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Comparing BDB/BDB.pm (file contents):
Revision 1.12 by root, Mon Aug 13 12:07:46 2007 UTC vs.
Revision 1.37 by root, Mon Jul 7 14:28:53 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 = '1.5';
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
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<octetstring> is a "binary string" (i.e. a perl string with no character
114indices >255), C<U32> is an unsigned 32 bit integer, C<int> is some 162indices >255), C<U32> is an unsigned 32 bit integer, C<int> is some
… …
126=head3 BDB functions 174=head3 BDB functions
127 175
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)
179 flags: RPCCLIENT
131 180
132 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, octetstring db_home, U32 open_flags, int mode, SV *callback = &PL_sv_undef)
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
133 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)
134 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)
185 flags: FORCE
135 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)
187 atype: LOCK_DEFAULT LOCK_EXPIRE LOCK_MAXLOCKS LOCK_MAXWRITE LOCK_MINLOCKS LOCK_MINWRITE LOCK_OLDEST LOCK_RANDOM LOCK_YOUNGEST
136 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)
137 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)
138 190
139 $db = db_create (DB_ENV *env = 0, U32 flags = 0) 191 $db = db_create (DB_ENV *env = 0, U32 flags = 0)
192 flags: XA_CREATE
140 193
141 db_open (DB *db, DB_TXN_ornull *txnid, octetstring file, octetstring database, int type, U32 flags, int mode, SV *callback = &PL_sv_undef) 194 db_open (DB *db, DB_TXN_ornull *txnid, octetstring file, octetstring database, int type, U32 flags, int mode, SV *callback = &PL_sv_undef)
195 flags: AUTO_COMMIT CREATE EXCL MULTIVERSION NOMMAP RDONLY READ_UNCOMMITTED THREAD TRUNCATE
142 db_close (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef) 196 db_close (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef)
197 flags: DB_NOSYNC
198 db_upgrade (DB *db, octetstring file, U32 flags = 0, SV *callback = &PL_sv_undef)
143 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) 199 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)
200 flags: FREELIST_ONLY FREE_SPACE
144 db_sync (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef) 201 db_sync (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef)
145 db_key_range (DB *db, DB_TXN_ornull *txn, SV *key, SV *key_range, U32 flags = 0, SV *callback = &PL_sv_undef) 202 db_key_range (DB *db, DB_TXN_ornull *txn, SV *key, SV *key_range, U32 flags = 0, SV *callback = &PL_sv_undef)
146 db_put (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef) 203 db_put (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
204 flags: APPEND NODUPDATA NOOVERWRITE
147 db_get (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef) 205 db_get (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
206 flags: CONSUME CONSUME_WAIT GET_BOTH SET_RECNO MULTIPLE READ_COMMITTED READ_UNCOMMITTED RMW
148 db_pget (DB *db, DB_TXN_ornull *txn, SV *key, SV *pkey, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef) 207 db_pget (DB *db, DB_TXN_ornull *txn, SV *key, SV *pkey, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
208 flags: CONSUME CONSUME_WAIT GET_BOTH SET_RECNO MULTIPLE READ_COMMITTED READ_UNCOMMITTED RMW
149 db_del (DB *db, DB_TXN_ornull *txn, SV *key, U32 flags = 0, SV *callback = &PL_sv_undef) 209 db_del (DB *db, DB_TXN_ornull *txn, SV *key, U32 flags = 0, SV *callback = &PL_sv_undef)
150 db_txn_commit (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef) 210 db_txn_commit (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef)
211 flags: TXN_NOSYNC TXN_SYNC
151 db_txn_abort (DB_TXN *txn, SV *callback = &PL_sv_undef) 212 db_txn_abort (DB_TXN *txn, SV *callback = &PL_sv_undef)
213
152 db_c_close (DBC *dbc, SV *callback = &PL_sv_undef) 214 db_c_close (DBC *dbc, SV *callback = &PL_sv_undef)
153 db_c_count (DBC *dbc, SV *count, U32 flags = 0, SV *callback = &PL_sv_undef) 215 db_c_count (DBC *dbc, SV *count, U32 flags = 0, SV *callback = &PL_sv_undef)
154 db_c_put (DBC *dbc, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef) 216 db_c_put (DBC *dbc, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
217 flags: AFTER BEFORE CURRENT KEYFIRST KEYLAST NODUPDATA
155 db_c_get (DBC *dbc, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef) 218 db_c_get (DBC *dbc, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
219 flags: CURRENT FIRST GET_BOTH GET_BOTH_RANGE GET_RECNO JOIN_ITEM LAST NEXT NEXT_DUP NEXT_NODUP PREV PREV_DUP PREV_NODUP SET SET_RANGE SET_RECNO READ_UNCOMMITTED MULTIPLE MULTIPLE_KEY RMW
156 db_c_pget (DBC *dbc, SV *key, SV *pkey, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef) 220 db_c_pget (DBC *dbc, SV *key, SV *pkey, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
157 db_c_del (DBC *dbc, U32 flags = 0, SV *callback = &PL_sv_undef) 221 db_c_del (DBC *dbc, U32 flags = 0, SV *callback = &PL_sv_undef)
158 222
159 db_sequence_open (DB_SEQUENCE *seq, DB_TXN_ornull *txnid, SV *key, U32 flags = 0, SV *callback = &PL_sv_undef) 223 db_sequence_open (DB_SEQUENCE *seq, DB_TXN_ornull *txnid, SV *key, U32 flags = 0, SV *callback = &PL_sv_undef)
224 flags: CREATE EXCL
160 db_sequence_close (DB_SEQUENCE *seq, U32 flags = 0, SV *callback = &PL_sv_undef) 225 db_sequence_close (DB_SEQUENCE *seq, U32 flags = 0, SV *callback = &PL_sv_undef)
161 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) 226 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)
227 flags: TXN_NOSYNC
162 db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef) 228 db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
229 flags: TXN_NOSYNC
163 230
231=head4 db_txn_finish (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef)
232
233This is not actually a Berkeley DB function but a BDB module
234extension. The background for this exytension is: It is very annoying to
235have to check every single BDB function for error returns and provide a
236codepath out of your transaction. While the BDB module still makes this
237possible, it contains the following extensions:
238
239When a transaction-protected function returns any operating system
240error (errno > 0), BDB will set the C<TXN_DEADLOCK> flag on the
241transaction. This flag is also set by Berkeley DB functions themselves
242when an operation fails with LOCK_DEADLOCK, and it causes all further
243operations on that transaction (including C<db_txn_commit>) to fail.
244
245The C<db_txn_finish> request will look at this flag, and, if it is set,
246will automatically call C<db_txn_abort> (setting errno to C<LOCK_DEADLOCK>
247if it isn't set to something else yet). If it isn't set, it will call
248C<db_txn_commit> and return the error normally.
249
250How to use this? Easy: just write your transaction normally:
251
252 my $txn = $db_env->txn_begin;
253 db_get $db, $txn, "key", my $data;
254 db_put $db, $txn, "key", $data + 1 unless $! == BDB::NOTFOUND;
255 db_txn_finish $txn;
256 die "transaction failed" if $!;
257
258That is, handle only the expected errors. If something unexpected happens
259(EIO, LOCK_NOTGRANTED or a deadlock in either db_get or db_put), then the remaining
260requests (db_put in this case) will simply be skipped (they will fail with
261LOCK_DEADLOCK) and the transaction will be aborted.
262
263You can use the C<< $txn->failed >> method to check wether a transaction
264has failed in this way and abort further processing (excluding
265C<db_txn_finish>).
164 266
165=head3 DB_ENV/database environment methods 267=head3 DB_ENV/database environment methods
166 268
167Methods available on DB_ENV/$env handles: 269Methods available on DB_ENV/$env handles:
168 270
… …
179 $int = $env->set_flags (U32 flags, int onoff) 281 $int = $env->set_flags (U32 flags, int onoff)
180 $env->set_errfile (FILE *errfile = 0) 282 $env->set_errfile (FILE *errfile = 0)
181 $env->set_msgfile (FILE *msgfile = 0) 283 $env->set_msgfile (FILE *msgfile = 0)
182 $int = $env->set_verbose (U32 which, int onoff = 1) 284 $int = $env->set_verbose (U32 which, int onoff = 1)
183 $int = $env->set_encrypt (const char *password, U32 flags = 0) 285 $int = $env->set_encrypt (const char *password, U32 flags = 0)
184 $int = $env->set_timeout (NV timeout, U32 flags) 286 $int = $env->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
185 $int = $env->set_mp_max_openfd (int maxopenfd); 287 $int = $env->set_mp_max_openfd (int maxopenfd);
186 $int = $env->set_mp_max_write (int maxwrite, int maxwrite_sleep); 288 $int = $env->set_mp_max_write (int maxwrite, int maxwrite_sleep);
187 $int = $env->set_mp_mmapsize (int mmapsize_mb) 289 $int = $env->set_mp_mmapsize (int mmapsize_mb)
188 $int = $env->set_lk_detect (U32 detect = DB_LOCK_DEFAULT) 290 $int = $env->set_lk_detect (U32 detect = DB_LOCK_DEFAULT)
189 $int = $env->set_lk_max_lockers (U32 max) 291 $int = $env->set_lk_max_lockers (U32 max)
190 $int = $env->set_lk_max_locks (U32 max) 292 $int = $env->set_lk_max_locks (U32 max)
191 $int = $env->set_lk_max_objects (U32 max) 293 $int = $env->set_lk_max_objects (U32 max)
192 $int = $env->set_lg_bsize (U32 max) 294 $int = $env->set_lg_bsize (U32 max)
193 $int = $env->set_lg_max (U32 max) 295 $int = $env->set_lg_max (U32 max)
296 $int = $env->mutex_set_increment (U32 increment)
297 $int = $env->mutex_set_tas_spins (U32 tas_spins)
298 $int = $env->mutex_set_max (U32 max)
299 $int = $env->mutex_set_align (U32 align)
194 300
195 $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0) 301 $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0)
302 flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC
196 303
197=head4 Example: 304=head4 Example:
198 305
199 use AnyEvent; 306 use AnyEvent;
200 use BDB; 307 use BDB;
… …
229 SvREFCNT_dec (env); 336 SvREFCNT_dec (env);
230 } 337 }
231 338
232 $int = $db->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0) 339 $int = $db->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0)
233 $int = $db->set_flags (U32 flags) 340 $int = $db->set_flags (U32 flags)
341 flags: CHKSUM ENCRYPT TXN_NOT_DURABLE
342 Btree: DUP DUPSORT RECNUM REVSPLITOFF
343 Hash: DUP DUPSORT
344 Queue: INORDER
345 Recno: RENUMBER SNAPSHOT
346
234 $int = $db->set_encrypt (const char *password, U32 flags) 347 $int = $db->set_encrypt (const char *password, U32 flags)
235 $int = $db->set_lorder (int lorder) 348 $int = $db->set_lorder (int lorder)
236 $int = $db->set_bt_minkey (U32 minkey) 349 $int = $db->set_bt_minkey (U32 minkey)
237 $int = $db->set_re_delim (int delim) 350 $int = $db->set_re_delim (int delim)
238 $int = $db->set_re_pad (int re_pad) 351 $int = $db->set_re_pad (int re_pad)
… …
241 $int = $db->set_h_ffactor (U32 h_ffactor) 354 $int = $db->set_h_ffactor (U32 h_ffactor)
242 $int = $db->set_h_nelem (U32 h_nelem) 355 $int = $db->set_h_nelem (U32 h_nelem)
243 $int = $db->set_q_extentsize (U32 extentsize) 356 $int = $db->set_q_extentsize (U32 extentsize)
244 357
245 $dbc = $db->cursor (DB_TXN_ornull *txn = 0, U32 flags = 0) 358 $dbc = $db->cursor (DB_TXN_ornull *txn = 0, U32 flags = 0)
359 flags: READ_COMMITTED READ_UNCOMMITTED WRITECURSOR TXN_SNAPSHOT
246 $seq = $db->sequence (U32 flags = 0) 360 $seq = $db->sequence (U32 flags = 0)
247 361
248=head4 Example: 362=head4 Example:
249 363
250 my $db = db_create $env; 364 my $db = db_create $env;
… …
269 DESTROY (DB_TXN_ornull *txn) 383 DESTROY (DB_TXN_ornull *txn)
270 CODE: 384 CODE:
271 if (txn) 385 if (txn)
272 txn->abort (txn); 386 txn->abort (txn);
273 387
274 $int = $txn->set_timeout (NV timeout, U32 flags) 388 $int = $txn->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
389 flags: SET_LOCK_TIMEOUT SET_TXN_TIMEOUT
390
391 $bool = $txn->failed
392 # see db_txn_finish documentation, above
275 393
276 394
277=head3 DBC/cursor methods 395=head3 DBC/cursor methods
278 396
279Methods available on DBC/$dbc handles: 397Methods available on DBC/$dbc handles:
280 398
281 DESTROY (DBC_ornull *dbc) 399 DESTROY (DBC_ornull *dbc)
282 CODE: 400 CODE:
283 if (dbc) 401 if (dbc)
284 dbc->c_close (dbc); 402 dbc->c_close (dbc);
403
404 $int = $cursor->set_priority ($priority = PRIORITY_*)
285 405
286=head4 Example: 406=head4 Example:
287 407
288 my $c = $db->cursor; 408 my $c = $db->cursor;
289 409
… …
306 seq->close (seq, 0); 426 seq->close (seq, 0);
307 427
308 $int = $seq->initial_value (db_seq_t value) 428 $int = $seq->initial_value (db_seq_t value)
309 $int = $seq->set_cachesize (U32 size) 429 $int = $seq->set_cachesize (U32 size)
310 $int = $seq->set_flags (U32 flags) 430 $int = $seq->set_flags (U32 flags)
431 flags: SEQ_DEC SEQ_INC SEQ_WRAP
311 $int = $seq->set_range (db_seq_t min, db_seq_t max) 432 $int = $seq->set_range (db_seq_t min, db_seq_t max)
312 433
313=head4 Example: 434=head4 Example:
314 435
315 my $seq = $db->sequence; 436 my $seq = $db->sequence;
… …
321=head2 SUPPORT FUNCTIONS 442=head2 SUPPORT FUNCTIONS
322 443
323=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION 444=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
324 445
325=over 4 446=over 4
447
448=item $msg = BDB::strerror [$errno]
449
450Returns the string corresponding to the given errno value. If no argument
451is given, use C<$!>.
452
453Note that the BDB module also patches the C<$!> variable directly, so you
454should be able to get a bdb error string by simply stringifying C<$!>.
326 455
327=item $fileno = BDB::poll_fileno 456=item $fileno = BDB::poll_fileno
328 457
329Return the I<request result pipe file descriptor>. This filehandle must be 458Return the I<request result pipe file descriptor>. This filehandle must be
330polled for reading by some mechanism outside this module (e.g. Event or 459polled for reading by some mechanism outside this module (e.g. Event or
… …
369interactiveness when perl is not fast enough to process all requests in 498interactiveness when perl is not fast enough to process all requests in
370time. 499time.
371 500
372For interactive programs, values such as C<0.01> to C<0.1> should be fine. 501For interactive programs, values such as C<0.01> to C<0.1> should be fine.
373 502
374Example: Install an Event watcher that automatically calls 503Example: Install an EV watcher that automatically calls
375BDB::poll_cb with low priority, to ensure that other parts of the 504BDB::poll_cb with low priority, to ensure that other parts of the
376program get the CPU sometimes even under high AIO load. 505program get the CPU sometimes even under high load.
377 506
378 # try not to spend much more than 0.1s in poll_cb 507 # try not to spend much more than 0.1s in poll_cb
379 BDB::max_poll_time 0.1; 508 BDB::max_poll_time 0.1;
380 509
381 # use a low priority so other tasks have priority 510 my $bdb_poll = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb);
382 Event->io (fd => BDB::poll_fileno,
383 poll => 'r', nice => 1,
384 cb => &BDB::poll_cb);
385 511
386=item BDB::poll_wait 512=item BDB::poll_wait
387 513
388If there are any outstanding requests and none of them in the result 514If there are any outstanding requests and none of them in the result
389phase, wait till the result filehandle becomes ready for reading (simply 515phase, wait till the result filehandle becomes ready for reading (simply
… …
401 527
402 BDB::poll_wait, BDB::poll_cb 528 BDB::poll_wait, BDB::poll_cb
403 529
404=item BDB::flush 530=item BDB::flush
405 531
406Wait till all outstanding AIO requests have been handled. 532Wait till all outstanding BDB requests have been handled.
407 533
408Strictly equivalent to: 534Strictly equivalent to:
409 535
410 BDB::poll_wait, BDB::poll_cb 536 BDB::poll_wait, BDB::poll_cb
411 while BDB::nreqs; 537 while BDB::nreqs;
… …
416 542
417=over 4 543=over 4
418 544
419=item BDB::min_parallel $nthreads 545=item BDB::min_parallel $nthreads
420 546
421Set the minimum number of AIO threads to C<$nthreads>. The current 547Set the minimum number of BDB threads to C<$nthreads>. The current
422default is C<8>, which means eight asynchronous operations can execute 548default is C<8>, which means eight asynchronous operations can execute
423concurrently at any one time (the number of outstanding requests, 549concurrently at any one time (the number of outstanding requests,
424however, is unlimited). 550however, is unlimited).
425 551
426BDB starts threads only on demand, when an AIO request is queued and 552BDB starts threads only on demand, when an BDB request is queued and
427no free thread exists. Please note that queueing up a hundred requests can 553no free thread exists. Please note that queueing up a hundred requests can
428create demand for a hundred threads, even if it turns out that everything 554create demand for a hundred threads, even if it turns out that everything
429is in the cache and could have been processed faster by a single thread. 555is in the cache and could have been processed faster by a single thread.
430 556
431It is recommended to keep the number of threads relatively low, as some 557It is recommended to keep the number of threads relatively low, as some
… …
436Under most circumstances you don't need to call this function, as the 562Under most circumstances you don't need to call this function, as the
437module selects a default that is suitable for low to moderate load. 563module selects a default that is suitable for low to moderate load.
438 564
439=item BDB::max_parallel $nthreads 565=item BDB::max_parallel $nthreads
440 566
441Sets the maximum number of AIO threads to C<$nthreads>. If more than the 567Sets the maximum number of BDB threads to C<$nthreads>. If more than the
442specified number of threads are currently running, this function kills 568specified number of threads are currently running, this function kills
443them. This function blocks until the limit is reached. 569them. This function blocks until the limit is reached.
444 570
445While C<$nthreads> are zero, aio requests get queued but not executed 571While C<$nthreads> are zero, aio requests get queued but not executed
446until the number of threads has been increased again. 572until the number of threads has been increased again.
… …
485 611
486=item BDB::set_sync_prepare $cb 612=item BDB::set_sync_prepare $cb
487 613
488Sets a callback that is called whenever a request is created without an 614Sets a callback that is called whenever a request is created without an
489explicit callback. It has to return two code references. The first is used 615explicit callback. It has to return two code references. The first is used
490as the request callback, and the second is called to wait until the first 616as the request callback (it should save the return status), and the second
617is called to wait until the first callback has been called (it must set
618C<$!> to the return status).
619
620This mechanism can be used to include BDB into other event mechanisms,
621such as L<AnyEvent::BDB> or L<Coro::BDB>.
622
491callback has been called. The default implementation works like this: 623The default implementation works like this:
492 624
493 sub { 625 sub {
494 my $status; 626 my $status;
495 ( 627 (
496 sub { $status = $! }, 628 sub { $status = $! },
497 sub { BDB::poll while !defined $status; $! = $status }, 629 sub { BDB::poll while !defined $status; $! = $status },
498 ) 630 )
499 } 631 }
632
633It simply blocks the process till the request has finished and then sets
634C<$!> to the return value. This means that if you don't use a callback,
635BDB will simply fall back to synchronous operations.
500 636
501=back 637=back
502 638
503=head3 STATISTICAL INFORMATION 639=head3 STATISTICAL INFORMATION
504 640
… …
549 685
550=head2 FORK BEHAVIOUR 686=head2 FORK BEHAVIOUR
551 687
552This module should do "the right thing" when the process using it forks: 688This module should do "the right thing" when the process using it forks:
553 689
554Before the fork, IO::AIO enters a quiescent state where no requests 690Before the fork, BDB enters a quiescent state where no requests
555can be added in other threads and no results will be processed. After 691can be added in other threads and no results will be processed. After
556the fork the parent simply leaves the quiescent state and continues 692the fork the parent simply leaves the quiescent state and continues
557request/result processing, while the child frees the request/result queue 693request/result processing, while the child frees the request/result queue
558(so that the requests started before the fork will only be handled in the 694(so that the requests started before the fork will only be handled in the
559parent). Threads will be started on demand until the limit set in the 695parent). Threads will be started on demand until the limit set in the
560parent process has been reached again. 696parent process has been reached again.
561 697
562In short: the parent will, after a short pause, continue as if fork had 698In short: the parent will, after a short pause, continue as if fork had
563not been called, while the child will act as if IO::AIO has not been used 699not been called, while the child will act as if BDB has not been used
564yet. 700yet.
701
702Win32 note: there is no fork on win32, and perls emulation of it is too
703broken to be supported, so do not use BDB in a windows pseudo-fork, better
704yet, switch to a more capable platform.
565 705
566=head2 MEMORY USAGE 706=head2 MEMORY USAGE
567 707
568Per-request usage: 708Per-request usage:
569 709
… …
571bytes of memory. In addition, stat requests need a stat buffer (possibly 711bytes of memory. In addition, stat requests need a stat buffer (possibly
572a few hundred bytes), readdir requires a result buffer and so on. Perl 712a few hundred bytes), readdir requires a result buffer and so on. Perl
573scalars and other data passed into aio requests will also be locked and 713scalars and other data passed into aio requests will also be locked and
574will consume memory till the request has entered the done state. 714will consume memory till the request has entered the done state.
575 715
576This is now awfully much, so queuing lots of requests is not usually a 716This is not awfully much, so queuing lots of requests is not usually a
577problem. 717problem.
578 718
579Per-thread usage: 719Per-thread usage:
580 720
581In the execution phase, some aio requests require more memory for 721In the execution phase, some aio requests require more memory for
582temporary buffers, and each thread requires a stack and other data 722temporary buffers, and each thread requires a stack and other data
583structures (usually around 16k-128k, depending on the OS). 723structures (usually around 16k-128k, depending on the OS).
584 724
585=head1 KNOWN BUGS 725=head1 KNOWN BUGS
586 726
587Known bugs will be fixed in the next release. 727Known bugs will be fixed in the next release, except:
728
729 If you use a transaction in any request, and the request returns
730 with an operating system error or DB_LOCK_NOTGRANTED, the internal
731 TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>,
732 above.
588 733
589=head1 SEE ALSO 734=head1 SEE ALSO
590 735
591L<Coro::AIO>. 736L<AnyEvent::BDB> (event loop integration), L<Coro::BDB> (more natural
737syntax), L<IO::AIO> (nice to have).
592 738
593=head1 AUTHOR 739=head1 AUTHOR
594 740
595 Marc Lehmann <schmorp@schmorp.de> 741 Marc Lehmann <schmorp@schmorp.de>
596 http://home.schmorp.de/ 742 http://home.schmorp.de/

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