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Comparing BDB/BDB.pm (file contents):
Revision 1.14 by root, Thu Sep 13 12:29:49 2007 UTC vs.
Revision 1.41 by root, Wed Jul 9 12:15:36 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 = '1.0'; 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 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 );
88 our @EXPORT = (@BDB_REQ, qw(dbreq_pri dbreq_nice db_env_create db_create)); 126 our @EXPORT = (@BDB_REQ, qw(dbreq_pri dbreq_nice db_env_create db_create));
… …
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 165Most 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).
119when the request is completed.
120 167
121The various C<DB_ENV> etc. arguments are handles return by 168The various C<DB_ENV> etc. arguments are handles return by
122C<db_env_create>, C<db_create>, C<txn_begin> and so on. If they have an 169C<db_env_create>, C<db_create>, C<txn_begin> and so on. If they have an
123appended C<_ornull> this means they are optional and you can pass C<undef> 170appended C<_ornull> this means they are optional and you can pass C<undef>
124for them, resulting a NULL pointer on the C level. 171for them, resulting a NULL pointer on the C level.
125 172
173The C<SV *callback> is the optional callback function to call when the
174request is completed. This last callback argument is special: the callback
175is simply the last argument passed. If there are "optional" arguments
176before the callback they can be left out. The callback itself can be left
177out or specified as C<undef>, in which case the function will be executed
178synchronously.
179
180For example, C<db_env_txn_checkpoint> usually is called with all integer
181arguments zero. These can be left out, so all of these specify a call
182to C<< DB_ENV->txn_checkpoint >>, to be executed asynchronously with a
183callback to be called:
184
185 db_env_txn_checkpoint $db_env, 0, 0, 0, sub { };
186 db_env_txn_checkpoint $db_env, 0, 0, sub { };
187 db_env_txn_checkpoint $db_env, sub { };
188
189While these all specify a call to C<< DB_ENV->txn_checkpoint >> to be
190executed synchronously:
191
192 db_env_txn_checkpoint $db_env, 0, 0, 0, undef;
193 db_env_txn_checkpoint $db_env, 0, 0, 0;
194 db_env_txn_checkpoint $db_env, 0;
195
126=head3 BDB functions 196=head3 BDB functions
127 197
128Functions in the BDB namespace, exported by default: 198Functions in the BDB namespace, exported by default:
129 199
130 $env = db_env_create (U32 env_flags = 0) 200 $env = db_env_create (U32 env_flags = 0)
131 flags: RPCCLIENT 201 flags: RPCCLIENT
132 202
133 db_env_open (DB_ENV *env, octetstring db_home, U32 open_flags, int mode, SV *callback = &PL_sv_undef) 203 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 204 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) 205 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) 206 db_env_txn_checkpoint (DB_ENV *env, U32 kbyte = 0, U32 min = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
137 flags: FORCE 207 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) 208 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 209 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) 210 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) 211 db_env_memp_trickle (DB_ENV *env, int percent, SV *dummy = 0, SV *callback = &PL_sv_undef)
212 db_env_dbremove (DB_ENV *env, DB_TXN_ornull *txnid, bdb_filename file, bdb_filename database, U32 flags = 0, SV *callback = &PL_sv_undef)
213 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)
142 214
143 $db = db_create (DB_ENV *env = 0, U32 flags = 0) 215 $db = db_create (DB_ENV *env = 0, U32 flags = 0)
144 flags: XA_CREATE 216 flags: XA_CREATE
145 217
146 db_open (DB *db, DB_TXN_ornull *txnid, octetstring file, octetstring database, int type, U32 flags, int mode, SV *callback = &PL_sv_undef) 218 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 219 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) 220 db_close (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef)
149 flags: DB_NOSYNC 221 flags: DB_NOSYNC
222 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) 223 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 224 flags: FREELIST_ONLY FREE_SPACE
152 db_sync (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef) 225 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) 226 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) 227 db_put (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
… …
177 db_sequence_get (DB_SEQUENCE *seq, DB_TXN_ornull *txnid, int delta, SV *seq_value, U32 flags = DB_TXN_NOSYNC, SV *callback = &PL_sv_undef) 250 db_sequence_get (DB_SEQUENCE *seq, DB_TXN_ornull *txnid, int delta, SV *seq_value, U32 flags = DB_TXN_NOSYNC, SV *callback = &PL_sv_undef)
178 flags: TXN_NOSYNC 251 flags: TXN_NOSYNC
179 db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef) 252 db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
180 flags: TXN_NOSYNC 253 flags: TXN_NOSYNC
181 254
255=head4 db_txn_finish (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef)
256
257This is not actually a Berkeley DB function but a BDB module
258extension. The background for this exytension is: It is very annoying to
259have to check every single BDB function for error returns and provide a
260codepath out of your transaction. While the BDB module still makes this
261possible, it contains the following extensions:
262
263When a transaction-protected function returns any operating system
264error (errno > 0), BDB will set the C<TXN_DEADLOCK> flag on the
265transaction. This flag is also set by Berkeley DB functions themselves
266when an operation fails with LOCK_DEADLOCK, and it causes all further
267operations on that transaction (including C<db_txn_commit>) to fail.
268
269The C<db_txn_finish> request will look at this flag, and, if it is set,
270will automatically call C<db_txn_abort> (setting errno to C<LOCK_DEADLOCK>
271if it isn't set to something else yet). If it isn't set, it will call
272C<db_txn_commit> and return the error normally.
273
274How to use this? Easy: just write your transaction normally:
275
276 my $txn = $db_env->txn_begin;
277 db_get $db, $txn, "key", my $data;
278 db_put $db, $txn, "key", $data + 1 unless $! == BDB::NOTFOUND;
279 db_txn_finish $txn;
280 die "transaction failed" if $!;
281
282That is, handle only the expected errors. If something unexpected happens
283(EIO, LOCK_NOTGRANTED or a deadlock in either db_get or db_put), then the remaining
284requests (db_put in this case) will simply be skipped (they will fail with
285LOCK_DEADLOCK) and the transaction will be aborted.
286
287You can use the C<< $txn->failed >> method to check wether a transaction
288has failed in this way and abort further processing (excluding
289C<db_txn_finish>).
290
182=head3 DB_ENV/database environment methods 291=head3 DB_ENV/database environment methods
183 292
184Methods available on DB_ENV/$env handles: 293Methods available on DB_ENV/$env handles:
185 294
186 DESTROY (DB_ENV_ornull *env) 295 DESTROY (DB_ENV_ornull *env)
… …
191 $int = $env->set_data_dir (const char *dir) 300 $int = $env->set_data_dir (const char *dir)
192 $int = $env->set_tmp_dir (const char *dir) 301 $int = $env->set_tmp_dir (const char *dir)
193 $int = $env->set_lg_dir (const char *dir) 302 $int = $env->set_lg_dir (const char *dir)
194 $int = $env->set_shm_key (long shm_key) 303 $int = $env->set_shm_key (long shm_key)
195 $int = $env->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0) 304 $int = $env->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0)
196 $int = $env->set_flags (U32 flags, int onoff) 305 $int = $env->set_flags (U32 flags, int onoff = 1)
306 $int = $env->log_set_config (U32 flags, int onoff = 1) [v4.7]
307 $int = $env->set_intermediate_dir_mode (const char *modestring) [v4.7]
197 $env->set_errfile (FILE *errfile = 0) 308 $env->set_errfile (FILE *errfile = 0)
198 $env->set_msgfile (FILE *msgfile = 0) 309 $env->set_msgfile (FILE *msgfile = 0)
199 $int = $env->set_verbose (U32 which, int onoff = 1) 310 $int = $env->set_verbose (U32 which, int onoff = 1)
200 $int = $env->set_encrypt (const char *password, U32 flags = 0) 311 $int = $env->set_encrypt (const char *password, U32 flags = 0)
201 $int = $env->set_timeout (NV timeout, U32 flags) 312 $int = $env->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
202 $int = $env->set_mp_max_openfd (int maxopenfd); 313 $int = $env->set_mp_max_openfd (int maxopenfd);
203 $int = $env->set_mp_max_write (int maxwrite, int maxwrite_sleep); 314 $int = $env->set_mp_max_write (int maxwrite, int maxwrite_sleep);
204 $int = $env->set_mp_mmapsize (int mmapsize_mb) 315 $int = $env->set_mp_mmapsize (int mmapsize_mb)
205 $int = $env->set_lk_detect (U32 detect = DB_LOCK_DEFAULT) 316 $int = $env->set_lk_detect (U32 detect = DB_LOCK_DEFAULT)
206 $int = $env->set_lk_max_lockers (U32 max) 317 $int = $env->set_lk_max_lockers (U32 max)
207 $int = $env->set_lk_max_locks (U32 max) 318 $int = $env->set_lk_max_locks (U32 max)
208 $int = $env->set_lk_max_objects (U32 max) 319 $int = $env->set_lk_max_objects (U32 max)
209 $int = $env->set_lg_bsize (U32 max) 320 $int = $env->set_lg_bsize (U32 max)
210 $int = $env->set_lg_max (U32 max) 321 $int = $env->set_lg_max (U32 max)
322 $int = $env->mutex_set_increment (U32 increment)
323 $int = $env->mutex_set_tas_spins (U32 tas_spins)
324 $int = $env->mutex_set_max (U32 max)
325 $int = $env->mutex_set_align (U32 align)
211 326
212 $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0) 327 $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0)
213 flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC 328 flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC
214 329
215=head4 Example: 330=head4 Example:
… …
294 DESTROY (DB_TXN_ornull *txn) 409 DESTROY (DB_TXN_ornull *txn)
295 CODE: 410 CODE:
296 if (txn) 411 if (txn)
297 txn->abort (txn); 412 txn->abort (txn);
298 413
299 $int = $txn->set_timeout (NV timeout, U32 flags) 414 $int = $txn->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
300 flags: SET_LOCK_TIMEOUT SET_TXN_TIMEOUT 415 flags: SET_LOCK_TIMEOUT SET_TXN_TIMEOUT
416
417 $bool = $txn->failed
418 # see db_txn_finish documentation, above
301 419
302 420
303=head3 DBC/cursor methods 421=head3 DBC/cursor methods
304 422
305Methods available on DBC/$dbc handles: 423Methods available on DBC/$dbc handles:
306 424
307 DESTROY (DBC_ornull *dbc) 425 DESTROY (DBC_ornull *dbc)
308 CODE: 426 CODE:
309 if (dbc) 427 if (dbc)
310 dbc->c_close (dbc); 428 dbc->c_close (dbc);
429
430 $int = $cursor->set_priority ($priority = PRIORITY_*)
311 431
312=head4 Example: 432=head4 Example:
313 433
314 my $c = $db->cursor; 434 my $c = $db->cursor;
315 435
… …
349 469
350=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION 470=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
351 471
352=over 4 472=over 4
353 473
474=item $msg = BDB::strerror [$errno]
475
476Returns the string corresponding to the given errno value. If no argument
477is given, use C<$!>.
478
479Note that the BDB module also patches the C<$!> variable directly, so you
480should be able to get a bdb error string by simply stringifying C<$!>.
481
354=item $fileno = BDB::poll_fileno 482=item $fileno = BDB::poll_fileno
355 483
356Return the I<request result pipe file descriptor>. This filehandle must be 484Return the I<request result pipe file descriptor>. This filehandle must be
357polled for reading by some mechanism outside this module (e.g. Event or 485polled for reading by some mechanism outside this module (e.g. Event or
358select, see below or the SYNOPSIS). If the pipe becomes readable you have 486select, see below or the SYNOPSIS). If the pipe becomes readable you have
… …
396interactiveness when perl is not fast enough to process all requests in 524interactiveness when perl is not fast enough to process all requests in
397time. 525time.
398 526
399For interactive programs, values such as C<0.01> to C<0.1> should be fine. 527For interactive programs, values such as C<0.01> to C<0.1> should be fine.
400 528
401Example: Install an Event watcher that automatically calls 529Example: Install an EV watcher that automatically calls
402BDB::poll_cb with low priority, to ensure that other parts of the 530BDB::poll_cb with low priority, to ensure that other parts of the
403program get the CPU sometimes even under high AIO load. 531program get the CPU sometimes even under high load.
404 532
405 # try not to spend much more than 0.1s in poll_cb 533 # try not to spend much more than 0.1s in poll_cb
406 BDB::max_poll_time 0.1; 534 BDB::max_poll_time 0.1;
407 535
408 # use a low priority so other tasks have priority 536 my $bdb_poll = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb);
409 Event->io (fd => BDB::poll_fileno,
410 poll => 'r', nice => 1,
411 cb => &BDB::poll_cb);
412 537
413=item BDB::poll_wait 538=item BDB::poll_wait
414 539
415If there are any outstanding requests and none of them in the result 540If there are any outstanding requests and none of them in the result
416phase, wait till the result filehandle becomes ready for reading (simply 541phase, wait till the result filehandle becomes ready for reading (simply
… …
428 553
429 BDB::poll_wait, BDB::poll_cb 554 BDB::poll_wait, BDB::poll_cb
430 555
431=item BDB::flush 556=item BDB::flush
432 557
433Wait till all outstanding AIO requests have been handled. 558Wait till all outstanding BDB requests have been handled.
434 559
435Strictly equivalent to: 560Strictly equivalent to:
436 561
437 BDB::poll_wait, BDB::poll_cb 562 BDB::poll_wait, BDB::poll_cb
438 while BDB::nreqs; 563 while BDB::nreqs;
439 564
440=back 565=back
441 566
567=head3 VERSION CHECKING
568
569BerkeleyDB comes in various versions, many of them have minor
570incompatibilities. This means that traditional "at least version x.x"
571checks are often not sufficient.
572
573Example: set the log_autoremove option in a way compatible with <v.47 and
574v4.7. Note the use of & on the constants to avoid triggering a compiletime
575bug when the symbol isn't available.
576
577 $DB_ENV->set_flags (&BDB::LOG_AUTOREMOVE ) if BDB::VERSION v0, v4.7;
578 $DB_ENV->log_set_config (&BDB::LOG_AUTO_REMOVE) if BDB::VERSION v4.7;
579
580=over 4
581
582=item BDB::VERSION
583
584The C<BDB::VERSION> function, when called without arguments, returns the
585Berkeley DB version as a v-string (usually with 3 components). You should
586use C<lt> and C<ge> operators exclusively to make comparisons.
587
588Example: check for at least version 4.7.
589
590 BDB::VERSION ge v4.7 or die;
591
592=item BDB::VERSION min-version
593
594Returns true if the BDB version is at least the given version (specified
595as a v-string), false otherwise.
596
597Example: check for at least version 4.5.
598
599 BDB::VERSION v4.7 or die;
600
601=item BDB::VERSION min-version, max-version
602
603Returns true of the BDB version is at least version C<min-version> (specify C<undef> or C<v0> for any minimum version)
604and less then C<max-version>.
605
606Example: check wether version is strictly less then v4.7.
607
608 BDB::VERSION v0, v4.7
609 or die "version 4.7 is not yet supported";
610
611=back
612
613=cut
614
615sub VERSION {
616 if (@_ > 0) {
617 return undef if VERSION_v lt $_[0];
618 if (@_ > 1) {
619 return undef if VERSION_v ge $_[1];
620 }
621 }
622
623 VERSION_v
624}
625
442=head3 CONTROLLING THE NUMBER OF THREADS 626=head3 CONTROLLING THE NUMBER OF THREADS
443 627
444=over 4 628=over 4
445 629
446=item BDB::min_parallel $nthreads 630=item BDB::min_parallel $nthreads
447 631
448Set the minimum number of AIO threads to C<$nthreads>. The current 632Set the minimum number of BDB threads to C<$nthreads>. The current
449default is C<8>, which means eight asynchronous operations can execute 633default is C<8>, which means eight asynchronous operations can execute
450concurrently at any one time (the number of outstanding requests, 634concurrently at any one time (the number of outstanding requests,
451however, is unlimited). 635however, is unlimited).
452 636
453BDB starts threads only on demand, when an AIO request is queued and 637BDB starts threads only on demand, when an BDB request is queued and
454no free thread exists. Please note that queueing up a hundred requests can 638no free thread exists. Please note that queueing up a hundred requests can
455create demand for a hundred threads, even if it turns out that everything 639create demand for a hundred threads, even if it turns out that everything
456is in the cache and could have been processed faster by a single thread. 640is in the cache and could have been processed faster by a single thread.
457 641
458It is recommended to keep the number of threads relatively low, as some 642It is recommended to keep the number of threads relatively low, as some
… …
463Under most circumstances you don't need to call this function, as the 647Under most circumstances you don't need to call this function, as the
464module selects a default that is suitable for low to moderate load. 648module selects a default that is suitable for low to moderate load.
465 649
466=item BDB::max_parallel $nthreads 650=item BDB::max_parallel $nthreads
467 651
468Sets the maximum number of AIO threads to C<$nthreads>. If more than the 652Sets the maximum number of BDB threads to C<$nthreads>. If more than the
469specified number of threads are currently running, this function kills 653specified number of threads are currently running, this function kills
470them. This function blocks until the limit is reached. 654them. This function blocks until the limit is reached.
471 655
472While C<$nthreads> are zero, aio requests get queued but not executed 656While C<$nthreads> are zero, aio requests get queued but not executed
473until the number of threads has been increased again. 657until the number of threads has been increased again.
… …
512 696
513=item BDB::set_sync_prepare $cb 697=item BDB::set_sync_prepare $cb
514 698
515Sets a callback that is called whenever a request is created without an 699Sets a callback that is called whenever a request is created without an
516explicit callback. It has to return two code references. The first is used 700explicit callback. It has to return two code references. The first is used
517as the request callback, and the second is called to wait until the first 701as the request callback (it should save the return status), and the second
702is called to wait until the first callback has been called (it must set
703C<$!> to the return status).
704
705This mechanism can be used to include BDB into other event mechanisms,
706such as L<AnyEvent::BDB> or L<Coro::BDB>.
707
518callback has been called. The default implementation works like this: 708The default implementation works like this:
519 709
520 sub { 710 sub {
521 my $status; 711 my $status;
522 ( 712 (
523 sub { $status = $! }, 713 sub { $status = $! },
524 sub { BDB::poll while !defined $status; $! = $status }, 714 sub { BDB::poll while !defined $status; $! = $status },
525 ) 715 )
526 } 716 }
717
718It simply blocks the process till the request has finished and then sets
719C<$!> to the return value. This means that if you don't use a callback,
720BDB will simply fall back to synchronous operations.
527 721
528=back 722=back
529 723
530=head3 STATISTICAL INFORMATION 724=head3 STATISTICAL INFORMATION
531 725
… …
576 770
577=head2 FORK BEHAVIOUR 771=head2 FORK BEHAVIOUR
578 772
579This module should do "the right thing" when the process using it forks: 773This module should do "the right thing" when the process using it forks:
580 774
581Before the fork, IO::AIO enters a quiescent state where no requests 775Before the fork, BDB enters a quiescent state where no requests
582can be added in other threads and no results will be processed. After 776can be added in other threads and no results will be processed. After
583the fork the parent simply leaves the quiescent state and continues 777the fork the parent simply leaves the quiescent state and continues
584request/result processing, while the child frees the request/result queue 778request/result processing, while the child frees the request/result queue
585(so that the requests started before the fork will only be handled in the 779(so that the requests started before the fork will only be handled in the
586parent). Threads will be started on demand until the limit set in the 780parent). Threads will be started on demand until the limit set in the
587parent process has been reached again. 781parent process has been reached again.
588 782
589In short: the parent will, after a short pause, continue as if fork had 783In short: the parent will, after a short pause, continue as if fork had
590not been called, while the child will act as if IO::AIO has not been used 784not been called, while the child will act as if BDB has not been used
591yet. 785yet.
786
787Win32 note: there is no fork on win32, and perls emulation of it is too
788broken to be supported, so do not use BDB in a windows pseudo-fork, better
789yet, switch to a more capable platform.
592 790
593=head2 MEMORY USAGE 791=head2 MEMORY USAGE
594 792
595Per-request usage: 793Per-request usage:
596 794
… …
609temporary buffers, and each thread requires a stack and other data 807temporary buffers, and each thread requires a stack and other data
610structures (usually around 16k-128k, depending on the OS). 808structures (usually around 16k-128k, depending on the OS).
611 809
612=head1 KNOWN BUGS 810=head1 KNOWN BUGS
613 811
614Known bugs will be fixed in the next release. 812Known bugs will be fixed in the next release, except:
813
814 If you use a transaction in any request, and the request returns
815 with an operating system error or DB_LOCK_NOTGRANTED, the internal
816 TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>,
817 above.
615 818
616=head1 SEE ALSO 819=head1 SEE ALSO
617 820
618L<Coro::AIO>. 821L<AnyEvent::BDB> (event loop integration), L<Coro::BDB> (more natural
822syntax), L<IO::AIO> (nice to have).
619 823
620=head1 AUTHOR 824=head1 AUTHOR
621 825
622 Marc Lehmann <schmorp@schmorp.de> 826 Marc Lehmann <schmorp@schmorp.de>
623 http://home.schmorp.de/ 827 http://home.schmorp.de/

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