1]; |
517 | |
9e4f83a0 |
518 | if ( $^O ne 'MSWin32' && !_is_writable( $self->_fh ) ) { |
a86430bd |
519 | $self->_throw_error( 'Cannot write to a readonly filehandle' ); |
520 | } |
d0b74c17 |
521 | |
522 | ## |
523 | # Request exclusive lock for writing |
524 | ## |
525 | $self->lock( LOCK_EX ); |
526 | |
a86430bd |
527 | my $md5 = $self->{engine}{digest}->($key); |
528 | |
e96daec8 |
529 | my $tag = $self->{engine}->find_bucket_list( $self->_base_offset, $md5 ); |
d0b74c17 |
530 | if (!$tag) { |
531 | $self->unlock(); |
532 | return; |
533 | } |
534 | |
535 | ## |
536 | # Delete bucket |
537 | ## |
e96daec8 |
538 | my $value = $self->{engine}->get_bucket_value( $tag, $md5 ); |
a86430bd |
539 | |
460b1067 |
540 | if (defined $value && !ref($value) && $self->_fileobj->{filter_fetch_value}) { |
541 | $value = $self->_fileobj->{filter_fetch_value}->($value); |
3b6a5056 |
542 | } |
543 | |
e96daec8 |
544 | my $result = $self->{engine}->delete_bucket( $tag, $md5 ); |
d0b74c17 |
545 | |
546 | ## |
547 | # If this object is an array and the key deleted was on the end of the stack, |
548 | # decrement the length variable. |
549 | ## |
550 | |
551 | $self->unlock(); |
552 | |
553 | return $value; |
ffed8b01 |
554 | } |
555 | |
556 | sub EXISTS { |
d0b74c17 |
557 | ## |
558 | # Check if a single key or element exists given plain key or array index |
559 | ## |
2ac02042 |
560 | my $self = $_[0]->_get_self; |
d0b74c17 |
561 | my $key = $_[1]; |
562 | |
563 | my $md5 = $self->{engine}{digest}->($key); |
564 | |
565 | ## |
566 | # Request shared lock for reading |
567 | ## |
568 | $self->lock( LOCK_SH ); |
569 | |
e96daec8 |
570 | my $tag = $self->{engine}->find_bucket_list( $self->_base_offset, $md5 ); |
d0b74c17 |
571 | if (!$tag) { |
572 | $self->unlock(); |
573 | |
574 | ## |
575 | # For some reason, the built-in exists() function returns '' for false |
576 | ## |
577 | return ''; |
578 | } |
579 | |
580 | ## |
581 | # Check if bucket exists and return 1 or '' |
582 | ## |
e96daec8 |
583 | my $result = $self->{engine}->bucket_exists( $tag, $md5 ) || ''; |
d0b74c17 |
584 | |
585 | $self->unlock(); |
586 | |
587 | return $result; |
ffed8b01 |
588 | } |
589 | |
590 | sub CLEAR { |
d0b74c17 |
591 | ## |
592 | # Clear all keys from hash, or all elements from array. |
593 | ## |
2ac02042 |
594 | my $self = $_[0]->_get_self; |
ffed8b01 |
595 | |
9e4f83a0 |
596 | if ( $^O ne 'MSWin32' && !_is_writable( $self->_fh ) ) { |
a86430bd |
597 | $self->_throw_error( 'Cannot write to a readonly filehandle' ); |
598 | } |
599 | |
d0b74c17 |
600 | ## |
601 | # Request exclusive lock for writing |
602 | ## |
603 | $self->lock( LOCK_EX ); |
604 | |
4d35d856 |
605 | my $fh = $self->_fh; |
629df3a3 |
606 | |
460b1067 |
607 | seek($fh, $self->_base_offset + $self->_fileobj->{file_offset}, SEEK_SET); |
d0b74c17 |
608 | if (eof $fh) { |
609 | $self->unlock(); |
610 | return; |
611 | } |
612 | |
f9c33187 |
613 | #XXX This needs updating to use _release_space |
9e4f83a0 |
614 | $self->{engine}->write_tag( |
e96daec8 |
615 | $self->_base_offset, $self->_type, |
f37c15ab |
616 | chr(0)x$self->{engine}{index_size}, |
2603d86e |
617 | ); |
d0b74c17 |
618 | |
619 | $self->unlock(); |
620 | |
621 | return 1; |
ffed8b01 |
622 | } |
623 | |
ffed8b01 |
624 | ## |
625 | # Public method aliases |
626 | ## |
7f441181 |
627 | sub put { (shift)->STORE( @_ ) } |
628 | sub store { (shift)->STORE( @_ ) } |
629 | sub get { (shift)->FETCH( @_ ) } |
630 | sub fetch { (shift)->FETCH( @_ ) } |
baa27ab6 |
631 | sub delete { (shift)->DELETE( @_ ) } |
632 | sub exists { (shift)->EXISTS( @_ ) } |
633 | sub clear { (shift)->CLEAR( @_ ) } |
ffed8b01 |
634 | |
635 | 1; |
ffed8b01 |
636 | __END__ |
637 | |
638 | =head1 NAME |
639 | |
640 | DBM::Deep - A pure perl multi-level hash/array DBM |
641 | |
642 | =head1 SYNOPSIS |
643 | |
644 | use DBM::Deep; |
645 | my $db = DBM::Deep->new( "foo.db" ); |
d0b74c17 |
646 | |
ffed8b01 |
647 | $db->{key} = 'value'; # tie() style |
648 | print $db->{key}; |
d0b74c17 |
649 | |
cbaa107d |
650 | $db->put('key' => 'value'); # OO style |
ffed8b01 |
651 | print $db->get('key'); |
d0b74c17 |
652 | |
ffed8b01 |
653 | # true multi-level support |
654 | $db->{my_complex} = [ |
d0b74c17 |
655 | 'hello', { perl => 'rules' }, |
656 | 42, 99, |
90f93b43 |
657 | ]; |
ffed8b01 |
658 | |
659 | =head1 DESCRIPTION |
660 | |
d0b74c17 |
661 | A unique flat-file database module, written in pure perl. True |
662 | multi-level hash/array support (unlike MLDBM, which is faked), hybrid |
663 | OO / tie() interface, cross-platform FTPable files, and quite fast. Can |
664 | handle millions of keys and unlimited hash levels without significant |
665 | slow-down. Written from the ground-up in pure perl -- this is NOT a |
666 | wrapper around a C-based DBM. Out-of-the-box compatibility with Unix, |
ffed8b01 |
667 | Mac OS X and Windows. |
668 | |
8db25060 |
669 | =head1 VERSION DIFFERENCES |
670 | |
671 | B<NOTE>: 0.99_01 and above have significant file format differences from 0.98 and |
672 | before. While attempts have been made to be backwards compatible, no guarantees. |
673 | |
ffed8b01 |
674 | =head1 INSTALLATION |
675 | |
90f93b43 |
676 | Hopefully you are using Perl's excellent CPAN module, which will download |
d0b74c17 |
677 | and install the module for you. If not, get the tarball, and run these |
ffed8b01 |
678 | commands: |
679 | |
d0b74c17 |
680 | tar zxf DBM-Deep-* |
681 | cd DBM-Deep-* |
682 | perl Makefile.PL |
683 | make |
684 | make test |
685 | make install |
ffed8b01 |
686 | |
687 | =head1 SETUP |
688 | |
d0b74c17 |
689 | Construction can be done OO-style (which is the recommended way), or using |
ffed8b01 |
690 | Perl's tie() function. Both are examined here. |
691 | |
692 | =head2 OO CONSTRUCTION |
693 | |
694 | The recommended way to construct a DBM::Deep object is to use the new() |
695 | method, which gets you a blessed, tied hash or array reference. |
696 | |
d0b74c17 |
697 | my $db = DBM::Deep->new( "foo.db" ); |
ffed8b01 |
698 | |
699 | This opens a new database handle, mapped to the file "foo.db". If this |
d0b74c17 |
700 | file does not exist, it will automatically be created. DB files are |
ffed8b01 |
701 | opened in "r+" (read/write) mode, and the type of object returned is a |
702 | hash, unless otherwise specified (see L<OPTIONS> below). |
703 | |
ffed8b01 |
704 | You can pass a number of options to the constructor to specify things like |
705 | locking, autoflush, etc. This is done by passing an inline hash: |
706 | |
d0b74c17 |
707 | my $db = DBM::Deep->new( |
708 | file => "foo.db", |
709 | locking => 1, |
710 | autoflush => 1 |
711 | ); |
ffed8b01 |
712 | |
713 | Notice that the filename is now specified I<inside> the hash with |
d0b74c17 |
714 | the "file" parameter, as opposed to being the sole argument to the |
ffed8b01 |
715 | constructor. This is required if any options are specified. |
716 | See L<OPTIONS> below for the complete list. |
717 | |
718 | |
719 | |
720 | You can also start with an array instead of a hash. For this, you must |
721 | specify the C<type> parameter: |
722 | |
d0b74c17 |
723 | my $db = DBM::Deep->new( |
724 | file => "foo.db", |
725 | type => DBM::Deep->TYPE_ARRAY |
726 | ); |
ffed8b01 |
727 | |
728 | B<Note:> Specifing the C<type> parameter only takes effect when beginning |
729 | a new DB file. If you create a DBM::Deep object with an existing file, the |
90f93b43 |
730 | C<type> will be loaded from the file header, and an error will be thrown if |
731 | the wrong type is passed in. |
ffed8b01 |
732 | |
733 | =head2 TIE CONSTRUCTION |
734 | |
90f93b43 |
735 | Alternately, you can create a DBM::Deep handle by using Perl's built-in |
736 | tie() function. The object returned from tie() can be used to call methods, |
737 | such as lock() and unlock(), but cannot be used to assign to the DBM::Deep |
738 | file (as expected with most tie'd objects). |
ffed8b01 |
739 | |
d0b74c17 |
740 | my %hash; |
741 | my $db = tie %hash, "DBM::Deep", "foo.db"; |
742 | |
743 | my @array; |
744 | my $db = tie @array, "DBM::Deep", "bar.db"; |
ffed8b01 |
745 | |
746 | As with the OO constructor, you can replace the DB filename parameter with |
747 | a hash containing one or more options (see L<OPTIONS> just below for the |
748 | complete list). |
749 | |
d0b74c17 |
750 | tie %hash, "DBM::Deep", { |
751 | file => "foo.db", |
752 | locking => 1, |
753 | autoflush => 1 |
754 | }; |
ffed8b01 |
755 | |
756 | =head2 OPTIONS |
757 | |
758 | There are a number of options that can be passed in when constructing your |
759 | DBM::Deep objects. These apply to both the OO- and tie- based approaches. |
760 | |
761 | =over |
762 | |
763 | =item * file |
764 | |
765 | Filename of the DB file to link the handle to. You can pass a full absolute |
d0b74c17 |
766 | filesystem path, partial path, or a plain filename if the file is in the |
714618f0 |
767 | current working directory. This is a required parameter (though q.v. fh). |
768 | |
769 | =item * fh |
770 | |
771 | If you want, you can pass in the fh instead of the file. This is most useful for doing |
772 | something like: |
773 | |
774 | my $db = DBM::Deep->new( { fh => \*DATA } ); |
775 | |
776 | You are responsible for making sure that the fh has been opened appropriately for your |
777 | needs. If you open it read-only and attempt to write, an exception will be thrown. If you |
778 | open it write-only or append-only, an exception will be thrown immediately as DBM::Deep |
779 | needs to read from the fh. |
780 | |
781 | =item * file_offset |
782 | |
783 | This is the offset within the file that the DBM::Deep db starts. Most of the time, you will |
784 | not need to set this. However, it's there if you want it. |
785 | |
786 | If you pass in fh and do not set this, it will be set appropriately. |
ffed8b01 |
787 | |
ffed8b01 |
788 | =item * type |
789 | |
790 | This parameter specifies what type of object to create, a hash or array. Use |
791 | one of these two constants: C<DBM::Deep-E<gt>TYPE_HASH> or C<DBM::Deep-E<gt>TYPE_ARRAY>. |
d0b74c17 |
792 | This only takes effect when beginning a new file. This is an optional |
ffed8b01 |
793 | parameter, and defaults to C<DBM::Deep-E<gt>TYPE_HASH>. |
794 | |
795 | =item * locking |
796 | |
797 | Specifies whether locking is to be enabled. DBM::Deep uses Perl's Fnctl flock() |
798 | function to lock the database in exclusive mode for writes, and shared mode for |
d0b74c17 |
799 | reads. Pass any true value to enable. This affects the base DB handle I<and |
800 | any child hashes or arrays> that use the same DB file. This is an optional |
ffed8b01 |
801 | parameter, and defaults to 0 (disabled). See L<LOCKING> below for more. |
802 | |
803 | =item * autoflush |
804 | |
d0b74c17 |
805 | Specifies whether autoflush is to be enabled on the underlying filehandle. |
806 | This obviously slows down write operations, but is required if you may have |
807 | multiple processes accessing the same DB file (also consider enable I<locking>). |
808 | Pass any true value to enable. This is an optional parameter, and defaults to 0 |
ffed8b01 |
809 | (disabled). |
810 | |
811 | =item * autobless |
812 | |
813 | If I<autobless> mode is enabled, DBM::Deep will preserve blessed hashes, and |
814 | restore them when fetched. This is an B<experimental> feature, and does have |
815 | side-effects. Basically, when hashes are re-blessed into their original |
816 | classes, they are no longer blessed into the DBM::Deep class! So you won't be |
817 | able to call any DBM::Deep methods on them. You have been warned. |
818 | This is an optional parameter, and defaults to 0 (disabled). |
819 | |
820 | =item * filter_* |
821 | |
822 | See L<FILTERS> below. |
823 | |
ffed8b01 |
824 | =back |
825 | |
826 | =head1 TIE INTERFACE |
827 | |
828 | With DBM::Deep you can access your databases using Perl's standard hash/array |
90f93b43 |
829 | syntax. Because all DBM::Deep objects are I<tied> to hashes or arrays, you can |
830 | treat them as such. DBM::Deep will intercept all reads/writes and direct them |
831 | to the right place -- the DB file. This has nothing to do with the |
832 | L<TIE CONSTRUCTION> section above. This simply tells you how to use DBM::Deep |
833 | using regular hashes and arrays, rather than calling functions like C<get()> |
834 | and C<put()> (although those work too). It is entirely up to you how to want |
835 | to access your databases. |
ffed8b01 |
836 | |
837 | =head2 HASHES |
838 | |
839 | You can treat any DBM::Deep object like a normal Perl hash reference. Add keys, |
840 | or even nested hashes (or arrays) using standard Perl syntax: |
841 | |
d0b74c17 |
842 | my $db = DBM::Deep->new( "foo.db" ); |
843 | |
844 | $db->{mykey} = "myvalue"; |
845 | $db->{myhash} = {}; |
846 | $db->{myhash}->{subkey} = "subvalue"; |
ffed8b01 |
847 | |
d0b74c17 |
848 | print $db->{myhash}->{subkey} . "\n"; |
ffed8b01 |
849 | |
850 | You can even step through hash keys using the normal Perl C<keys()> function: |
851 | |
d0b74c17 |
852 | foreach my $key (keys %$db) { |
853 | print "$key: " . $db->{$key} . "\n"; |
854 | } |
ffed8b01 |
855 | |
856 | Remember that Perl's C<keys()> function extracts I<every> key from the hash and |
d0b74c17 |
857 | pushes them onto an array, all before the loop even begins. If you have an |
858 | extra large hash, this may exhaust Perl's memory. Instead, consider using |
859 | Perl's C<each()> function, which pulls keys/values one at a time, using very |
ffed8b01 |
860 | little memory: |
861 | |
d0b74c17 |
862 | while (my ($key, $value) = each %$db) { |
863 | print "$key: $value\n"; |
864 | } |
ffed8b01 |
865 | |
866 | Please note that when using C<each()>, you should always pass a direct |
867 | hash reference, not a lookup. Meaning, you should B<never> do this: |
868 | |
d0b74c17 |
869 | # NEVER DO THIS |
870 | while (my ($key, $value) = each %{$db->{foo}}) { # BAD |
ffed8b01 |
871 | |
872 | This causes an infinite loop, because for each iteration, Perl is calling |
873 | FETCH() on the $db handle, resulting in a "new" hash for foo every time, so |
d0b74c17 |
874 | it effectively keeps returning the first key over and over again. Instead, |
ffed8b01 |
875 | assign a temporary variable to C<$db->{foo}>, then pass that to each(). |
876 | |
877 | =head2 ARRAYS |
878 | |
879 | As with hashes, you can treat any DBM::Deep object like a normal Perl array |
d0b74c17 |
880 | reference. This includes inserting, removing and manipulating elements, |
ffed8b01 |
881 | and the C<push()>, C<pop()>, C<shift()>, C<unshift()> and C<splice()> functions. |
d0b74c17 |
882 | The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>, |
ffed8b01 |
883 | or simply be a nested array reference inside a hash. Example: |
884 | |
d0b74c17 |
885 | my $db = DBM::Deep->new( |
886 | file => "foo-array.db", |
887 | type => DBM::Deep->TYPE_ARRAY |
888 | ); |
889 | |
890 | $db->[0] = "foo"; |
891 | push @$db, "bar", "baz"; |
892 | unshift @$db, "bah"; |
893 | |
894 | my $last_elem = pop @$db; # baz |
895 | my $first_elem = shift @$db; # bah |
896 | my $second_elem = $db->[1]; # bar |
897 | |
898 | my $num_elements = scalar @$db; |
ffed8b01 |
899 | |
900 | =head1 OO INTERFACE |
901 | |
902 | In addition to the I<tie()> interface, you can also use a standard OO interface |
903 | to manipulate all aspects of DBM::Deep databases. Each type of object (hash or |
d0b74c17 |
904 | array) has its own methods, but both types share the following common methods: |
ffed8b01 |
905 | C<put()>, C<get()>, C<exists()>, C<delete()> and C<clear()>. |
906 | |
907 | =over |
908 | |
4d35d856 |
909 | =item * new() / clone() |
910 | |
911 | These are the constructor and copy-functions. |
912 | |
90f93b43 |
913 | =item * put() / store() |
ffed8b01 |
914 | |
915 | Stores a new hash key/value pair, or sets an array element value. Takes two |
916 | arguments, the hash key or array index, and the new value. The value can be |
917 | a scalar, hash ref or array ref. Returns true on success, false on failure. |
918 | |
d0b74c17 |
919 | $db->put("foo", "bar"); # for hashes |
920 | $db->put(1, "bar"); # for arrays |
ffed8b01 |
921 | |
90f93b43 |
922 | =item * get() / fetch() |
ffed8b01 |
923 | |
924 | Fetches the value of a hash key or array element. Takes one argument: the hash |
d0b74c17 |
925 | key or array index. Returns a scalar, hash ref or array ref, depending on the |
ffed8b01 |
926 | data type stored. |
927 | |
d0b74c17 |
928 | my $value = $db->get("foo"); # for hashes |
929 | my $value = $db->get(1); # for arrays |
ffed8b01 |
930 | |
931 | =item * exists() |
932 | |
d0b74c17 |
933 | Checks if a hash key or array index exists. Takes one argument: the hash key |
ffed8b01 |
934 | or array index. Returns true if it exists, false if not. |
935 | |
d0b74c17 |
936 | if ($db->exists("foo")) { print "yay!\n"; } # for hashes |
937 | if ($db->exists(1)) { print "yay!\n"; } # for arrays |
ffed8b01 |
938 | |
939 | =item * delete() |
940 | |
941 | Deletes one hash key/value pair or array element. Takes one argument: the hash |
942 | key or array index. Returns true on success, false if not found. For arrays, |
943 | the remaining elements located after the deleted element are NOT moved over. |
944 | The deleted element is essentially just undefined, which is exactly how Perl's |
d0b74c17 |
945 | internal arrays work. Please note that the space occupied by the deleted |
946 | key/value or element is B<not> reused again -- see L<UNUSED SPACE RECOVERY> |
ffed8b01 |
947 | below for details and workarounds. |
948 | |
d0b74c17 |
949 | $db->delete("foo"); # for hashes |
950 | $db->delete(1); # for arrays |
ffed8b01 |
951 | |
952 | =item * clear() |
953 | |
d0b74c17 |
954 | Deletes B<all> hash keys or array elements. Takes no arguments. No return |
955 | value. Please note that the space occupied by the deleted keys/values or |
956 | elements is B<not> reused again -- see L<UNUSED SPACE RECOVERY> below for |
ffed8b01 |
957 | details and workarounds. |
958 | |
d0b74c17 |
959 | $db->clear(); # hashes or arrays |
ffed8b01 |
960 | |
4d35d856 |
961 | =item * lock() / unlock() |
962 | |
963 | q.v. Locking. |
964 | |
965 | =item * optimize() |
966 | |
967 | Recover lost disk space. |
968 | |
969 | =item * import() / export() |
970 | |
971 | Data going in and out. |
972 | |
ffed8b01 |
973 | =back |
974 | |
975 | =head2 HASHES |
976 | |
d0b74c17 |
977 | For hashes, DBM::Deep supports all the common methods described above, and the |
ffed8b01 |
978 | following additional methods: C<first_key()> and C<next_key()>. |
979 | |
980 | =over |
981 | |
982 | =item * first_key() |
983 | |
d0b74c17 |
984 | Returns the "first" key in the hash. As with built-in Perl hashes, keys are |
985 | fetched in an undefined order (which appears random). Takes no arguments, |
ffed8b01 |
986 | returns the key as a scalar value. |
987 | |
d0b74c17 |
988 | my $key = $db->first_key(); |
ffed8b01 |
989 | |
990 | =item * next_key() |
991 | |
992 | Returns the "next" key in the hash, given the previous one as the sole argument. |
993 | Returns undef if there are no more keys to be fetched. |
994 | |
d0b74c17 |
995 | $key = $db->next_key($key); |
ffed8b01 |
996 | |
997 | =back |
998 | |
999 | Here are some examples of using hashes: |
1000 | |
d0b74c17 |
1001 | my $db = DBM::Deep->new( "foo.db" ); |
1002 | |
1003 | $db->put("foo", "bar"); |
1004 | print "foo: " . $db->get("foo") . "\n"; |
1005 | |
1006 | $db->put("baz", {}); # new child hash ref |
1007 | $db->get("baz")->put("buz", "biz"); |
1008 | print "buz: " . $db->get("baz")->get("buz") . "\n"; |
1009 | |
1010 | my $key = $db->first_key(); |
1011 | while ($key) { |
1012 | print "$key: " . $db->get($key) . "\n"; |
1013 | $key = $db->next_key($key); |
1014 | } |
1015 | |
1016 | if ($db->exists("foo")) { $db->delete("foo"); } |
ffed8b01 |
1017 | |
1018 | =head2 ARRAYS |
1019 | |
d0b74c17 |
1020 | For arrays, DBM::Deep supports all the common methods described above, and the |
1021 | following additional methods: C<length()>, C<push()>, C<pop()>, C<shift()>, |
ffed8b01 |
1022 | C<unshift()> and C<splice()>. |
1023 | |
1024 | =over |
1025 | |
1026 | =item * length() |
1027 | |
1028 | Returns the number of elements in the array. Takes no arguments. |
1029 | |
d0b74c17 |
1030 | my $len = $db->length(); |
ffed8b01 |
1031 | |
1032 | =item * push() |
1033 | |
d0b74c17 |
1034 | Adds one or more elements onto the end of the array. Accepts scalars, hash |
ffed8b01 |
1035 | refs or array refs. No return value. |
1036 | |
d0b74c17 |
1037 | $db->push("foo", "bar", {}); |
ffed8b01 |
1038 | |
1039 | =item * pop() |
1040 | |
1041 | Fetches the last element in the array, and deletes it. Takes no arguments. |
1042 | Returns undef if array is empty. Returns the element value. |
1043 | |
d0b74c17 |
1044 | my $elem = $db->pop(); |
ffed8b01 |
1045 | |
1046 | =item * shift() |
1047 | |
d0b74c17 |
1048 | Fetches the first element in the array, deletes it, then shifts all the |
1049 | remaining elements over to take up the space. Returns the element value. This |
1050 | method is not recommended with large arrays -- see L<LARGE ARRAYS> below for |
ffed8b01 |
1051 | details. |
1052 | |
d0b74c17 |
1053 | my $elem = $db->shift(); |
ffed8b01 |
1054 | |
1055 | =item * unshift() |
1056 | |
d0b74c17 |
1057 | Inserts one or more elements onto the beginning of the array, shifting all |
1058 | existing elements over to make room. Accepts scalars, hash refs or array refs. |
1059 | No return value. This method is not recommended with large arrays -- see |
ffed8b01 |
1060 | <LARGE ARRAYS> below for details. |
1061 | |
d0b74c17 |
1062 | $db->unshift("foo", "bar", {}); |
ffed8b01 |
1063 | |
1064 | =item * splice() |
1065 | |
d0b74c17 |
1066 | Performs exactly like Perl's built-in function of the same name. See L<perldoc |
ffed8b01 |
1067 | -f splice> for usage -- it is too complicated to document here. This method is |
1068 | not recommended with large arrays -- see L<LARGE ARRAYS> below for details. |
1069 | |
1070 | =back |
1071 | |
1072 | Here are some examples of using arrays: |
1073 | |
d0b74c17 |
1074 | my $db = DBM::Deep->new( |
1075 | file => "foo.db", |
1076 | type => DBM::Deep->TYPE_ARRAY |
1077 | ); |
1078 | |
1079 | $db->push("bar", "baz"); |
1080 | $db->unshift("foo"); |
1081 | $db->put(3, "buz"); |
1082 | |
1083 | my $len = $db->length(); |
1084 | print "length: $len\n"; # 4 |
1085 | |
1086 | for (my $k=0; $k<$len; $k++) { |
1087 | print "$k: " . $db->get($k) . "\n"; |
1088 | } |
1089 | |
1090 | $db->splice(1, 2, "biz", "baf"); |
1091 | |
1092 | while (my $elem = shift @$db) { |
1093 | print "shifted: $elem\n"; |
1094 | } |
ffed8b01 |
1095 | |
1096 | =head1 LOCKING |
1097 | |
d0b74c17 |
1098 | Enable automatic file locking by passing a true value to the C<locking> |
ffed8b01 |
1099 | parameter when constructing your DBM::Deep object (see L<SETUP> above). |
1100 | |
d0b74c17 |
1101 | my $db = DBM::Deep->new( |
1102 | file => "foo.db", |
1103 | locking => 1 |
1104 | ); |
ffed8b01 |
1105 | |
d0b74c17 |
1106 | This causes DBM::Deep to C<flock()> the underlying filehandle with exclusive |
1107 | mode for writes, and shared mode for reads. This is required if you have |
1108 | multiple processes accessing the same database file, to avoid file corruption. |
1109 | Please note that C<flock()> does NOT work for files over NFS. See L<DB OVER |
ffed8b01 |
1110 | NFS> below for more. |
1111 | |
1112 | =head2 EXPLICIT LOCKING |
1113 | |
d0b74c17 |
1114 | You can explicitly lock a database, so it remains locked for multiple |
1115 | transactions. This is done by calling the C<lock()> method, and passing an |
90f93b43 |
1116 | optional lock mode argument (defaults to exclusive mode). This is particularly |
d0b74c17 |
1117 | useful for things like counters, where the current value needs to be fetched, |
ffed8b01 |
1118 | then incremented, then stored again. |
1119 | |
d0b74c17 |
1120 | $db->lock(); |
1121 | my $counter = $db->get("counter"); |
1122 | $counter++; |
1123 | $db->put("counter", $counter); |
1124 | $db->unlock(); |
1125 | |
1126 | # or... |
ffed8b01 |
1127 | |
d0b74c17 |
1128 | $db->lock(); |
1129 | $db->{counter}++; |
1130 | $db->unlock(); |
ffed8b01 |
1131 | |
1132 | You can pass C<lock()> an optional argument, which specifies which mode to use |
d0b74c17 |
1133 | (exclusive or shared). Use one of these two constants: C<DBM::Deep-E<gt>LOCK_EX> |
1134 | or C<DBM::Deep-E<gt>LOCK_SH>. These are passed directly to C<flock()>, and are the |
ffed8b01 |
1135 | same as the constants defined in Perl's C<Fcntl> module. |
1136 | |
d0b74c17 |
1137 | $db->lock( DBM::Deep->LOCK_SH ); |
1138 | # something here |
1139 | $db->unlock(); |
ffed8b01 |
1140 | |
ffed8b01 |
1141 | =head1 IMPORTING/EXPORTING |
1142 | |
1143 | You can import existing complex structures by calling the C<import()> method, |
1144 | and export an entire database into an in-memory structure using the C<export()> |
1145 | method. Both are examined here. |
1146 | |
1147 | =head2 IMPORTING |
1148 | |
1149 | Say you have an existing hash with nested hashes/arrays inside it. Instead of |
d0b74c17 |
1150 | walking the structure and adding keys/elements to the database as you go, |
1151 | simply pass a reference to the C<import()> method. This recursively adds |
ffed8b01 |
1152 | everything to an existing DBM::Deep object for you. Here is an example: |
1153 | |
d0b74c17 |
1154 | my $struct = { |
1155 | key1 => "value1", |
1156 | key2 => "value2", |
1157 | array1 => [ "elem0", "elem1", "elem2" ], |
1158 | hash1 => { |
1159 | subkey1 => "subvalue1", |
1160 | subkey2 => "subvalue2" |
1161 | } |
1162 | }; |
1163 | |
1164 | my $db = DBM::Deep->new( "foo.db" ); |
1165 | $db->import( $struct ); |
1166 | |
1167 | print $db->{key1} . "\n"; # prints "value1" |
1168 | |
1169 | This recursively imports the entire C<$struct> object into C<$db>, including |
ffed8b01 |
1170 | all nested hashes and arrays. If the DBM::Deep object contains exsiting data, |
d0b74c17 |
1171 | keys are merged with the existing ones, replacing if they already exist. |
1172 | The C<import()> method can be called on any database level (not just the base |
ffed8b01 |
1173 | level), and works with both hash and array DB types. |
1174 | |
ffed8b01 |
1175 | B<Note:> Make sure your existing structure has no circular references in it. |
1176 | These will cause an infinite loop when importing. |
1177 | |
1178 | =head2 EXPORTING |
1179 | |
d0b74c17 |
1180 | Calling the C<export()> method on an existing DBM::Deep object will return |
1181 | a reference to a new in-memory copy of the database. The export is done |
ffed8b01 |
1182 | recursively, so all nested hashes/arrays are all exported to standard Perl |
1183 | objects. Here is an example: |
1184 | |
d0b74c17 |
1185 | my $db = DBM::Deep->new( "foo.db" ); |
1186 | |
1187 | $db->{key1} = "value1"; |
1188 | $db->{key2} = "value2"; |
1189 | $db->{hash1} = {}; |
1190 | $db->{hash1}->{subkey1} = "subvalue1"; |
1191 | $db->{hash1}->{subkey2} = "subvalue2"; |
1192 | |
1193 | my $struct = $db->export(); |
1194 | |
1195 | print $struct->{key1} . "\n"; # prints "value1" |
ffed8b01 |
1196 | |
1197 | This makes a complete copy of the database in memory, and returns a reference |
d0b74c17 |
1198 | to it. The C<export()> method can be called on any database level (not just |
1199 | the base level), and works with both hash and array DB types. Be careful of |
1200 | large databases -- you can store a lot more data in a DBM::Deep object than an |
ffed8b01 |
1201 | in-memory Perl structure. |
1202 | |
ffed8b01 |
1203 | B<Note:> Make sure your database has no circular references in it. |
1204 | These will cause an infinite loop when exporting. |
1205 | |
1206 | =head1 FILTERS |
1207 | |
1208 | DBM::Deep has a number of hooks where you can specify your own Perl function |
1209 | to perform filtering on incoming or outgoing data. This is a perfect |
1210 | way to extend the engine, and implement things like real-time compression or |
d0b74c17 |
1211 | encryption. Filtering applies to the base DB level, and all child hashes / |
1212 | arrays. Filter hooks can be specified when your DBM::Deep object is first |
1213 | constructed, or by calling the C<set_filter()> method at any time. There are |
ffed8b01 |
1214 | four available filter hooks, described below: |
1215 | |
1216 | =over |
1217 | |
1218 | =item * filter_store_key |
1219 | |
d0b74c17 |
1220 | This filter is called whenever a hash key is stored. It |
ffed8b01 |
1221 | is passed the incoming key, and expected to return a transformed key. |
1222 | |
1223 | =item * filter_store_value |
1224 | |
d0b74c17 |
1225 | This filter is called whenever a hash key or array element is stored. It |
ffed8b01 |
1226 | is passed the incoming value, and expected to return a transformed value. |
1227 | |
1228 | =item * filter_fetch_key |
1229 | |
d0b74c17 |
1230 | This filter is called whenever a hash key is fetched (i.e. via |
ffed8b01 |
1231 | C<first_key()> or C<next_key()>). It is passed the transformed key, |
1232 | and expected to return the plain key. |
1233 | |
1234 | =item * filter_fetch_value |
1235 | |
d0b74c17 |
1236 | This filter is called whenever a hash key or array element is fetched. |
ffed8b01 |
1237 | It is passed the transformed value, and expected to return the plain value. |
1238 | |
1239 | =back |
1240 | |
1241 | Here are the two ways to setup a filter hook: |
1242 | |
d0b74c17 |
1243 | my $db = DBM::Deep->new( |
1244 | file => "foo.db", |
1245 | filter_store_value => \&my_filter_store, |
1246 | filter_fetch_value => \&my_filter_fetch |
1247 | ); |
1248 | |
1249 | # or... |
1250 | |
1251 | $db->set_filter( "filter_store_value", \&my_filter_store ); |
1252 | $db->set_filter( "filter_fetch_value", \&my_filter_fetch ); |
ffed8b01 |
1253 | |
1254 | Your filter function will be called only when dealing with SCALAR keys or |
1255 | values. When nested hashes and arrays are being stored/fetched, filtering |
d0b74c17 |
1256 | is bypassed. Filters are called as static functions, passed a single SCALAR |
ffed8b01 |
1257 | argument, and expected to return a single SCALAR value. If you want to |
1258 | remove a filter, set the function reference to C<undef>: |
1259 | |
d0b74c17 |
1260 | $db->set_filter( "filter_store_value", undef ); |
ffed8b01 |
1261 | |
1262 | =head2 REAL-TIME ENCRYPTION EXAMPLE |
1263 | |
d0b74c17 |
1264 | Here is a working example that uses the I<Crypt::Blowfish> module to |
ffed8b01 |
1265 | do real-time encryption / decryption of keys & values with DBM::Deep Filters. |
d0b74c17 |
1266 | Please visit L<http://search.cpan.org/search?module=Crypt::Blowfish> for more |
ffed8b01 |
1267 | on I<Crypt::Blowfish>. You'll also need the I<Crypt::CBC> module. |
1268 | |
d0b74c17 |
1269 | use DBM::Deep; |
1270 | use Crypt::Blowfish; |
1271 | use Crypt::CBC; |
1272 | |
1273 | my $cipher = Crypt::CBC->new({ |
1274 | 'key' => 'my secret key', |
1275 | 'cipher' => 'Blowfish', |
1276 | 'iv' => '$KJh#(}q', |
1277 | 'regenerate_key' => 0, |
1278 | 'padding' => 'space', |
1279 | 'prepend_iv' => 0 |
1280 | }); |
1281 | |
1282 | my $db = DBM::Deep->new( |
1283 | file => "foo-encrypt.db", |
1284 | filter_store_key => \&my_encrypt, |
1285 | filter_store_value => \&my_encrypt, |
1286 | filter_fetch_key => \&my_decrypt, |
1287 | filter_fetch_value => \&my_decrypt, |
1288 | ); |
1289 | |
1290 | $db->{key1} = "value1"; |
1291 | $db->{key2} = "value2"; |
1292 | print "key1: " . $db->{key1} . "\n"; |
1293 | print "key2: " . $db->{key2} . "\n"; |
1294 | |
1295 | undef $db; |
1296 | exit; |
1297 | |
1298 | sub my_encrypt { |
1299 | return $cipher->encrypt( $_[0] ); |
1300 | } |
1301 | sub my_decrypt { |
1302 | return $cipher->decrypt( $_[0] ); |
1303 | } |
ffed8b01 |
1304 | |
1305 | =head2 REAL-TIME COMPRESSION EXAMPLE |
1306 | |
1307 | Here is a working example that uses the I<Compress::Zlib> module to do real-time |
1308 | compression / decompression of keys & values with DBM::Deep Filters. |
d0b74c17 |
1309 | Please visit L<http://search.cpan.org/search?module=Compress::Zlib> for |
ffed8b01 |
1310 | more on I<Compress::Zlib>. |
1311 | |
d0b74c17 |
1312 | use DBM::Deep; |
1313 | use Compress::Zlib; |
1314 | |
1315 | my $db = DBM::Deep->new( |
1316 | file => "foo-compress.db", |
1317 | filter_store_key => \&my_compress, |
1318 | filter_store_value => \&my_compress, |
1319 | filter_fetch_key => \&my_decompress, |
1320 | filter_fetch_value => \&my_decompress, |
1321 | ); |
1322 | |
1323 | $db->{key1} = "value1"; |
1324 | $db->{key2} = "value2"; |
1325 | print "key1: " . $db->{key1} . "\n"; |
1326 | print "key2: " . $db->{key2} . "\n"; |
1327 | |
1328 | undef $db; |
1329 | exit; |
1330 | |
1331 | sub my_compress { |
1332 | return Compress::Zlib::memGzip( $_[0] ) ; |
1333 | } |
1334 | sub my_decompress { |
1335 | return Compress::Zlib::memGunzip( $_[0] ) ; |
1336 | } |
ffed8b01 |
1337 | |
1338 | B<Note:> Filtering of keys only applies to hashes. Array "keys" are |
1339 | actually numerical index numbers, and are not filtered. |
1340 | |
1341 | =head1 ERROR HANDLING |
1342 | |
1343 | Most DBM::Deep methods return a true value for success, and call die() on |
95967a5e |
1344 | failure. You can wrap calls in an eval block to catch the die. |
ffed8b01 |
1345 | |
d0b74c17 |
1346 | my $db = DBM::Deep->new( "foo.db" ); # create hash |
1347 | eval { $db->push("foo"); }; # ILLEGAL -- push is array-only call |
1348 | |
90f93b43 |
1349 | print $@; # prints error message |
429e4192 |
1350 | |
ffed8b01 |
1351 | =head1 LARGEFILE SUPPORT |
1352 | |
1353 | If you have a 64-bit system, and your Perl is compiled with both LARGEFILE |
1354 | and 64-bit support, you I<may> be able to create databases larger than 2 GB. |
1355 | DBM::Deep by default uses 32-bit file offset tags, but these can be changed |
044e6288 |
1356 | by specifying the 'pack_size' parameter when constructing the file. |
ffed8b01 |
1357 | |
044e6288 |
1358 | DBM::Deep->new( |
1359 | filename => $filename, |
1360 | pack_size => 'large', |
1361 | ); |
ffed8b01 |
1362 | |
d0b74c17 |
1363 | This tells DBM::Deep to pack all file offsets with 8-byte (64-bit) quad words |
1364 | instead of 32-bit longs. After setting these values your DB files have a |
ffed8b01 |
1365 | theoretical maximum size of 16 XB (exabytes). |
1366 | |
044e6288 |
1367 | You can also use C<pack_size =E<gt> 'small'> in order to use 16-bit file |
1368 | offsets. |
1369 | |
ffed8b01 |
1370 | B<Note:> Changing these values will B<NOT> work for existing database files. |
044e6288 |
1371 | Only change this for new files. Once the value has been set, it is stored in |
1372 | the file's header and cannot be changed for the life of the file. These |
1373 | parameters are per-file, meaning you can access 32-bit and 64-bit files, as |
1374 | you chose. |
ffed8b01 |
1375 | |
044e6288 |
1376 | B<Note:> We have not personally tested files larger than 2 GB -- all my |
1377 | systems have only a 32-bit Perl. However, I have received user reports that |
1378 | this does indeed work! |
ffed8b01 |
1379 | |
1380 | =head1 LOW-LEVEL ACCESS |
1381 | |
90f93b43 |
1382 | If you require low-level access to the underlying filehandle that DBM::Deep uses, |
4d35d856 |
1383 | you can call the C<_fh()> method, which returns the handle: |
ffed8b01 |
1384 | |
d0b74c17 |
1385 | my $fh = $db->_fh(); |
ffed8b01 |
1386 | |
1387 | This method can be called on the root level of the datbase, or any child |
1388 | hashes or arrays. All levels share a I<root> structure, which contains things |
90f93b43 |
1389 | like the filehandle, a reference counter, and all the options specified |
460b1067 |
1390 | when you created the object. You can get access to this file object by |
1391 | calling the C<_fileobj()> method. |
ffed8b01 |
1392 | |
460b1067 |
1393 | my $file_obj = $db->_fileobj(); |
ffed8b01 |
1394 | |
1395 | This is useful for changing options after the object has already been created, |
f5be9b03 |
1396 | such as enabling/disabling locking. You can also store your own temporary user |
1397 | data in this structure (be wary of name collision), which is then accessible from |
1398 | any child hash or array. |
ffed8b01 |
1399 | |
1400 | =head1 CUSTOM DIGEST ALGORITHM |
1401 | |
1402 | DBM::Deep by default uses the I<Message Digest 5> (MD5) algorithm for hashing |
1403 | keys. However you can override this, and use another algorithm (such as SHA-256) |
d0b74c17 |
1404 | or even write your own. But please note that DBM::Deep currently expects zero |
044e6288 |
1405 | collisions, so your algorithm has to be I<perfect>, so to speak. Collision |
1406 | detection may be introduced in a later version. |
ffed8b01 |
1407 | |
044e6288 |
1408 | You can specify a custom digest algorithm by passing it into the parameter |
1409 | list for new(), passing a reference to a subroutine as the 'digest' parameter, |
1410 | and the length of the algorithm's hashes (in bytes) as the 'hash_size' |
1411 | parameter. Here is a working example that uses a 256-bit hash from the |
d0b74c17 |
1412 | I<Digest::SHA256> module. Please see |
044e6288 |
1413 | L<http://search.cpan.org/search?module=Digest::SHA256> for more information. |
ffed8b01 |
1414 | |
d0b74c17 |
1415 | use DBM::Deep; |
1416 | use Digest::SHA256; |
1417 | |
1418 | my $context = Digest::SHA256::new(256); |
1419 | |
044e6288 |
1420 | my $db = DBM::Deep->new( |
1421 | filename => "foo-sha.db", |
1422 | digest => \&my_digest, |
1423 | hash_size => 32, |
1424 | ); |
d0b74c17 |
1425 | |
1426 | $db->{key1} = "value1"; |
1427 | $db->{key2} = "value2"; |
1428 | print "key1: " . $db->{key1} . "\n"; |
1429 | print "key2: " . $db->{key2} . "\n"; |
1430 | |
1431 | undef $db; |
1432 | exit; |
1433 | |
1434 | sub my_digest { |
1435 | return substr( $context->hash($_[0]), 0, 32 ); |
1436 | } |
ffed8b01 |
1437 | |
1438 | B<Note:> Your returned digest strings must be B<EXACTLY> the number |
044e6288 |
1439 | of bytes you specify in the hash_size parameter (in this case 32). |
ffed8b01 |
1440 | |
260a80b4 |
1441 | B<Note:> If you do choose to use a custom digest algorithm, you must set it |
1442 | every time you access this file. Otherwise, the default (MD5) will be used. |
1443 | |
ffed8b01 |
1444 | =head1 CIRCULAR REFERENCES |
1445 | |
1446 | DBM::Deep has B<experimental> support for circular references. Meaning you |
1447 | can have a nested hash key or array element that points to a parent object. |
1448 | This relationship is stored in the DB file, and is preserved between sessions. |
1449 | Here is an example: |
1450 | |
d0b74c17 |
1451 | my $db = DBM::Deep->new( "foo.db" ); |
1452 | |
1453 | $db->{foo} = "bar"; |
1454 | $db->{circle} = $db; # ref to self |
1455 | |
4b93c86a |
1456 | print $db->{foo} . "\n"; # prints "bar" |
1457 | print $db->{circle}->{foo} . "\n"; # prints "bar" again |
ffed8b01 |
1458 | |
69c94980 |
1459 | B<Note>: Passing the object to a function that recursively walks the |
ffed8b01 |
1460 | object tree (such as I<Data::Dumper> or even the built-in C<optimize()> or |
69c94980 |
1461 | C<export()> methods) will result in an infinite loop. This will be fixed in |
1462 | a future release. |
ffed8b01 |
1463 | |
1464 | =head1 CAVEATS / ISSUES / BUGS |
1465 | |
1466 | This section describes all the known issues with DBM::Deep. It you have found |
1467 | something that is not listed here, please send e-mail to L<jhuckaby@cpan.org>. |
1468 | |
1469 | =head2 UNUSED SPACE RECOVERY |
1470 | |
14a3acb6 |
1471 | One major caveat with DBM::Deep is that space occupied by existing keys and |
ffed8b01 |
1472 | values is not recovered when they are deleted. Meaning if you keep deleting |
1473 | and adding new keys, your file will continuously grow. I am working on this, |
d0b74c17 |
1474 | but in the meantime you can call the built-in C<optimize()> method from time to |
ffed8b01 |
1475 | time (perhaps in a crontab or something) to recover all your unused space. |
1476 | |
d0b74c17 |
1477 | $db->optimize(); # returns true on success |
ffed8b01 |
1478 | |
1479 | This rebuilds the ENTIRE database into a new file, then moves it on top of |
1480 | the original. The new file will have no unused space, thus it will take up as |
d0b74c17 |
1481 | little disk space as possible. Please note that this operation can take |
1482 | a long time for large files, and you need enough disk space to temporarily hold |
1483 | 2 copies of your DB file. The temporary file is created in the same directory |
1484 | as the original, named with a ".tmp" extension, and is deleted when the |
1485 | operation completes. Oh, and if locking is enabled, the DB is automatically |
ffed8b01 |
1486 | locked for the entire duration of the copy. |
1487 | |
d0b74c17 |
1488 | B<WARNING:> Only call optimize() on the top-level node of the database, and |
1489 | make sure there are no child references lying around. DBM::Deep keeps a reference |
ffed8b01 |
1490 | counter, and if it is greater than 1, optimize() will abort and return undef. |
1491 | |
eea0d863 |
1492 | =head2 REFERENCES |
1493 | |
1494 | (The reasons given assume a high level of Perl understanding, specifically of |
1495 | references. You can safely skip this section.) |
1496 | |
1497 | Currently, the only references supported are HASH and ARRAY. The other reference |
1498 | types (SCALAR, CODE, GLOB, and REF) cannot be supported for various reasons. |
1499 | |
1500 | =over 4 |
1501 | |
1502 | =item * GLOB |
1503 | |
1504 | These are things like filehandles and other sockets. They can't be supported |
1505 | because it's completely unclear how DBM::Deep should serialize them. |
1506 | |
1507 | =item * SCALAR / REF |
1508 | |
1509 | The discussion here refers to the following type of example: |
1510 | |
1511 | my $x = 25; |
1512 | $db->{key1} = \$x; |
1513 | |
1514 | $x = 50; |
1515 | |
1516 | # In some other process ... |
1517 | |
1518 | my $val = ${ $db->{key1} }; |
1519 | |
1520 | is( $val, 50, "What actually gets stored in the DB file?" ); |
1521 | |
1522 | The problem is one of synchronization. When the variable being referred to |
1523 | changes value, the reference isn't notified. This means that the new value won't |
1524 | be stored in the datafile for other processes to read. There is no TIEREF. |
1525 | |
1526 | It is theoretically possible to store references to values already within a |
1527 | DBM::Deep object because everything already is synchronized, but the change to |
1528 | the internals would be quite large. Specifically, DBM::Deep would have to tie |
1529 | every single value that is stored. This would bloat the RAM footprint of |
1530 | DBM::Deep at least twofold (if not more) and be a significant performance drain, |
1531 | all to support a feature that has never been requested. |
1532 | |
1533 | =item * CODE |
1534 | |
1535 | L<http://search.cpan.org/search?module=Data::Dump::Streamer> provides a |
1536 | mechanism for serializing coderefs, including saving off all closure state. |
1537 | However, just as for SCALAR and REF, that closure state may change without |
1538 | notifying the DBM::Deep object storing the reference. |
1539 | |
1540 | =back |
1541 | |
ffed8b01 |
1542 | =head2 FILE CORRUPTION |
1543 | |
14a3acb6 |
1544 | The current level of error handling in DBM::Deep is minimal. Files I<are> checked |
1545 | for a 32-bit signature when opened, but other corruption in files can cause |
1546 | segmentation faults. DBM::Deep may try to seek() past the end of a file, or get |
ffed8b01 |
1547 | stuck in an infinite loop depending on the level of corruption. File write |
1548 | operations are not checked for failure (for speed), so if you happen to run |
d0b74c17 |
1549 | out of disk space, DBM::Deep will probably fail in a bad way. These things will |
ffed8b01 |
1550 | be addressed in a later version of DBM::Deep. |
1551 | |
1552 | =head2 DB OVER NFS |
1553 | |
14a3acb6 |
1554 | Beware of using DB files over NFS. DBM::Deep uses flock(), which works well on local |
d0b74c17 |
1555 | filesystems, but will NOT protect you from file corruption over NFS. I've heard |
1556 | about setting up your NFS server with a locking daemon, then using lockf() to |
1557 | lock your files, but your mileage may vary there as well. From what I |
1558 | understand, there is no real way to do it. However, if you need access to the |
1559 | underlying filehandle in DBM::Deep for using some other kind of locking scheme like |
ffed8b01 |
1560 | lockf(), see the L<LOW-LEVEL ACCESS> section above. |
1561 | |
1562 | =head2 COPYING OBJECTS |
1563 | |
d0b74c17 |
1564 | Beware of copying tied objects in Perl. Very strange things can happen. |
1565 | Instead, use DBM::Deep's C<clone()> method which safely copies the object and |
ffed8b01 |
1566 | returns a new, blessed, tied hash or array to the same level in the DB. |
1567 | |
d0b74c17 |
1568 | my $copy = $db->clone(); |
ffed8b01 |
1569 | |
90f93b43 |
1570 | B<Note>: Since clone() here is cloning the object, not the database location, any |
1571 | modifications to either $db or $copy will be visible in both. |
1572 | |
ffed8b01 |
1573 | =head2 LARGE ARRAYS |
1574 | |
1575 | Beware of using C<shift()>, C<unshift()> or C<splice()> with large arrays. |
1576 | These functions cause every element in the array to move, which can be murder |
1577 | on DBM::Deep, as every element has to be fetched from disk, then stored again in |
90f93b43 |
1578 | a different location. This will be addressed in the forthcoming version 1.00. |
ffed8b01 |
1579 | |
9be51a89 |
1580 | =head2 WRITEONLY FILES |
1581 | |
1582 | If you pass in a filehandle to new(), you may have opened it in either a readonly or |
1583 | writeonly mode. STORE will verify that the filehandle is writable. However, there |
1584 | doesn't seem to be a good way to determine if a filehandle is readable. And, if the |
1585 | filehandle isn't readable, it's not clear what will happen. So, don't do that. |
1586 | |
ffed8b01 |
1587 | =head1 PERFORMANCE |
1588 | |
1589 | This section discusses DBM::Deep's speed and memory usage. |
1590 | |
1591 | =head2 SPEED |
1592 | |
d0b74c17 |
1593 | Obviously, DBM::Deep isn't going to be as fast as some C-based DBMs, such as |
ffed8b01 |
1594 | the almighty I<BerkeleyDB>. But it makes up for it in features like true |
1595 | multi-level hash/array support, and cross-platform FTPable files. Even so, |
1596 | DBM::Deep is still pretty fast, and the speed stays fairly consistent, even |
1597 | with huge databases. Here is some test data: |
d0b74c17 |
1598 | |
1599 | Adding 1,000,000 keys to new DB file... |
1600 | |
1601 | At 100 keys, avg. speed is 2,703 keys/sec |
1602 | At 200 keys, avg. speed is 2,642 keys/sec |
1603 | At 300 keys, avg. speed is 2,598 keys/sec |
1604 | At 400 keys, avg. speed is 2,578 keys/sec |
1605 | At 500 keys, avg. speed is 2,722 keys/sec |
1606 | At 600 keys, avg. speed is 2,628 keys/sec |
1607 | At 700 keys, avg. speed is 2,700 keys/sec |
1608 | At 800 keys, avg. speed is 2,607 keys/sec |
1609 | At 900 keys, avg. speed is 2,190 keys/sec |
1610 | At 1,000 keys, avg. speed is 2,570 keys/sec |
1611 | At 2,000 keys, avg. speed is 2,417 keys/sec |
1612 | At 3,000 keys, avg. speed is 1,982 keys/sec |
1613 | At 4,000 keys, avg. speed is 1,568 keys/sec |
1614 | At 5,000 keys, avg. speed is 1,533 keys/sec |
1615 | At 6,000 keys, avg. speed is 1,787 keys/sec |
1616 | At 7,000 keys, avg. speed is 1,977 keys/sec |
1617 | At 8,000 keys, avg. speed is 2,028 keys/sec |
1618 | At 9,000 keys, avg. speed is 2,077 keys/sec |
1619 | At 10,000 keys, avg. speed is 2,031 keys/sec |
1620 | At 20,000 keys, avg. speed is 1,970 keys/sec |
1621 | At 30,000 keys, avg. speed is 2,050 keys/sec |
1622 | At 40,000 keys, avg. speed is 2,073 keys/sec |
1623 | At 50,000 keys, avg. speed is 1,973 keys/sec |
1624 | At 60,000 keys, avg. speed is 1,914 keys/sec |
1625 | At 70,000 keys, avg. speed is 2,091 keys/sec |
1626 | At 80,000 keys, avg. speed is 2,103 keys/sec |
1627 | At 90,000 keys, avg. speed is 1,886 keys/sec |
1628 | At 100,000 keys, avg. speed is 1,970 keys/sec |
1629 | At 200,000 keys, avg. speed is 2,053 keys/sec |
1630 | At 300,000 keys, avg. speed is 1,697 keys/sec |
1631 | At 400,000 keys, avg. speed is 1,838 keys/sec |
1632 | At 500,000 keys, avg. speed is 1,941 keys/sec |
1633 | At 600,000 keys, avg. speed is 1,930 keys/sec |
1634 | At 700,000 keys, avg. speed is 1,735 keys/sec |
1635 | At 800,000 keys, avg. speed is 1,795 keys/sec |
1636 | At 900,000 keys, avg. speed is 1,221 keys/sec |
1637 | At 1,000,000 keys, avg. speed is 1,077 keys/sec |
1638 | |
1639 | This test was performed on a PowerMac G4 1gHz running Mac OS X 10.3.2 & Perl |
1640 | 5.8.1, with an 80GB Ultra ATA/100 HD spinning at 7200RPM. The hash keys and |
1641 | values were between 6 - 12 chars in length. The DB file ended up at 210MB. |
ffed8b01 |
1642 | Run time was 12 min 3 sec. |
1643 | |
1644 | =head2 MEMORY USAGE |
1645 | |
1646 | One of the great things about DBM::Deep is that it uses very little memory. |
1647 | Even with huge databases (1,000,000+ keys) you will not see much increased |
14a3acb6 |
1648 | memory on your process. DBM::Deep relies solely on the filesystem for storing |
ffed8b01 |
1649 | and fetching data. Here is output from I</usr/bin/top> before even opening a |
1650 | database handle: |
1651 | |
d0b74c17 |
1652 | PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND |
1653 | 22831 root 11 0 2716 2716 1296 R 0.0 0.2 0:07 perl |
ffed8b01 |
1654 | |
d0b74c17 |
1655 | Basically the process is taking 2,716K of memory. And here is the same |
ffed8b01 |
1656 | process after storing and fetching 1,000,000 keys: |
1657 | |
d0b74c17 |
1658 | PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND |
1659 | 22831 root 14 0 2772 2772 1328 R 0.0 0.2 13:32 perl |
ffed8b01 |
1660 | |
d0b74c17 |
1661 | Notice the memory usage increased by only 56K. Test was performed on a 700mHz |
ffed8b01 |
1662 | x86 box running Linux RedHat 7.2 & Perl 5.6.1. |
1663 | |
1664 | =head1 DB FILE FORMAT |
1665 | |
1666 | In case you were interested in the underlying DB file format, it is documented |
d0b74c17 |
1667 | here in this section. You don't need to know this to use the module, it's just |
ffed8b01 |
1668 | included for reference. |
1669 | |
1670 | =head2 SIGNATURE |
1671 | |
1672 | DBM::Deep files always start with a 32-bit signature to identify the file type. |
1673 | This is at offset 0. The signature is "DPDB" in network byte order. This is |
90f93b43 |
1674 | checked for when the file is opened and an error will be thrown if it's not found. |
ffed8b01 |
1675 | |
1676 | =head2 TAG |
1677 | |
1678 | The DBM::Deep file is in a I<tagged format>, meaning each section of the file |
d0b74c17 |
1679 | has a standard header containing the type of data, the length of data, and then |
1680 | the data itself. The type is a single character (1 byte), the length is a |
ffed8b01 |
1681 | 32-bit unsigned long in network byte order, and the data is, well, the data. |
1682 | Here is how it unfolds: |
1683 | |
1684 | =head2 MASTER INDEX |
1685 | |
d0b74c17 |
1686 | Immediately after the 32-bit file signature is the I<Master Index> record. |
1687 | This is a standard tag header followed by 1024 bytes (in 32-bit mode) or 2048 |
1688 | bytes (in 64-bit mode) of data. The type is I<H> for hash or I<A> for array, |
ffed8b01 |
1689 | depending on how the DBM::Deep object was constructed. |
1690 | |
d0b74c17 |
1691 | The index works by looking at a I<MD5 Hash> of the hash key (or array index |
1692 | number). The first 8-bit char of the MD5 signature is the offset into the |
1693 | index, multipled by 4 in 32-bit mode, or 8 in 64-bit mode. The value of the |
ffed8b01 |
1694 | index element is a file offset of the next tag for the key/element in question, |
1695 | which is usually a I<Bucket List> tag (see below). |
1696 | |
ffed8b01 |
1697 | The next tag I<could> be another index, depending on how many keys/elements |
1698 | exist. See L<RE-INDEXING> below for details. |
1699 | |
1700 | =head2 BUCKET LIST |
1701 | |
d0b74c17 |
1702 | A I<Bucket List> is a collection of 16 MD5 hashes for keys/elements, plus |
1703 | file offsets to where the actual data is stored. It starts with a standard |
1704 | tag header, with type I<B>, and a data size of 320 bytes in 32-bit mode, or |
ffed8b01 |
1705 | 384 bytes in 64-bit mode. Each MD5 hash is stored in full (16 bytes), plus |
1706 | the 32-bit or 64-bit file offset for the I<Bucket> containing the actual data. |
d0b74c17 |
1707 | When the list fills up, a I<Re-Index> operation is performed (See |
ffed8b01 |
1708 | L<RE-INDEXING> below). |
1709 | |
1710 | =head2 BUCKET |
1711 | |
1712 | A I<Bucket> is a tag containing a key/value pair (in hash mode), or a |
1713 | index/value pair (in array mode). It starts with a standard tag header with |
1714 | type I<D> for scalar data (string, binary, etc.), or it could be a nested |
1715 | hash (type I<H>) or array (type I<A>). The value comes just after the tag |
1716 | header. The size reported in the tag header is only for the value, but then, |
d0b74c17 |
1717 | just after the value is another size (32-bit unsigned long) and then the plain |
1718 | key itself. Since the value is likely to be fetched more often than the plain |
ffed8b01 |
1719 | key, I figured it would be I<slightly> faster to store the value first. |
1720 | |
ffed8b01 |
1721 | If the type is I<H> (hash) or I<A> (array), the value is another I<Master Index> |
1722 | record for the nested structure, where the process begins all over again. |
1723 | |
1724 | =head2 RE-INDEXING |
1725 | |
1726 | After a I<Bucket List> grows to 16 records, its allocated space in the file is |
d0b74c17 |
1727 | exhausted. Then, when another key/element comes in, the list is converted to a |
1728 | new index record. However, this index will look at the next char in the MD5 |
1729 | hash, and arrange new Bucket List pointers accordingly. This process is called |
1730 | I<Re-Indexing>. Basically, a new index tag is created at the file EOF, and all |
1731 | 17 (16 + new one) keys/elements are removed from the old Bucket List and |
1732 | inserted into the new index. Several new Bucket Lists are created in the |
1733 | process, as a new MD5 char from the key is being examined (it is unlikely that |
ffed8b01 |
1734 | the keys will all share the same next char of their MD5s). |
1735 | |
ffed8b01 |
1736 | Because of the way the I<MD5> algorithm works, it is impossible to tell exactly |
d0b74c17 |
1737 | when the Bucket Lists will turn into indexes, but the first round tends to |
1738 | happen right around 4,000 keys. You will see a I<slight> decrease in |
1739 | performance here, but it picks back up pretty quick (see L<SPEED> above). Then |
1740 | it takes B<a lot> more keys to exhaust the next level of Bucket Lists. It's |
1741 | right around 900,000 keys. This process can continue nearly indefinitely -- |
1742 | right up until the point the I<MD5> signatures start colliding with each other, |
1743 | and this is B<EXTREMELY> rare -- like winning the lottery 5 times in a row AND |
1744 | getting struck by lightning while you are walking to cash in your tickets. |
1745 | Theoretically, since I<MD5> hashes are 128-bit values, you I<could> have up to |
1746 | 340,282,366,921,000,000,000,000,000,000,000,000,000 keys/elements (I believe |
ffed8b01 |
1747 | this is 340 unodecillion, but don't quote me). |
1748 | |
1749 | =head2 STORING |
1750 | |
d0b74c17 |
1751 | When a new key/element is stored, the key (or index number) is first run through |
1752 | I<Digest::MD5> to get a 128-bit signature (example, in hex: |
ffed8b01 |
1753 | b05783b0773d894396d475ced9d2f4f6). Then, the I<Master Index> record is checked |
37c5bcf0 |
1754 | for the first char of the signature (in this case I<b0>). If it does not exist, |
d0b74c17 |
1755 | a new I<Bucket List> is created for our key (and the next 15 future keys that |
1756 | happen to also have I<b> as their first MD5 char). The entire MD5 is written |
ffed8b01 |
1757 | to the I<Bucket List> along with the offset of the new I<Bucket> record (EOF at |
d0b74c17 |
1758 | this point, unless we are replacing an existing I<Bucket>), where the actual |
ffed8b01 |
1759 | data will be stored. |
1760 | |
1761 | =head2 FETCHING |
1762 | |
d0b74c17 |
1763 | Fetching an existing key/element involves getting a I<Digest::MD5> of the key |
1764 | (or index number), then walking along the indexes. If there are enough |
1765 | keys/elements in this DB level, there might be nested indexes, each linked to |
1766 | a particular char of the MD5. Finally, a I<Bucket List> is pointed to, which |
1767 | contains up to 16 full MD5 hashes. Each is checked for equality to the key in |
1768 | question. If we found a match, the I<Bucket> tag is loaded, where the value and |
ffed8b01 |
1769 | plain key are stored. |
1770 | |
ffed8b01 |
1771 | Fetching the plain key occurs when calling the I<first_key()> and I<next_key()> |
1772 | methods. In this process the indexes are walked systematically, and each key |
1773 | fetched in increasing MD5 order (which is why it appears random). Once the |
d0b74c17 |
1774 | I<Bucket> is found, the value is skipped and the plain key returned instead. |
1775 | B<Note:> Do not count on keys being fetched as if the MD5 hashes were |
1776 | alphabetically sorted. This only happens on an index-level -- as soon as the |
1777 | I<Bucket Lists> are hit, the keys will come out in the order they went in -- |
1778 | so it's pretty much undefined how the keys will come out -- just like Perl's |
ffed8b01 |
1779 | built-in hashes. |
1780 | |
261d1296 |
1781 | =head1 CODE COVERAGE |
1782 | |
37c5bcf0 |
1783 | We use B<Devel::Cover> to test the code coverage of our tests, below is the |
90f93b43 |
1784 | B<Devel::Cover> report on this module's test suite. |
7910cf68 |
1785 | |
386bab6c |
1786 | ----------------------------------- ------ ------ ------ ------ ------ ------ |
1787 | File stmt bran cond sub time total |
1788 | ----------------------------------- ------ ------ ------ ------ ------ ------ |
1789 | blib/lib/DBM/Deep.pm 94.9 80.6 73.0 100.0 37.9 90.4 |
1790 | blib/lib/DBM/Deep/Array.pm 100.0 91.1 100.0 100.0 18.2 98.1 |
1791 | blib/lib/DBM/Deep/Engine.pm 98.9 87.3 80.0 100.0 34.2 95.2 |
1792 | blib/lib/DBM/Deep/Hash.pm 100.0 87.5 100.0 100.0 9.7 97.3 |
1793 | Total 97.9 85.9 79.7 100.0 100.0 94.3 |
1794 | ----------------------------------- ------ ------ ------ ------ ------ ------ |
37c5bcf0 |
1795 | |
1796 | =head1 MORE INFORMATION |
1797 | |
1798 | Check out the DBM::Deep Google Group at L<http://groups.google.com/group/DBM-Deep> |
1799 | or send email to L<DBM-Deep@googlegroups.com>. |
261d1296 |
1800 | |
aeeb5497 |
1801 | =head1 AUTHORS |
ffed8b01 |
1802 | |
1803 | Joseph Huckaby, L<jhuckaby@cpan.org> |
37c5bcf0 |
1804 | |
aeeb5497 |
1805 | Rob Kinyon, L<rkinyon@cpan.org> |
ffed8b01 |
1806 | |
1807 | Special thanks to Adam Sah and Rich Gaushell! You know why :-) |
1808 | |
1809 | =head1 SEE ALSO |
1810 | |
1811 | perltie(1), Tie::Hash(3), Digest::MD5(3), Fcntl(3), flock(2), lockf(3), nfs(5), |
1812 | Digest::SHA256(3), Crypt::Blowfish(3), Compress::Zlib(3) |
1813 | |
1814 | =head1 LICENSE |
1815 | |
aeeb5497 |
1816 | Copyright (c) 2002-2006 Joseph Huckaby. All Rights Reserved. |
ffed8b01 |
1817 | This is free software, you may use it and distribute it under the |
1818 | same terms as Perl itself. |
1819 | |
1820 | =cut |