1Cache::FastMmap(3)    User Contributed Perl Documentation   Cache::FastMmap(3)
2
3
4

NAME

6       Cache::FastMmap - Uses an mmap'ed file to act as a shared memory
7       interprocess cache
8

SYNOPSIS

10         use Cache::FastMmap;
11
12         # Uses vaguely sane defaults
13         $Cache = Cache::FastMmap->new();
14
15         # Uses Storable to serialize $Value to bytes for storage
16         $Cache->set($Key, $Value);
17         $Value = $Cache->get($Key);
18
19         $Cache = Cache::FastMmap->new(serializer => '');
20
21         # Stores stringified bytes of $Value directly
22         $Cache->set($Key, $Value);
23         $Value = $Cache->get($Key);
24

ABSTRACT

26       A shared memory cache through an mmap'ed file. It's core is written in
27       C for performance. It uses fcntl locking to ensure multiple processes
28       can safely access the cache at the same time. It uses a basic LRU
29       algorithm to keep the most used entries in the cache.
30

DESCRIPTION

32       In multi-process environments (eg mod_perl, forking daemons, etc), it's
33       common to want to cache information, but have that cache shared between
34       processes. Many solutions already exist, and may suit your situation
35       better:
36
37       ·   MLDBM::Sync - acts as a database, data is not automatically
38           expired, slow
39
40       ·   IPC::MM - hash implementation is broken, data is not automatically
41           expired, slow
42
43       ·   Cache::FileCache - lots of features, slow
44
45       ·   Cache::SharedMemoryCache - lots of features, VERY slow. Uses
46           IPC::ShareLite which freeze/thaws ALL data at each read/write
47
48       ·   DBI - use your favourite RDBMS. can perform well, need a DB server
49           running. very global. socket connection latency
50
51       ·   Cache::Mmap - similar to this module, in pure perl. slows down with
52           larger pages
53
54       ·   BerkeleyDB - very fast (data ends up mostly in shared memory cache)
55           but acts as a database overall, so data is not automatically
56           expired
57
58       In the case I was working on, I needed:
59
60       ·   Automatic expiry and space management
61
62       ·   Very fast access to lots of small items
63
64       ·   The ability to fetch/store many items in one go
65
66       Which is why I developed this module. It tries to be quite efficient
67       through a number of means:
68
69       ·   Core code is written in C for performance
70
71       ·   It uses multiple pages within a file, and uses Fcntl to only lock a
72           page at a time to reduce contention when multiple processes access
73           the cache.
74
75       ·   It uses a dual level hashing system (hash to find page, then hash
76           within each page to find a slot) to make most "get()" calls O(1)
77           and fast
78
79       ·   On each "set()", if there are slots and page space available, only
80           the slot has to be updated and the data written at the end of the
81           used data space. If either runs out, a re-organisation of the page
82           is performed to create new slots/space which is done in an
83           efficient way
84
85       The class also supports read-through, and write-back or write-through
86       callbacks to access the real data if it's not in the cache, meaning
87       that code like this:
88
89         my $Value = $Cache->get($Key);
90         if (!defined $Value) {
91           $Value = $RealDataSource->get($Key);
92           $Cache->set($Key, $Value)
93         }
94
95       Isn't required, you instead specify in the constructor:
96
97         Cache::FastMmap->new(
98           ...
99           context => $RealDataSourceHandle,
100           read_cb => sub { $_[0]->get($_[1]) },
101           write_cb => sub { $_[0]->set($_[1], $_[2]) },
102         );
103
104       And then:
105
106         my $Value = $Cache->get($Key);
107
108         $Cache->set($Key, $NewValue);
109
110       Will just work and will be read/written to the underlying data source
111       as needed automatically.
112

PERFORMANCE

114       If you're storing relatively large and complex structures into the
115       cache, then you're limited by the speed of the Storable module.  If
116       you're storing simple structures, or raw data, then Cache::FastMmap has
117       noticeable performance improvements.
118
119       See <http://cpan.robm.fastmail.fm/cache_perf.html> for some comparisons
120       to other modules.
121

COMPATIBILITY

123       Cache::FastMmap uses mmap to map a file as the shared cache space, and
124       fcntl to do page locking. This means it should work on most UNIX like
125       operating systems.
126
127       Ash Berlin has written a Win32 layer using MapViewOfFile et al. to
128       provide support for Win32 platform.
129

MEMORY SIZE

131       Because Cache::FastMmap mmap's a shared file into your processes memory
132       space, this can make each process look quite large, even though it's
133       just mmap'd memory that's shared between all processes that use the
134       cache, and may even be swapped out if the cache is getting low usage.
135
136       However, the OS will think your process is quite large, which might
137       mean you hit some BSD::Resource or 'ulimits' you set previously that
138       you thought were sane, but aren't anymore, so be aware.
139

CACHE FILES AND OS ISSUES

141       Because Cache::FastMmap uses an mmap'ed file, when you put values into
142       the cache, you are actually "dirtying" pages in memory that belong to
143       the cache file. Your OS will want to write those dirty pages back to
144       the file on the actual physical disk, but the rate it does that at is
145       very OS dependent.
146
147       In Linux, you have some control over how the OS writes those pages back
148       using a number of parameters in /proc/sys/vm
149
150         dirty_background_ratio
151         dirty_expire_centisecs
152         dirty_ratio
153         dirty_writeback_centisecs
154
155       How you tune these depends heavily on your setup.
156
157       As an interesting point, if you use a highmem linux kernel, a change
158       between 2.6.16 and 2.6.20 made the kernel flush memory a LOT more.
159       There's details in this kernel mailing list thread:
160       <http://www.uwsg.iu.edu/hypermail/linux/kernel/0711.3/0804.html>
161
162       In most cases, people are not actually concerned about the persistence
163       of data in the cache, and so are happy to disable writing of any cache
164       data back to disk at all. Baically what they want is an in memory only
165       shared cache. The best way to do that is to use a "tmpfs" filesystem
166       and put all cache files on there.
167
168       For instance, all our machines have a /tmpfs mount point that we create
169       in /etc/fstab as:
170
171         none /tmpfs tmpfs defaults,noatime,size=1000M 0 0
172
173       And we put all our cache files on there. The tmpfs filesystem is smart
174       enough to only use memory as required by files actually on the tmpfs,
175       so making it 1G in size doesn't actually use 1G of memory, it only uses
176       as much as the cache files we put on it. In all cases, we ensure that
177       we never run out of real memory, so the cache files effectively act
178       just as named access points to shared memory.
179
180       Some people have suggested using anonymous mmaped memory. Unfortunately
181       we need a file descriptor to do the fcntl locking on, so we'd have to
182       create a separate file on a filesystem somewhere anyway. It seems
183       easier to just create an explicit "tmpfs" filesystem.
184

PAGE SIZE AND KEY/VALUE LIMITS

186       To reduce lock contention, Cache::FastMmap breaks up the file into
187       pages. When you get/set a value, it hashes the key to get a page, then
188       locks that page, and uses a hash table within the page to get/store the
189       actual key/value pair.
190
191       One consequence of this is that you cannot store values larger than a
192       page in the cache at all. Attempting to store values larger than a page
193       size will fail (the set() function will return false).
194
195       Also keep in mind that each page has it's own hash table, and that we
196       store the key and value data of each item. So if you are expecting to
197       store large values and/or keys in the cache, you should use page sizes
198       that are definitely larger than your largest key + value size + a few
199       kbytes for the overhead.
200

USAGE

202       Because the cache uses shared memory through an mmap'd file, you have
203       to make sure each process connects up to the file. There's probably two
204       main ways to do this:
205
206       ·   Create the cache in the parent process, and then when it forks,
207           each child will inherit the same file descriptor, mmap'ed memory,
208           etc and just work. This is the recommended way. (BEWARE: This only
209           works under UNIX as Win32 has no concept of forking)
210
211       ·   Explicitly connect up in each forked child to the share file. In
212           this case, make sure the file already exists and the children
213           connect with init_file => 0 to avoid deleting the cache contents
214           and possible race corruption conditions. Also be careful that
215           multiple children may race to create the file at the same time,
216           each overwriting and corrupting content. Use a separate lock file
217           if you must to ensure only one child creates the file. (This is the
218           only possible way under Win32)
219
220       The first way is usually the easiest. If you're using the cache in a
221       Net::Server based module, you'll want to open the cache in the
222       "pre_loop_hook", because that's executed before the fork, but after the
223       process ownership has changed and any chroot has been done.
224
225       In mod_perl, just open the cache at the global level in the appropriate
226       module, which is executed as the server is starting and before it
227       starts forking children, but you'll probably want to chmod or chown the
228       file to the permissions of the apache process.
229

METHODS

231       new(%Opts)
232           Create a new Cache::FastMmap object.
233
234           Basic global parameters are:
235
236           ·   share_file
237
238               File to mmap for sharing of data.  default on unix:
239               /tmp/sharefile-$pid-$time-$random default on windows:
240               %TEMP%\sharefile-$pid-$time-$random
241
242           ·   init_file
243
244               Clear any existing values and re-initialise file. Useful to do
245               in a parent that forks off children to ensure that file is
246               empty at the start (default: 0)
247
248               Note: This is quite important to do in the parent to ensure a
249               consistent file structure. The shared file is not perfectly
250               transaction safe, and so if a child is killed at the wrong
251               instant, it might leave the cache file in an inconsistent
252               state.
253
254           ·   serializer
255
256               Use a serialization library to serialize perl data structures
257               before storing in the cache. If not set, the raw value in the
258               variable passed to set() is stored as a string. You must set
259               this if you want to store anything other than basic scalar
260               values. Supported values are:
261
262                 ''         for none
263                 'storable' for 'Storable'
264                 'sereal'   for 'Sereal'
265                 'json'     for 'JSON'
266                 [ $s, $d ] for custom serializer/de-serializer
267
268               If this parameter has a value the module will attempt to load
269               the associated package and then use the API of that package to
270               serialize data before storing in the cache, and deserialize it
271               upon retrieval from the cache. (default: 'storable')
272
273               You can use a custom serializer/de-serializer by passing an
274               array-ref with two values. The first should be a subroutine
275               reference that takes the data to serialize as a single argument
276               and returns an octet stream to store. The second should be a
277               subroutine reference that takes the octet stream as a single
278               argument and returns the original data structure.
279
280               One thing to note, the data structure passed to the serializer
281               is always a *scalar* reference to the original data passed in
282               to the ->set(...)  call. If your serializer doesn't support
283               that, you might need to dereference it first before storing,
284               but rembember to return a reference again in the de-serializer.
285
286               (Note: Historically this module only supported a boolean value
287               for the `raw_values` parameter and defaulted to 0, which meant
288               it used Storable to serialze all values.)
289
290           ·   raw_values
291
292               Deprecated. Use serializer above
293
294           ·   compressor
295
296               Compress the value (but not the key) before storing into the
297               cache, using the compression package identified by the value of
298               the parameter. Supported values are:
299
300                 'zlib'     for 'Compress::Zlib'
301                 'lz4'      for 'Compress::LZ4'
302                 'snappy'   for 'Compress::Snappy'
303                 [ $c, $d ] for custom compressor/de-compressor
304
305               If this parameter has a value the module will attempt to load
306               the associated package and then use the API of that package to
307               compress data before storing in the cache, and uncompress it
308               upon retrieval from the cache. (default: undef)
309
310               You can use a custom compressor/de-compressor by passing an
311               array-ref with two values. The first should be a subroutine
312               reference that takes the data to compress as a single octet
313               stream argument and returns an octet stream to store. The
314               second should be a subroutine reference that takes the
315               compressed octet stream as a single argument and returns the
316               original uncompressed data.
317
318               (Note: Historically this module only supported a boolean value
319               for the `compress` parameter and defaulted to use
320               Compress::Zlib. The note for the old `compress` parameter
321               stated: "Some initial testing shows that the uncompressing
322               tends to be very fast, though the compressing can be quite
323               slow, so it's probably best to use this option only if you know
324               values in the cache are long-lived and have a high hit rate."
325
326               Comparable test results for the other compression tools are not
327               yet available; submission of benchmarks welcome. However, the
328               documentation for the 'Snappy' library
329               (http://google.github.io/snappy/) states: For instance,
330               compared to the fastest mode of zlib, Snappy is an order of
331               magnitude faster for most inputs, but the resulting compressed
332               files are anywhere from 20% to 100% bigger. )
333
334           ·   compress
335
336               Deprecated. Please use compressor, see above.
337
338           ·   enable_stats
339
340               Enable some basic statistics capturing. When enabled, every
341               read to the cache is counted, and every read to the cache that
342               finds a value in the cache is also counted. You can then
343               retrieve these values via the get_statistics() call. This
344               causes every read action to do a write on a page, which can
345               cause some more IO, so it's disabled by default. (default: 0)
346
347           ·   expire_time
348
349               Maximum time to hold values in the cache in seconds. A value of
350               0 means does no explicit expiry time, and values are expired
351               only based on LRU usage. Can be expressed as 1m, 1h, 1d for
352               minutes/hours/days respectively. (default: 0)
353
354           You may specify the cache size as:
355
356           ·   cache_size
357
358               Size of cache. Can be expresses as 1k, 1m for kilobytes or
359               megabytes respectively. Automatically guesses page size/page
360               count values.
361
362           Or specify explicit page size/page count values. If none of these
363           are specified, the values page_size = 64k and num_pages = 89 are
364           used.
365
366           ·   page_size
367
368               Size of each page. Must be a power of 2 between 4k and 1024k.
369               If not, is rounded to the nearest value.
370
371           ·   num_pages
372
373               Number of pages. Should be a prime number for best hashing
374
375           The cache allows the use of callbacks for reading/writing data to
376           an underlying data store.
377
378           ·   context
379
380               Opaque reference passed as the first parameter to any callback
381               function if specified
382
383           ·   read_cb
384
385               Callback to read data from the underlying data store.  Called
386               as:
387
388                 $read_cb->($context, $Key)
389
390               Should return the value to use. This value will be saved in the
391               cache for future retrievals. Return undef if there is no value
392               for the given key
393
394           ·   write_cb
395
396               Callback to write data to the underlying data store.  Called
397               as:
398
399                 $write_cb->($context, $Key, $Value, $ExpiryTime)
400
401               In 'write_through' mode, it's always called as soon as a
402               set(...)  is called on the Cache::FastMmap class. In
403               'write_back' mode, it's called when a value is expunged from
404               the cache if it's been changed by a set(...) rather than read
405               from the underlying store with the read_cb above.
406
407               Note: Expired items do result in the write_cb being called if
408               'write_back' caching is enabled and the item has been changed.
409               You can check the $ExpiryTime against "time()" if you only want
410               to write back values which aren't expired.
411
412               Also remember that write_cb may be called in a different
413               process to the one that placed the data in the cache in the
414               first place
415
416           ·   delete_cb
417
418               Callback to delete data from the underlying data store.  Called
419               as:
420
421                 $delete_cb->($context, $Key)
422
423               Called as soon as remove(...) is called on the Cache::FastMmap
424               class
425
426           ·   cache_not_found
427
428               If set to true, then if the read_cb is called and it returns
429               undef to say nothing was found, then that information is stored
430               in the cache, so that next time a get(...) is called on that
431               key, undef is returned immediately rather than again calling
432               the read_cb
433
434           ·   write_action
435
436               Either 'write_back' or 'write_through'. (default:
437               write_through)
438
439           ·   allow_recursive
440
441               If you're using a callback function, then normally the cache is
442               not re-enterable, and attempting to call a get/set on the cache
443               will cause an error. By setting this to one, the cache will
444               unlock any pages before calling the callback. During the unlock
445               time, other processes may change data in current cache page,
446               causing possible unexpected effects. You shouldn't set this
447               unless you know you want to be able to recall to the cache
448               within a callback.  (default: 0)
449
450           ·   empty_on_exit
451
452               When you have 'write_back' mode enabled, then you really want
453               to make sure all values from the cache are expunged when your
454               program exits so any changes are written back.
455
456               The trick is that we only want to do this in the parent
457               process, we don't want any child processes to empty the cache
458               when they exit.  So if you set this, it takes the PID via $$,
459               and only calls empty in the DESTROY method if $$ matches the
460               pid we captured at the start. (default: 0)
461
462           ·   unlink_on_exit
463
464               Unlink the share file when the cache is destroyed.
465
466               As with empty_on_exit, this will only unlink the file if the
467               DESTROY occurs in the same PID that the cache was created in so
468               that any forked children don't unlink the file.
469
470               This value defaults to 1 if the share_file specified does not
471               already exist. If the share_file specified does already exist,
472               it defaults to 0.
473
474           ·   catch_deadlocks
475
476               Sets an alarm(10) before each page is locked via
477               fcntl(F_SETLKW) to catch any deadlock. This used to be the
478               default behaviour, but it's not really needed in the default
479               case and could clobber sub-second Time::HiRes alarms setup by
480               other code. Defaults to 0.
481
482       get($Key, [ \%Options ])
483           Search cache for given Key. Returns undef if not found. If read_cb
484           specified and not found, calls the callback to try and find the
485           value for the key, and if found (or 'cache_not_found' is set),
486           stores it into the cache and returns the found value.
487
488           %Options is optional, and is used by get_and_set() to control the
489           locking behaviour. For now, you should probably ignore it unless
490           you read the code to understand how it works
491
492       set($Key, $Value, [ \%Options ])
493           Store specified key/value pair into cache
494
495           %Options is optional, and is used by get_and_set() to control the
496           locking behaviour. For now, you should probably ignore it unless
497           you read the code to understand how it works
498
499           This method returns true if the value was stored in the cache,
500           false otherwise. See the PAGE SIZE AND KEY/VALUE LIMITS section for
501           more details.
502
503       get_and_set($Key, $Sub)
504           Atomically retrieve and set the value of a Key.
505
506           The page is locked while retrieving the $Key and is unlocked only
507           after the value is set, thus guaranteeing the value does not change
508           between the get and set operations.
509
510           $Sub is a reference to a subroutine that is called to calculate the
511           new value to store. $Sub gets $Key and the current value as
512           parameters, and should return the new value to set in the cache for
513           the given $Key.
514
515           If the subroutine returns an empty list, no value is stored back in
516           the cache. This avoids updating the expiry time on an entry if you
517           want to do a "get if in cache, store if not present" type callback.
518
519           For example, to atomically increment a value in the cache, you can
520           just use:
521
522             $Cache->get_and_set($Key, sub { return ++$_[1]; });
523
524           In scalar context, the return value from this function is the *new*
525           value stored back into the cache.
526
527           In list context, a two item array is returned; the new value stored
528           back into the cache and a boolean that's true if the value was
529           stored in the cache, false otherwise. See the PAGE SIZE AND
530           KEY/VALUE LIMITS section for more details.
531
532           Notes:
533
534           ·   Do not perform any get/set operations from the callback sub, as
535               these operations lock the page and you may end up with a dead
536               lock!
537
538           ·   If your sub does a die/throws an exception, the page will
539               correctly be unlocked (1.15 onwards)
540
541       remove($Key, [ \%Options ])
542           Delete the given key from the cache
543
544           %Options is optional, and is used by get_and_remove() to control
545           the locking behaviour. For now, you should probably ignore it
546           unless you read the code to understand how it works
547
548       get_and_remove($Key)
549           Atomically retrieve value of a Key while removing it from the
550           cache.
551
552           The page is locked while retrieving the $Key and is unlocked only
553           after the value is removed, thus guaranteeing the value stored by
554           someone else isn't removed by us.
555
556       clear()
557           Clear all items from the cache
558
559           Note: If you're using callbacks, this has no effect on items in the
560           underlying data store. No delete callbacks are made
561
562       purge()
563           Clear all expired items from the cache
564
565           Note: If you're using callbacks, this has no effect on items in the
566           underlying data store. No delete callbacks are made, and no write
567           callbacks are made for the expired data
568
569       empty($OnlyExpired)
570           Empty all items from the cache, or if $OnlyExpired is true, only
571           expired items.
572
573           Note: If 'write_back' mode is enabled, any changed items are
574           written back to the underlying store. Expired items are written
575           back to the underlying store as well.
576
577       get_keys($Mode)
578           Get a list of keys/values held in the cache. May immediately be out
579           of date because of the shared access nature of the cache
580
581           If $Mode == 0, an array of keys is returned
582
583           If $Mode == 1, then an array of hashrefs, with 'key',
584           'last_access', 'expire_time' and 'flags' keys is returned
585
586           If $Mode == 2, then hashrefs also contain 'value' key
587
588       get_statistics($Clear)
589           Returns a two value list of (nreads, nreadhits). This only works if
590           you passed enable_stats in the constructor
591
592           nreads is the total number of read attempts done on the cache since
593           it was created
594
595           nreadhits is the total number of read attempts done on the cache
596           since it was created that found the key/value in the cache
597
598           If $Clear is true, the values are reset immediately after they are
599           retrieved
600
601       multi_get($PageKey, [ $Key1, $Key2, ... ])
602           The two multi_xxx routines act a bit differently to the other
603           routines. With the multi_get, you pass a separate PageKey value and
604           then multiple keys. The PageKey value is hashed, and that page
605           locked. Then that page is searched for each key. It returns a hash
606           ref of Key => Value items found in that page in the cache.
607
608           The main advantage of this is just a speed one, if you happen to
609           need to search for a lot of items on each call.
610
611           For instance, say you have users and a bunch of pieces of separate
612           information for each user. On a particular run, you need to
613           retrieve a sub-set of that information for a user. You could do
614           lots of get() calls, or you could use the 'username' as the page
615           key, and just use one multi_get() and multi_set() call instead.
616
617           A couple of things to note:
618
619           1.  This makes multi_get()/multi_set() and get()/set()
620               incompatible. Don't mix calls to the two, because you won't
621               find the data you're expecting
622
623           2.  The writeback and callback modes of operation do not work with
624               multi_get()/multi_set(). Don't attempt to use them together.
625
626       multi_set($PageKey, { $Key1 = $Value1, $Key2 => $Value2, ... }, [
627       \%Options ])>
628           Store specified key/value pair into cache
629

INTERNAL METHODS

631       _expunge_all($Mode, $WB)
632           Expunge all items from the cache
633
634           Expunged items (that have not expired) are written back to the
635           underlying store if write_back is enabled
636
637       _expunge_page($Mode, $WB, $Len)
638           Expunge items from the current page to make space for $Len bytes
639           key/value items
640
641           Expunged items (that have not expired) are written back to the
642           underlying store if write_back is enabled
643
644       _lock_page($Page)
645           Lock a given page in the cache, and return an object reference that
646           when DESTROYed, unlocks the page
647

INCOMPATIBLE CHANGES

649       ·   From 1.15
650
651           ·   Default share_file name is no-longer /tmp/sharefile, but
652               /tmp/sharefile-$pid-$time.  This ensures that different
653               runs/processes don't interfere with each other, but means you
654               may not connect up to the file you expect. You should be
655               choosing an explicit name in most cases.
656
657               On Unix systems, you can pass in the environment variable
658               TMPDIR to override the default directory of /tmp
659
660           ·   The new option unlink_on_exit defaults to true if you pass a
661               filename for the share_file which doesn't already exist. This
662               means if you have one process that creates the file, and
663               another that expects the file to be there, by default it won't
664               be.
665
666               Otherwise the defaults seem sensible to cleanup unneeded share
667               files rather than leaving them around to accumulate.
668
669       ·   From 1.29
670
671           ·   Default share_file name is no longer /tmp/sharefile-$pid-$time
672               but /tmp/sharefile-$pid-$time-$random.
673
674       ·   From 1.31
675
676           ·   Before 1.31, if you were using raw_values => 0 mode, then the
677               write_cb would be called with raw frozen data, rather than the
678               thawed object.  From 1.31 onwards, it correctly calls write_cb
679               with the thawed object value (eg what was passed to the ->set()
680               call in the first place)
681
682       ·   From 1.36
683
684           ·   Before 1.36, an alarm(10) would be set before each attempt to
685               lock a page. The only purpose of this was to detect deadlocks,
686               which should only happen if the Cache::FastMmap code was buggy,
687               or a callback function in get_and_set() made another call into
688               Cache::FastMmap.
689
690               However this added unnecessary extra system calls for every
691               lookup, and for users using Time::HiRes, it could clobber any
692               existing alarms that had been set with sub-second resolution.
693
694               So this has now been made an optional feature via the
695               catch_deadlocks option passed to new.
696

SEE ALSO

698       MLDBM::Sync, IPC::MM, Cache::FileCache, Cache::SharedMemoryCache, DBI,
699       Cache::Mmap, BerkeleyDB
700
701       Latest news/details can also be found at:
702
703       <http://cpan.robm.fastmail.fm/cachefastmmap/>
704
705       Available on github at:
706
707       <https://github.com/robmueller/cache-fastmmap/>
708

AUTHOR

710       Rob Mueller <mailto:cpan@robm.fastmail.fm>
711
713       Copyright (C) 2003-2017 by FastMail Pty Ltd
714
715       This library is free software; you can redistribute it and/or modify it
716       under the same terms as Perl itself.
717
718
719
720perl v5.30.0                      2019-07-26                Cache::FastMmap(3)
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