[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 1.12 by root, Tue Jul 29 03:33:16 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	WIN32 FILENAMES/DATABASE NAME MESS
		92	Perl on Win32 supports only ASCII filenames (the reason is that it
		93	abuses an internal flag to store wether a filename is Unicode or ANSI,
		94	but that flag is used for somethign else in the perl core, so there is
		95	no way to detect wether a filename is ANSI or Unicode-encoded). The BDB
		96	module tries to work around this issue by assuming that the filename is
		97	an ANSI filename and BDB was built for unicode support.
		98
		99	BERKELEYDB FUNCTIONS
		100	All of these are functions. The create functions simply return a new
		101	object and never block. All the remaining functions take an optional
		102	callback as last argument. If it is missing, then the function will be
		103	executed synchronously. In both cases, $! will reflect the return value
		104	of the function.
		105
		106	BDB functions that cannot block (mostly functions that manipulate
		107	settings) are method calls on the relevant objects, so the rule of thumb
		108	is: if it's a method, it's not blocking, if it's a function, it takes a
		109	callback as last argument.
		110
		111	In the following, $int signifies an integer return value, "bdb_filename"
		112	is a "filename" (octets on unix, madness on windows), "U32" is an
		113	unsigned 32 bit integer, "int" is some integer, "NV" is a floating point
		114	value.
		115
		116	Most "SV *" types are generic perl scalars (for input and output of data
		117	values).
		118
		119	The various "DB_ENV" etc. arguments are handles return by
		120	"db_env_create", "db_create", "txn_begin" and so on. If they have an
		121	appended "_ornull" this means they are optional and you can pass "undef"
		122	for them, resulting a NULL pointer on the C level.
		123
		124	The "SV *callback" is the optional callback function to call when the
		125	request is completed. This last callback argument is special: the
		126	callback is simply the last argument passed. If there are "optional"
		127	arguments before the callback they can be left out. The callback itself
		128	can be left out or specified as "undef", in which case the function will
		129	be executed synchronously.
		130
		131	For example, "db_env_txn_checkpoint" usually is called with all integer
		132	arguments zero. These can be left out, so all of these specify a call to
		133	"DB_ENV->txn_checkpoint", to be executed asynchronously with a callback
		134	to be called:
		135
		136	db_env_txn_checkpoint $db_env, 0, 0, 0, sub { };
		137	db_env_txn_checkpoint $db_env, 0, 0, sub { };
		138	db_env_txn_checkpoint $db_env, sub { };
		139
		140	While these all specify a call to "DB_ENV->txn_checkpoint" to be
		141	executed synchronously:
		142
		143	db_env_txn_checkpoint $db_env, 0, 0, 0, undef;
		144	db_env_txn_checkpoint $db_env, 0, 0, 0;
		145	db_env_txn_checkpoint $db_env, 0;
		146
		147	BDB functions
		148	Functions in the BDB namespace, exported by default:
		149
		150	$env = db_env_create (U32 env_flags = 0)
		151	flags: RPCCLIENT
		152
		153	db_env_open (DB_ENV env, bdb_filename db_home, U32 open_flags, int mode, SV callback = &PL_sv_undef)
		154	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
		155	db_env_close (DB_ENV env, U32 flags = 0, SV callback = &PL_sv_undef)
		156	db_env_txn_checkpoint (DB_ENV env, U32 kbyte = 0, U32 min = 0, U32 flags = 0, SV callback = &PL_sv_undef)
		157	flags: FORCE
		158	db_env_lock_detect (DB_ENV env, U32 flags = 0, U32 atype = DB_LOCK_DEFAULT, SV dummy = 0, SV *callback = &PL_sv_undef)
		159	atype: LOCK_DEFAULT LOCK_EXPIRE LOCK_MAXLOCKS LOCK_MAXWRITE LOCK_MINLOCKS LOCK_MINWRITE LOCK_OLDEST LOCK_RANDOM LOCK_YOUNGEST
		160	db_env_memp_sync (DB_ENV env, SV dummy = 0, SV *callback = &PL_sv_undef)
		161	db_env_memp_trickle (DB_ENV env, int percent, SV dummy = 0, SV *callback = &PL_sv_undef)
		162	db_env_dbremove (DB_ENV env, DB_TXN_ornull txnid, bdb_filename file, bdb_filename database, U32 flags = 0, SV *callback = &PL_sv_undef)
		163	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)
		164
		165	$db = db_create (DB_ENV *env = 0, U32 flags = 0)
		166	flags: XA_CREATE
		167
		168	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)
		169	flags: AUTO_COMMIT CREATE EXCL MULTIVERSION NOMMAP RDONLY READ_UNCOMMITTED THREAD TRUNCATE
		170	db_close (DB db, U32 flags = 0, SV callback = &PL_sv_undef)
		171	flags: DB_NOSYNC
		172	db_upgrade (DB db, bdb_filename file, U32 flags = 0, SV callback = &PL_sv_undef)
		173	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)
		174	flags: FREELIST_ONLY FREE_SPACE
		175	db_sync (DB db, U32 flags = 0, SV callback = &PL_sv_undef)
		176	db_key_range (DB db, DB_TXN_ornull txn, SV key, SV key_range, U32 flags = 0, SV *callback = &PL_sv_undef)
		177	db_put (DB db, DB_TXN_ornull txn, SV key, SV data, U32 flags = 0, SV *callback = &PL_sv_undef)
		178	flags: APPEND NODUPDATA NOOVERWRITE
		179	db_exists (DB db, DB_TXN_ornull txn, SV key, U32 flags = 0, SV callback = 0) (v4.6)
		180	db_get (DB db, DB_TXN_ornull txn, SV key, SV data, U32 flags = 0, SV *callback = &PL_sv_undef)
		181	flags: CONSUME CONSUME_WAIT GET_BOTH SET_RECNO MULTIPLE READ_COMMITTED READ_UNCOMMITTED RMW
		182	db_pget (DB db, DB_TXN_ornull txn, SV key, SV pkey, SV data, U32 flags = 0, SV callback = &PL_sv_undef)
		183	flags: CONSUME CONSUME_WAIT GET_BOTH SET_RECNO MULTIPLE READ_COMMITTED READ_UNCOMMITTED RMW
		184	db_del (DB db, DB_TXN_ornull txn, SV key, U32 flags = 0, SV callback = &PL_sv_undef)
		185	db_txn_commit (DB_TXN txn, U32 flags = 0, SV callback = &PL_sv_undef)
		186	flags: TXN_NOSYNC TXN_SYNC
		187	db_txn_abort (DB_TXN txn, SV callback = &PL_sv_undef)
		188
		189	db_c_close (DBC dbc, SV callback = &PL_sv_undef)
		190	db_c_count (DBC dbc, SV count, U32 flags = 0, SV *callback = &PL_sv_undef)
		191	db_c_put (DBC dbc, SV key, SV data, U32 flags = 0, SV callback = &PL_sv_undef)
		192	flags: AFTER BEFORE CURRENT KEYFIRST KEYLAST NODUPDATA
		193	db_c_get (DBC dbc, SV key, SV data, U32 flags = 0, SV callback = &PL_sv_undef)
		194	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
		195	db_c_pget (DBC dbc, SV key, SV pkey, SV data, U32 flags = 0, SV *callback = &PL_sv_undef)
		196	db_c_del (DBC dbc, U32 flags = 0, SV callback = &PL_sv_undef)
		197
		198	db_sequence_open (DB_SEQUENCE seq, DB_TXN_ornull txnid, SV key, U32 flags = 0, SV callback = &PL_sv_undef)
		199	flags: CREATE EXCL
		200	db_sequence_close (DB_SEQUENCE seq, U32 flags = 0, SV callback = &PL_sv_undef)
		201	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)
		202	flags: TXN_NOSYNC
		203	db_sequence_remove (DB_SEQUENCE seq, DB_TXN_ornull txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
		204	flags: TXN_NOSYNC
		205
		206	db_txn_finish (DB_TXN txn, U32 flags = 0, SV callback = &PL_sv_undef)
		207	This is not actually a Berkeley DB function but a BDB module extension.
		208	The background for this exytension is: It is very annoying to have to
		209	check every single BDB function for error returns and provide a codepath
		210	out of your transaction. While the BDB module still makes this possible,
		211	it contains the following extensions:
		212
		213	When a transaction-protected function returns any operating system error
		214	(errno > 0), BDB will set the "TXN_DEADLOCK" flag on the transaction.
		215	This flag is also set by Berkeley DB functions themselves when an
		216	operation fails with LOCK_DEADLOCK, and it causes all further operations
		217	on that transaction (including "db_txn_commit") to fail.
		218
		219	The "db_txn_finish" request will look at this flag, and, if it is set,
		220	will automatically call "db_txn_abort" (setting errno to "LOCK_DEADLOCK"
		221	if it isn't set to something else yet). If it isn't set, it will call
		222	"db_txn_commit" and return the error normally.
		223
		224	How to use this? Easy: just write your transaction normally:
		225
		226	my $txn = $db_env->txn_begin;
		227	db_get $db, $txn, "key", my $data;
		228	db_put $db, $txn, "key", $data + 1 unless $! == BDB::NOTFOUND;
		229	db_txn_finish $txn;
		230	die "transaction failed" if $!;
		231
		232	That is, handle only the expected errors. If something unexpected
		233	happens (EIO, LOCK_NOTGRANTED or a deadlock in either db_get or db_put),
		234	then the remaining requests (db_put in this case) will simply be skipped
		235	(they will fail with LOCK_DEADLOCK) and the transaction will be aborted.
		236
		237	You can use the "$txn->failed" method to check wether a transaction has
		238	failed in this way and abort further processing (excluding
		239	"db_txn_finish").
		240
		241	DB_ENV/database environment methods
		242	Methods available on DB_ENV/$env handles:
		243
		244	DESTROY (DB_ENV_ornull *env)
		245	CODE:
		246	if (env)
		247	env->close (env, 0);
		248
		249	$int = $env->set_data_dir (const char *dir)
		250	$int = $env->set_tmp_dir (const char *dir)
		251	$int = $env->set_lg_dir (const char *dir)
		252	$int = $env->set_shm_key (long shm_key)
		253	$int = $env->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0)
		254	$int = $env->set_flags (U32 flags, int onoff = 1)
		255	$int = $env->log_set_config (U32 flags, int onoff = 1) (v4.7)
		256	$int = $env->set_intermediate_dir_mode (const char *modestring) (v4.7)
		257	$env->set_errfile (FILE *errfile = 0)
		258	$env->set_msgfile (FILE *msgfile = 0)
		259	$int = $env->set_verbose (U32 which, int onoff = 1)
		260	$int = $env->set_encrypt (const char *password, U32 flags = 0)
		261	$int = $env->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
		262	$int = $env->set_mp_max_openfd (int maxopenfd);
		263	$int = $env->set_mp_max_write (int maxwrite, int maxwrite_sleep);
		264	$int = $env->set_mp_mmapsize (int mmapsize_mb)
		265	$int = $env->set_lk_detect (U32 detect = DB_LOCK_DEFAULT)
		266	$int = $env->set_lk_max_lockers (U32 max)
		267	$int = $env->set_lk_max_locks (U32 max)
		268	$int = $env->set_lk_max_objects (U32 max)
		269	$int = $env->set_lg_bsize (U32 max)
		270	$int = $env->set_lg_max (U32 max)
		271	$int = $env->mutex_set_increment (U32 increment)
		272	$int = $env->mutex_set_tas_spins (U32 tas_spins)
		273	$int = $env->mutex_set_max (U32 max)
		274	$int = $env->mutex_set_align (U32 align)
		275
		276	$txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0)
		277	flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC
		278	$txn = $env->cdsgroup_begin; (v4.5)
		279
		280	Example:
		281	use AnyEvent;
		282	use BDB;
		283
		284	our $FH; open $FH, "<&=" . BDB::poll_fileno;
		285	our $WATCHER = AnyEvent->io (fh => $FH, poll => 'r', cb => \&BDB::poll_cb);
		286
		287	BDB::min_parallel 8;
		288
		289	my $env = db_env_create;
		290
		291	mkdir "bdtest", 0700;
		292	db_env_open
		293	$env,
		294	"bdtest",
		295	BDB::INIT_LOCK \| BDB::INIT_LOG \| BDB::INIT_MPOOL \| BDB::INIT_TXN \| BDB::RECOVER \| BDB::USE_ENVIRON \| BDB::CREATE,
		296	0600;
		297
		298	$env->set_flags (BDB::AUTO_COMMIT \| BDB::TXN_NOSYNC, 1);
		299
		300	DB/database methods
		301	Methods available on DB/$db handles:
		302
		303	DESTROY (DB_ornull *db)
		304	CODE:
		305	if (db)
		306	{
		307	SV env = (SV )db->app_private;
		308	db->close (db, 0);
		309	SvREFCNT_dec (env);
		310	}
		311
		312	$int = $db->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0)
		313	$int = $db->set_flags (U32 flags)
		314	flags: CHKSUM ENCRYPT TXN_NOT_DURABLE
		315	Btree: DUP DUPSORT RECNUM REVSPLITOFF
		316	Hash: DUP DUPSORT
		317	Queue: INORDER
		318	Recno: RENUMBER SNAPSHOT
		319
		320	$int = $db->set_encrypt (const char *password, U32 flags)
		321	$int = $db->set_lorder (int lorder)
		322	$int = $db->set_bt_minkey (U32 minkey)
		323	$int = $db->set_re_delim (int delim)
		324	$int = $db->set_re_pad (int re_pad)
		325	$int = $db->set_re_source (char *source)
		326	$int = $db->set_re_len (U32 re_len)
		327	$int = $db->set_h_ffactor (U32 h_ffactor)
		328	$int = $db->set_h_nelem (U32 h_nelem)
		329	$int = $db->set_q_extentsize (U32 extentsize)
		330
		331	$dbc = $db->cursor (DB_TXN_ornull *txn = 0, U32 flags = 0)
		332	flags: READ_COMMITTED READ_UNCOMMITTED WRITECURSOR TXN_SNAPSHOT
		333	$seq = $db->sequence (U32 flags = 0)
		334
		335	Example:
		336	my $db = db_create $env;
		337	db_open $db, undef, "table", undef, BDB::BTREE, BDB::AUTO_COMMIT \| BDB::CREATE \| BDB::READ_UNCOMMITTED, 0600;
		338
		339	for (1..1000) {
		340	db_put $db, undef, "key $_", "data $_";
		341
		342	db_key_range $db, undef, "key $_", my $keyrange;
		343	my ($lt, $eq, $gt) = @$keyrange;
		344	}
		345
		346	db_del $db, undef, "key $_" for 1..1000;
		347
		348	db_sync $db;
		349
		350	DB_TXN/transaction methods
		351	Methods available on DB_TXN/$txn handles:
		352
		353	DESTROY (DB_TXN_ornull *txn)
		354	CODE:
		355	if (txn)
		356	txn->abort (txn);
		357
		358	$int = $txn->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
		359	flags: SET_LOCK_TIMEOUT SET_TXN_TIMEOUT
		360
		361	$bool = $txn->failed
		362	# see db_txn_finish documentation, above
		363
		364	DBC/cursor methods
		365	Methods available on DBC/$dbc handles:
		366
		367	DESTROY (DBC_ornull *dbc)
		368	CODE:
		369	if (dbc)
		370	dbc->c_close (dbc);
		371
		372	$int = $cursor->set_priority ($priority = PRIORITY_*) (v4.6)
		373
		374	Example:
		375	my $c = $db->cursor;
		376
		377	for (;;) {
		378	db_c_get $c, my $key, my $data, BDB::NEXT;
		379	warn "<$!,$key,$data>";
		380	last if $!;
		381	}
		382
		383	db_c_close $c;
		384
		385	DB_SEQUENCE/sequence methods
		386	Methods available on DB_SEQUENCE/$seq handles:
		387
		388	DESTROY (DB_SEQUENCE_ornull *seq)
		389	CODE:
		390	if (seq)
		391	seq->close (seq, 0);
		392
		393	$int = $seq->initial_value (db_seq_t value)
		394	$int = $seq->set_cachesize (U32 size)
		395	$int = $seq->set_flags (U32 flags)
		396	flags: SEQ_DEC SEQ_INC SEQ_WRAP
		397	$int = $seq->set_range (db_seq_t min, db_seq_t max)
		398
		399	Example:
		400	my $seq = $db->sequence;
		401
		402	db_sequence_open $seq, undef, "seq", BDB::CREATE;
		403	db_sequence_get $seq, undef, 1, my $value;
		404
44	SUPPORT FUNCTIONS	405	SUPPORT FUNCTIONS
45	EVENT PROCESSING AND EVENT LOOP INTEGRATION	406	EVENT PROCESSING AND EVENT LOOP INTEGRATION
		407	$msg = BDB::strerror [$errno]
		408	Returns the string corresponding to the given errno value. If no
		409	argument is given, use $!.
		410
		411	Note that the BDB module also patches the $! variable directly, so
		412	you should be able to get a bdb error string by simply stringifying
		413	$!.
		414
46	$fileno = BDB::AIO::poll_fileno	415	$fileno = BDB::poll_fileno
47	Return the request result pipe file descriptor. This filehandle	416	Return the request result pipe file descriptor. This filehandle
48	must be polled for reading by some mechanism outside this module	417	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	418	(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.	419	becomes readable you have to call "poll_cb" to check the results.
51		420
52	See "poll_cb" for an example.	421	See "poll_cb" for an example.
53		422
54	BDB::AIO::poll_cb	423	BDB::poll_cb
55	Process some outstanding events on the result pipe. You have to call	424	Process some outstanding events on the result pipe. You have to call
56	this regularly. Returns the number of events processed. Returns	425	this regularly. Returns the number of events processed. Returns
57	immediately when no events are outstanding. The amount of events	426	immediately when no events are outstanding. The amount of events
58	processed depends on the settings of "BDB::AIO::max_poll_req" and	427	processed depends on the settings of "BDB::max_poll_req" and
59	"BDB::AIO::max_poll_time".	428	"BDB::max_poll_time".
60		429
61	If not all requests were processed for whatever reason, the	430	If not all requests were processed for whatever reason, the
62	filehandle will still be ready when "poll_cb" returns.	431	filehandle will still be ready when "poll_cb" returns.
63		432
64	Example: Install an Event watcher that automatically calls	433	Example: Install an Event watcher that automatically calls
65	BDB::AIO::poll_cb with high priority:	434	BDB::poll_cb with high priority:
66		435
67	Event->io (fd => BDB::AIO::poll_fileno,	436	Event->io (fd => BDB::poll_fileno,
68	poll => 'r', async => 1,	437	poll => 'r', async => 1,
69	cb => \&BDB::AIO::poll_cb);	438	cb => \&BDB::poll_cb);
70		439
71	BDB::AIO::max_poll_reqs $nreqs	440	BDB::max_poll_reqs $nreqs
72	BDB::AIO::max_poll_time $seconds	441	BDB::max_poll_time $seconds
73	These set the maximum number of requests (default 0, meaning	442	These set the maximum number of requests (default 0, meaning
74	infinity) that are being processed by "BDB::AIO::poll_cb" in one	443	infinity) that are being processed by "BDB::poll_cb" in one call,
75	call, respectively the maximum amount of time (default 0, meaning	444	respectively the maximum amount of time (default 0, meaning
76	infinity) spent in "BDB::AIO::poll_cb" to process requests (more	445	infinity) spent in "BDB::poll_cb" to process requests (more
77	correctly the mininum amount of time "poll_cb" is allowed to use).	446	correctly the mininum amount of time "poll_cb" is allowed to use).
78		447
79	Setting "max_poll_time" to a non-zero value creates an overhead of	448	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	449	one syscall per request processed, which is not normally a problem
81	unless your callbacks are really really fast or your OS is really	450	unless your callbacks are really really fast or your OS is really
…		…
86	interactiveness when perl is not fast enough to process all requests	455	interactiveness when perl is not fast enough to process all requests
87	in time.	456	in time.
88		457
89	For interactive programs, values such as 0.01 to 0.1 should be fine.	458	For interactive programs, values such as 0.01 to 0.1 should be fine.
90		459
91	Example: Install an Event watcher that automatically calls	460	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	461	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.	462	CPU sometimes even under high load.
94		463
95	# try not to spend much more than 0.1s in poll_cb	464	# try not to spend much more than 0.1s in poll_cb
96	BDB::AIO::max_poll_time 0.1;	465	BDB::max_poll_time 0.1;
97		466
98	# use a low priority so other tasks have priority	467	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		468
103	BDB::AIO::poll_wait	469	BDB::poll_wait
104	If there are any outstanding requests and none of them in the result	470	If there are any outstanding requests and none of them in the result
105	phase, wait till the result filehandle becomes ready for reading	471	phase, wait till the result filehandle becomes ready for reading
106	(simply does a "select" on the filehandle. This is useful if you	472	(simply does a "select" on the filehandle. This is useful if you
107	want to synchronously wait for some requests to finish).	473	want to synchronously wait for some requests to finish).
108		474
109	See "nreqs" for an example.	475	See "nreqs" for an example.
110		476
111	BDB::AIO::poll	477	BDB::poll
112	Waits until some requests have been handled.	478	Waits until some requests have been handled.
113		479
114	Returns the number of requests processed, but is otherwise strictly	480	Returns the number of requests processed, but is otherwise strictly
115	equivalent to:	481	equivalent to:
116		482
117	BDB::AIO::poll_wait, BDB::AIO::poll_cb	483	BDB::poll_wait, BDB::poll_cb
118		484
119	BDB::AIO::flush	485	BDB::flush
120	Wait till all outstanding AIO requests have been handled.	486	Wait till all outstanding BDB requests have been handled.
121		487
122	Strictly equivalent to:	488	Strictly equivalent to:
123		489
124	BDB::AIO::poll_wait, BDB::AIO::poll_cb	490	BDB::poll_wait, BDB::poll_cb
125	while BDB::AIO::nreqs;	491	while BDB::nreqs;
		492
		493	VERSION CHECKING
		494	BerkeleyDB comes in various versions, many of them have minor
		495	incompatibilities. This means that traditional "at least version x.x"
		496	checks are often not sufficient.
		497
		498	Example: set the log_autoremove option in a way compatible with <v4.7
		499	and v4.7. Note the use of & on the constants to avoid triggering a
		500	compiletime bug when the symbol isn't available.
		501
		502	$DB_ENV->set_flags (&BDB::LOG_AUTOREMOVE ) if BDB::VERSION v0, v4.7;
		503	$DB_ENV->log_set_config (&BDB::LOG_AUTO_REMOVE) if BDB::VERSION v4.7;
		504
		505	BDB::VERSION
		506	The "BDB::VERSION" function, when called without arguments, returns
		507	the Berkeley DB version as a v-string (usually with 3 components).
		508	You should use "lt" and "ge" operators exclusively to make
		509	comparisons.
		510
		511	Example: check for at least version 4.7.
		512
		513	BDB::VERSION ge v4.7 or die;
		514
		515	BDB::VERSION min-version
		516	Returns true if the BDB version is at least the given version
		517	(specified as a v-string), false otherwise.
		518
		519	Example: check for at least version 4.5.
		520
		521	BDB::VERSION v4.7 or die;
		522
		523	BDB::VERSION min-version, max-version
		524	Returns true of the BDB version is at least version "min-version"
		525	(specify "undef" or "v0" for any minimum version) and less then
		526	"max-version".
		527
		528	Example: check wether version is strictly less then v4.7.
		529
		530	BDB::VERSION v0, v4.7
		531	or die "version 4.7 is not yet supported";
126		532
127	CONTROLLING THE NUMBER OF THREADS	533	CONTROLLING THE NUMBER OF THREADS
128	BDB::AIO::min_parallel $nthreads	534	BDB::min_parallel $nthreads
129	Set the minimum number of AIO threads to $nthreads. The current	535	Set the minimum number of BDB threads to $nthreads. The current
130	default is 8, which means eight asynchronous operations can execute	536	default is 8, which means eight asynchronous operations can execute
131	concurrently at any one time (the number of outstanding requests,	537	concurrently at any one time (the number of outstanding requests,
132	however, is unlimited).	538	however, is unlimited).
133		539
134	BDB::AIO starts threads only on demand, when an AIO request is	540	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	541	no free thread exists. Please note that queueing up a hundred
136	hundred requests can create demand for a hundred threads, even if it	542	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	543	out that everything is in the cache and could have been processed
138	processed faster by a single thread.	544	faster by a single thread.
139		545
140	It is recommended to keep the number of threads relatively low, as	546	It is recommended to keep the number of threads relatively low, as
141	some Linux kernel versions will scale negatively with the number of	547	some Linux kernel versions will scale negatively with the number of
142	threads (higher parallelity => MUCH higher latency). With current	548	threads (higher parallelity => MUCH higher latency). With current
143	Linux 2.6 versions, 4-32 threads should be fine.	549	Linux 2.6 versions, 4-32 threads should be fine.
144		550
145	Under most circumstances you don't need to call this function, as	551	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	552	the module selects a default that is suitable for low to moderate
147	load.	553	load.
148		554
149	BDB::AIO::max_parallel $nthreads	555	BDB::max_parallel $nthreads
150	Sets the maximum number of AIO threads to $nthreads. If more than	556	Sets the maximum number of BDB threads to $nthreads. If more than
151	the specified number of threads are currently running, this function	557	the specified number of threads are currently running, this function
152	kills them. This function blocks until the limit is reached.	558	kills them. This function blocks until the limit is reached.
153		559
154	While $nthreads are zero, aio requests get queued but not executed	560	While $nthreads are zero, aio requests get queued but not executed
155	until the number of threads has been increased again.	561	until the number of threads has been increased again.
…		…
158	ensure that all threads are killed and that there are no outstanding	564	ensure that all threads are killed and that there are no outstanding
159	requests.	565	requests.
160		566
161	Under normal circumstances you don't need to call this function.	567	Under normal circumstances you don't need to call this function.
162		568
163	BDB::AIO::max_idle $nthreads	569	BDB::max_idle $nthreads
164	Limit the number of threads (default: 4) that are allowed to idle	570	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	571	(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	572	seconds). That means if a thread becomes idle while $nthreads other
167	threads are also idle, it will free its resources and exit.	573	threads are also idle, it will free its resources and exit.
168		574
…		…
173		579
174	The default is probably ok in most situations, especially if thread	580	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	581	creation is fast. If thread creation is very slow on your system you
176	might want to use larger values.	582	might want to use larger values.
177		583
178	$oldmaxreqs = BDB::AIO::max_outstanding $maxreqs	584	$oldmaxreqs = BDB::max_outstanding $maxreqs
179	This is a very bad function to use in interactive programs because	585	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	586	it blocks, and a bad way to reduce concurrency because it is
181	inexact: Better use an "aio_group" together with a feed callback.	587	inexact: Better use an "aio_group" together with a feed callback.
182		588
183	Sets the maximum number of outstanding requests to $nreqs. If you to	589	Sets the maximum number of outstanding requests to $nreqs. If you to
…		…
191	You can still queue as many requests as you want. Therefore,	597	You can still queue as many requests as you want. Therefore,
192	"max_oustsanding" is mainly useful in simple scripts (with low	598	"max_oustsanding" is mainly useful in simple scripts (with low
193	values) or as a stop gap to shield against fatal memory overflow	599	values) or as a stop gap to shield against fatal memory overflow
194	(with large values).	600	(with large values).
195		601
		602	BDB::set_sync_prepare $cb
		603	Sets a callback that is called whenever a request is created without
		604	an explicit callback. It has to return two code references. The
		605	first is used as the request callback (it should save the return
		606	status), and the second is called to wait until the first callback
		607	has been called (it must set $! to the return status).
		608
		609	This mechanism can be used to include BDB into other event
		610	mechanisms, such as AnyEvent::BDB or Coro::BDB.
		611
		612	The default implementation works like this:
		613
		614	sub {
		615	my $status;
		616	(
		617	sub { $status = $! },
		618	sub { BDB::poll while !defined $status; $! = $status },
		619	)
		620	}
		621
		622	It simply blocks the process till the request has finished and then
		623	sets $! to the return value. This means that if you don't use a
		624	callback, BDB will simply fall back to synchronous operations.
		625
196	STATISTICAL INFORMATION	626	STATISTICAL INFORMATION
197	BDB::AIO::nreqs	627	BDB::nreqs
198	Returns the number of requests currently in the ready, execute or	628	Returns the number of requests currently in the ready, execute or
199	pending states (i.e. for which their callback has not been invoked	629	pending states (i.e. for which their callback has not been invoked
200	yet).	630	yet).
201		631
202	Example: wait till there are no outstanding requests anymore:	632	Example: wait till there are no outstanding requests anymore:
203		633
204	BDB::AIO::poll_wait, BDB::AIO::poll_cb	634	BDB::poll_wait, BDB::poll_cb
205	while BDB::AIO::nreqs;	635	while BDB::nreqs;
206		636
207	BDB::AIO::nready	637	BDB::nready
208	Returns the number of requests currently in the ready state (not yet	638	Returns the number of requests currently in the ready state (not yet
209	executed).	639	executed).
210		640
211	BDB::AIO::npending	641	BDB::npending
212	Returns the number of requests currently in the pending state	642	Returns the number of requests currently in the pending state
213	(executed, but not yet processed by poll_cb).	643	(executed, but not yet processed by poll_cb).
214		644
215	FORK BEHAVIOUR	645	FORK BEHAVIOUR
216	This module should do "the right thing" when the process using it forks:	646	This module should do "the right thing" when the process using it forks:
217		647
218	Before the fork, IO::AIO enters a quiescent state where no requests can	648	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	649	added in other threads and no results will be processed. After the fork
220	fork the parent simply leaves the quiescent state and continues	650	the parent simply leaves the quiescent state and continues
221	request/result processing, while the child frees the request/result	651	request/result processing, while the child frees the request/result
222	queue (so that the requests started before the fork will only be handled	652	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	653	in the parent). Threads will be started on demand until the limit set in
224	the parent process has been reached again.	654	the parent process has been reached again.
225		655
226	In short: the parent will, after a short pause, continue as if fork had	656	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	657	not been called, while the child will act as if BDB has not been used
228	used yet.	658	yet.
		659
		660	Win32 note: there is no fork on win32, and perls emulation of it is too
		661	broken to be supported, so do not use BDB in a windows pseudo-fork,
		662	better yet, switch to a more capable platform.
229		663
230	MEMORY USAGE	664	MEMORY USAGE
231	Per-request usage:	665	Per-request usage:
232		666
233	Each aio request uses - depending on your architecture - around 100-200	667	Each aio request uses - depending on your architecture - around 100-200
234	bytes of memory. In addition, stat requests need a stat buffer (possibly	668	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	669	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	670	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.	671	will consume memory till the request has entered the done state.
238		672
239	This is now awfully much, so queuing lots of requests is not usually a	673	This is not awfully much, so queuing lots of requests is not usually a
240	problem.	674	problem.
241		675
242	Per-thread usage:	676	Per-thread usage:
243		677
244	In the execution phase, some aio requests require more memory for	678	In the execution phase, some aio requests require more memory for
245	temporary buffers, and each thread requires a stack and other data	679	temporary buffers, and each thread requires a stack and other data
246	structures (usually around 16k-128k, depending on the OS).	680	structures (usually around 16k-128k, depending on the OS).
247		681
248	KNOWN BUGS	682	KNOWN BUGS
249	Known bugs will be fixed in the next release.	683	Known bugs will be fixed in the next release, except:
		684
		685	If you use a transaction in any request, and the request returns
		686	with an operating system error or DB_LOCK_NOTGRANTED, the internal
		687	TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>,
		688	above.
250		689
251	SEE ALSO	690	SEE ALSO
252	Coro::AIO.	691	AnyEvent::BDB (event loop integration), Coro::BDB (more natural syntax),
		692	IO::AIO (nice to have).
253		693
254	AUTHOR	694	AUTHOR
255	Marc Lehmann <schmorp@schmorp.de>	695	Marc Lehmann <schmorp@schmorp.de>
256	http://home.schmorp.de/	696	http://home.schmorp.de/
257		697

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Comparing BDB/README (file contents): Revision 1.1 by root, Mon Feb 5 18:40:55 2007 UTC vs. Revision 1.12 by root, Tue Jul 29 03:33:16 2008 UTC

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Comparing BDB/README (file contents):
Revision 1.1 by root, Mon Feb 5 18:40:55 2007 UTC vs.
Revision 1.12 by root, Tue Jul 29 03:33:16 2008 UTC