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3 | BDB - Asynchronous Berkeley DB access |
3 | BDB - Asynchronous Berkeley DB access |
4 | |
4 | |
5 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
6 | |
6 | |
7 | use BDB; |
7 | use BDB; |
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8 | |
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9 | my $env = db_env_create; |
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10 | |
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11 | mkdir "bdtest", 0700; |
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12 | db_env_open |
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13 | $env, |
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14 | "bdtest", |
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15 | BDB::INIT_LOCK | BDB::INIT_LOG | BDB::INIT_MPOOL |
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16 | | BDB::INIT_TXN | BDB::RECOVER | BDB::USE_ENVIRON | BDB::CREATE, |
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17 | 0600; |
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18 | |
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19 | $env->set_flags (BDB::AUTO_COMMIT | BDB::TXN_NOSYNC, 1); |
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20 | |
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21 | my $db = db_create $env; |
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22 | db_open $db, undef, "table", undef, BDB::BTREE, BDB::AUTO_COMMIT | BDB::CREATE |
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23 | | BDB::READ_UNCOMMITTED, 0600; |
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24 | db_put $db, undef, "key", "data", 0, sub { |
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25 | db_del $db, undef, "key"; |
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26 | }; |
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27 | db_sync $db; |
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28 | |
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29 | # automatic result processing with AnyEvent: |
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30 | our $FH; open $FH, "<&=" . BDB::poll_fileno; |
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31 | our $WATCHER = AnyEvent->io (fh => $FH, poll => 'r', cb => \&BDB::poll_cb); |
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32 | |
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33 | # automatic result processing with EV: |
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34 | my $WATCHER = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb; |
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35 | |
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36 | # with Glib: |
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37 | add_watch Glib::IO BDB::poll_fileno, |
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38 | in => sub { BDB::poll_cb; 1 }; |
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39 | |
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40 | # or simply flush manually |
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41 | BDB::flush; |
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42 | |
8 | |
43 | |
9 | =head1 DESCRIPTION |
44 | =head1 DESCRIPTION |
10 | |
45 | |
11 | See the BerkeleyDB documentation (L<http://www.oracle.com/technology/documentation/berkeley-db/db/index.html>). |
46 | See the BerkeleyDB documentation (L<http://www.oracle.com/technology/documentation/berkeley-db/db/index.html>). |
12 | The BDB API is very similar to the C API (the translation has been very faithful). |
47 | The BDB API is very similar to the C API (the translation has been very faithful). |
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72 | use strict 'vars'; |
107 | use strict 'vars'; |
73 | |
108 | |
74 | use base 'Exporter'; |
109 | use base 'Exporter'; |
75 | |
110 | |
76 | BEGIN { |
111 | BEGIN { |
77 | our $VERSION = '1.1'; |
112 | our $VERSION = '1.3'; |
78 | |
113 | |
79 | our @BDB_REQ = qw( |
114 | our @BDB_REQ = qw( |
80 | db_env_open db_env_close db_env_txn_checkpoint db_env_lock_detect |
115 | db_env_open db_env_close db_env_txn_checkpoint db_env_lock_detect |
81 | db_env_memp_sync db_env_memp_trickle |
116 | db_env_memp_sync db_env_memp_trickle |
82 | db_open db_close db_compact db_sync db_put db_get db_pget db_del db_key_range |
117 | db_open db_close db_compact db_sync db_put db_get db_pget db_del db_key_range |
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179 | db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef) |
214 | db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef) |
180 | flags: TXN_NOSYNC |
215 | flags: TXN_NOSYNC |
181 | |
216 | |
182 | =head4 db_txn_finish (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef) |
217 | =head4 db_txn_finish (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef) |
183 | |
218 | |
184 | This is not a Berkeley DB function but a BDB module extension. It is very |
219 | This is not actually a Berkeley DB function but a BDB module |
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220 | extension. The background for this exytension is: It is very annoying to |
185 | annoying to have to check every single BDB function for error returns and |
221 | have to check every single BDB function for error returns and provide a |
186 | provide a codepath out of your transaction. While the BDB module still |
222 | codepath out of your transaction. While the BDB module still makes this |
187 | makes this possible, it contains the following extensions: |
223 | possible, it contains the following extensions: |
188 | |
224 | |
189 | When a transaction-protected function returns any operating system |
225 | When a transaction-protected function returns any operating system |
190 | error (errno > 0), BDB will set the C<TXN_DEADLOCK> flag on the |
226 | error (errno > 0), BDB will set the C<TXN_DEADLOCK> flag on the |
191 | transaction. This flag is also set by Berkeley DB functions externally |
227 | transaction. This flag is also set by Berkeley DB functions themselves |
192 | when an operation fails with LOCK_DEADLOCK, and it causes all further |
228 | when an operation fails with LOCK_DEADLOCK, and it causes all further |
193 | operations on that transaction (including C<db_txn_commit>) to fail. |
229 | operations on that transaction (including C<db_txn_commit>) to fail. |
194 | |
230 | |
195 | The C<db_txn_finish> request will look at this flag, and, if it is set, |
231 | The C<db_txn_finish> request will look at this flag, and, if it is set, |
196 | will automatically call C<db_txn_abort> (setting errno to C<LOCK_DEADLOCK> |
232 | will automatically call C<db_txn_abort> (setting errno to C<LOCK_DEADLOCK> |
197 | if it isn't set). If it isn't set, it will call C<db_txn_commit> and |
233 | if it isn't set to something else yet). If it isn't set, it will call |
198 | return the error normally. |
234 | C<db_txn_commit> and return the error normally. |
199 | |
235 | |
200 | How to use this? Easy: just write your transaction normally: |
236 | How to use this? Easy: just write your transaction normally: |
201 | |
237 | |
202 | my $txn = $db_env->txn_begin; |
238 | my $txn = $db_env->txn_begin; |
203 | db_get $db, $txn, "key", my $data; |
239 | db_get $db, $txn, "key", my $data; |
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208 | That is, handle only the expected errors. If something unexpected happens |
244 | That is, handle only the expected errors. If something unexpected happens |
209 | (EIO, LOCK_NOTGRANTED or a deadlock in either db_get or db_put), then the remaining |
245 | (EIO, LOCK_NOTGRANTED or a deadlock in either db_get or db_put), then the remaining |
210 | requests (db_put in this case) will simply be skipped (they will fail with |
246 | requests (db_put in this case) will simply be skipped (they will fail with |
211 | LOCK_DEADLOCK) and the transaction will be aborted. |
247 | LOCK_DEADLOCK) and the transaction will be aborted. |
212 | |
248 | |
213 | You cna use the C<< $txn->failed >> method to check wether a transaction |
249 | You can use the C<< $txn->failed >> method to check wether a transaction |
214 | has failed in this way and abort further processing (excluding |
250 | has failed in this way and abort further processing (excluding |
215 | C<db_txn_finish>). |
251 | C<db_txn_finish>). |
216 | |
252 | |
217 | =head3 DB_ENV/database environment methods |
253 | =head3 DB_ENV/database environment methods |
218 | |
254 | |
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241 | $int = $env->set_lk_max_lockers (U32 max) |
277 | $int = $env->set_lk_max_lockers (U32 max) |
242 | $int = $env->set_lk_max_locks (U32 max) |
278 | $int = $env->set_lk_max_locks (U32 max) |
243 | $int = $env->set_lk_max_objects (U32 max) |
279 | $int = $env->set_lk_max_objects (U32 max) |
244 | $int = $env->set_lg_bsize (U32 max) |
280 | $int = $env->set_lg_bsize (U32 max) |
245 | $int = $env->set_lg_max (U32 max) |
281 | $int = $env->set_lg_max (U32 max) |
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282 | $int = $env->mutex_set_increment (U32 increment) |
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283 | $int = $env->mutex_set_tas_spins (U32 tas_spins) |
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284 | $int = $env->mutex_set_max (U32 max) |
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285 | $int = $env->mutex_set_align (U32 align) |
246 | |
286 | |
247 | $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0) |
287 | $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0) |
248 | flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC |
288 | flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC |
249 | |
289 | |
250 | =head4 Example: |
290 | =head4 Example: |
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434 | interactiveness when perl is not fast enough to process all requests in |
474 | interactiveness when perl is not fast enough to process all requests in |
435 | time. |
475 | time. |
436 | |
476 | |
437 | For interactive programs, values such as C<0.01> to C<0.1> should be fine. |
477 | For interactive programs, values such as C<0.01> to C<0.1> should be fine. |
438 | |
478 | |
439 | Example: Install an Event watcher that automatically calls |
479 | Example: Install an EV watcher that automatically calls |
440 | BDB::poll_cb with low priority, to ensure that other parts of the |
480 | BDB::poll_cb with low priority, to ensure that other parts of the |
441 | program get the CPU sometimes even under high AIO load. |
481 | program get the CPU sometimes even under high load. |
442 | |
482 | |
443 | # try not to spend much more than 0.1s in poll_cb |
483 | # try not to spend much more than 0.1s in poll_cb |
444 | BDB::max_poll_time 0.1; |
484 | BDB::max_poll_time 0.1; |
445 | |
485 | |
446 | # use a low priority so other tasks have priority |
486 | my $bdb_poll = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb); |
447 | Event->io (fd => BDB::poll_fileno, |
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448 | poll => 'r', nice => 1, |
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449 | cb => &BDB::poll_cb); |
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450 | |
487 | |
451 | =item BDB::poll_wait |
488 | =item BDB::poll_wait |
452 | |
489 | |
453 | If there are any outstanding requests and none of them in the result |
490 | If there are any outstanding requests and none of them in the result |
454 | phase, wait till the result filehandle becomes ready for reading (simply |
491 | phase, wait till the result filehandle becomes ready for reading (simply |
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466 | |
503 | |
467 | BDB::poll_wait, BDB::poll_cb |
504 | BDB::poll_wait, BDB::poll_cb |
468 | |
505 | |
469 | =item BDB::flush |
506 | =item BDB::flush |
470 | |
507 | |
471 | Wait till all outstanding AIO requests have been handled. |
508 | Wait till all outstanding BDB requests have been handled. |
472 | |
509 | |
473 | Strictly equivalent to: |
510 | Strictly equivalent to: |
474 | |
511 | |
475 | BDB::poll_wait, BDB::poll_cb |
512 | BDB::poll_wait, BDB::poll_cb |
476 | while BDB::nreqs; |
513 | while BDB::nreqs; |
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481 | |
518 | |
482 | =over 4 |
519 | =over 4 |
483 | |
520 | |
484 | =item BDB::min_parallel $nthreads |
521 | =item BDB::min_parallel $nthreads |
485 | |
522 | |
486 | Set the minimum number of AIO threads to C<$nthreads>. The current |
523 | Set the minimum number of BDB threads to C<$nthreads>. The current |
487 | default is C<8>, which means eight asynchronous operations can execute |
524 | default is C<8>, which means eight asynchronous operations can execute |
488 | concurrently at any one time (the number of outstanding requests, |
525 | concurrently at any one time (the number of outstanding requests, |
489 | however, is unlimited). |
526 | however, is unlimited). |
490 | |
527 | |
491 | BDB starts threads only on demand, when an AIO request is queued and |
528 | BDB starts threads only on demand, when an BDB request is queued and |
492 | no free thread exists. Please note that queueing up a hundred requests can |
529 | no free thread exists. Please note that queueing up a hundred requests can |
493 | create demand for a hundred threads, even if it turns out that everything |
530 | create demand for a hundred threads, even if it turns out that everything |
494 | is in the cache and could have been processed faster by a single thread. |
531 | is in the cache and could have been processed faster by a single thread. |
495 | |
532 | |
496 | It is recommended to keep the number of threads relatively low, as some |
533 | It is recommended to keep the number of threads relatively low, as some |
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501 | Under most circumstances you don't need to call this function, as the |
538 | Under most circumstances you don't need to call this function, as the |
502 | module selects a default that is suitable for low to moderate load. |
539 | module selects a default that is suitable for low to moderate load. |
503 | |
540 | |
504 | =item BDB::max_parallel $nthreads |
541 | =item BDB::max_parallel $nthreads |
505 | |
542 | |
506 | Sets the maximum number of AIO threads to C<$nthreads>. If more than the |
543 | Sets the maximum number of BDB threads to C<$nthreads>. If more than the |
507 | specified number of threads are currently running, this function kills |
544 | specified number of threads are currently running, this function kills |
508 | them. This function blocks until the limit is reached. |
545 | them. This function blocks until the limit is reached. |
509 | |
546 | |
510 | While C<$nthreads> are zero, aio requests get queued but not executed |
547 | While C<$nthreads> are zero, aio requests get queued but not executed |
511 | until the number of threads has been increased again. |
548 | until the number of threads has been increased again. |
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614 | |
651 | |
615 | =head2 FORK BEHAVIOUR |
652 | =head2 FORK BEHAVIOUR |
616 | |
653 | |
617 | This module should do "the right thing" when the process using it forks: |
654 | This module should do "the right thing" when the process using it forks: |
618 | |
655 | |
619 | Before the fork, IO::AIO enters a quiescent state where no requests |
656 | Before the fork, BDB enters a quiescent state where no requests |
620 | can be added in other threads and no results will be processed. After |
657 | can be added in other threads and no results will be processed. After |
621 | the fork the parent simply leaves the quiescent state and continues |
658 | the fork the parent simply leaves the quiescent state and continues |
622 | request/result processing, while the child frees the request/result queue |
659 | request/result processing, while the child frees the request/result queue |
623 | (so that the requests started before the fork will only be handled in the |
660 | (so that the requests started before the fork will only be handled in the |
624 | parent). Threads will be started on demand until the limit set in the |
661 | parent). Threads will be started on demand until the limit set in the |
625 | parent process has been reached again. |
662 | parent process has been reached again. |
626 | |
663 | |
627 | In short: the parent will, after a short pause, continue as if fork had |
664 | In short: the parent will, after a short pause, continue as if fork had |
628 | not been called, while the child will act as if IO::AIO has not been used |
665 | not been called, while the child will act as if BDB has not been used |
629 | yet. |
666 | yet. |
630 | |
667 | |
631 | =head2 MEMORY USAGE |
668 | =head2 MEMORY USAGE |
632 | |
669 | |
633 | Per-request usage: |
670 | Per-request usage: |
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656 | TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>, |
693 | TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>, |
657 | above. |
694 | above. |
658 | |
695 | |
659 | =head1 SEE ALSO |
696 | =head1 SEE ALSO |
660 | |
697 | |
661 | L<Coro::AIO>. |
698 | L<Coro::BDB>, L<IO::AIO>. |
662 | |
699 | |
663 | =head1 AUTHOR |
700 | =head1 AUTHOR |
664 | |
701 | |
665 | Marc Lehmann <schmorp@schmorp.de> |
702 | Marc Lehmann <schmorp@schmorp.de> |
666 | http://home.schmorp.de/ |
703 | http://home.schmorp.de/ |