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Revision 1.15 by root, Thu Sep 13 21:34:00 2007 UTC vs.
Revision 1.40 by root, Tue Jul 8 08:35:12 2008 UTC

… …
3BDB - Asynchronous Berkeley DB access 3BDB - Asynchronous Berkeley DB access
4 4
5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 use BDB; 7 use BDB;
8
9 my $env = db_env_create;
10
11 mkdir "bdtest", 0700;
12 db_env_open
13 $env,
14 "bdtest",
15 BDB::INIT_LOCK | BDB::INIT_LOG | BDB::INIT_MPOOL
16 | BDB::INIT_TXN | BDB::RECOVER | BDB::USE_ENVIRON | BDB::CREATE,
17 0600;
18
19 $env->set_flags (BDB::AUTO_COMMIT | BDB::TXN_NOSYNC, 1);
20
21 my $db = db_create $env;
22 db_open $db, undef, "table", undef, BDB::BTREE, BDB::AUTO_COMMIT | BDB::CREATE
23 | BDB::READ_UNCOMMITTED, 0600;
24 db_put $db, undef, "key", "data", 0, sub {
25 db_del $db, undef, "key";
26 };
27 db_sync $db;
28
29 # when you also use Coro, management is easy:
30 use Coro::BDB;
31
32 # automatic event loop intergration with AnyEvent:
33 use AnyEvent::BDB;
34
35 # automatic result processing with EV:
36 my $WATCHER = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb;
37
38 # with Glib:
39 add_watch Glib::IO BDB::poll_fileno,
40 in => sub { BDB::poll_cb; 1 };
41
42 # or simply flush manually
43 BDB::flush;
44
8 45
9=head1 DESCRIPTION 46=head1 DESCRIPTION
10 47
11See the BerkeleyDB documentation (L<http://www.oracle.com/technology/documentation/berkeley-db/db/index.html>). 48See the BerkeleyDB documentation (L<http://www.oracle.com/technology/documentation/berkeley-db/db/index.html>).
12The BDB API is very similar to the C API (the translation has been very faithful). 49The BDB API is very similar to the C API (the translation has been very faithful).
… …
72use strict 'vars'; 109use strict 'vars';
73 110
74use base 'Exporter'; 111use base 'Exporter';
75 112
76BEGIN { 113BEGIN {
77 our $VERSION = '1.1'; 114 our $VERSION = '1.6';
78 115
79 our @BDB_REQ = qw( 116 our @BDB_REQ = qw(
80 db_env_open db_env_close db_env_txn_checkpoint db_env_lock_detect 117 db_env_open db_env_close db_env_txn_checkpoint db_env_lock_detect
81 db_env_memp_sync db_env_memp_trickle 118 db_env_memp_sync db_env_memp_trickle db_env_dbrename db_env_dbremove
82 db_open db_close db_compact db_sync db_put db_get db_pget db_del db_key_range 119 db_open db_close db_compact db_sync db_upgrade
120 db_put db_get db_pget db_del db_key_range
83 db_txn_commit db_txn_abort db_txn_finish 121 db_txn_commit db_txn_abort db_txn_finish
84 db_c_close db_c_count db_c_put db_c_get db_c_pget db_c_del 122 db_c_close db_c_count db_c_put db_c_get db_c_pget db_c_del
85 db_sequence_open db_sequence_close 123 db_sequence_open db_sequence_close
86 db_sequence_get db_sequence_remove 124 db_sequence_get db_sequence_remove
87 ); 125 );
… …
95 133
96 require XSLoader; 134 require XSLoader;
97 XSLoader::load ("BDB", $VERSION); 135 XSLoader::load ("BDB", $VERSION);
98} 136}
99 137
138=head2 WIN32 FILENAMES/DATABASE NAME MESS
139
140Perl on Win32 supports only ASCII filenames (the reason is that it abuses
141an internal flag to store wether a filename is Unicode or ANSI, but that
142flag is used for somethign else in the perl core, so there is no way to
143detect wether a filename is ANSI or Unicode-encoded). The BDB module
144tries to work around this issue by assuming that the filename is an ANSI
145filename and BDB was built for unicode support.
146
100=head2 BERKELEYDB FUNCTIONS 147=head2 BERKELEYDB FUNCTIONS
101 148
102All of these are functions. The create functions simply return a new 149All of these are functions. The create functions simply return a new
103object and never block. All the remaining functions all take an optional 150object and never block. All the remaining functions take an optional
104callback as last argument. If it is missing, then the fucntion will be 151callback as last argument. If it is missing, then the function will be
105executed synchronously. 152executed synchronously. In both cases, C<$!> will reflect the return value
153of the function.
106 154
107BDB functions that cannot block (mostly functions that manipulate 155BDB functions that cannot block (mostly functions that manipulate
108settings) are method calls on the relevant objects, so the rule of thumb 156settings) are method calls on the relevant objects, so the rule of thumb
109is: if its a method, its not blocking, if its a function, it takes a 157is: if it's a method, it's not blocking, if it's a function, it takes a
110callback as last argument. 158callback as last argument.
111 159
112In the following, C<$int> signifies an integer return value, 160In the following, C<$int> signifies an integer return value,
113C<octetstring> is a "binary string" (i.e. a perl string with no character 161C<bdb_filename> is a "filename" (octets on unix, madness on windows),
114indices >255), C<U32> is an unsigned 32 bit integer, C<int> is some 162C<U32> is an unsigned 32 bit integer, C<int> is some integer, C<NV> is a
115integer, C<NV> is a floating point value. 163floating point value.
116 164
117The C<SV *> types are generic perl scalars (for input and output of data 165The C<SV *> types are generic perl scalars (for input and output of data
118values), and the C<SV *callback> is the optional callback function to call 166values), and the C<SV *callback> is the optional callback function to call
119when the request is completed. 167when the request is completed.
120 168
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128Functions in the BDB namespace, exported by default: 176Functions in the BDB namespace, exported by default:
129 177
130 $env = db_env_create (U32 env_flags = 0) 178 $env = db_env_create (U32 env_flags = 0)
131 flags: RPCCLIENT 179 flags: RPCCLIENT
132 180
133 db_env_open (DB_ENV *env, octetstring db_home, U32 open_flags, int mode, SV *callback = &PL_sv_undef) 181 db_env_open (DB_ENV *env, bdb_filename db_home, U32 open_flags, int mode, SV *callback = &PL_sv_undef)
134 open_flags: INIT_CDB INIT_LOCK INIT_LOG INIT_MPOOL INIT_REP INIT_TXN RECOVER RECOVER_FATAL USE_ENVIRON USE_ENVIRON_ROOT CREATE LOCKDOWN PRIVATE REGISTER SYSTEM_MEM 182 open_flags: INIT_CDB INIT_LOCK INIT_LOG INIT_MPOOL INIT_REP INIT_TXN RECOVER RECOVER_FATAL USE_ENVIRON USE_ENVIRON_ROOT CREATE LOCKDOWN PRIVATE REGISTER SYSTEM_MEM
135 db_env_close (DB_ENV *env, U32 flags = 0, SV *callback = &PL_sv_undef) 183 db_env_close (DB_ENV *env, U32 flags = 0, SV *callback = &PL_sv_undef)
136 db_env_txn_checkpoint (DB_ENV *env, U32 kbyte = 0, U32 min = 0, U32 flags = 0, SV *callback = &PL_sv_undef) 184 db_env_txn_checkpoint (DB_ENV *env, U32 kbyte = 0, U32 min = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
137 flags: FORCE 185 flags: FORCE
138 db_env_lock_detect (DB_ENV *env, U32 flags = 0, U32 atype = DB_LOCK_DEFAULT, SV *dummy = 0, SV *callback = &PL_sv_undef) 186 db_env_lock_detect (DB_ENV *env, U32 flags = 0, U32 atype = DB_LOCK_DEFAULT, SV *dummy = 0, SV *callback = &PL_sv_undef)
139 atype: LOCK_DEFAULT LOCK_EXPIRE LOCK_MAXLOCKS LOCK_MAXWRITE LOCK_MINLOCKS LOCK_MINWRITE LOCK_OLDEST LOCK_RANDOM LOCK_YOUNGEST 187 atype: LOCK_DEFAULT LOCK_EXPIRE LOCK_MAXLOCKS LOCK_MAXWRITE LOCK_MINLOCKS LOCK_MINWRITE LOCK_OLDEST LOCK_RANDOM LOCK_YOUNGEST
140 db_env_memp_sync (DB_ENV *env, SV *dummy = 0, SV *callback = &PL_sv_undef) 188 db_env_memp_sync (DB_ENV *env, SV *dummy = 0, SV *callback = &PL_sv_undef)
141 db_env_memp_trickle (DB_ENV *env, int percent, SV *dummy = 0, SV *callback = &PL_sv_undef) 189 db_env_memp_trickle (DB_ENV *env, int percent, SV *dummy = 0, SV *callback = &PL_sv_undef)
190 db_env_dbremove (DB_ENV *env, DB_TXN_ornull *txnid, bdb_filename file, bdb_filename database, U32 flags = 0, SV *callback = &PL_sv_undef)
191 db_env_dbrename (DB_ENV *env, DB_TXN_ornull *txnid, bdb_filename file, bdb_filename database, bdb_filename newname, U32 flags = 0, SV *callback = &PL_sv_undef)
142 192
143 $db = db_create (DB_ENV *env = 0, U32 flags = 0) 193 $db = db_create (DB_ENV *env = 0, U32 flags = 0)
144 flags: XA_CREATE 194 flags: XA_CREATE
145 195
146 db_open (DB *db, DB_TXN_ornull *txnid, octetstring file, octetstring database, int type, U32 flags, int mode, SV *callback = &PL_sv_undef) 196 db_open (DB *db, DB_TXN_ornull *txnid, bdb_filename file, bdb_filename database, int type, U32 flags, int mode, SV *callback = &PL_sv_undef)
147 flags: AUTO_COMMIT CREATE EXCL MULTIVERSION NOMMAP RDONLY READ_UNCOMMITTED THREAD TRUNCATE 197 flags: AUTO_COMMIT CREATE EXCL MULTIVERSION NOMMAP RDONLY READ_UNCOMMITTED THREAD TRUNCATE
148 db_close (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef) 198 db_close (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef)
149 flags: DB_NOSYNC 199 flags: DB_NOSYNC
200 db_upgrade (DB *db, bdb_filename file, U32 flags = 0, SV *callback = &PL_sv_undef)
150 db_compact (DB *db, DB_TXN_ornull *txn = 0, SV *start = 0, SV *stop = 0, SV *unused1 = 0, U32 flags = DB_FREE_SPACE, SV *unused2 = 0, SV *callback = &PL_sv_undef) 201 db_compact (DB *db, DB_TXN_ornull *txn = 0, SV *start = 0, SV *stop = 0, SV *unused1 = 0, U32 flags = DB_FREE_SPACE, SV *unused2 = 0, SV *callback = &PL_sv_undef)
151 flags: FREELIST_ONLY FREE_SPACE 202 flags: FREELIST_ONLY FREE_SPACE
152 db_sync (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef) 203 db_sync (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef)
153 db_key_range (DB *db, DB_TXN_ornull *txn, SV *key, SV *key_range, U32 flags = 0, SV *callback = &PL_sv_undef) 204 db_key_range (DB *db, DB_TXN_ornull *txn, SV *key, SV *key_range, U32 flags = 0, SV *callback = &PL_sv_undef)
154 db_put (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef) 205 db_put (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
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179 db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef) 230 db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
180 flags: TXN_NOSYNC 231 flags: TXN_NOSYNC
181 232
182=head4 db_txn_finish (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef) 233=head4 db_txn_finish (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef)
183 234
184This is not a Berkeley DB function but a BDB module extension. It is very 235This is not actually a Berkeley DB function but a BDB module
236extension. The background for this exytension is: It is very annoying to
185annoying to have to check every single BDB function for error returns and 237have to check every single BDB function for error returns and provide a
186provide a codepath out of your transaction. While the BDB module still 238codepath out of your transaction. While the BDB module still makes this
187makes this possible, it contains the following extensions: 239possible, it contains the following extensions:
188 240
189When a transaction-protected function returns any operating system 241When a transaction-protected function returns any operating system
190error (errno > 0), BDB will set the C<TXN_DEADLOCK> flag on the 242error (errno > 0), BDB will set the C<TXN_DEADLOCK> flag on the
191transaction. This flag is also set by Berkeley DB functions externally 243transaction. This flag is also set by Berkeley DB functions themselves
192when an operation fails with LOCK_DEADLOCK, and it causes all further 244when an operation fails with LOCK_DEADLOCK, and it causes all further
193operations on that transaction (including C<db_txn_commit>) to fail. 245operations on that transaction (including C<db_txn_commit>) to fail.
194 246
195The C<db_txn_finish> request will look at this flag, and, if it is set, 247The C<db_txn_finish> request will look at this flag, and, if it is set,
196will automatically call C<db_txn_abort> (setting errno to C<LOCK_DEADLOCK> 248will automatically call C<db_txn_abort> (setting errno to C<LOCK_DEADLOCK>
197if it isn't set). If it isn't set, it will call C<db_txn_commit> and 249if it isn't set to something else yet). If it isn't set, it will call
198return the error normally. 250C<db_txn_commit> and return the error normally.
199 251
200How to use this? Easy: just write your transaction normally: 252How to use this? Easy: just write your transaction normally:
201 253
202 my $txn = $db_env->txn_begin; 254 my $txn = $db_env->txn_begin;
203 db_get $db, $txn, "key", my $data; 255 db_get $db, $txn, "key", my $data;
… …
208That is, handle only the expected errors. If something unexpected happens 260That 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 261(EIO, LOCK_NOTGRANTED or a deadlock in either db_get or db_put), then the remaining
210requests (db_put in this case) will simply be skipped (they will fail with 262requests (db_put in this case) will simply be skipped (they will fail with
211LOCK_DEADLOCK) and the transaction will be aborted. 263LOCK_DEADLOCK) and the transaction will be aborted.
212 264
213You cna use the C<< $txn->failed >> method to check wether a transaction 265You can use the C<< $txn->failed >> method to check wether a transaction
214has failed in this way and abort further processing (excluding 266has failed in this way and abort further processing (excluding
215C<db_txn_finish>). 267C<db_txn_finish>).
216 268
217=head3 DB_ENV/database environment methods 269=head3 DB_ENV/database environment methods
218 270
… …
226 $int = $env->set_data_dir (const char *dir) 278 $int = $env->set_data_dir (const char *dir)
227 $int = $env->set_tmp_dir (const char *dir) 279 $int = $env->set_tmp_dir (const char *dir)
228 $int = $env->set_lg_dir (const char *dir) 280 $int = $env->set_lg_dir (const char *dir)
229 $int = $env->set_shm_key (long shm_key) 281 $int = $env->set_shm_key (long shm_key)
230 $int = $env->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0) 282 $int = $env->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0)
231 $int = $env->set_flags (U32 flags, int onoff) 283 $int = $env->set_flags (U32 flags, int onoff = 1)
284 $int = $env->log_set_config (U32 flags, int onoff = 1) [v4.7]
285 $int = $env->set_intermediate_dir_mode (const char *modestring) [v4.7]
232 $env->set_errfile (FILE *errfile = 0) 286 $env->set_errfile (FILE *errfile = 0)
233 $env->set_msgfile (FILE *msgfile = 0) 287 $env->set_msgfile (FILE *msgfile = 0)
234 $int = $env->set_verbose (U32 which, int onoff = 1) 288 $int = $env->set_verbose (U32 which, int onoff = 1)
235 $int = $env->set_encrypt (const char *password, U32 flags = 0) 289 $int = $env->set_encrypt (const char *password, U32 flags = 0)
236 $int = $env->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT) 290 $int = $env->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
… …
241 $int = $env->set_lk_max_lockers (U32 max) 295 $int = $env->set_lk_max_lockers (U32 max)
242 $int = $env->set_lk_max_locks (U32 max) 296 $int = $env->set_lk_max_locks (U32 max)
243 $int = $env->set_lk_max_objects (U32 max) 297 $int = $env->set_lk_max_objects (U32 max)
244 $int = $env->set_lg_bsize (U32 max) 298 $int = $env->set_lg_bsize (U32 max)
245 $int = $env->set_lg_max (U32 max) 299 $int = $env->set_lg_max (U32 max)
300 $int = $env->mutex_set_increment (U32 increment)
301 $int = $env->mutex_set_tas_spins (U32 tas_spins)
302 $int = $env->mutex_set_max (U32 max)
303 $int = $env->mutex_set_align (U32 align)
246 304
247 $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0) 305 $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 306 flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC
249 307
250=head4 Example: 308=head4 Example:
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345 DESTROY (DBC_ornull *dbc) 403 DESTROY (DBC_ornull *dbc)
346 CODE: 404 CODE:
347 if (dbc) 405 if (dbc)
348 dbc->c_close (dbc); 406 dbc->c_close (dbc);
349 407
408 $int = $cursor->set_priority ($priority = PRIORITY_*)
409
350=head4 Example: 410=head4 Example:
351 411
352 my $c = $db->cursor; 412 my $c = $db->cursor;
353 413
354 for (;;) { 414 for (;;) {
… …
387 447
388=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION 448=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
389 449
390=over 4 450=over 4
391 451
452=item $msg = BDB::strerror [$errno]
453
454Returns the string corresponding to the given errno value. If no argument
455is given, use C<$!>.
456
457Note that the BDB module also patches the C<$!> variable directly, so you
458should be able to get a bdb error string by simply stringifying C<$!>.
459
392=item $fileno = BDB::poll_fileno 460=item $fileno = BDB::poll_fileno
393 461
394Return the I<request result pipe file descriptor>. This filehandle must be 462Return the I<request result pipe file descriptor>. This filehandle must be
395polled for reading by some mechanism outside this module (e.g. Event or 463polled for reading by some mechanism outside this module (e.g. Event or
396select, see below or the SYNOPSIS). If the pipe becomes readable you have 464select, see below or the SYNOPSIS). If the pipe becomes readable you have
… …
434interactiveness when perl is not fast enough to process all requests in 502interactiveness when perl is not fast enough to process all requests in
435time. 503time.
436 504
437For interactive programs, values such as C<0.01> to C<0.1> should be fine. 505For interactive programs, values such as C<0.01> to C<0.1> should be fine.
438 506
439Example: Install an Event watcher that automatically calls 507Example: Install an EV watcher that automatically calls
440BDB::poll_cb with low priority, to ensure that other parts of the 508BDB::poll_cb with low priority, to ensure that other parts of the
441program get the CPU sometimes even under high AIO load. 509program get the CPU sometimes even under high load.
442 510
443 # try not to spend much more than 0.1s in poll_cb 511 # try not to spend much more than 0.1s in poll_cb
444 BDB::max_poll_time 0.1; 512 BDB::max_poll_time 0.1;
445 513
446 # use a low priority so other tasks have priority 514 my $bdb_poll = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb);
447 Event->io (fd => BDB::poll_fileno,
448 poll => 'r', nice => 1,
449 cb => &BDB::poll_cb);
450 515
451=item BDB::poll_wait 516=item BDB::poll_wait
452 517
453If there are any outstanding requests and none of them in the result 518If there are any outstanding requests and none of them in the result
454phase, wait till the result filehandle becomes ready for reading (simply 519phase, wait till the result filehandle becomes ready for reading (simply
… …
466 531
467 BDB::poll_wait, BDB::poll_cb 532 BDB::poll_wait, BDB::poll_cb
468 533
469=item BDB::flush 534=item BDB::flush
470 535
471Wait till all outstanding AIO requests have been handled. 536Wait till all outstanding BDB requests have been handled.
472 537
473Strictly equivalent to: 538Strictly equivalent to:
474 539
475 BDB::poll_wait, BDB::poll_cb 540 BDB::poll_wait, BDB::poll_cb
476 while BDB::nreqs; 541 while BDB::nreqs;
477 542
478=back 543=back
479 544
545=head3 VERSION CHECKING
546
547BerkeleyDB comes in various versions, many of them have minor
548incompatibilities. This means that traditional "at least version x.x"
549checks are often not sufficient.
550
551Example: set the log_autoremove option in a way compatible with <v.47 and
552v4.7. Note the use of & on the constants to avoid triggering a compiletime
553bug when the symbol isn't available.
554
555 $DB_ENV->set_flags (&BDB::LOG_AUTOREMOVE ) if BDB::VERSION v0, v4.7;
556 $DB_ENV->log_set_config (&BDB::LOG_AUTO_REMOVE) if BDB::VERSION v4.7;
557
558=over 4
559
560=item BDB::VERSION
561
562The C<BDB::VERSION> function, when called without arguments, returns the
563Berkeley DB version as a v-string (usually with 3 components). You should
564use C<lt> and C<ge> operators exclusively to make comparisons.
565
566Example: check for at least version 4.7.
567
568 BDB::VERSION ge v4.7 or die;
569
570=item BDB::VERSION min-version
571
572Returns true if the BDB version is at least the given version (specified
573as a v-string), false otherwise.
574
575Example: check for at least version 4.5.
576
577 BDB::VERSION v4.7 or die;
578
579=item BDB::VERSION min-version, max-version
580
581Returns true of the BDB version is at least version C<min-version> (specify C<undef> or C<v0> for any minimum version)
582and less then C<max-version>.
583
584Example: check wether version is strictly less then v4.7.
585
586 BDB::VERSION v0, v4.7
587 or die "version 4.7 is not yet supported";
588
589=back
590
591=cut
592
593sub VERSION {
594 if (@_ > 0) {
595 return undef if VERSION_v lt $_[0];
596 if (@_ > 1) {
597 return undef if VERSION_v ge $_[1];
598 }
599 }
600
601 VERSION_v
602}
603
480=head3 CONTROLLING THE NUMBER OF THREADS 604=head3 CONTROLLING THE NUMBER OF THREADS
481 605
482=over 4 606=over 4
483 607
484=item BDB::min_parallel $nthreads 608=item BDB::min_parallel $nthreads
485 609
486Set the minimum number of AIO threads to C<$nthreads>. The current 610Set the minimum number of BDB threads to C<$nthreads>. The current
487default is C<8>, which means eight asynchronous operations can execute 611default is C<8>, which means eight asynchronous operations can execute
488concurrently at any one time (the number of outstanding requests, 612concurrently at any one time (the number of outstanding requests,
489however, is unlimited). 613however, is unlimited).
490 614
491BDB starts threads only on demand, when an AIO request is queued and 615BDB starts threads only on demand, when an BDB request is queued and
492no free thread exists. Please note that queueing up a hundred requests can 616no free thread exists. Please note that queueing up a hundred requests can
493create demand for a hundred threads, even if it turns out that everything 617create demand for a hundred threads, even if it turns out that everything
494is in the cache and could have been processed faster by a single thread. 618is in the cache and could have been processed faster by a single thread.
495 619
496It is recommended to keep the number of threads relatively low, as some 620It is recommended to keep the number of threads relatively low, as some
… …
501Under most circumstances you don't need to call this function, as the 625Under most circumstances you don't need to call this function, as the
502module selects a default that is suitable for low to moderate load. 626module selects a default that is suitable for low to moderate load.
503 627
504=item BDB::max_parallel $nthreads 628=item BDB::max_parallel $nthreads
505 629
506Sets the maximum number of AIO threads to C<$nthreads>. If more than the 630Sets the maximum number of BDB threads to C<$nthreads>. If more than the
507specified number of threads are currently running, this function kills 631specified number of threads are currently running, this function kills
508them. This function blocks until the limit is reached. 632them. This function blocks until the limit is reached.
509 633
510While C<$nthreads> are zero, aio requests get queued but not executed 634While C<$nthreads> are zero, aio requests get queued but not executed
511until the number of threads has been increased again. 635until the number of threads has been increased again.
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550 674
551=item BDB::set_sync_prepare $cb 675=item BDB::set_sync_prepare $cb
552 676
553Sets a callback that is called whenever a request is created without an 677Sets a callback that is called whenever a request is created without an
554explicit callback. It has to return two code references. The first is used 678explicit callback. It has to return two code references. The first is used
555as the request callback, and the second is called to wait until the first 679as the request callback (it should save the return status), and the second
680is called to wait until the first callback has been called (it must set
681C<$!> to the return status).
682
683This mechanism can be used to include BDB into other event mechanisms,
684such as L<AnyEvent::BDB> or L<Coro::BDB>.
685
556callback has been called. The default implementation works like this: 686The default implementation works like this:
557 687
558 sub { 688 sub {
559 my $status; 689 my $status;
560 ( 690 (
561 sub { $status = $! }, 691 sub { $status = $! },
562 sub { BDB::poll while !defined $status; $! = $status }, 692 sub { BDB::poll while !defined $status; $! = $status },
563 ) 693 )
564 } 694 }
695
696It simply blocks the process till the request has finished and then sets
697C<$!> to the return value. This means that if you don't use a callback,
698BDB will simply fall back to synchronous operations.
565 699
566=back 700=back
567 701
568=head3 STATISTICAL INFORMATION 702=head3 STATISTICAL INFORMATION
569 703
… …
614 748
615=head2 FORK BEHAVIOUR 749=head2 FORK BEHAVIOUR
616 750
617This module should do "the right thing" when the process using it forks: 751This module should do "the right thing" when the process using it forks:
618 752
619Before the fork, IO::AIO enters a quiescent state where no requests 753Before the fork, BDB enters a quiescent state where no requests
620can be added in other threads and no results will be processed. After 754can be added in other threads and no results will be processed. After
621the fork the parent simply leaves the quiescent state and continues 755the fork the parent simply leaves the quiescent state and continues
622request/result processing, while the child frees the request/result queue 756request/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 757(so that the requests started before the fork will only be handled in the
624parent). Threads will be started on demand until the limit set in the 758parent). Threads will be started on demand until the limit set in the
625parent process has been reached again. 759parent process has been reached again.
626 760
627In short: the parent will, after a short pause, continue as if fork had 761In short: the parent will, after a short pause, continue as if fork had
628not been called, while the child will act as if IO::AIO has not been used 762not been called, while the child will act as if BDB has not been used
629yet. 763yet.
764
765Win32 note: there is no fork on win32, and perls emulation of it is too
766broken to be supported, so do not use BDB in a windows pseudo-fork, better
767yet, switch to a more capable platform.
630 768
631=head2 MEMORY USAGE 769=head2 MEMORY USAGE
632 770
633Per-request usage: 771Per-request usage:
634 772
… …
656 TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>, 794 TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>,
657 above. 795 above.
658 796
659=head1 SEE ALSO 797=head1 SEE ALSO
660 798
661L<Coro::AIO>. 799L<AnyEvent::BDB> (event loop integration), L<Coro::BDB> (more natural
800syntax), L<IO::AIO> (nice to have).
662 801
663=head1 AUTHOR 802=head1 AUTHOR
664 803
665 Marc Lehmann <schmorp@schmorp.de> 804 Marc Lehmann <schmorp@schmorp.de>
666 http://home.schmorp.de/ 805 http://home.schmorp.de/

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