[ViewVC] Diff of: cvs/BDB/README

Comparing BDB/README (file contents):
Revision 1.1 by root, Mon Feb 5 18:40:55 2007 UTC vs.
Revision 1.14 by root, Tue Oct 21 02:21:25 2008 UTC

…		…
1	NAME	1	NAME
2	BDB::AIO - Asynchronous Berkeley DB access	2	BDB - Asynchronous Berkeley DB access
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use BDB::AIO;	5	use BDB;
		6
		7	my $env = db_env_create;
		8
		9	mkdir "bdtest", 0700;
		10	db_env_open
		11	$env,
		12	"bdtest",
		13	BDB::INIT_LOCK \| BDB::INIT_LOG \| BDB::INIT_MPOOL
		14	\| BDB::INIT_TXN \| BDB::RECOVER \| BDB::USE_ENVIRON \| BDB::CREATE,
		15	0600;
		16
		17	$env->set_flags (BDB::AUTO_COMMIT \| BDB::TXN_NOSYNC, 1);
		18
		19	my $db = db_create $env;
		20	db_open $db, undef, "table", undef, BDB::BTREE, BDB::AUTO_COMMIT \| BDB::CREATE
		21	\| BDB::READ_UNCOMMITTED, 0600;
		22	db_put $db, undef, "key", "data", 0, sub {
		23	db_del $db, undef, "key";
		24	};
		25	db_sync $db;
		26
		27	# when you also use Coro, management is easy:
		28	use Coro::BDB;
		29
		30	# automatic event loop intergration with AnyEvent:
		31	use AnyEvent::BDB;
		32
		33	# automatic result processing with EV:
		34	my $WATCHER = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb;
		35
		36	# with Glib:
		37	add_watch Glib::IO BDB::poll_fileno,
		38	in => sub { BDB::poll_cb; 1 };
		39
		40	# or simply flush manually
		41	BDB::flush;
6		42
7	DESCRIPTION	43	DESCRIPTION
8	EXAMPLE	44	See the BerkeleyDB documentation
		45	(<http://www.oracle.com/technology/documentation/berkeley-db/db/index.ht
		46	ml>). The BDB API is very similar to the C API (the translation has been
		47	very faithful).
		48
		49	See also the example sections in the document below and possibly the eg/
		50	subdirectory of the BDB distribution. Last not least see the IO::AIO
		51	documentation, as that module uses almost the same asynchronous request
		52	model as this module.
		53
		54	I know this is woefully inadequate documentation. Send a patch!
		55
9	REQUEST ANATOMY AND LIFETIME	56	REQUEST ANATOMY AND LIFETIME
10	Every request method creates a request. which is a C data structure not	57	Every request method creates a request. which is a C data structure not
11	directly visible to Perl.	58	directly visible to Perl.
12		59
13	During their existance, bdb requests travel through the following	60	During their existance, bdb requests travel through the following
39	Request has reached the end of its lifetime and holds no resources	86	Request has reached the end of its lifetime and holds no resources
40	anymore (except possibly for the Perl object, but its connection to	87	anymore (except possibly for the Perl object, but its connection to
41	the actual aio request is severed and calling its methods will	88	the actual aio request is severed and calling its methods will
42	either do nothing or result in a runtime error).	89	either do nothing or result in a runtime error).
43		90
		91	BERKELEYDB FUNCTIONS
		92	All of these are functions. The create functions simply return a new
		93	object and never block. All the remaining functions take an optional
		94	callback as last argument. If it is missing, then the function will be
		95	executed synchronously. In both cases, $! will reflect the return value
		96	of the function.
		97
		98	BDB functions that cannot block (mostly functions that manipulate
		99	settings) are method calls on the relevant objects, so the rule of thumb
		100	is: if it's a method, it's not blocking, if it's a function, it takes a
		101	callback as last argument.
		102
		103	In the following, $int signifies an integer return value, "bdb_filename"
		104	is a "filename" (octets on unix, madness on windows), "U32" is an
		105	unsigned 32 bit integer, "int" is some integer, "NV" is a floating point
		106	value.
		107
		108	Most "SV *" types are generic perl scalars (for input and output of data
		109	values).
		110
		111	The various "DB_ENV" etc. arguments are handles return by
		112	"db_env_create", "db_create", "txn_begin" and so on. If they have an
		113	appended "_ornull" this means they are optional and you can pass "undef"
		114	for them, resulting a NULL pointer on the C level.
		115
		116	The "SV *callback" is the optional callback function to call when the
		117	request is completed. This last callback argument is special: the
		118	callback is simply the last argument passed. If there are "optional"
		119	arguments before the callback they can be left out. The callback itself
		120	can be left out or specified as "undef", in which case the function will
		121	be executed synchronously.
		122
		123	For example, "db_env_txn_checkpoint" usually is called with all integer
		124	arguments zero. These can be left out, so all of these specify a call to
		125	"DB_ENV->txn_checkpoint", to be executed asynchronously with a callback
		126	to be called:
		127
		128	db_env_txn_checkpoint $db_env, 0, 0, 0, sub { };
		129	db_env_txn_checkpoint $db_env, 0, 0, sub { };
		130	db_env_txn_checkpoint $db_env, sub { };
		131
		132	While these all specify a call to "DB_ENV->txn_checkpoint" to be
		133	executed synchronously:
		134
		135	db_env_txn_checkpoint $db_env, 0, 0, 0, undef;
		136	db_env_txn_checkpoint $db_env, 0, 0, 0;
		137	db_env_txn_checkpoint $db_env, 0;
		138
		139	BDB functions
		140	Functions in the BDB namespace, exported by default:
		141
		142	$env = db_env_create (U32 env_flags = 0)
		143	flags: RPCCLIENT
		144
		145	db_env_open (DB_ENV env, bdb_filename db_home, U32 open_flags, int mode, SV callback = &PL_sv_undef)
		146	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
		147	db_env_close (DB_ENV env, U32 flags = 0, SV callback = &PL_sv_undef)
		148	db_env_txn_checkpoint (DB_ENV env, U32 kbyte = 0, U32 min = 0, U32 flags = 0, SV callback = &PL_sv_undef)
		149	flags: FORCE
		150	db_env_lock_detect (DB_ENV env, U32 flags = 0, U32 atype = DB_LOCK_DEFAULT, SV dummy = 0, SV *callback = &PL_sv_undef)
		151	atype: LOCK_DEFAULT LOCK_EXPIRE LOCK_MAXLOCKS LOCK_MAXWRITE LOCK_MINLOCKS LOCK_MINWRITE LOCK_OLDEST LOCK_RANDOM LOCK_YOUNGEST
		152	db_env_memp_sync (DB_ENV env, SV dummy = 0, SV *callback = &PL_sv_undef)
		153	db_env_memp_trickle (DB_ENV env, int percent, SV dummy = 0, SV *callback = &PL_sv_undef)
		154	db_env_dbremove (DB_ENV env, DB_TXN_ornull txnid, bdb_filename file, bdb_filename database, U32 flags = 0, SV *callback = &PL_sv_undef)
		155	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)
		156	db_env_log_archive (DB_ENV env, SV listp, U32 flags = 0, SV *callback = &PL_sv_undef)
		157
		158	$db = db_create (DB_ENV *env = 0, U32 flags = 0)
		159	flags: XA_CREATE
		160
		161	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)
		162	flags: AUTO_COMMIT CREATE EXCL MULTIVERSION NOMMAP RDONLY READ_UNCOMMITTED THREAD TRUNCATE
		163	db_close (DB db, U32 flags = 0, SV callback = &PL_sv_undef)
		164	flags: DB_NOSYNC
		165	db_upgrade (DB db, bdb_filename file, U32 flags = 0, SV callback = &PL_sv_undef)
		166	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)
		167	flags: FREELIST_ONLY FREE_SPACE
		168	db_sync (DB db, U32 flags = 0, SV callback = &PL_sv_undef)
		169	db_key_range (DB db, DB_TXN_ornull txn, SV key, SV key_range, U32 flags = 0, SV *callback = &PL_sv_undef)
		170	db_put (DB db, DB_TXN_ornull txn, SV key, SV data, U32 flags = 0, SV *callback = &PL_sv_undef)
		171	flags: APPEND NODUPDATA NOOVERWRITE
		172	db_exists (DB db, DB_TXN_ornull txn, SV key, U32 flags = 0, SV callback = 0) (v4.6)
		173	db_get (DB db, DB_TXN_ornull txn, SV key, SV data, U32 flags = 0, SV *callback = &PL_sv_undef)
		174	flags: CONSUME CONSUME_WAIT GET_BOTH SET_RECNO MULTIPLE READ_COMMITTED READ_UNCOMMITTED RMW
		175	db_pget (DB db, DB_TXN_ornull txn, SV key, SV pkey, SV data, U32 flags = 0, SV callback = &PL_sv_undef)
		176	flags: CONSUME CONSUME_WAIT GET_BOTH SET_RECNO MULTIPLE READ_COMMITTED READ_UNCOMMITTED RMW
		177	db_del (DB db, DB_TXN_ornull txn, SV key, U32 flags = 0, SV callback = &PL_sv_undef)
		178	db_txn_commit (DB_TXN txn, U32 flags = 0, SV callback = &PL_sv_undef)
		179	flags: TXN_NOSYNC TXN_SYNC
		180	db_txn_abort (DB_TXN txn, SV callback = &PL_sv_undef)
		181
		182	db_c_close (DBC dbc, SV callback = &PL_sv_undef)
		183	db_c_count (DBC dbc, SV count, U32 flags = 0, SV *callback = &PL_sv_undef)
		184	db_c_put (DBC dbc, SV key, SV data, U32 flags = 0, SV callback = &PL_sv_undef)
		185	flags: AFTER BEFORE CURRENT KEYFIRST KEYLAST NODUPDATA
		186	db_c_get (DBC dbc, SV key, SV data, U32 flags = 0, SV callback = &PL_sv_undef)
		187	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
		188	db_c_pget (DBC dbc, SV key, SV pkey, SV data, U32 flags = 0, SV *callback = &PL_sv_undef)
		189	db_c_del (DBC dbc, U32 flags = 0, SV callback = &PL_sv_undef)
		190
		191	db_sequence_open (DB_SEQUENCE seq, DB_TXN_ornull txnid, SV key, U32 flags = 0, SV callback = &PL_sv_undef)
		192	flags: CREATE EXCL
		193	db_sequence_close (DB_SEQUENCE seq, U32 flags = 0, SV callback = &PL_sv_undef)
		194	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)
		195	flags: TXN_NOSYNC
		196	db_sequence_remove (DB_SEQUENCE seq, DB_TXN_ornull txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
		197	flags: TXN_NOSYNC
		198
		199	db_txn_finish (DB_TXN txn, U32 flags = 0, SV callback = &PL_sv_undef)
		200	This is not actually a Berkeley DB function but a BDB module extension.
		201	The background for this exytension is: It is very annoying to have to
		202	check every single BDB function for error returns and provide a codepath
		203	out of your transaction. While the BDB module still makes this possible,
		204	it contains the following extensions:
		205
		206	When a transaction-protected function returns any operating system error
		207	(errno > 0), BDB will set the "TXN_DEADLOCK" flag on the transaction.
		208	This flag is also set by Berkeley DB functions themselves when an
		209	operation fails with LOCK_DEADLOCK, and it causes all further operations
		210	on that transaction (including "db_txn_commit") to fail.
		211
		212	The "db_txn_finish" request will look at this flag, and, if it is set,
		213	will automatically call "db_txn_abort" (setting errno to "LOCK_DEADLOCK"
		214	if it isn't set to something else yet). If it isn't set, it will call
		215	"db_txn_commit" and return the error normally.
		216
		217	How to use this? Easy: just write your transaction normally:
		218
		219	my $txn = $db_env->txn_begin;
		220	db_get $db, $txn, "key", my $data;
		221	db_put $db, $txn, "key", $data + 1 unless $! == BDB::NOTFOUND;
		222	db_txn_finish $txn;
		223	die "transaction failed" if $!;
		224
		225	That is, handle only the expected errors. If something unexpected
		226	happens (EIO, LOCK_NOTGRANTED or a deadlock in either db_get or db_put),
		227	then the remaining requests (db_put in this case) will simply be skipped
		228	(they will fail with LOCK_DEADLOCK) and the transaction will be aborted.
		229
		230	You can use the "$txn->failed" method to check wether a transaction has
		231	failed in this way and abort further processing (excluding
		232	"db_txn_finish").
		233
		234	DB_ENV/database environment methods
		235	Methods available on DB_ENV/$env handles:
		236
		237	DESTROY (DB_ENV_ornull *env)
		238	CODE:
		239	if (env)
		240	env->close (env, 0);
		241
		242	$int = $env->set_data_dir (const char *dir)
		243	$int = $env->set_tmp_dir (const char *dir)
		244	$int = $env->set_lg_dir (const char *dir)
		245	$int = $env->set_shm_key (long shm_key)
		246	$int = $env->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0)
		247	$int = $env->set_flags (U32 flags, int onoff = 1)
		248	$int = $env->log_set_config (U32 flags, int onoff = 1) (v4.7)
		249	$int = $env->set_intermediate_dir_mode (const char *modestring) (v4.7)
		250	$env->set_errfile (FILE *errfile = 0)
		251	$env->set_msgfile (FILE *msgfile = 0)
		252	$int = $env->set_verbose (U32 which, int onoff = 1)
		253	$int = $env->set_encrypt (const char *password, U32 flags = 0)
		254	$int = $env->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
		255	$int = $env->set_mp_max_openfd (int maxopenfd);
		256	$int = $env->set_mp_max_write (int maxwrite, int maxwrite_sleep);
		257	$int = $env->set_mp_mmapsize (int mmapsize_mb)
		258	$int = $env->set_lk_detect (U32 detect = DB_LOCK_DEFAULT)
		259	$int = $env->set_lk_max_lockers (U32 max)
		260	$int = $env->set_lk_max_locks (U32 max)
		261	$int = $env->set_lk_max_objects (U32 max)
		262	$int = $env->set_lg_bsize (U32 max)
		263	$int = $env->set_lg_max (U32 max)
		264	$int = $env->mutex_set_increment (U32 increment)
		265	$int = $env->mutex_set_tas_spins (U32 tas_spins)
		266	$int = $env->mutex_set_max (U32 max)
		267	$int = $env->mutex_set_align (U32 align)
		268
		269	$txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0)
		270	flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC
		271	$txn = $env->cdsgroup_begin; (v4.5)
		272
		273	Example:
		274	use AnyEvent;
		275	use BDB;
		276
		277	our $FH; open $FH, "<&=" . BDB::poll_fileno;
		278	our $WATCHER = AnyEvent->io (fh => $FH, poll => 'r', cb => \&BDB::poll_cb);
		279
		280	BDB::min_parallel 8;
		281
		282	my $env = db_env_create;
		283
		284	mkdir "bdtest", 0700;
		285	db_env_open
		286	$env,
		287	"bdtest",
		288	BDB::INIT_LOCK \| BDB::INIT_LOG \| BDB::INIT_MPOOL \| BDB::INIT_TXN \| BDB::RECOVER \| BDB::USE_ENVIRON \| BDB::CREATE,
		289	0600;
		290
		291	$env->set_flags (BDB::AUTO_COMMIT \| BDB::TXN_NOSYNC, 1);
		292
		293	DB/database methods
		294	Methods available on DB/$db handles:
		295
		296	DESTROY (DB_ornull *db)
		297	CODE:
		298	if (db)
		299	{
		300	SV env = (SV )db->app_private;
		301	db->close (db, 0);
		302	SvREFCNT_dec (env);
		303	}
		304
		305	$int = $db->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0)
		306	$int = $db->set_flags (U32 flags)
		307	flags: CHKSUM ENCRYPT TXN_NOT_DURABLE
		308	Btree: DUP DUPSORT RECNUM REVSPLITOFF
		309	Hash: DUP DUPSORT
		310	Queue: INORDER
		311	Recno: RENUMBER SNAPSHOT
		312
		313	$int = $db->set_encrypt (const char *password, U32 flags)
		314	$int = $db->set_lorder (int lorder)
		315	$int = $db->set_bt_minkey (U32 minkey)
		316	$int = $db->set_re_delim (int delim)
		317	$int = $db->set_re_pad (int re_pad)
		318	$int = $db->set_re_source (char *source)
		319	$int = $db->set_re_len (U32 re_len)
		320	$int = $db->set_h_ffactor (U32 h_ffactor)
		321	$int = $db->set_h_nelem (U32 h_nelem)
		322	$int = $db->set_q_extentsize (U32 extentsize)
		323
		324	$dbc = $db->cursor (DB_TXN_ornull *txn = 0, U32 flags = 0)
		325	flags: READ_COMMITTED READ_UNCOMMITTED WRITECURSOR TXN_SNAPSHOT
		326	$seq = $db->sequence (U32 flags = 0)
		327
		328	Example:
		329	my $db = db_create $env;
		330	db_open $db, undef, "table", undef, BDB::BTREE, BDB::AUTO_COMMIT \| BDB::CREATE \| BDB::READ_UNCOMMITTED, 0600;
		331
		332	for (1..1000) {
		333	db_put $db, undef, "key $_", "data $_";
		334
		335	db_key_range $db, undef, "key $_", my $keyrange;
		336	my ($lt, $eq, $gt) = @$keyrange;
		337	}
		338
		339	db_del $db, undef, "key $_" for 1..1000;
		340
		341	db_sync $db;
		342
		343	DB_TXN/transaction methods
		344	Methods available on DB_TXN/$txn handles:
		345
		346	DESTROY (DB_TXN_ornull *txn)
		347	CODE:
		348	if (txn)
		349	txn->abort (txn);
		350
		351	$int = $txn->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
		352	flags: SET_LOCK_TIMEOUT SET_TXN_TIMEOUT
		353
		354	$bool = $txn->failed
		355	# see db_txn_finish documentation, above
		356
		357	DBC/cursor methods
		358	Methods available on DBC/$dbc handles:
		359
		360	DESTROY (DBC_ornull *dbc)
		361	CODE:
		362	if (dbc)
		363	dbc->c_close (dbc);
		364
		365	$int = $cursor->set_priority ($priority = PRIORITY_*) (v4.6)
		366
		367	Example:
		368	my $c = $db->cursor;
		369
		370	for (;;) {
		371	db_c_get $c, my $key, my $data, BDB::NEXT;
		372	warn "<$!,$key,$data>";
		373	last if $!;
		374	}
		375
		376	db_c_close $c;
		377
		378	DB_SEQUENCE/sequence methods
		379	Methods available on DB_SEQUENCE/$seq handles:
		380
		381	DESTROY (DB_SEQUENCE_ornull *seq)
		382	CODE:
		383	if (seq)
		384	seq->close (seq, 0);
		385
		386	$int = $seq->initial_value (db_seq_t value)
		387	$int = $seq->set_cachesize (U32 size)
		388	$int = $seq->set_flags (U32 flags)
		389	flags: SEQ_DEC SEQ_INC SEQ_WRAP
		390	$int = $seq->set_range (db_seq_t min, db_seq_t max)
		391
		392	Example:
		393	my $seq = $db->sequence;
		394
		395	db_sequence_open $seq, undef, "seq", BDB::CREATE;
		396	db_sequence_get $seq, undef, 1, my $value;
		397
44	SUPPORT FUNCTIONS	398	SUPPORT FUNCTIONS
45	EVENT PROCESSING AND EVENT LOOP INTEGRATION	399	EVENT PROCESSING AND EVENT LOOP INTEGRATION
		400	$msg = BDB::strerror [$errno]
		401	Returns the string corresponding to the given errno value. If no
		402	argument is given, use $!.
		403
		404	Note that the BDB module also patches the $! variable directly, so
		405	you should be able to get a bdb error string by simply stringifying
		406	$!.
		407
46	$fileno = BDB::AIO::poll_fileno	408	$fileno = BDB::poll_fileno
47	Return the request result pipe file descriptor. This filehandle	409	Return the request result pipe file descriptor. This filehandle
48	must be polled for reading by some mechanism outside this module	410	must be polled for reading by some mechanism outside this module
49	(e.g. Event or select, see below or the SYNOPSIS). If the pipe	411	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
50	becomes readable you have to call "poll_cb" to check the results.	412	becomes readable you have to call "poll_cb" to check the results.
51		413
52	See "poll_cb" for an example.	414	See "poll_cb" for an example.
53		415
54	BDB::AIO::poll_cb	416	BDB::poll_cb
55	Process some outstanding events on the result pipe. You have to call	417	Process some outstanding events on the result pipe. You have to call
56	this regularly. Returns the number of events processed. Returns	418	this regularly. Returns the number of events processed. Returns
57	immediately when no events are outstanding. The amount of events	419	immediately when no events are outstanding. The amount of events
58	processed depends on the settings of "BDB::AIO::max_poll_req" and	420	processed depends on the settings of "BDB::max_poll_req" and
59	"BDB::AIO::max_poll_time".	421	"BDB::max_poll_time".
60		422
61	If not all requests were processed for whatever reason, the	423	If not all requests were processed for whatever reason, the
62	filehandle will still be ready when "poll_cb" returns.	424	filehandle will still be ready when "poll_cb" returns.
63		425
64	Example: Install an Event watcher that automatically calls	426	Example: Install an Event watcher that automatically calls
65	BDB::AIO::poll_cb with high priority:	427	BDB::poll_cb with high priority:
66		428
67	Event->io (fd => BDB::AIO::poll_fileno,	429	Event->io (fd => BDB::poll_fileno,
68	poll => 'r', async => 1,	430	poll => 'r', async => 1,
69	cb => \&BDB::AIO::poll_cb);	431	cb => \&BDB::poll_cb);
70		432
71	BDB::AIO::max_poll_reqs $nreqs	433	BDB::max_poll_reqs $nreqs
72	BDB::AIO::max_poll_time $seconds	434	BDB::max_poll_time $seconds
73	These set the maximum number of requests (default 0, meaning	435	These set the maximum number of requests (default 0, meaning
74	infinity) that are being processed by "BDB::AIO::poll_cb" in one	436	infinity) that are being processed by "BDB::poll_cb" in one call,
75	call, respectively the maximum amount of time (default 0, meaning	437	respectively the maximum amount of time (default 0, meaning
76	infinity) spent in "BDB::AIO::poll_cb" to process requests (more	438	infinity) spent in "BDB::poll_cb" to process requests (more
77	correctly the mininum amount of time "poll_cb" is allowed to use).	439	correctly the mininum amount of time "poll_cb" is allowed to use).
78		440
79	Setting "max_poll_time" to a non-zero value creates an overhead of	441	Setting "max_poll_time" to a non-zero value creates an overhead of
80	one syscall per request processed, which is not normally a problem	442	one syscall per request processed, which is not normally a problem
81	unless your callbacks are really really fast or your OS is really	443	unless your callbacks are really really fast or your OS is really
…		…
86	interactiveness when perl is not fast enough to process all requests	448	interactiveness when perl is not fast enough to process all requests
87	in time.	449	in time.
88		450
89	For interactive programs, values such as 0.01 to 0.1 should be fine.	451	For interactive programs, values such as 0.01 to 0.1 should be fine.
90		452
91	Example: Install an Event watcher that automatically calls	453	Example: Install an EV watcher that automatically calls BDB::poll_cb
92	BDB::AIO::poll_cb with low priority, to ensure that other parts of	454	with low priority, to ensure that other parts of the program get the
93	the program get the CPU sometimes even under high AIO load.	455	CPU sometimes even under high load.
94		456
95	# try not to spend much more than 0.1s in poll_cb	457	# try not to spend much more than 0.1s in poll_cb
96	BDB::AIO::max_poll_time 0.1;	458	BDB::max_poll_time 0.1;
97		459
98	# use a low priority so other tasks have priority	460	my $bdb_poll = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb);
99	Event->io (fd => BDB::AIO::poll_fileno,
100	poll => 'r', nice => 1,
101	cb => &BDB::AIO::poll_cb);
102		461
103	BDB::AIO::poll_wait	462	BDB::poll_wait
104	If there are any outstanding requests and none of them in the result	463	If there are any outstanding requests and none of them in the result
105	phase, wait till the result filehandle becomes ready for reading	464	phase, wait till the result filehandle becomes ready for reading
106	(simply does a "select" on the filehandle. This is useful if you	465	(simply does a "select" on the filehandle. This is useful if you
107	want to synchronously wait for some requests to finish).	466	want to synchronously wait for some requests to finish).
108		467
109	See "nreqs" for an example.	468	See "nreqs" for an example.
110		469
111	BDB::AIO::poll	470	BDB::poll
112	Waits until some requests have been handled.	471	Waits until some requests have been handled.
113		472
114	Returns the number of requests processed, but is otherwise strictly	473	Returns the number of requests processed, but is otherwise strictly
115	equivalent to:	474	equivalent to:
116		475
117	BDB::AIO::poll_wait, BDB::AIO::poll_cb	476	BDB::poll_wait, BDB::poll_cb
118		477
119	BDB::AIO::flush	478	BDB::flush
120	Wait till all outstanding AIO requests have been handled.	479	Wait till all outstanding BDB requests have been handled.
121		480
122	Strictly equivalent to:	481	Strictly equivalent to:
123		482
124	BDB::AIO::poll_wait, BDB::AIO::poll_cb	483	BDB::poll_wait, BDB::poll_cb
125	while BDB::AIO::nreqs;	484	while BDB::nreqs;
126		485
		486	VERSION CHECKING
		487	BerkeleyDB comes in various versions, many of them have minor
		488	incompatibilities. This means that traditional "at least version x.x"
		489	checks are often not sufficient.
		490
		491	Example: set the log_autoremove option in a way compatible with <v4.7
		492	and v4.7. Note the use of & on the constants to avoid triggering a
		493	compiletime bug when the symbol isn't available.
		494
		495	$DB_ENV->set_flags (&BDB::LOG_AUTOREMOVE ) if BDB::VERSION v0, v4.7;
		496	$DB_ENV->log_set_config (&BDB::LOG_AUTO_REMOVE) if BDB::VERSION v4.7;
		497
		498	BDB::VERSION
		499	The "BDB::VERSION" function, when called without arguments, returns
		500	the Berkeley DB version as a v-string (usually with 3 components).
		501	You should use "lt" and "ge" operators exclusively to make
		502	comparisons.
		503
		504	Example: check for at least version 4.7.
		505
		506	BDB::VERSION ge v4.7 or die;
		507
		508	BDB::VERSION min-version
		509	Returns true if the BDB version is at least the given version
		510	(specified as a v-string), false otherwise.
		511
		512	Example: check for at least version 4.5.
		513
		514	BDB::VERSION v4.7 or die;
		515
		516	BDB::VERSION min-version, max-version
		517	Returns true of the BDB version is at least version "min-version"
		518	(specify "undef" or "v0" for any minimum version) and less then
		519	"max-version".
		520
		521	Example: check wether version is strictly less then v4.7.
		522
		523	BDB::VERSION v0, v4.7
		524	or die "version 4.7 is not yet supported";
		525
127	CONTROLLING THE NUMBER OF THREADS	526	CONTROLLING THE NUMBER OF THREADS
128	BDB::AIO::min_parallel $nthreads	527	BDB::min_parallel $nthreads
129	Set the minimum number of AIO threads to $nthreads. The current	528	Set the minimum number of BDB threads to $nthreads. The current
130	default is 8, which means eight asynchronous operations can execute	529	default is 8, which means eight asynchronous operations can execute
131	concurrently at any one time (the number of outstanding requests,	530	concurrently at any one time (the number of outstanding requests,
132	however, is unlimited).	531	however, is unlimited).
133		532
134	BDB::AIO starts threads only on demand, when an AIO request is	533	BDB starts threads only on demand, when an BDB request is queued and
135	queued and no free thread exists. Please note that queueing up a	534	no free thread exists. Please note that queueing up a hundred
136	hundred requests can create demand for a hundred threads, even if it	535	requests can create demand for a hundred threads, even if it turns
137	turns out that everything is in the cache and could have been	536	out that everything is in the cache and could have been processed
138	processed faster by a single thread.	537	faster by a single thread.
139		538
140	It is recommended to keep the number of threads relatively low, as	539	It is recommended to keep the number of threads relatively low, as
141	some Linux kernel versions will scale negatively with the number of	540	some Linux kernel versions will scale negatively with the number of
142	threads (higher parallelity => MUCH higher latency). With current	541	threads (higher parallelity => MUCH higher latency). With current
143	Linux 2.6 versions, 4-32 threads should be fine.	542	Linux 2.6 versions, 4-32 threads should be fine.
144		543
145	Under most circumstances you don't need to call this function, as	544	Under most circumstances you don't need to call this function, as
146	the module selects a default that is suitable for low to moderate	545	the module selects a default that is suitable for low to moderate
147	load.	546	load.
148		547
149	BDB::AIO::max_parallel $nthreads	548	BDB::max_parallel $nthreads
150	Sets the maximum number of AIO threads to $nthreads. If more than	549	Sets the maximum number of BDB threads to $nthreads. If more than
151	the specified number of threads are currently running, this function	550	the specified number of threads are currently running, this function
152	kills them. This function blocks until the limit is reached.	551	kills them. This function blocks until the limit is reached.
153		552
154	While $nthreads are zero, aio requests get queued but not executed	553	While $nthreads are zero, aio requests get queued but not executed
155	until the number of threads has been increased again.	554	until the number of threads has been increased again.
…		…
158	ensure that all threads are killed and that there are no outstanding	557	ensure that all threads are killed and that there are no outstanding
159	requests.	558	requests.
160		559
161	Under normal circumstances you don't need to call this function.	560	Under normal circumstances you don't need to call this function.
162		561
163	BDB::AIO::max_idle $nthreads	562	BDB::max_idle $nthreads
164	Limit the number of threads (default: 4) that are allowed to idle	563	Limit the number of threads (default: 4) that are allowed to idle
165	(i.e., threads that did not get a request to process within 10	564	(i.e., threads that did not get a request to process within 10
166	seconds). That means if a thread becomes idle while $nthreads other	565	seconds). That means if a thread becomes idle while $nthreads other
167	threads are also idle, it will free its resources and exit.	566	threads are also idle, it will free its resources and exit.
168		567
…		…
173		572
174	The default is probably ok in most situations, especially if thread	573	The default is probably ok in most situations, especially if thread
175	creation is fast. If thread creation is very slow on your system you	574	creation is fast. If thread creation is very slow on your system you
176	might want to use larger values.	575	might want to use larger values.
177		576
178	$oldmaxreqs = BDB::AIO::max_outstanding $maxreqs	577	$oldmaxreqs = BDB::max_outstanding $maxreqs
179	This is a very bad function to use in interactive programs because	578	This is a very bad function to use in interactive programs because
180	it blocks, and a bad way to reduce concurrency because it is	579	it blocks, and a bad way to reduce concurrency because it is
181	inexact: Better use an "aio_group" together with a feed callback.	580	inexact: Better use an "aio_group" together with a feed callback.
182		581
183	Sets the maximum number of outstanding requests to $nreqs. If you to	582	Sets the maximum number of outstanding requests to $nreqs. If you to
…		…
191	You can still queue as many requests as you want. Therefore,	590	You can still queue as many requests as you want. Therefore,
192	"max_oustsanding" is mainly useful in simple scripts (with low	591	"max_oustsanding" is mainly useful in simple scripts (with low
193	values) or as a stop gap to shield against fatal memory overflow	592	values) or as a stop gap to shield against fatal memory overflow
194	(with large values).	593	(with large values).
195		594
		595	$old_cb = BDB::set_sync_prepare $cb
		596	Sets a callback that is called whenever a request is created without
		597	an explicit callback. It has to return two code references. The
		598	first is used as the request callback (it should save the return
		599	status), and the second is called to wait until the first callback
		600	has been called (it must set $! to the return status).
		601
		602	This mechanism can be used to include BDB into other event
		603	mechanisms, such as Coro::BDB.
		604
		605	To allow other, callback-based, events to be executed while
		606	callback-less ones are run, you could use this sync prepare
		607	function:
		608
		609	sub {
		610	my $status;
		611	(
		612	sub { $status = $! },
		613	sub { BDB::poll while !defined $status; $! = $status },
		614	)
		615	}
		616
		617	It works by polling for results till the request has finished and
		618	then sets $! to the return value. This means that if you don't use a
		619	callback, BDB would simply fall back to synchronous operations.
		620
		621	By default, or if the sync prepare function is set to "undef", is to
		622	execute callback-less BDB requests in the foreground thread, setting
		623	$! to the return value, without polling for other events.
		624
196	STATISTICAL INFORMATION	625	STATISTICAL INFORMATION
197	BDB::AIO::nreqs	626	BDB::nreqs
198	Returns the number of requests currently in the ready, execute or	627	Returns the number of requests currently in the ready, execute or
199	pending states (i.e. for which their callback has not been invoked	628	pending states (i.e. for which their callback has not been invoked
200	yet).	629	yet).
201		630
202	Example: wait till there are no outstanding requests anymore:	631	Example: wait till there are no outstanding requests anymore:
203		632
204	BDB::AIO::poll_wait, BDB::AIO::poll_cb	633	BDB::poll_wait, BDB::poll_cb
205	while BDB::AIO::nreqs;	634	while BDB::nreqs;
206		635
207	BDB::AIO::nready	636	BDB::nready
208	Returns the number of requests currently in the ready state (not yet	637	Returns the number of requests currently in the ready state (not yet
209	executed).	638	executed).
210		639
211	BDB::AIO::npending	640	BDB::npending
212	Returns the number of requests currently in the pending state	641	Returns the number of requests currently in the pending state
213	(executed, but not yet processed by poll_cb).	642	(executed, but not yet processed by poll_cb).
214		643
		644	COMMON PITFALLS
		645	Unexpected Crashes
		646	Remember that, by default, BDB will execute requests in parallel, in
		647	somewhat random order. That means that it is easy to run a "db_get"
		648	request on thesa me database as a concurrent "db_close" request, leading
		649	to a crash, silent data corruption, eventually the next world war on
		650	terrorism.
		651
		652	If you only ever use foreground requests (without a callback), this will
		653	not be an issue.
		654
		655	Unexpected Freezes or Deadlocks
		656	Remember that, by default, BDB will execute requests in parallel, which
		657	easily leads to deadlocks (even concurrent put's on the same database
		658	can deadlock).
		659
		660	You either need to run deadlock detection (and handle the resulting
		661	errors), or make sure only one process ever updates the database, ine
		662	one thread, e.g. by using only foreground requests (without a callback).
		663
215	FORK BEHAVIOUR	664	FORK BEHAVIOUR
216	This module should do "the right thing" when the process using it forks:	665	This module should do "the right thing" when the process using it forks:
217		666
218	Before the fork, IO::AIO enters a quiescent state where no requests can	667	Before the fork, BDB enters a quiescent state where no requests can be
219	be added in other threads and no results will be processed. After the	668	added in other threads and no results will be processed. After the fork
220	fork the parent simply leaves the quiescent state and continues	669	the parent simply leaves the quiescent state and continues
221	request/result processing, while the child frees the request/result	670	request/result processing, while the child frees the request/result
222	queue (so that the requests started before the fork will only be handled	671	queue (so that the requests started before the fork will only be handled
223	in the parent). Threads will be started on demand until the limit set in	672	in the parent). Threads will be started on demand until the limit set in
224	the parent process has been reached again.	673	the parent process has been reached again.
225		674
226	In short: the parent will, after a short pause, continue as if fork had	675	In short: the parent will, after a short pause, continue as if fork had
227	not been called, while the child will act as if IO::AIO has not been	676	not been called, while the child will act as if BDB has not been used
228	used yet.	677	yet.
229		678
		679	Win32 note: there is no fork on win32, and perls emulation of it is too
		680	broken to be supported, so do not use BDB in a windows pseudo-fork,
		681	better yet, switch to a more capable platform.
		682
230	MEMORY USAGE	683	MEMORY USAGE
231	Per-request usage:	684	Per-request usage:
232		685
233	Each aio request uses - depending on your architecture - around 100-200	686	Each aio request uses - depending on your architecture - around 100-200
234	bytes of memory. In addition, stat requests need a stat buffer (possibly	687	bytes of memory. In addition, stat requests need a stat buffer (possibly
235	a few hundred bytes), readdir requires a result buffer and so on. Perl	688	a few hundred bytes), readdir requires a result buffer and so on. Perl
236	scalars and other data passed into aio requests will also be locked and	689	scalars and other data passed into aio requests will also be locked and
237	will consume memory till the request has entered the done state.	690	will consume memory till the request has entered the done state.
238		691
239	This is now awfully much, so queuing lots of requests is not usually a	692	This is not awfully much, so queuing lots of requests is not usually a
240	problem.	693	problem.
241		694
242	Per-thread usage:	695	Per-thread usage:
243		696
244	In the execution phase, some aio requests require more memory for	697	In the execution phase, some aio requests require more memory for
245	temporary buffers, and each thread requires a stack and other data	698	temporary buffers, and each thread requires a stack and other data
246	structures (usually around 16k-128k, depending on the OS).	699	structures (usually around 16k-128k, depending on the OS).
247		700
		701	WIN32 FILENAMES/DATABASE NAME MESS
		702	Perl on Win32 supports only ASCII filenames (the reason is that it
		703	abuses an internal flag to store wether a filename is Unicode or ANSI,
		704	but that flag is used for somethign else in the perl core, so there is
		705	no way to detect wether a filename is ANSI or Unicode-encoded). The BDB
		706	module tries to work around this issue by assuming that the filename is
		707	an ANSI filename and BDB was built for unicode support.
		708
248	KNOWN BUGS	709	KNOWN BUGS
249	Known bugs will be fixed in the next release.	710	Known bugs will be fixed in the next release, except:
		711
		712	If you use a transaction in any request, and the request returns
		713	with an operating system error or DB_LOCK_NOTGRANTED, the internal
		714	TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>,
		715	above.
250		716
251	SEE ALSO	717	SEE ALSO
252	Coro::AIO.	718	AnyEvent::BDB (event loop integration), Coro::BDB (more natural syntax),
		719	IO::AIO (nice to have).
253		720
254	AUTHOR	721	AUTHOR
255	Marc Lehmann <schmorp@schmorp.de>	722	Marc Lehmann <schmorp@schmorp.de>
256	http://home.schmorp.de/	723	http://home.schmorp.de/
257		724

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Revision 1.14 by root, Tue Oct 21 02:21:25 2008 UTC