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1 | =head1 NAME |
2 | |
3 | DBM::Deep - A pure perl multi-level hash/array DBM that supports transactions |
4 | |
5 | =head1 SYNOPSIS |
6 | |
7 | use DBM::Deep; |
8 | my $db = DBM::Deep->new( "foo.db" ); |
9 | |
10 | $db->{key} = 'value'; |
11 | print $db->{key}; |
12 | |
13 | $db->put('key' => 'value'); |
14 | print $db->get('key'); |
15 | |
16 | # true multi-level support |
17 | $db->{my_complex} = [ |
18 | 'hello', { perl => 'rules' }, |
19 | 42, 99, |
20 | ]; |
21 | |
22 | $db->begin_work; |
23 | |
24 | # Do stuff here |
25 | |
26 | $db->rollback; |
27 | $db->commit; |
28 | |
29 | tie my %db, 'DBM::Deep', 'foo.db'; |
30 | $db{key} = 'value'; |
31 | print $db{key}; |
32 | |
33 | tied(%db)->put('key' => 'value'); |
34 | print tied(%db)->get('key'); |
35 | |
36 | =head1 DESCRIPTION |
37 | |
38 | A unique flat-file database module, written in pure perl. True multi-level |
39 | hash/array support (unlike MLDBM, which is faked), hybrid OO / tie() |
40 | interface, cross-platform FTPable files, ACID transactions, and is quite fast. |
41 | Can handle millions of keys and unlimited levels without significant |
42 | slow-down. Written from the ground-up in pure perl -- this is NOT a wrapper |
43 | around a C-based DBM. Out-of-the-box compatibility with Unix, Mac OS X and |
44 | Windows. |
45 | |
46 | =head1 VERSION DIFFERENCES |
47 | |
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48 | B<NOTE>: 1.0000 has significant file format differences from prior versions. |
49 | THere is a backwards-compatibility layer at C<utils/upgrade_db.pl>. Files |
50 | created by 1.0000 or higher are B<NOT> compatible with scripts using prior |
51 | versions. |
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52 | |
53 | =head1 SETUP |
54 | |
55 | Construction can be done OO-style (which is the recommended way), or using |
56 | Perl's tie() function. Both are examined here. |
57 | |
58 | =head2 OO Construction |
59 | |
60 | The recommended way to construct a DBM::Deep object is to use the new() |
61 | method, which gets you a blessed I<and> tied hash (or array) reference. |
62 | |
63 | my $db = DBM::Deep->new( "foo.db" ); |
64 | |
65 | This opens a new database handle, mapped to the file "foo.db". If this |
66 | file does not exist, it will automatically be created. DB files are |
67 | opened in "r+" (read/write) mode, and the type of object returned is a |
68 | hash, unless otherwise specified (see L<OPTIONS> below). |
69 | |
70 | You can pass a number of options to the constructor to specify things like |
71 | locking, autoflush, etc. This is done by passing an inline hash (or hashref): |
72 | |
73 | my $db = DBM::Deep->new( |
74 | file => "foo.db", |
75 | locking => 1, |
76 | autoflush => 1 |
77 | ); |
78 | |
79 | Notice that the filename is now specified I<inside> the hash with |
80 | the "file" parameter, as opposed to being the sole argument to the |
81 | constructor. This is required if any options are specified. |
82 | See L<OPTIONS> below for the complete list. |
83 | |
84 | You can also start with an array instead of a hash. For this, you must |
85 | specify the C<type> parameter: |
86 | |
87 | my $db = DBM::Deep->new( |
88 | file => "foo.db", |
89 | type => DBM::Deep->TYPE_ARRAY |
90 | ); |
91 | |
92 | B<Note:> Specifing the C<type> parameter only takes effect when beginning |
93 | a new DB file. If you create a DBM::Deep object with an existing file, the |
94 | C<type> will be loaded from the file header, and an error will be thrown if |
95 | the wrong type is passed in. |
96 | |
97 | =head2 Tie Construction |
98 | |
99 | Alternately, you can create a DBM::Deep handle by using Perl's built-in |
100 | tie() function. The object returned from tie() can be used to call methods, |
101 | such as lock() and unlock(). (That object can be retrieved from the tied |
102 | variable at any time using tied() - please see L<perltie/> for more info. |
103 | |
104 | my %hash; |
105 | my $db = tie %hash, "DBM::Deep", "foo.db"; |
106 | |
107 | my @array; |
108 | my $db = tie @array, "DBM::Deep", "bar.db"; |
109 | |
110 | As with the OO constructor, you can replace the DB filename parameter with |
111 | a hash containing one or more options (see L<OPTIONS> just below for the |
112 | complete list). |
113 | |
114 | tie %hash, "DBM::Deep", { |
115 | file => "foo.db", |
116 | locking => 1, |
117 | autoflush => 1 |
118 | }; |
119 | |
120 | =head2 Options |
121 | |
122 | There are a number of options that can be passed in when constructing your |
123 | DBM::Deep objects. These apply to both the OO- and tie- based approaches. |
124 | |
125 | =over |
126 | |
127 | =item * file |
128 | |
129 | Filename of the DB file to link the handle to. You can pass a full absolute |
130 | filesystem path, partial path, or a plain filename if the file is in the |
131 | current working directory. This is a required parameter (though q.v. fh). |
132 | |
133 | =item * fh |
134 | |
135 | If you want, you can pass in the fh instead of the file. This is most useful for doing |
136 | something like: |
137 | |
138 | my $db = DBM::Deep->new( { fh => \*DATA } ); |
139 | |
140 | You are responsible for making sure that the fh has been opened appropriately for your |
141 | needs. If you open it read-only and attempt to write, an exception will be thrown. If you |
142 | open it write-only or append-only, an exception will be thrown immediately as DBM::Deep |
143 | needs to read from the fh. |
144 | |
145 | =item * file_offset |
146 | |
147 | This is the offset within the file that the DBM::Deep db starts. Most of the time, you will |
148 | not need to set this. However, it's there if you want it. |
149 | |
150 | If you pass in fh and do not set this, it will be set appropriately. |
151 | |
152 | =item * type |
153 | |
154 | This parameter specifies what type of object to create, a hash or array. Use |
155 | one of these two constants: |
156 | |
157 | =over 4 |
158 | |
159 | =item * C<DBM::Deep-E<gt>TYPE_HASH> |
160 | |
161 | =item * C<DBM::Deep-E<gt>TYPE_ARRAY>. |
162 | |
163 | =back |
164 | |
165 | This only takes effect when beginning a new file. This is an optional |
166 | parameter, and defaults to C<DBM::Deep-E<gt>TYPE_HASH>. |
167 | |
168 | =item * locking |
169 | |
170 | Specifies whether locking is to be enabled. DBM::Deep uses Perl's flock() |
171 | function to lock the database in exclusive mode for writes, and shared mode |
172 | for reads. Pass any true value to enable. This affects the base DB handle |
173 | I<and any child hashes or arrays> that use the same DB file. This is an |
174 | optional parameter, and defaults to 1 (enabled). See L<LOCKING> below for |
175 | more. |
176 | |
177 | =item * autoflush |
178 | |
179 | Specifies whether autoflush is to be enabled on the underlying filehandle. |
180 | This obviously slows down write operations, but is required if you may have |
181 | multiple processes accessing the same DB file (also consider enable I<locking>). |
182 | Pass any true value to enable. This is an optional parameter, and defaults to 1 |
183 | (enabled). |
184 | |
185 | =item * filter_* |
186 | |
187 | See L</FILTERS> below. |
188 | |
189 | =back |
190 | |
191 | The following parameters may be specified in the constructor the first time the |
192 | datafile is created. However, they will be stored in the header of the file and |
193 | cannot be overridden by subsequent openings of the file - the values will be set |
194 | from the values stored in the datafile's header. |
195 | |
196 | =over 4 |
197 | |
198 | =item * num_txns |
199 | |
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200 | This is the number of transactions that can be running at one time. The |
201 | default is one - the HEAD. The minimum is one and the maximum is 255. The more |
202 | transactions, the larger and quicker the datafile grows. |
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203 | |
204 | See L</TRANSACTIONS> below. |
205 | |
206 | =item * max_buckets |
207 | |
208 | This is the number of entries that can be added before a reindexing. The larger |
209 | this number is made, the larger a file gets, but the better performance you will |
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210 | have. The default and minimum number this can be is 16. The maximum is 256, but |
211 | more than 64 isn't recommended. |
212 | |
213 | =item * data_sector_size |
214 | |
215 | This is the size in bytes of a given data sector. Data sectors will chain, so |
216 | a value of any size can be stored. However, chaining is expensive in terms of |
217 | time. Setting this value to something close to the expected common length of |
218 | your scalars will improve your performance. If it is too small, your file will |
219 | have a lot of chaining. If it is too large, your file will have a lot of dead |
220 | space in it. |
221 | |
222 | The default for this is 64 bytes. The minimum value is 32 and the maximum is |
223 | 256 bytes. |
224 | |
225 | B<Note:> There are between 6 and 10 bytes taken up in each data sector for |
226 | bookkeeping. (It's 4 + the number of bytes in your L</pack_size>.) This is |
227 | included within the data_sector_size, thus the effective value is 6-10 bytes |
228 | less than what you specified. |
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229 | |
230 | =item * pack_size |
231 | |
232 | This is the size of the file pointer used throughout the file. The valid values |
233 | are: |
234 | |
235 | =over 4 |
236 | |
237 | =item * small |
238 | |
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239 | This uses 2-byte offsets, allowing for a maximum file size of 65 KB. |
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240 | |
241 | =item * medium (default) |
242 | |
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243 | This uses 4-byte offsets, allowing for a maximum file size of 4 GB. |
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244 | |
245 | =item * large |
246 | |
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247 | This uses 8-byte offsets, allowing for a maximum file size of 16 XB |
248 | (exabytes). This can only be enabled if your Perl is compiled for 64-bit. |
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249 | |
250 | =back |
251 | |
252 | See L</LARGEFILE SUPPORT> for more information. |
253 | |
254 | =back |
255 | |
256 | =head1 TIE INTERFACE |
257 | |
258 | With DBM::Deep you can access your databases using Perl's standard hash/array |
259 | syntax. Because all DBM::Deep objects are I<tied> to hashes or arrays, you can |
260 | treat them as such. DBM::Deep will intercept all reads/writes and direct them |
261 | to the right place -- the DB file. This has nothing to do with the |
262 | L<TIE CONSTRUCTION> section above. This simply tells you how to use DBM::Deep |
263 | using regular hashes and arrays, rather than calling functions like C<get()> |
264 | and C<put()> (although those work too). It is entirely up to you how to want |
265 | to access your databases. |
266 | |
267 | =head2 Hashes |
268 | |
269 | You can treat any DBM::Deep object like a normal Perl hash reference. Add keys, |
270 | or even nested hashes (or arrays) using standard Perl syntax: |
271 | |
272 | my $db = DBM::Deep->new( "foo.db" ); |
273 | |
274 | $db->{mykey} = "myvalue"; |
275 | $db->{myhash} = {}; |
276 | $db->{myhash}->{subkey} = "subvalue"; |
277 | |
278 | print $db->{myhash}->{subkey} . "\n"; |
279 | |
280 | You can even step through hash keys using the normal Perl C<keys()> function: |
281 | |
282 | foreach my $key (keys %$db) { |
283 | print "$key: " . $db->{$key} . "\n"; |
284 | } |
285 | |
286 | Remember that Perl's C<keys()> function extracts I<every> key from the hash and |
287 | pushes them onto an array, all before the loop even begins. If you have an |
288 | extremely large hash, this may exhaust Perl's memory. Instead, consider using |
289 | Perl's C<each()> function, which pulls keys/values one at a time, using very |
290 | little memory: |
291 | |
292 | while (my ($key, $value) = each %$db) { |
293 | print "$key: $value\n"; |
294 | } |
295 | |
296 | Please note that when using C<each()>, you should always pass a direct |
297 | hash reference, not a lookup. Meaning, you should B<never> do this: |
298 | |
299 | # NEVER DO THIS |
300 | while (my ($key, $value) = each %{$db->{foo}}) { # BAD |
301 | |
302 | This causes an infinite loop, because for each iteration, Perl is calling |
303 | FETCH() on the $db handle, resulting in a "new" hash for foo every time, so |
304 | it effectively keeps returning the first key over and over again. Instead, |
305 | assign a temporary variable to C<$db->{foo}>, then pass that to each(). |
306 | |
307 | =head2 Arrays |
308 | |
309 | As with hashes, you can treat any DBM::Deep object like a normal Perl array |
310 | reference. This includes inserting, removing and manipulating elements, |
311 | and the C<push()>, C<pop()>, C<shift()>, C<unshift()> and C<splice()> functions. |
312 | The object must have first been created using type C<DBM::Deep-E<gt>TYPE_ARRAY>, |
313 | or simply be a nested array reference inside a hash. Example: |
314 | |
315 | my $db = DBM::Deep->new( |
316 | file => "foo-array.db", |
317 | type => DBM::Deep->TYPE_ARRAY |
318 | ); |
319 | |
320 | $db->[0] = "foo"; |
321 | push @$db, "bar", "baz"; |
322 | unshift @$db, "bah"; |
323 | |
324 | my $last_elem = pop @$db; # baz |
325 | my $first_elem = shift @$db; # bah |
326 | my $second_elem = $db->[1]; # bar |
327 | |
328 | my $num_elements = scalar @$db; |
329 | |
330 | =head1 OO INTERFACE |
331 | |
332 | In addition to the I<tie()> interface, you can also use a standard OO interface |
333 | to manipulate all aspects of DBM::Deep databases. Each type of object (hash or |
334 | array) has its own methods, but both types share the following common methods: |
335 | C<put()>, C<get()>, C<exists()>, C<delete()> and C<clear()>. C<fetch()> and |
336 | C<store(> are aliases to C<put()> and C<get()>, respectively. |
337 | |
338 | =over |
339 | |
340 | =item * new() / clone() |
341 | |
342 | These are the constructor and copy-functions. |
343 | |
344 | =item * put() / store() |
345 | |
346 | Stores a new hash key/value pair, or sets an array element value. Takes two |
347 | arguments, the hash key or array index, and the new value. The value can be |
348 | a scalar, hash ref or array ref. Returns true on success, false on failure. |
349 | |
350 | $db->put("foo", "bar"); # for hashes |
351 | $db->put(1, "bar"); # for arrays |
352 | |
353 | =item * get() / fetch() |
354 | |
355 | Fetches the value of a hash key or array element. Takes one argument: the hash |
356 | key or array index. Returns a scalar, hash ref or array ref, depending on the |
357 | data type stored. |
358 | |
359 | my $value = $db->get("foo"); # for hashes |
360 | my $value = $db->get(1); # for arrays |
361 | |
362 | =item * exists() |
363 | |
364 | Checks if a hash key or array index exists. Takes one argument: the hash key |
365 | or array index. Returns true if it exists, false if not. |
366 | |
367 | if ($db->exists("foo")) { print "yay!\n"; } # for hashes |
368 | if ($db->exists(1)) { print "yay!\n"; } # for arrays |
369 | |
370 | =item * delete() |
371 | |
372 | Deletes one hash key/value pair or array element. Takes one argument: the hash |
373 | key or array index. Returns true on success, false if not found. For arrays, |
374 | the remaining elements located after the deleted element are NOT moved over. |
375 | The deleted element is essentially just undefined, which is exactly how Perl's |
376 | internal arrays work. |
377 | |
378 | $db->delete("foo"); # for hashes |
379 | $db->delete(1); # for arrays |
380 | |
381 | =item * clear() |
382 | |
383 | Deletes B<all> hash keys or array elements. Takes no arguments. No return |
384 | value. |
385 | |
386 | $db->clear(); # hashes or arrays |
387 | |
388 | =item * lock() / unlock() |
389 | |
390 | q.v. Locking. |
391 | |
392 | =item * optimize() |
393 | |
394 | Recover lost disk space. This is important to do, especially if you use |
395 | transactions. |
396 | |
397 | =item * import() / export() |
398 | |
399 | Data going in and out. |
400 | |
401 | =item * begin_work() / commit() / rollback() |
402 | |
403 | These are the transactional functions. L</TRANSACTIONS> for more information. |
404 | |
405 | =back |
406 | |
407 | =head2 Hashes |
408 | |
409 | For hashes, DBM::Deep supports all the common methods described above, and the |
410 | following additional methods: C<first_key()> and C<next_key()>. |
411 | |
412 | =over |
413 | |
414 | =item * first_key() |
415 | |
416 | Returns the "first" key in the hash. As with built-in Perl hashes, keys are |
417 | fetched in an undefined order (which appears random). Takes no arguments, |
418 | returns the key as a scalar value. |
419 | |
420 | my $key = $db->first_key(); |
421 | |
422 | =item * next_key() |
423 | |
424 | Returns the "next" key in the hash, given the previous one as the sole argument. |
425 | Returns undef if there are no more keys to be fetched. |
426 | |
427 | $key = $db->next_key($key); |
428 | |
429 | =back |
430 | |
431 | Here are some examples of using hashes: |
432 | |
433 | my $db = DBM::Deep->new( "foo.db" ); |
434 | |
435 | $db->put("foo", "bar"); |
436 | print "foo: " . $db->get("foo") . "\n"; |
437 | |
438 | $db->put("baz", {}); # new child hash ref |
439 | $db->get("baz")->put("buz", "biz"); |
440 | print "buz: " . $db->get("baz")->get("buz") . "\n"; |
441 | |
442 | my $key = $db->first_key(); |
443 | while ($key) { |
444 | print "$key: " . $db->get($key) . "\n"; |
445 | $key = $db->next_key($key); |
446 | } |
447 | |
448 | if ($db->exists("foo")) { $db->delete("foo"); } |
449 | |
450 | =head2 Arrays |
451 | |
452 | For arrays, DBM::Deep supports all the common methods described above, and the |
453 | following additional methods: C<length()>, C<push()>, C<pop()>, C<shift()>, |
454 | C<unshift()> and C<splice()>. |
455 | |
456 | =over |
457 | |
458 | =item * length() |
459 | |
460 | Returns the number of elements in the array. Takes no arguments. |
461 | |
462 | my $len = $db->length(); |
463 | |
464 | =item * push() |
465 | |
466 | Adds one or more elements onto the end of the array. Accepts scalars, hash |
467 | refs or array refs. No return value. |
468 | |
469 | $db->push("foo", "bar", {}); |
470 | |
471 | =item * pop() |
472 | |
473 | Fetches the last element in the array, and deletes it. Takes no arguments. |
474 | Returns undef if array is empty. Returns the element value. |
475 | |
476 | my $elem = $db->pop(); |
477 | |
478 | =item * shift() |
479 | |
480 | Fetches the first element in the array, deletes it, then shifts all the |
481 | remaining elements over to take up the space. Returns the element value. This |
482 | method is not recommended with large arrays -- see L<LARGE ARRAYS> below for |
483 | details. |
484 | |
485 | my $elem = $db->shift(); |
486 | |
487 | =item * unshift() |
488 | |
489 | Inserts one or more elements onto the beginning of the array, shifting all |
490 | existing elements over to make room. Accepts scalars, hash refs or array refs. |
491 | No return value. This method is not recommended with large arrays -- see |
492 | <LARGE ARRAYS> below for details. |
493 | |
494 | $db->unshift("foo", "bar", {}); |
495 | |
496 | =item * splice() |
497 | |
498 | Performs exactly like Perl's built-in function of the same name. See L<perldoc |
499 | -f splice> for usage -- it is too complicated to document here. This method is |
500 | not recommended with large arrays -- see L<LARGE ARRAYS> below for details. |
501 | |
502 | =back |
503 | |
504 | Here are some examples of using arrays: |
505 | |
506 | my $db = DBM::Deep->new( |
507 | file => "foo.db", |
508 | type => DBM::Deep->TYPE_ARRAY |
509 | ); |
510 | |
511 | $db->push("bar", "baz"); |
512 | $db->unshift("foo"); |
513 | $db->put(3, "buz"); |
514 | |
515 | my $len = $db->length(); |
516 | print "length: $len\n"; # 4 |
517 | |
518 | for (my $k=0; $k<$len; $k++) { |
519 | print "$k: " . $db->get($k) . "\n"; |
520 | } |
521 | |
522 | $db->splice(1, 2, "biz", "baf"); |
523 | |
524 | while (my $elem = shift @$db) { |
525 | print "shifted: $elem\n"; |
526 | } |
527 | |
528 | =head1 LOCKING |
529 | |
530 | Enable or disable automatic file locking by passing a boolean value to the |
531 | C<locking> parameter when constructing your DBM::Deep object (see L<SETUP> |
532 | above). |
533 | |
534 | my $db = DBM::Deep->new( |
535 | file => "foo.db", |
536 | locking => 1 |
537 | ); |
538 | |
539 | This causes DBM::Deep to C<flock()> the underlying filehandle with exclusive |
540 | mode for writes, and shared mode for reads. This is required if you have |
541 | multiple processes accessing the same database file, to avoid file corruption. |
542 | Please note that C<flock()> does NOT work for files over NFS. See L<DB OVER |
543 | NFS> below for more. |
544 | |
545 | =head2 Explicit Locking |
546 | |
547 | You can explicitly lock a database, so it remains locked for multiple |
548 | actions. This is done by calling the C<lock()> method, and passing an |
549 | optional lock mode argument (defaults to exclusive mode). This is particularly |
550 | useful for things like counters, where the current value needs to be fetched, |
551 | then incremented, then stored again. |
552 | |
553 | $db->lock(); |
554 | my $counter = $db->get("counter"); |
555 | $counter++; |
556 | $db->put("counter", $counter); |
557 | $db->unlock(); |
558 | |
559 | # or... |
560 | |
561 | $db->lock(); |
562 | $db->{counter}++; |
563 | $db->unlock(); |
564 | |
565 | You can pass C<lock()> an optional argument, which specifies which mode to use |
566 | (exclusive or shared). Use one of these two constants: |
567 | C<DBM::Deep-E<gt>LOCK_EX> or C<DBM::Deep-E<gt>LOCK_SH>. These are passed |
568 | directly to C<flock()>, and are the same as the constants defined in Perl's |
569 | L<Fcntl/> module. |
570 | |
571 | $db->lock( $db->LOCK_SH ); |
572 | # something here |
573 | $db->unlock(); |
574 | |
575 | =head1 IMPORTING/EXPORTING |
576 | |
577 | You can import existing complex structures by calling the C<import()> method, |
578 | and export an entire database into an in-memory structure using the C<export()> |
579 | method. Both are examined here. |
580 | |
581 | =head2 Importing |
582 | |
583 | Say you have an existing hash with nested hashes/arrays inside it. Instead of |
584 | walking the structure and adding keys/elements to the database as you go, |
585 | simply pass a reference to the C<import()> method. This recursively adds |
586 | everything to an existing DBM::Deep object for you. Here is an example: |
587 | |
588 | my $struct = { |
589 | key1 => "value1", |
590 | key2 => "value2", |
591 | array1 => [ "elem0", "elem1", "elem2" ], |
592 | hash1 => { |
593 | subkey1 => "subvalue1", |
594 | subkey2 => "subvalue2" |
595 | } |
596 | }; |
597 | |
598 | my $db = DBM::Deep->new( "foo.db" ); |
599 | $db->import( $struct ); |
600 | |
601 | print $db->{key1} . "\n"; # prints "value1" |
602 | |
603 | This recursively imports the entire C<$struct> object into C<$db>, including |
604 | all nested hashes and arrays. If the DBM::Deep object contains exsiting data, |
605 | keys are merged with the existing ones, replacing if they already exist. |
606 | The C<import()> method can be called on any database level (not just the base |
607 | level), and works with both hash and array DB types. |
608 | |
609 | B<Note:> Make sure your existing structure has no circular references in it. |
610 | These will cause an infinite loop when importing. There are plans to fix this |
611 | in a later release. |
612 | |
2120a181 |
613 | =head2 Exporting |
614 | |
615 | Calling the C<export()> method on an existing DBM::Deep object will return |
616 | a reference to a new in-memory copy of the database. The export is done |
617 | recursively, so all nested hashes/arrays are all exported to standard Perl |
618 | objects. Here is an example: |
619 | |
620 | my $db = DBM::Deep->new( "foo.db" ); |
621 | |
622 | $db->{key1} = "value1"; |
623 | $db->{key2} = "value2"; |
624 | $db->{hash1} = {}; |
625 | $db->{hash1}->{subkey1} = "subvalue1"; |
626 | $db->{hash1}->{subkey2} = "subvalue2"; |
627 | |
628 | my $struct = $db->export(); |
629 | |
630 | print $struct->{key1} . "\n"; # prints "value1" |
631 | |
632 | This makes a complete copy of the database in memory, and returns a reference |
633 | to it. The C<export()> method can be called on any database level (not just |
634 | the base level), and works with both hash and array DB types. Be careful of |
635 | large databases -- you can store a lot more data in a DBM::Deep object than an |
636 | in-memory Perl structure. |
637 | |
638 | B<Note:> Make sure your database has no circular references in it. |
639 | These will cause an infinite loop when exporting. There are plans to fix this |
640 | in a later release. |
641 | |
642 | =head1 FILTERS |
643 | |
644 | DBM::Deep has a number of hooks where you can specify your own Perl function |
645 | to perform filtering on incoming or outgoing data. This is a perfect |
646 | way to extend the engine, and implement things like real-time compression or |
647 | encryption. Filtering applies to the base DB level, and all child hashes / |
648 | arrays. Filter hooks can be specified when your DBM::Deep object is first |
649 | constructed, or by calling the C<set_filter()> method at any time. There are |
650 | four available filter hooks, described below: |
651 | |
652 | =over |
653 | |
654 | =item * filter_store_key |
655 | |
656 | This filter is called whenever a hash key is stored. It |
657 | is passed the incoming key, and expected to return a transformed key. |
658 | |
659 | =item * filter_store_value |
660 | |
661 | This filter is called whenever a hash key or array element is stored. It |
662 | is passed the incoming value, and expected to return a transformed value. |
663 | |
664 | =item * filter_fetch_key |
665 | |
666 | This filter is called whenever a hash key is fetched (i.e. via |
667 | C<first_key()> or C<next_key()>). It is passed the transformed key, |
668 | and expected to return the plain key. |
669 | |
670 | =item * filter_fetch_value |
671 | |
672 | This filter is called whenever a hash key or array element is fetched. |
673 | It is passed the transformed value, and expected to return the plain value. |
674 | |
675 | =back |
676 | |
677 | Here are the two ways to setup a filter hook: |
678 | |
679 | my $db = DBM::Deep->new( |
680 | file => "foo.db", |
681 | filter_store_value => \&my_filter_store, |
682 | filter_fetch_value => \&my_filter_fetch |
683 | ); |
684 | |
685 | # or... |
686 | |
687 | $db->set_filter( "filter_store_value", \&my_filter_store ); |
688 | $db->set_filter( "filter_fetch_value", \&my_filter_fetch ); |
689 | |
690 | Your filter function will be called only when dealing with SCALAR keys or |
691 | values. When nested hashes and arrays are being stored/fetched, filtering |
692 | is bypassed. Filters are called as static functions, passed a single SCALAR |
693 | argument, and expected to return a single SCALAR value. If you want to |
694 | remove a filter, set the function reference to C<undef>: |
695 | |
696 | $db->set_filter( "filter_store_value", undef ); |
697 | |
698 | =head2 Real-time Encryption Example |
699 | |
700 | Here is a working example that uses the I<Crypt::Blowfish> module to |
701 | do real-time encryption / decryption of keys & values with DBM::Deep Filters. |
702 | Please visit L<http://search.cpan.org/search?module=Crypt::Blowfish> for more |
703 | on I<Crypt::Blowfish>. You'll also need the I<Crypt::CBC> module. |
704 | |
705 | use DBM::Deep; |
706 | use Crypt::Blowfish; |
707 | use Crypt::CBC; |
708 | |
709 | my $cipher = Crypt::CBC->new({ |
710 | 'key' => 'my secret key', |
711 | 'cipher' => 'Blowfish', |
712 | 'iv' => '$KJh#(}q', |
713 | 'regenerate_key' => 0, |
714 | 'padding' => 'space', |
715 | 'prepend_iv' => 0 |
716 | }); |
717 | |
718 | my $db = DBM::Deep->new( |
719 | file => "foo-encrypt.db", |
720 | filter_store_key => \&my_encrypt, |
721 | filter_store_value => \&my_encrypt, |
722 | filter_fetch_key => \&my_decrypt, |
723 | filter_fetch_value => \&my_decrypt, |
724 | ); |
725 | |
726 | $db->{key1} = "value1"; |
727 | $db->{key2} = "value2"; |
728 | print "key1: " . $db->{key1} . "\n"; |
729 | print "key2: " . $db->{key2} . "\n"; |
730 | |
731 | undef $db; |
732 | exit; |
733 | |
734 | sub my_encrypt { |
735 | return $cipher->encrypt( $_[0] ); |
736 | } |
737 | sub my_decrypt { |
738 | return $cipher->decrypt( $_[0] ); |
739 | } |
740 | |
741 | =head2 Real-time Compression Example |
742 | |
743 | Here is a working example that uses the I<Compress::Zlib> module to do real-time |
744 | compression / decompression of keys & values with DBM::Deep Filters. |
745 | Please visit L<http://search.cpan.org/search?module=Compress::Zlib> for |
746 | more on I<Compress::Zlib>. |
747 | |
748 | use DBM::Deep; |
749 | use Compress::Zlib; |
750 | |
751 | my $db = DBM::Deep->new( |
752 | file => "foo-compress.db", |
753 | filter_store_key => \&my_compress, |
754 | filter_store_value => \&my_compress, |
755 | filter_fetch_key => \&my_decompress, |
756 | filter_fetch_value => \&my_decompress, |
757 | ); |
758 | |
759 | $db->{key1} = "value1"; |
760 | $db->{key2} = "value2"; |
761 | print "key1: " . $db->{key1} . "\n"; |
762 | print "key2: " . $db->{key2} . "\n"; |
763 | |
764 | undef $db; |
765 | exit; |
766 | |
767 | sub my_compress { |
768 | return Compress::Zlib::memGzip( $_[0] ) ; |
769 | } |
770 | sub my_decompress { |
771 | return Compress::Zlib::memGunzip( $_[0] ) ; |
772 | } |
773 | |
774 | B<Note:> Filtering of keys only applies to hashes. Array "keys" are |
775 | actually numerical index numbers, and are not filtered. |
776 | |
777 | =head1 ERROR HANDLING |
778 | |
779 | Most DBM::Deep methods return a true value for success, and call die() on |
780 | failure. You can wrap calls in an eval block to catch the die. |
781 | |
782 | my $db = DBM::Deep->new( "foo.db" ); # create hash |
783 | eval { $db->push("foo"); }; # ILLEGAL -- push is array-only call |
784 | |
785 | print $@; # prints error message |
786 | |
787 | =head1 LARGEFILE SUPPORT |
788 | |
789 | If you have a 64-bit system, and your Perl is compiled with both LARGEFILE |
e9b0b5f0 |
790 | and 64-bit support, you I<may> be able to create databases larger than 4 GB. |
2120a181 |
791 | DBM::Deep by default uses 32-bit file offset tags, but these can be changed |
792 | by specifying the 'pack_size' parameter when constructing the file. |
793 | |
794 | DBM::Deep->new( |
795 | filename => $filename, |
796 | pack_size => 'large', |
797 | ); |
798 | |
799 | This tells DBM::Deep to pack all file offsets with 8-byte (64-bit) quad words |
800 | instead of 32-bit longs. After setting these values your DB files have a |
801 | theoretical maximum size of 16 XB (exabytes). |
802 | |
803 | You can also use C<pack_size =E<gt> 'small'> in order to use 16-bit file |
804 | offsets. |
805 | |
806 | B<Note:> Changing these values will B<NOT> work for existing database files. |
807 | Only change this for new files. Once the value has been set, it is stored in |
808 | the file's header and cannot be changed for the life of the file. These |
809 | parameters are per-file, meaning you can access 32-bit and 64-bit files, as |
810 | you choose. |
811 | |
e9b0b5f0 |
812 | B<Note:> We have not personally tested files larger than 4 GB -- all my |
2120a181 |
813 | systems have only a 32-bit Perl. However, I have received user reports that |
e9b0b5f0 |
814 | this does indeed work. |
2120a181 |
815 | |
816 | =head1 LOW-LEVEL ACCESS |
817 | |
818 | If you require low-level access to the underlying filehandle that DBM::Deep uses, |
819 | you can call the C<_fh()> method, which returns the handle: |
820 | |
821 | my $fh = $db->_fh(); |
822 | |
823 | This method can be called on the root level of the datbase, or any child |
824 | hashes or arrays. All levels share a I<root> structure, which contains things |
825 | like the filehandle, a reference counter, and all the options specified |
826 | when you created the object. You can get access to this file object by |
827 | calling the C<_storage()> method. |
828 | |
829 | my $file_obj = $db->_storage(); |
830 | |
831 | This is useful for changing options after the object has already been created, |
832 | such as enabling/disabling locking. You can also store your own temporary user |
833 | data in this structure (be wary of name collision), which is then accessible from |
834 | any child hash or array. |
835 | |
836 | =head1 CUSTOM DIGEST ALGORITHM |
837 | |
838 | DBM::Deep by default uses the I<Message Digest 5> (MD5) algorithm for hashing |
839 | keys. However you can override this, and use another algorithm (such as SHA-256) |
840 | or even write your own. But please note that DBM::Deep currently expects zero |
841 | collisions, so your algorithm has to be I<perfect>, so to speak. Collision |
842 | detection may be introduced in a later version. |
843 | |
844 | You can specify a custom digest algorithm by passing it into the parameter |
845 | list for new(), passing a reference to a subroutine as the 'digest' parameter, |
846 | and the length of the algorithm's hashes (in bytes) as the 'hash_size' |
847 | parameter. Here is a working example that uses a 256-bit hash from the |
848 | I<Digest::SHA256> module. Please see |
849 | L<http://search.cpan.org/search?module=Digest::SHA256> for more information. |
850 | |
851 | use DBM::Deep; |
852 | use Digest::SHA256; |
853 | |
854 | my $context = Digest::SHA256::new(256); |
855 | |
856 | my $db = DBM::Deep->new( |
857 | filename => "foo-sha.db", |
858 | digest => \&my_digest, |
859 | hash_size => 32, |
860 | ); |
861 | |
862 | $db->{key1} = "value1"; |
863 | $db->{key2} = "value2"; |
864 | print "key1: " . $db->{key1} . "\n"; |
865 | print "key2: " . $db->{key2} . "\n"; |
866 | |
867 | undef $db; |
868 | exit; |
869 | |
870 | sub my_digest { |
871 | return substr( $context->hash($_[0]), 0, 32 ); |
872 | } |
873 | |
874 | B<Note:> Your returned digest strings must be B<EXACTLY> the number |
875 | of bytes you specify in the hash_size parameter (in this case 32). |
876 | |
877 | B<Note:> If you do choose to use a custom digest algorithm, you must set it |
878 | every time you access this file. Otherwise, the default (MD5) will be used. |
879 | |
880 | =head1 CIRCULAR REFERENCES |
881 | |
882 | B<NOTE>: DBM::Deep 0.99_03 has turned off circular references pending |
883 | evaluation of some edge cases. I hope to be able to re-enable circular |
884 | references in a future version after 1.00. This means that circular references |
885 | are B<NO LONGER> available. |
886 | |
887 | DBM::Deep has B<experimental> support for circular references. Meaning you |
888 | can have a nested hash key or array element that points to a parent object. |
889 | This relationship is stored in the DB file, and is preserved between sessions. |
890 | Here is an example: |
891 | |
892 | my $db = DBM::Deep->new( "foo.db" ); |
893 | |
894 | $db->{foo} = "bar"; |
895 | $db->{circle} = $db; # ref to self |
896 | |
897 | print $db->{foo} . "\n"; # prints "bar" |
898 | print $db->{circle}->{foo} . "\n"; # prints "bar" again |
899 | |
900 | B<Note>: Passing the object to a function that recursively walks the |
901 | object tree (such as I<Data::Dumper> or even the built-in C<optimize()> or |
902 | C<export()> methods) will result in an infinite loop. This will be fixed in |
903 | a future release. |
904 | |
905 | =head1 TRANSACTIONS |
906 | |
907 | New in 0.99_01 is ACID transactions. Every DBM::Deep object is completely |
908 | transaction-ready - it is not an option you have to turn on. You do have to |
909 | specify how many transactions may run simultaneously (q.v. L</num_txns>). |
910 | |
911 | Three new methods have been added to support them. They are: |
912 | |
913 | =over 4 |
914 | |
915 | =item * begin_work() |
916 | |
917 | This starts a transaction. |
918 | |
919 | =item * commit() |
920 | |
921 | This applies the changes done within the transaction to the mainline and ends |
922 | the transaction. |
923 | |
924 | =item * rollback() |
925 | |
926 | This discards the changes done within the transaction to the mainline and ends |
927 | the transaction. |
928 | |
929 | =back |
930 | |
931 | Transactions in DBM::Deep are done using a variant of the MVCC method, the |
932 | same method used by the InnoDB MySQL engine. |
933 | |
2120a181 |
934 | =head1 PERFORMANCE |
935 | |
936 | Because DBM::Deep is a conncurrent datastore, every change is flushed to disk |
937 | immediately and every read goes to disk. This means that DBM::Deep functions |
938 | at the speed of disk (generally 10-20ms) vs. the speed of RAM (generally |
939 | 50-70ns), or at least 150-200x slower than the comparable in-memory |
940 | datastructure in Perl. |
941 | |
942 | There are several techniques you can use to speed up how DBM::Deep functions. |
943 | |
944 | =over 4 |
945 | |
946 | =item * Put it on a ramdisk |
947 | |
948 | The easiest and quickest mechanism to making DBM::Deep run faster is to create |
949 | a ramdisk and locate the DBM::Deep file there. Doing this as an option may |
950 | become a feature of DBM::Deep, assuming there is a good ramdisk wrapper on CPAN. |
951 | |
952 | =item * Work at the tightest level possible |
953 | |
954 | It is much faster to assign the level of your db that you are working with to |
955 | an intermediate variable than to re-look it up every time. Thus |
956 | |
957 | # BAD |
958 | while ( my ($k, $v) = each %{$db->{foo}{bar}{baz}} ) { |
959 | ... |
960 | } |
961 | |
962 | # GOOD |
963 | my $x = $db->{foo}{bar}{baz}; |
964 | while ( my ($k, $v) = each %$x ) { |
965 | ... |
966 | } |
967 | |
968 | =item * Make your file as tight as possible |
969 | |
970 | If you know that you are not going to use more than 65K in your database, |
971 | consider using the C<pack_size =E<gt> 'small'> option. This will instruct |
972 | DBM::Deep to use 16bit addresses, meaning that the seek times will be less. |
973 | |
974 | =back |
975 | |
e9b0b5f0 |
976 | =head1 MIGRATION |
977 | |
978 | As of 1.0000, the file format has changed. Furthermore, DBM::Deep is now |
979 | designed to potentially change file format between point-releases, if needed to |
980 | support a requested feature. To aid in this, a migration script is provided |
981 | within the CPAN distribution called C<utils/upgrade_db.pl>. |
982 | |
983 | B<NOTE:> This script is not installed onto your system because it carries a copy |
984 | of every version prior to the current version. |
985 | |
2120a181 |
986 | =head1 TODO |
987 | |
988 | The following are items that are planned to be added in future releases. These |
989 | are separate from the L<CAVEATS, ISSUES & BUGS> below. |
990 | |
991 | =head2 Sub-Transactions |
992 | |
993 | Right now, you cannot run a transaction within a transaction. Removing this |
994 | restriction is technically straightforward, but the combinatorial explosion of |
995 | possible usecases hurts my head. If this is something you want to see |
996 | immediately, please submit many testcases. |
997 | |
998 | =head2 Caching |
999 | |
1000 | If a user is willing to assert upon opening the file that this process will be |
1001 | the only consumer of that datafile, then there are a number of caching |
1002 | possibilities that can be taken advantage of. This does, however, mean that |
1003 | DBM::Deep is more vulnerable to losing data due to unflushed changes. It also |
1004 | means a much larger in-memory footprint. As such, it's not clear exactly how |
1005 | this should be done. Suggestions are welcome. |
1006 | |
1007 | =head2 Ram-only |
1008 | |
1009 | The techniques used in DBM::Deep simply require a seekable contiguous |
1010 | datastore. This could just as easily be a large string as a file. By using |
1011 | substr, the STM capabilities of DBM::Deep could be used within a |
1012 | single-process. I have no idea how I'd specify this, though. Suggestions are |
1013 | welcome. |
1014 | |
1015 | =head2 Importing using Data::Walker |
1016 | |
1017 | Right now, importing is done using C<Clone::clone()> to make a complete copy |
1018 | in memory, then tying that copy. It would be much better to use |
1019 | L<Data::Walker/> to walk the data structure instead, particularly in the case |
1020 | of large datastructures. |
1021 | |
1022 | =head2 Different contention resolution mechanisms |
1023 | |
1024 | Currently, the only contention resolution mechanism is last-write-wins. This |
1025 | is the mechanism used by most RDBMSes and should be good enough for most uses. |
1026 | For advanced uses of STM, other contention mechanisms will be needed. If you |
1027 | have an idea of how you'd like to see contention resolution in DBM::Deep, |
1028 | please let me know. |
1029 | |
1030 | =head1 CAVEATS, ISSUES & BUGS |
1031 | |
1032 | This section describes all the known issues with DBM::Deep. These are issues |
1033 | that are either intractable or depend on some feature within Perl working |
1034 | exactly right. It you have found something that is not listed below, please |
1035 | send an e-mail to L<rkinyon@cpan.org>. Likewise, if you think you know of a |
1036 | way around one of these issues, please let me know. |
1037 | |
1038 | =head2 References |
1039 | |
1040 | (The following assumes a high level of Perl understanding, specifically of |
1041 | references. Most users can safely skip this section.) |
1042 | |
1043 | Currently, the only references supported are HASH and ARRAY. The other reference |
1044 | types (SCALAR, CODE, GLOB, and REF) cannot be supported for various reasons. |
1045 | |
1046 | =over 4 |
1047 | |
1048 | =item * GLOB |
1049 | |
1050 | These are things like filehandles and other sockets. They can't be supported |
1051 | because it's completely unclear how DBM::Deep should serialize them. |
1052 | |
1053 | =item * SCALAR / REF |
1054 | |
1055 | The discussion here refers to the following type of example: |
1056 | |
1057 | my $x = 25; |
1058 | $db->{key1} = \$x; |
1059 | |
1060 | $x = 50; |
1061 | |
1062 | # In some other process ... |
1063 | |
1064 | my $val = ${ $db->{key1} }; |
1065 | |
1066 | is( $val, 50, "What actually gets stored in the DB file?" ); |
1067 | |
1068 | The problem is one of synchronization. When the variable being referred to |
1069 | changes value, the reference isn't notified, which is kind of the point of |
1070 | references. This means that the new value won't be stored in the datafile for |
1071 | other processes to read. There is no TIEREF. |
1072 | |
1073 | It is theoretically possible to store references to values already within a |
1074 | DBM::Deep object because everything already is synchronized, but the change to |
1075 | the internals would be quite large. Specifically, DBM::Deep would have to tie |
1076 | every single value that is stored. This would bloat the RAM footprint of |
1077 | DBM::Deep at least twofold (if not more) and be a significant performance drain, |
1078 | all to support a feature that has never been requested. |
1079 | |
1080 | =item * CODE |
1081 | |
1082 | L<Data::Dump::Streamer/> provides a mechanism for serializing coderefs, |
1083 | including saving off all closure state. This would allow for DBM::Deep to |
1084 | store the code for a subroutine. Then, whenever the subroutine is read, the |
1085 | code could be C<eval()>'ed into being. However, just as for SCALAR and REF, |
1086 | that closure state may change without notifying the DBM::Deep object storing |
1087 | the reference. Again, this would generally be considered a feature. |
1088 | |
1089 | =back |
1090 | |
1091 | =head2 File corruption |
1092 | |
1093 | The current level of error handling in DBM::Deep is minimal. Files I<are> checked |
1094 | for a 32-bit signature when opened, but any other form of corruption in the |
1095 | datafile can cause segmentation faults. DBM::Deep may try to C<seek()> past |
1096 | the end of a file, or get stuck in an infinite loop depending on the level and |
1097 | type of corruption. File write operations are not checked for failure (for |
1098 | speed), so if you happen to run out of disk space, DBM::Deep will probably fail in |
1099 | a bad way. These things will be addressed in a later version of DBM::Deep. |
1100 | |
1101 | =head2 DB over NFS |
1102 | |
1103 | Beware of using DBM::Deep files over NFS. DBM::Deep uses flock(), which works |
1104 | well on local filesystems, but will NOT protect you from file corruption over |
1105 | NFS. I've heard about setting up your NFS server with a locking daemon, then |
1106 | using C<lockf()> to lock your files, but your mileage may vary there as well. |
1107 | From what I understand, there is no real way to do it. However, if you need |
1108 | access to the underlying filehandle in DBM::Deep for using some other kind of |
1109 | locking scheme like C<lockf()>, see the L<LOW-LEVEL ACCESS> section above. |
1110 | |
1111 | =head2 Copying Objects |
1112 | |
1113 | Beware of copying tied objects in Perl. Very strange things can happen. |
1114 | Instead, use DBM::Deep's C<clone()> method which safely copies the object and |
1115 | returns a new, blessed and tied hash or array to the same level in the DB. |
1116 | |
1117 | my $copy = $db->clone(); |
1118 | |
1119 | B<Note>: Since clone() here is cloning the object, not the database location, any |
1120 | modifications to either $db or $copy will be visible to both. |
1121 | |
1122 | =head2 Large Arrays |
1123 | |
1124 | Beware of using C<shift()>, C<unshift()> or C<splice()> with large arrays. |
1125 | These functions cause every element in the array to move, which can be murder |
1126 | on DBM::Deep, as every element has to be fetched from disk, then stored again in |
1127 | a different location. This will be addressed in a future version. |
1128 | |
1129 | =head2 Writeonly Files |
1130 | |
1131 | If you pass in a filehandle to new(), you may have opened it in either a readonly or |
1132 | writeonly mode. STORE will verify that the filehandle is writable. However, there |
1133 | doesn't seem to be a good way to determine if a filehandle is readable. And, if the |
1134 | filehandle isn't readable, it's not clear what will happen. So, don't do that. |
1135 | |
1136 | =head2 Assignments Within Transactions |
1137 | |
1138 | The following will I<not> work as one might expect: |
1139 | |
1140 | my $x = { a => 1 }; |
1141 | |
1142 | $db->begin_work; |
1143 | $db->{foo} = $x; |
1144 | $db->rollback; |
1145 | |
1146 | is( $x->{a}, 1 ); # This will fail! |
1147 | |
1148 | The problem is that the moment a reference used as the rvalue to a DBM::Deep |
1149 | object's lvalue, it becomes tied itself. This is so that future changes to |
1150 | C<$x> can be tracked within the DBM::Deep file and is considered to be a |
1151 | feature. By the time the rollback occurs, there is no knowledge that there had |
1152 | been an C<$x> or what memory location to assign an C<export()> to. |
1153 | |
1154 | B<NOTE:> This does not affect importing because imports do a walk over the |
1155 | reference to be imported in order to explicitly leave it untied. |
1156 | |
1157 | =head1 CODE COVERAGE |
1158 | |
1159 | B<Devel::Cover> is used to test the code coverage of the tests. Below is the |
1160 | B<Devel::Cover> report on this distribution's test suite. |
1161 | |
807f63a7 |
1162 | ----------------------------------- ------ ------ ------ ------ ------ ------ |
1163 | File stmt bran cond sub time total |
1164 | ----------------------------------- ------ ------ ------ ------ ------ ------ |
1165 | blib/lib/DBM/Deep.pm 94.4 85.0 90.5 100.0 5.0 93.4 |
1166 | blib/lib/DBM/Deep/Array.pm 100.0 94.6 100.0 100.0 4.7 98.8 |
1167 | blib/lib/DBM/Deep/Engine.pm 97.2 85.8 82.4 100.0 51.3 93.8 |
1168 | blib/lib/DBM/Deep/File.pm 97.2 81.6 66.7 100.0 36.5 91.9 |
1169 | blib/lib/DBM/Deep/Hash.pm 100.0 100.0 100.0 100.0 2.5 100.0 |
1170 | Total 97.2 87.4 83.9 100.0 100.0 94.6 |
1171 | ----------------------------------- ------ ------ ------ ------ ------ ------ |
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1172 | |
1173 | =head1 MORE INFORMATION |
1174 | |
1175 | Check out the DBM::Deep Google Group at L<http://groups.google.com/group/DBM-Deep> |
1176 | or send email to L<DBM-Deep@googlegroups.com>. You can also visit #dbm-deep on |
1177 | irc.perl.org |
1178 | |
1179 | The source code repository is at L<http://svn.perl.org/modules/DBM-Deep> |
1180 | |
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1181 | =head1 MAINTAINERS |
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1182 | |
1183 | Rob Kinyon, L<rkinyon@cpan.org> |
1184 | |
1185 | Originally written by Joseph Huckaby, L<jhuckaby@cpan.org> |
1186 | |
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1187 | =head1 SPONSORS |
1188 | |
1189 | Stonehenge Consulting (L<http://www.stonehenge.com/>) sponsored the |
1190 | developement of transactions and freespace management, leading to the 1.0000 |
1191 | release. A great debt of gratitude goes out to them for their continuing |
1192 | leadership in and support of the Perl community. |
1193 | |
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1194 | =head1 CONTRIBUTORS |
1195 | |
1196 | The following have contributed greatly to make DBM::Deep what it is today: |
1197 | |
1198 | =over 4 |
1199 | |
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1200 | =item * Adam Sah and Rich Gaushell for innumerable contributions early on. |
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1201 | |
1202 | =item * Dan Golden and others at YAPC::NA 2006 for helping me design through transactions. |
1203 | |
1204 | =back |
1205 | |
1206 | =head1 SEE ALSO |
1207 | |
1208 | perltie(1), Tie::Hash(3), Digest::MD5(3), Fcntl(3), flock(2), lockf(3), nfs(5), |
1209 | Digest::SHA256(3), Crypt::Blowfish(3), Compress::Zlib(3) |
1210 | |
1211 | =head1 LICENSE |
1212 | |
1213 | Copyright (c) 2007 Rob Kinyon. All Rights Reserved. |
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1214 | This is free software, you may use it and distribute it under the same terms |
1215 | as Perl itself. |
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1216 | |
1217 | =cut |