1 |
=head1 NAME |
2 |
|
3 |
BDB - Asynchronous Berkeley DB access |
4 |
|
5 |
=head1 SYNOPSIS |
6 |
|
7 |
use BDB; |
8 |
|
9 |
my $env = db_env_create; |
10 |
|
11 |
mkdir "bdtest", 0700; |
12 |
db_env_open |
13 |
$env, |
14 |
"bdtest", |
15 |
BDB::INIT_LOCK | BDB::INIT_LOG | BDB::INIT_MPOOL |
16 |
| BDB::INIT_TXN | BDB::RECOVER | BDB::USE_ENVIRON | BDB::CREATE, |
17 |
0600; |
18 |
|
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$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 integration 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 |
|
45 |
|
46 |
=head1 DESCRIPTION |
47 |
|
48 |
See the BerkeleyDB documentation (L<http://www.oracle.com/technology/documentation/berkeley-db/db/index.html>). |
49 |
The BDB API is very similar to the C API (the translation has been very faithful). |
50 |
|
51 |
See also the example sections in the document below and possibly the eg/ |
52 |
subdirectory of the BDB distribution. Last not least see the IO::AIO |
53 |
documentation, as that module uses almost the same asynchronous request |
54 |
model as this module. |
55 |
|
56 |
I know this is woefully inadequate documentation. Send a patch! |
57 |
|
58 |
|
59 |
=head1 REQUEST ANATOMY AND LIFETIME |
60 |
|
61 |
Every request method creates a request. which is a C data structure not |
62 |
directly visible to Perl. |
63 |
|
64 |
During their existance, bdb requests travel through the following states, |
65 |
in order: |
66 |
|
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=over 4 |
68 |
|
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=item ready |
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|
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Immediately after a request is created it is put into the ready state, |
72 |
waiting for a thread to execute it. |
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|
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=item execute |
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|
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A thread has accepted the request for processing and is currently |
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executing it (e.g. blocking in read). |
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|
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=item pending |
80 |
|
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The request has been executed and is waiting for result processing. |
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|
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While request submission and execution is fully asynchronous, result |
84 |
processing is not and relies on the perl interpreter calling C<poll_cb> |
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(or another function with the same effect). |
86 |
|
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=item result |
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|
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The request results are processed synchronously by C<poll_cb>. |
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|
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The C<poll_cb> function will process all outstanding aio requests by |
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calling their callbacks, freeing memory associated with them and managing |
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any groups they are contained in. |
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|
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=item done |
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|
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Request has reached the end of its lifetime and holds no resources anymore |
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(except possibly for the Perl object, but its connection to the actual |
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aio request is severed and calling its methods will either do nothing or |
100 |
result in a runtime error). |
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|
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=back |
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|
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=cut |
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|
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package BDB; |
107 |
|
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use common::sense; |
109 |
|
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use base 'Exporter'; |
111 |
|
112 |
our $VERSION; |
113 |
|
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BEGIN { |
115 |
$VERSION = '1.85'; |
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|
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our @BDB_REQ = qw( |
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db_env_open db_env_close db_env_txn_checkpoint db_env_lock_detect |
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db_env_memp_sync db_env_memp_trickle db_env_dbrename db_env_dbremove |
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db_env_log_archive |
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db_open db_close db_compact db_sync db_verify db_upgrade |
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db_put db_exists db_get db_pget db_del db_key_range |
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db_txn_commit db_txn_abort db_txn_finish |
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db_c_close db_c_count db_c_put db_c_get db_c_pget db_c_del |
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db_sequence_open db_sequence_close |
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db_sequence_get db_sequence_remove |
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); |
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our @EXPORT = (@BDB_REQ, qw(dbreq_pri dbreq_nice db_env_create db_create)); |
129 |
our @EXPORT_OK = qw( |
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poll_fileno poll_cb poll_wait flush |
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min_parallel max_parallel max_idle |
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nreqs nready npending nthreads |
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max_poll_time max_poll_reqs |
134 |
); |
135 |
|
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require XSLoader; |
137 |
XSLoader::load ("BDB", $VERSION); |
138 |
} |
139 |
|
140 |
=head1 BERKELEYDB FUNCTIONS |
141 |
|
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All of these are functions. The create functions simply return a new |
143 |
object and never block. All the remaining functions take an optional |
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callback as last argument. If it is missing, then the function will be |
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executed synchronously. In both cases, C<$!> will reflect the return value |
146 |
of the function. |
147 |
|
148 |
BDB functions that cannot block (mostly functions that manipulate |
149 |
settings) are method calls on the relevant objects, so the rule of thumb |
150 |
is: if it's a method, it's not blocking, if it's a function, it takes a |
151 |
callback as last argument. |
152 |
|
153 |
In the following, C<$int> signifies an integer return value, |
154 |
C<bdb_filename> is a "filename" (octets on unix, madness on windows), |
155 |
C<U32> is an unsigned 32 bit integer, C<int> is some integer, C<NV> is a |
156 |
floating point value. |
157 |
|
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Most C<SV *> types are generic perl scalars (for input and output of data |
159 |
values). |
160 |
|
161 |
The various C<DB_ENV> etc. arguments are handles return by |
162 |
C<db_env_create>, C<db_create>, C<txn_begin> and so on. If they have an |
163 |
appended C<_ornull> this means they are optional and you can pass C<undef> |
164 |
for them, resulting a NULL pointer on the C level. |
165 |
|
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The C<SV *callback> is the optional callback function to call when the |
167 |
request is completed. This last callback argument is special: the callback |
168 |
is simply the last argument passed. If there are "optional" arguments |
169 |
before the callback they can be left out. The callback itself can be left |
170 |
out or specified as C<undef>, in which case the function will be executed |
171 |
synchronously. |
172 |
|
173 |
For example, C<db_env_txn_checkpoint> usually is called with all integer |
174 |
arguments zero. These can be left out, so all of these specify a call |
175 |
to C<< DB_ENV->txn_checkpoint >>, to be executed asynchronously with a |
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callback to be called: |
177 |
|
178 |
db_env_txn_checkpoint $db_env, 0, 0, 0, sub { }; |
179 |
db_env_txn_checkpoint $db_env, 0, 0, sub { }; |
180 |
db_env_txn_checkpoint $db_env, sub { }; |
181 |
|
182 |
While these all specify a call to C<< DB_ENV->txn_checkpoint >> to be |
183 |
executed synchronously: |
184 |
|
185 |
db_env_txn_checkpoint $db_env, 0, 0, 0, undef; |
186 |
db_env_txn_checkpoint $db_env, 0, 0, 0; |
187 |
db_env_txn_checkpoint $db_env, 0; |
188 |
|
189 |
=head2 BDB functions |
190 |
|
191 |
Functions in the BDB namespace, exported by default: |
192 |
|
193 |
$env = db_env_create (U32 env_flags = 0) |
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flags: RPCCLIENT |
195 |
|
196 |
db_env_open (DB_ENV *env, bdb_filename db_home, U32 open_flags, int mode, SV *callback = 0) |
197 |
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 |
198 |
db_env_close (DB_ENV *env, U32 flags = 0, SV *callback = 0) |
199 |
db_env_txn_checkpoint (DB_ENV *env, U32 kbyte = 0, U32 min = 0, U32 flags = 0, SV *callback = 0) |
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flags: FORCE |
201 |
db_env_lock_detect (DB_ENV *env, U32 flags = 0, U32 atype = DB_LOCK_DEFAULT, SV *dummy = 0, SV *callback = 0) |
202 |
atype: LOCK_DEFAULT LOCK_EXPIRE LOCK_MAXLOCKS LOCK_MAXWRITE LOCK_MINLOCKS LOCK_MINWRITE LOCK_OLDEST LOCK_RANDOM LOCK_YOUNGEST |
203 |
db_env_memp_sync (DB_ENV *env, SV *dummy = 0, SV *callback = 0) |
204 |
db_env_memp_trickle (DB_ENV *env, int percent, SV *dummy = 0, SV *callback = 0) |
205 |
db_env_dbremove (DB_ENV *env, DB_TXN_ornull *txnid, bdb_filename file, bdb_filename database, U32 flags = 0, SV *callback = 0) |
206 |
db_env_dbrename (DB_ENV *env, DB_TXN_ornull *txnid, bdb_filename file, bdb_filename database, bdb_filename newname, U32 flags = 0, SV *callback = 0) |
207 |
db_env_log_archive (DB_ENV *env, SV *listp, U32 flags = 0, SV *callback = 0) |
208 |
|
209 |
$db = db_create (DB_ENV *env = 0, U32 flags = 0) |
210 |
flags: XA_CREATE |
211 |
|
212 |
db_open (DB *db, DB_TXN_ornull *txnid, bdb_filename file, bdb_filename database, int type, U32 flags, int mode, SV *callback = 0) |
213 |
flags: AUTO_COMMIT CREATE EXCL MULTIVERSION NOMMAP RDONLY READ_UNCOMMITTED THREAD TRUNCATE |
214 |
db_close (DB *db, U32 flags = 0, SV *callback = 0) |
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flags: DB_NOSYNC |
216 |
db_verify (DB *db, bdb_filename file, bdb_filename database = 0, SV *dummy = 0, U32 flags = 0, SV *callback = 0) |
217 |
db_upgrade (DB *db, bdb_filename file, U32 flags = 0, SV *callback = 0) |
218 |
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 = 0) |
219 |
flags: FREELIST_ONLY FREE_SPACE |
220 |
db_sync (DB *db, U32 flags = 0, SV *callback = 0) |
221 |
db_key_range (DB *db, DB_TXN_ornull *txn, SV *key, SV *key_range, U32 flags = 0, SV *callback = 0) |
222 |
db_put (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = 0) |
223 |
flags: APPEND NODUPDATA NOOVERWRITE |
224 |
db_exists (DB *db, DB_TXN_ornull *txn, SV *key, U32 flags = 0, SV *callback = 0) (v4.6) |
225 |
db_get (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = 0) |
226 |
flags: CONSUME CONSUME_WAIT GET_BOTH SET_RECNO MULTIPLE READ_COMMITTED READ_UNCOMMITTED RMW |
227 |
db_pget (DB *db, DB_TXN_ornull *txn, SV *key, SV *pkey, SV *data, U32 flags = 0, SV *callback = 0) |
228 |
flags: CONSUME CONSUME_WAIT GET_BOTH SET_RECNO MULTIPLE READ_COMMITTED READ_UNCOMMITTED RMW |
229 |
db_del (DB *db, DB_TXN_ornull *txn, SV *key, U32 flags = 0, SV *callback = 0) |
230 |
db_txn_commit (DB_TXN *txn, U32 flags = 0, SV *callback = 0) |
231 |
flags: TXN_NOSYNC TXN_SYNC |
232 |
db_txn_abort (DB_TXN *txn, SV *callback = 0) |
233 |
|
234 |
db_c_close (DBC *dbc, SV *callback = 0) |
235 |
db_c_count (DBC *dbc, SV *count, U32 flags = 0, SV *callback = 0) |
236 |
db_c_put (DBC *dbc, SV *key, SV *data, U32 flags = 0, SV *callback = 0) |
237 |
flags: AFTER BEFORE CURRENT KEYFIRST KEYLAST NODUPDATA |
238 |
db_c_get (DBC *dbc, SV *key, SV *data, U32 flags = 0, SV *callback = 0) |
239 |
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 |
240 |
db_c_pget (DBC *dbc, SV *key, SV *pkey, SV *data, U32 flags = 0, SV *callback = 0) |
241 |
db_c_del (DBC *dbc, U32 flags = 0, SV *callback = 0) |
242 |
|
243 |
db_sequence_open (DB_SEQUENCE *seq, DB_TXN_ornull *txnid, SV *key, U32 flags = 0, SV *callback = 0) |
244 |
flags: CREATE EXCL |
245 |
db_sequence_close (DB_SEQUENCE *seq, U32 flags = 0, SV *callback = 0) |
246 |
db_sequence_get (DB_SEQUENCE *seq, DB_TXN_ornull *txnid, int delta, SV *seq_value, U32 flags = DB_TXN_NOSYNC, SV *callback = 0) |
247 |
flags: TXN_NOSYNC |
248 |
db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = 0) |
249 |
flags: TXN_NOSYNC |
250 |
|
251 |
=head3 db_txn_finish (DB_TXN *txn, U32 flags = 0, SV *callback = 0) |
252 |
|
253 |
This is not actually a Berkeley DB function but a BDB module |
254 |
extension. The background for this exytension is: It is very annoying to |
255 |
have to check every single BDB function for error returns and provide a |
256 |
codepath out of your transaction. While the BDB module still makes this |
257 |
possible, it contains the following extensions: |
258 |
|
259 |
When a transaction-protected function returns any operating system |
260 |
error (errno > 0), BDB will set the C<TXN_DEADLOCK> flag on the |
261 |
transaction. This flag is also set by Berkeley DB functions themselves |
262 |
when an operation fails with LOCK_DEADLOCK, and it causes all further |
263 |
operations on that transaction (including C<db_txn_commit>) to fail. |
264 |
|
265 |
The C<db_txn_finish> request will look at this flag, and, if it is set, |
266 |
will automatically call C<db_txn_abort> (setting errno to C<LOCK_DEADLOCK> |
267 |
if it isn't set to something else yet). If it isn't set, it will call |
268 |
C<db_txn_commit> and return the error normally. |
269 |
|
270 |
How to use this? Easy: just write your transaction normally: |
271 |
|
272 |
my $txn = $db_env->txn_begin; |
273 |
db_get $db, $txn, "key", my $data; |
274 |
db_put $db, $txn, "key", $data + 1 unless $! == BDB::NOTFOUND; |
275 |
db_txn_finish $txn; |
276 |
die "transaction failed" if $!; |
277 |
|
278 |
That is, handle only the expected errors. If something unexpected happens |
279 |
(EIO, LOCK_NOTGRANTED or a deadlock in either db_get or db_put), then the remaining |
280 |
requests (db_put in this case) will simply be skipped (they will fail with |
281 |
LOCK_DEADLOCK) and the transaction will be aborted. |
282 |
|
283 |
You can use the C<< $txn->failed >> method to check wether a transaction |
284 |
has failed in this way and abort further processing (excluding |
285 |
C<db_txn_finish>). |
286 |
|
287 |
|
288 |
=head2 DB_ENV/database environment methods |
289 |
|
290 |
Methods available on DB_ENV/$env handles: |
291 |
|
292 |
DESTROY (DB_ENV_ornull *env) |
293 |
CODE: |
294 |
if (env) |
295 |
env->close (env, 0); |
296 |
|
297 |
$int = $env->set_data_dir (const char *dir) |
298 |
$int = $env->set_tmp_dir (const char *dir) |
299 |
$int = $env->set_lg_dir (const char *dir) |
300 |
$int = $env->set_shm_key (long shm_key) |
301 |
$int = $env->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0) |
302 |
$int = $env->set_flags (U32 flags, int onoff = 1) |
303 |
$int = $env->log_set_config (U32 flags, int onoff = 1) (v4.7) |
304 |
$int = $env->set_intermediate_dir_mode (const char *modestring) (v4.7) |
305 |
$env->set_errfile (FILE *errfile = 0) |
306 |
$env->set_msgfile (FILE *msgfile = 0) |
307 |
$int = $env->set_verbose (U32 which, int onoff = 1) |
308 |
$int = $env->set_encrypt (const char *password, U32 flags = 0) |
309 |
$int = $env->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT) |
310 |
$int = $env->set_mp_max_openfd (int maxopenfd); |
311 |
$int = $env->set_mp_max_write (int maxwrite, int maxwrite_sleep); |
312 |
$int = $env->set_mp_mmapsize (int mmapsize_mb) |
313 |
$int = $env->set_lk_detect (U32 detect = DB_LOCK_DEFAULT) |
314 |
$int = $env->set_lk_max_lockers (U32 max) |
315 |
$int = $env->set_lk_max_locks (U32 max) |
316 |
$int = $env->set_lk_max_objects (U32 max) |
317 |
$int = $env->set_lg_bsize (U32 max) |
318 |
$int = $env->set_lg_max (U32 max) |
319 |
$int = $env->mutex_set_increment (U32 increment) |
320 |
$int = $env->mutex_set_tas_spins (U32 tas_spins) |
321 |
$int = $env->mutex_set_max (U32 max) |
322 |
$int = $env->mutex_set_align (U32 align) |
323 |
|
324 |
$txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0) |
325 |
flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC |
326 |
$txn = $env->cdsgroup_begin; (v4.5) |
327 |
|
328 |
=head3 Example: |
329 |
|
330 |
use AnyEvent; |
331 |
use BDB; |
332 |
|
333 |
our $FH; open $FH, "<&=" . BDB::poll_fileno; |
334 |
our $WATCHER = AnyEvent->io (fh => $FH, poll => 'r', cb => \&BDB::poll_cb); |
335 |
|
336 |
BDB::min_parallel 8; |
337 |
|
338 |
my $env = db_env_create; |
339 |
|
340 |
mkdir "bdtest", 0700; |
341 |
db_env_open |
342 |
$env, |
343 |
"bdtest", |
344 |
BDB::INIT_LOCK | BDB::INIT_LOG | BDB::INIT_MPOOL | BDB::INIT_TXN | BDB::RECOVER | BDB::USE_ENVIRON | BDB::CREATE, |
345 |
0600; |
346 |
|
347 |
$env->set_flags (BDB::AUTO_COMMIT | BDB::TXN_NOSYNC, 1); |
348 |
|
349 |
|
350 |
=head2 DB/database methods |
351 |
|
352 |
Methods available on DB/$db handles: |
353 |
|
354 |
DESTROY (DB_ornull *db) |
355 |
CODE: |
356 |
if (db) |
357 |
{ |
358 |
SV *env = (SV *)db->app_private; |
359 |
db->close (db, 0); |
360 |
SvREFCNT_dec (env); |
361 |
} |
362 |
|
363 |
$int = $db->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0) |
364 |
$int = $db->set_flags (U32 flags) |
365 |
flags: CHKSUM ENCRYPT TXN_NOT_DURABLE |
366 |
Btree: DUP DUPSORT RECNUM REVSPLITOFF |
367 |
Hash: DUP DUPSORT |
368 |
Queue: INORDER |
369 |
Recno: RENUMBER SNAPSHOT |
370 |
|
371 |
$int = $db->set_encrypt (const char *password, U32 flags) |
372 |
$int = $db->set_lorder (int lorder) |
373 |
$int = $db->set_bt_minkey (U32 minkey) |
374 |
$int = $db->set_re_delim (int delim) |
375 |
$int = $db->set_re_pad (int re_pad) |
376 |
$int = $db->set_re_source (char *source) |
377 |
$int = $db->set_re_len (U32 re_len) |
378 |
$int = $db->set_h_ffactor (U32 h_ffactor) |
379 |
$int = $db->set_h_nelem (U32 h_nelem) |
380 |
$int = $db->set_q_extentsize (U32 extentsize) |
381 |
|
382 |
$dbc = $db->cursor (DB_TXN_ornull *txn = 0, U32 flags = 0) |
383 |
flags: READ_COMMITTED READ_UNCOMMITTED WRITECURSOR TXN_SNAPSHOT |
384 |
$seq = $db->sequence (U32 flags = 0) |
385 |
|
386 |
=head3 Example: |
387 |
|
388 |
my $db = db_create $env; |
389 |
db_open $db, undef, "table", undef, BDB::BTREE, BDB::AUTO_COMMIT | BDB::CREATE | BDB::READ_UNCOMMITTED, 0600; |
390 |
|
391 |
for (1..1000) { |
392 |
db_put $db, undef, "key $_", "data $_"; |
393 |
|
394 |
db_key_range $db, undef, "key $_", my $keyrange; |
395 |
my ($lt, $eq, $gt) = @$keyrange; |
396 |
} |
397 |
|
398 |
db_del $db, undef, "key $_" for 1..1000; |
399 |
|
400 |
db_sync $db; |
401 |
|
402 |
|
403 |
=head2 DB_TXN/transaction methods |
404 |
|
405 |
Methods available on DB_TXN/$txn handles: |
406 |
|
407 |
DESTROY (DB_TXN_ornull *txn) |
408 |
CODE: |
409 |
if (txn) |
410 |
txn->abort (txn); |
411 |
|
412 |
$int = $txn->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT) |
413 |
flags: SET_LOCK_TIMEOUT SET_TXN_TIMEOUT |
414 |
|
415 |
$bool = $txn->failed |
416 |
# see db_txn_finish documentation, above |
417 |
|
418 |
|
419 |
=head2 DBC/cursor methods |
420 |
|
421 |
Methods available on DBC/$dbc handles: |
422 |
|
423 |
DESTROY (DBC_ornull *dbc) |
424 |
CODE: |
425 |
if (dbc) |
426 |
dbc->c_close (dbc); |
427 |
|
428 |
$int = $cursor->set_priority ($priority = PRIORITY_*) (v4.6) |
429 |
|
430 |
=head3 Example: |
431 |
|
432 |
my $c = $db->cursor; |
433 |
|
434 |
for (;;) { |
435 |
db_c_get $c, my $key, my $data, BDB::NEXT; |
436 |
warn "<$!,$key,$data>"; |
437 |
last if $!; |
438 |
} |
439 |
|
440 |
db_c_close $c; |
441 |
|
442 |
|
443 |
=head2 DB_SEQUENCE/sequence methods |
444 |
|
445 |
Methods available on DB_SEQUENCE/$seq handles: |
446 |
|
447 |
DESTROY (DB_SEQUENCE_ornull *seq) |
448 |
CODE: |
449 |
if (seq) |
450 |
seq->close (seq, 0); |
451 |
|
452 |
$int = $seq->initial_value (db_seq_t value) |
453 |
$int = $seq->set_cachesize (U32 size) |
454 |
$int = $seq->set_flags (U32 flags) |
455 |
flags: SEQ_DEC SEQ_INC SEQ_WRAP |
456 |
$int = $seq->set_range (db_seq_t min, db_seq_t max) |
457 |
|
458 |
=head3 Example: |
459 |
|
460 |
my $seq = $db->sequence; |
461 |
|
462 |
db_sequence_open $seq, undef, "seq", BDB::CREATE; |
463 |
db_sequence_get $seq, undef, 1, my $value; |
464 |
|
465 |
|
466 |
=head1 SUPPORT FUNCTIONS |
467 |
|
468 |
=head2 EVENT PROCESSING AND EVENT LOOP INTEGRATION |
469 |
|
470 |
=over 4 |
471 |
|
472 |
=item $msg = BDB::strerror [$errno] |
473 |
|
474 |
Returns the string corresponding to the given errno value. If no argument |
475 |
is given, use C<$!>. |
476 |
|
477 |
Note that the BDB module also patches the C<$!> variable directly, so you |
478 |
should be able to get a bdb error string by simply stringifying C<$!>. |
479 |
|
480 |
=item $fileno = BDB::poll_fileno |
481 |
|
482 |
Return the I<request result pipe file descriptor>. This filehandle must be |
483 |
polled for reading by some mechanism outside this module (e.g. Event or |
484 |
select, see below or the SYNOPSIS). If the pipe becomes readable you have |
485 |
to call C<poll_cb> to check the results. |
486 |
|
487 |
See C<poll_cb> for an example. |
488 |
|
489 |
=item BDB::poll_cb |
490 |
|
491 |
Process some outstanding events on the result pipe. You have to call this |
492 |
regularly. Returns the number of events processed. Returns immediately |
493 |
when no events are outstanding. The amount of events processed depends on |
494 |
the settings of C<BDB::max_poll_req> and C<BDB::max_poll_time>. |
495 |
|
496 |
If not all requests were processed for whatever reason, the filehandle |
497 |
will still be ready when C<poll_cb> returns. |
498 |
|
499 |
Example: Install an Event watcher that automatically calls |
500 |
BDB::poll_cb with high priority: |
501 |
|
502 |
Event->io (fd => BDB::poll_fileno, |
503 |
poll => 'r', async => 1, |
504 |
cb => \&BDB::poll_cb); |
505 |
|
506 |
=item BDB::max_poll_reqs $nreqs |
507 |
|
508 |
=item BDB::max_poll_time $seconds |
509 |
|
510 |
These set the maximum number of requests (default C<0>, meaning infinity) |
511 |
that are being processed by C<BDB::poll_cb> in one call, respectively |
512 |
the maximum amount of time (default C<0>, meaning infinity) spent in |
513 |
C<BDB::poll_cb> to process requests (more correctly the mininum amount |
514 |
of time C<poll_cb> is allowed to use). |
515 |
|
516 |
Setting C<max_poll_time> to a non-zero value creates an overhead of one |
517 |
syscall per request processed, which is not normally a problem unless your |
518 |
callbacks are really really fast or your OS is really really slow (I am |
519 |
not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead. |
520 |
|
521 |
Setting these is useful if you want to ensure some level of |
522 |
interactiveness when perl is not fast enough to process all requests in |
523 |
time. |
524 |
|
525 |
For interactive programs, values such as C<0.01> to C<0.1> should be fine. |
526 |
|
527 |
Example: Install an EV watcher that automatically calls |
528 |
BDB::poll_cb with low priority, to ensure that other parts of the |
529 |
program get the CPU sometimes even under high load. |
530 |
|
531 |
# try not to spend much more than 0.1s in poll_cb |
532 |
BDB::max_poll_time 0.1; |
533 |
|
534 |
my $bdb_poll = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb); |
535 |
|
536 |
=item BDB::poll_wait |
537 |
|
538 |
If there are any outstanding requests and none of them in the result |
539 |
phase, wait till the result filehandle becomes ready for reading (simply |
540 |
does a C<select> on the filehandle. This is useful if you want to |
541 |
synchronously wait for some requests to finish). |
542 |
|
543 |
See C<nreqs> for an example. |
544 |
|
545 |
=item BDB::poll |
546 |
|
547 |
Waits until some requests have been handled. |
548 |
|
549 |
Returns the number of requests processed, but is otherwise strictly |
550 |
equivalent to: |
551 |
|
552 |
BDB::poll_wait, BDB::poll_cb |
553 |
|
554 |
=item BDB::flush |
555 |
|
556 |
Wait till all outstanding BDB requests have been handled. |
557 |
|
558 |
Strictly equivalent to: |
559 |
|
560 |
BDB::poll_wait, BDB::poll_cb |
561 |
while BDB::nreqs; |
562 |
|
563 |
=back |
564 |
|
565 |
=head2 VERSION CHECKING |
566 |
|
567 |
BerkeleyDB comes in various versions, many of them have minor |
568 |
incompatibilities. This means that traditional "at least version x.x" |
569 |
checks are often not sufficient. |
570 |
|
571 |
Example: set the log_autoremove option in a way compatible with <v4.7 and |
572 |
v4.7. Note the use of & on the constants to avoid triggering a compiletime |
573 |
bug when the symbol isn't available. |
574 |
|
575 |
$DB_ENV->set_flags (&BDB::LOG_AUTOREMOVE ) if BDB::VERSION v0, v4.7; |
576 |
$DB_ENV->log_set_config (&BDB::LOG_AUTO_REMOVE) if BDB::VERSION v4.7; |
577 |
|
578 |
=over 4 |
579 |
|
580 |
=item BDB::VERSION |
581 |
|
582 |
The C<BDB::VERSION> function, when called without arguments, returns the |
583 |
Berkeley DB version as a v-string (usually with 3 components). You should |
584 |
use C<lt> and C<ge> operators exclusively to make comparisons. |
585 |
|
586 |
Example: check for at least version 4.7. |
587 |
|
588 |
BDB::VERSION ge v4.7 or die; |
589 |
|
590 |
=item BDB::VERSION min-version |
591 |
|
592 |
Returns true if the BDB version is at least the given version (specified |
593 |
as a v-string), false otherwise. |
594 |
|
595 |
Example: check for at least version 4.5. |
596 |
|
597 |
BDB::VERSION v4.7 or die; |
598 |
|
599 |
=item BDB::VERSION min-version, max-version |
600 |
|
601 |
Returns true of the BDB version is at least version C<min-version> (specify C<undef> or C<v0> for any minimum version) |
602 |
and less then C<max-version>. |
603 |
|
604 |
Example: check wether version is strictly less then v4.7. |
605 |
|
606 |
BDB::VERSION v0, v4.7 |
607 |
or die "version 4.7 is not yet supported"; |
608 |
|
609 |
=back |
610 |
|
611 |
=cut |
612 |
|
613 |
sub VERSION { |
614 |
# I was dumb enough to override the VERSION method here, so let's try |
615 |
# to fix it up. |
616 |
|
617 |
if ($_[0] eq __PACKAGE__) { |
618 |
$VERSION |
619 |
} else { |
620 |
if (@_ > 0) { |
621 |
return undef if VERSION_v lt $_[0]; |
622 |
if (@_ > 1) { |
623 |
return undef if VERSION_v ge $_[1]; |
624 |
} |
625 |
} |
626 |
|
627 |
VERSION_v |
628 |
} |
629 |
} |
630 |
|
631 |
=head2 CONTROLLING THE NUMBER OF THREADS |
632 |
|
633 |
=over 4 |
634 |
|
635 |
=item BDB::min_parallel $nthreads |
636 |
|
637 |
Set the minimum number of BDB threads to C<$nthreads>. The current |
638 |
default is C<8>, which means eight asynchronous operations can execute |
639 |
concurrently at any one time (the number of outstanding requests, |
640 |
however, is unlimited). |
641 |
|
642 |
BDB starts threads only on demand, when an BDB request is queued and |
643 |
no free thread exists. Please note that queueing up a hundred requests can |
644 |
create demand for a hundred threads, even if it turns out that everything |
645 |
is in the cache and could have been processed faster by a single thread. |
646 |
|
647 |
It is recommended to keep the number of threads relatively low, as some |
648 |
Linux kernel versions will scale negatively with the number of threads |
649 |
(higher parallelity => MUCH higher latency). With current Linux 2.6 |
650 |
versions, 4-32 threads should be fine. |
651 |
|
652 |
Under most circumstances you don't need to call this function, as the |
653 |
module selects a default that is suitable for low to moderate load. |
654 |
|
655 |
=item BDB::max_parallel $nthreads |
656 |
|
657 |
Sets the maximum number of BDB threads to C<$nthreads>. If more than the |
658 |
specified number of threads are currently running, this function kills |
659 |
them. This function blocks until the limit is reached. |
660 |
|
661 |
While C<$nthreads> are zero, aio requests get queued but not executed |
662 |
until the number of threads has been increased again. |
663 |
|
664 |
This module automatically runs C<max_parallel 0> at program end, to ensure |
665 |
that all threads are killed and that there are no outstanding requests. |
666 |
|
667 |
Under normal circumstances you don't need to call this function. |
668 |
|
669 |
=item BDB::max_idle $nthreads |
670 |
|
671 |
Limit the number of threads (default: 4) that are allowed to idle (i.e., |
672 |
threads that did not get a request to process within 10 seconds). That |
673 |
means if a thread becomes idle while C<$nthreads> other threads are also |
674 |
idle, it will free its resources and exit. |
675 |
|
676 |
This is useful when you allow a large number of threads (e.g. 100 or 1000) |
677 |
to allow for extremely high load situations, but want to free resources |
678 |
under normal circumstances (1000 threads can easily consume 30MB of RAM). |
679 |
|
680 |
The default is probably ok in most situations, especially if thread |
681 |
creation is fast. If thread creation is very slow on your system you might |
682 |
want to use larger values. |
683 |
|
684 |
=item $oldmaxreqs = BDB::max_outstanding $maxreqs |
685 |
|
686 |
This is a very bad function to use in interactive programs because it |
687 |
blocks, and a bad way to reduce concurrency because it is inexact: Better |
688 |
use an C<aio_group> together with a feed callback. |
689 |
|
690 |
Sets the maximum number of outstanding requests to C<$nreqs>. If you |
691 |
to queue up more than this number of requests, the next call to the |
692 |
C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>) |
693 |
function will block until the limit is no longer exceeded. |
694 |
|
695 |
The default value is very large, so there is no practical limit on the |
696 |
number of outstanding requests. |
697 |
|
698 |
You can still queue as many requests as you want. Therefore, |
699 |
C<max_oustsanding> is mainly useful in simple scripts (with low values) or |
700 |
as a stop gap to shield against fatal memory overflow (with large values). |
701 |
|
702 |
=item $old_cb = BDB::set_sync_prepare $cb |
703 |
|
704 |
Sets a callback that is called whenever a request is created without an |
705 |
explicit callback. It has to return two code references. The first is used |
706 |
as the request callback (it should save the return status), and the second |
707 |
is called to wait until the first callback has been called (it must set |
708 |
C<$!> to the return status). |
709 |
|
710 |
This mechanism can be used to include BDB into other event mechanisms, |
711 |
such as L<Coro::BDB>. |
712 |
|
713 |
To allow other, callback-based, events to be executed while callback-less |
714 |
ones are run, you could use this sync prepare function: |
715 |
|
716 |
sub { |
717 |
my $status; |
718 |
( |
719 |
sub { $status = $! }, |
720 |
sub { BDB::poll while !defined $status; $! = $status }, |
721 |
) |
722 |
} |
723 |
|
724 |
It works by polling for results till the request has finished and then |
725 |
sets C<$!> to the return value. This means that if you don't use a |
726 |
callback, BDB would simply fall back to synchronous operations. |
727 |
|
728 |
By default, or if the sync prepare function is set to C<undef>, is to |
729 |
execute callback-less BDB requests in the foreground thread, setting C<$!> |
730 |
to the return value, without polling for other events. |
731 |
|
732 |
=back |
733 |
|
734 |
=head2 STATISTICAL INFORMATION |
735 |
|
736 |
=over 4 |
737 |
|
738 |
=item BDB::nreqs |
739 |
|
740 |
Returns the number of requests currently in the ready, execute or pending |
741 |
states (i.e. for which their callback has not been invoked yet). |
742 |
|
743 |
Example: wait till there are no outstanding requests anymore: |
744 |
|
745 |
BDB::poll_wait, BDB::poll_cb |
746 |
while BDB::nreqs; |
747 |
|
748 |
=item BDB::nready |
749 |
|
750 |
Returns the number of requests currently in the ready state (not yet |
751 |
executed). |
752 |
|
753 |
=item BDB::npending |
754 |
|
755 |
Returns the number of requests currently in the pending state (executed, |
756 |
but not yet processed by poll_cb). |
757 |
|
758 |
=back |
759 |
|
760 |
=cut |
761 |
|
762 |
set_sync_prepare (undef); |
763 |
|
764 |
min_parallel 8; |
765 |
|
766 |
END { flush } |
767 |
|
768 |
1; |
769 |
|
770 |
=head1 COMMON PITFALLS |
771 |
|
772 |
=head2 Unexpected Crashes |
773 |
|
774 |
Remember that, by default, BDB will execute requests in parallel, in |
775 |
somewhat random order. That means that it is easy to run a C<db_get> |
776 |
request on thesa me database as a concurrent C<db_close> request, leading |
777 |
to a crash, silent data corruption, eventually the next world war on |
778 |
terrorism. |
779 |
|
780 |
If you only ever use foreground requests (without a callback), this will |
781 |
not be an issue. |
782 |
|
783 |
=head2 Unexpected Freezes or Deadlocks |
784 |
|
785 |
Remember that, by default, BDB will execute requests in parallel, which |
786 |
easily leads to deadlocks (even concurrent put's on the same database can |
787 |
deadlock). |
788 |
|
789 |
You either need to run deadlock detection (and handle the resulting |
790 |
errors), or make sure only one process ever updates the database, ine one |
791 |
thread, e.g. by using only foreground requests (without a callback). |
792 |
|
793 |
=head1 FORK BEHAVIOUR |
794 |
|
795 |
This module should do "the right thing" when the process using it forks: |
796 |
|
797 |
Before the fork, BDB enters a quiescent state where no requests |
798 |
can be added in other threads and no results will be processed. After |
799 |
the fork the parent simply leaves the quiescent state and continues |
800 |
request/result processing, while the child frees the request/result queue |
801 |
(so that the requests started before the fork will only be handled in the |
802 |
parent). Threads will be started on demand until the limit set in the |
803 |
parent process has been reached again. |
804 |
|
805 |
In short: the parent will, after a short pause, continue as if fork had |
806 |
not been called, while the child will act as if BDB has not been used |
807 |
yet. |
808 |
|
809 |
Win32 note: there is no fork on win32, and perls emulation of it is too |
810 |
broken to be supported, so do not use BDB in a windows pseudo-fork, better |
811 |
yet, switch to a more capable platform. |
812 |
|
813 |
=head1 MEMORY USAGE |
814 |
|
815 |
Per-request usage: |
816 |
|
817 |
Each aio request uses - depending on your architecture - around 100-200 |
818 |
bytes of memory. In addition, stat requests need a stat buffer (possibly |
819 |
a few hundred bytes), readdir requires a result buffer and so on. Perl |
820 |
scalars and other data passed into aio requests will also be locked and |
821 |
will consume memory till the request has entered the done state. |
822 |
|
823 |
This is not awfully much, so queuing lots of requests is not usually a |
824 |
problem. |
825 |
|
826 |
Per-thread usage: |
827 |
|
828 |
In the execution phase, some aio requests require more memory for |
829 |
temporary buffers, and each thread requires a stack and other data |
830 |
structures (usually around 16k-128k, depending on the OS). |
831 |
|
832 |
=head1 WIN32 FILENAMES/DATABASE NAME MESS |
833 |
|
834 |
Perl on Win32 supports only ASCII filenames (the reason is that it abuses |
835 |
an internal flag to store wether a filename is Unicode or ANSI, but that |
836 |
flag is used for somethign else in the perl core, so there is no way to |
837 |
detect wether a filename is ANSI or Unicode-encoded). The BDB module |
838 |
tries to work around this issue by assuming that the filename is an ANSI |
839 |
filename and BDB was built for unicode support. |
840 |
|
841 |
=head1 KNOWN BUGS |
842 |
|
843 |
Known bugs will be fixed in the next release, except: |
844 |
|
845 |
If you use a transaction in any request, and the request returns |
846 |
with an operating system error or DB_LOCK_NOTGRANTED, the internal |
847 |
TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>, |
848 |
above. |
849 |
|
850 |
=head1 SEE ALSO |
851 |
|
852 |
L<AnyEvent::BDB> (event loop integration), L<Coro::BDB> (more natural |
853 |
syntax), L<IO::AIO> (nice to have). |
854 |
|
855 |
=head1 AUTHOR |
856 |
|
857 |
Marc Lehmann <schmorp@schmorp.de> |
858 |
http://home.schmorp.de/ |
859 |
|
860 |
=cut |
861 |
|