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MongoDB::MongoClient(3User Contributed Perl DocumentatiMongoDB::MongoClient(3)

NAME
       MongoDB::MongoClient - A	connection to a	MongoDB	server or multi-server
       deployment

VERSION
       version v1.8.0

SYNOPSIS
	   use MongoDB;	# also loads MongoDB::MongoClient

	   # connect to	localhost:27017
	   my $client =	MongoDB::MongoClient->new;

	   # connect to	specific host and port
	   my $client =	MongoDB::MongoClient->new(
	       host => "mongodb://mongo.example.com:27017"
	   );

	   # connect to	a replica set (set name	*required*)
	   my $client =	MongoDB::MongoClient->new(
	       host => "mongodb://mongo1.example.com,mongo2.example.com",
	       replica_set_name	=> 'myset',
	   );

	   # connect to	a replica set with URI (set name *required*)
	   my $client =	MongoDB::MongoClient->new(
	       host => "mongodb://mongo1.example.com,mongo2.example.com/?replicaSet=myset",
	   );

	   my $db = $client->get_database("test");
	   my $coll = $db->get_collection("people");

	   $coll->insert({ name	=> "John Doe", age => 42 });
	   my @people =	$coll->find()->all();

DESCRIPTION
       The "MongoDB::MongoClient" class	represents a client connection to one
       or more MongoDB servers.

       By default, it connects to a single server running on the local machine
       listening on the	default	port 27017:

	   # connects to localhost:27017
	   my $client =	MongoDB::MongoClient->new;

       It can connect to a database server running anywhere, though:

	   my $client =	MongoDB::MongoClient->new(host => 'example.com:12345');

       See the "host" attribute	for more options for connecting	to MongoDB.

       MongoDB can be started in authentication	mode
       <http://docs.mongodb.org/manual/core/authentication/>, which requires
       clients to log in before	manipulating data.  By default,	MongoDB	does
       not start in this mode, so no username or password is required to make
       a fully functional connection.  To configure the	client for
       authentication, see the "AUTHENTICATION"	section.

       The actual socket connections are lazy and created on demand.  When the
       client object goes out of scope,	all socket will	be closed.  Note that
       MongoDB::Database, MongoDB::Collection and related classes could	hold a
       reference to the	client as well.	 Only when all references are out of
       scope will the sockets be closed.

ATTRIBUTES
   host
       The "host" attribute specifies either a single server to	connect	to (as
       "hostname" or "hostname:port"), or else a connection string URI with a
       seed list of one	or more	servers	plus connection	options.

       Defaults	to the connection string URI "mongodb://localhost:27017".

       For IPv6	support, you must have a recent	version	of IO::Socket::IP
       installed.  This	module ships with the Perl core	since v5.20.0 and is
       available on CPAN for older Perls.

   app_name
       This attribute specifies	an application name that should	be associated
       with this client.  The application name will be communicated to the
       server as part of the initial connection	handshake, and will appear in
       connection-level	and operation-level diagnostics	on the server
       generated on behalf of this client.  This may be	set in a connection
       string with the "appName" option.

       The default is the empty	string,	which indicates	a lack of an
       application name.

       The application name must not exceed 128	bytes.

   auth_mechanism
       This attribute determines how the client	authenticates with the server.
       Valid values are:

       o   NONE

       o   DEFAULT

       o   MONGODB-CR

       o   MONGODB-X509

       o   GSSAPI

       o   PLAIN

       o   SCRAM-SHA-1

       If not specified, then if no username is	provided, it defaults to NONE.
       If a username is	provided, it is	set to DEFAULT,	which chooses
       SCRAM-SHA-1 if available	or MONGODB-CR otherwise.

       This may	be set in a connection string with the "authMechanism" option.

   auth_mechanism_properties
       This is an optional hash	reference of authentication mechanism specific
       properties.  See	"AUTHENTICATION" for details.

       This may	be set in a connection string with the
       "authMechanismProperties" option.  If given, the	value must be
       key/value pairs joined with a ":".  Multiple pairs must be separated by
       a comma.	 If ": or "," appear in	a key or value,	they must be URL
       encoded.

   bson_codec
       An object that provides the "encode_one"	and "decode_one" methods, such
       as from MongoDB::BSON.  It may be initialized with a hash reference
       that will be coerced into a new MongoDB::BSON object.

       If not provided,	one will be generated as follows:

	   MongoDB::BSON->new(
	       dbref_callback => sub { return MongoDB::DBRef->new(shift) },
	       dt_type	      => $client->dt_type,
	       prefer_numeric => $MongoDB::BSON::looks_like_number || 0,
	       (
		   $MongoDB::BSON::char	ne '$' ?
		       ( op_char => $MongoDB::BSON::char ) : ()
	       ),
	   );

       This will inflate all DBRefs to MongoDB::DBRef objects, set "dt_type"
       based on	the client's "db_type" accessor, and set the "prefer_numeric"
       and "op_char" attributes	based on the deprecated	legacy global
       variables.

   connect_timeout_ms
       This attribute specifies	the amount of time in milliseconds to wait for
       a new connection	to a server.

       The default is 10,000 ms.

       If set to a negative value, connection operations will block
       indefinitely until the server replies or	until the operating system
       TCP/IP stack gives up (e.g. if the name can't resolve or	there is no
       process listening on the	target host/port).

       A zero value polls the socket during connection and is thus likely to
       fail except when	talking	to a local process (and	perhaps	even then).

       This may	be set in a connection string with the "connectTimeoutMS"
       option.

   db_name
       Optional.  If an	"auth_mechanism" requires a database for
       authentication, this attribute will be used.  Otherwise,	it will	be
       ignored.	Defaults to "admin".

       This may	be provided in the connection string URI as a path between the
       authority and option parameter sections.	 For example, to authenticate
       against the "admin" database (showing a configuration option only for
       illustration):

	   mongodb://localhost/admin?readPreference=primary

   heartbeat_frequency_ms
       The time	in milliseconds	(non-negative) between scans of	all servers to
       check if	they are up and	update their latency.  Defaults	to 60,000 ms.

       This may	be set in a connection string with the "heartbeatFrequencyMS"
       option.

   j
       If true,	the client will	block until write operations have been
       committed to the	server's journal. Prior	to MongoDB 2.6,	this option
       was ignored if the server was running without journaling. Starting with
       MongoDB 2.6, write operations will fail if this option is used when the
       server is running without journaling.

       This may	be set in a connection string with the "journal" option	as the
       strings 'true' or 'false'.

   local_threshold_ms
       The width of the	'latency window': when choosing	between	multiple
       suitable	servers	for an operation, the acceptable delta in milliseconds
       (non-negative) between shortest and longest average round-trip times.
       Servers within the latency window are selected randomly.

       Set this	to "0" to always select	the server with	the shortest average
       round trip time.	 Set this to a very high value to always randomly
       choose any known	server.

       Defaults	to 15 ms.

       See "SERVER SELECTION" for more details.

       This may	be set in a connection string with the "localThresholdMS"
       option.

   max_staleness_seconds
       The "max_staleness_seconds" parameter represents	the maximum
       replication lag in seconds (wall	clock time) that a secondary can
       suffer and still	be eligible for	reads. The default is -1, which
       disables	staleness checks.  Otherwise, it must be a positive integer.

       Note: this will only be used for	server versions	3.4 or greater,	as
       that was	when support for staleness tracking was	added.

       If the read preference mode is 'primary', then "max_staleness_seconds"
       must not	be supplied.

       The "max_staleness_seconds" must	be at least the
       "heartbeat_frequency_ms"	plus 10	seconds	(which is how often the	server
       makes idle writes to the	oplog).

       This may	be set in a connection string with the "maxStalenessSeconds"
       option.

   max_time_ms
       Specifies the maximum amount of time in (non-negative) milliseconds
       that the	server should use for working on a database command.  Defaults
       to 0, which disables this feature.  Make	sure this value	is shorter
       than "socket_timeout_ms".

       Note: this will only be used for	server versions	2.6 or greater,	as
       that was	when the $maxTimeMS meta-operator was introduced.

       You are strongly	encouraged to set this variable	if you know your
       environment has MongoDB 2.6 or later, as	getting	a definitive error
       response	from the server	is vastly preferred over a getting a network
       socket timeout.

       This may	be set in a connection string with the "maxTimeMS" option.

   password
       If an "auth_mechanism" requires a password, this	attribute will be
       used.  Otherwise, it will be ignored.

       This may	be provided in the connection string URI as a
       "username:password" pair	in the leading portion of the authority
       section before a	"@" character.	For example, to	authenticate as	user
       "mulder"	with password "trustno1":

	   mongodb://mulder:trustno1@localhost

       If the username or password have	a ":" or "@" in	it, they must be URL
       encoded.	 An empty password still requires a ":"	character.

   port
       If a network port is not	specified as part of the "host"	attribute,
       this attribute provides the port	to use.	 It defaults to	27107.

   read_pref_mode
       The read	preference mode	determines which server	types are candidates
       for a read operation.  Valid values are:

       o   primary

       o   primaryPreferred

       o   secondary

       o   secondaryPreferred

       o   nearest

       For core	documentation on read preference see
       <http://docs.mongodb.org/manual/core/read-preference/>.

       This may	be set in a connection string with the "readPreference"
       option.

   read_pref_tag_sets
       The "read_pref_tag_sets"	parameter is an	ordered	list of	tag sets used
       to restrict the eligibility of servers, such as for data	center
       awareness.  It must be an array reference of hash references.

       The application of "read_pref_tag_sets" varies depending	on the
       "read_pref_mode"	parameter.  If the "read_pref_mode" is 'primary', then
       "read_pref_tag_sets" must not be	supplied.

       For core	documentation on read preference see
       <http://docs.mongodb.org/manual/core/read-preference/>.

       This may	be set in a connection string with the "readPreferenceTags"
       option.	If given, the value must be key/value pairs joined with	a ":".
       Multiple	pairs must be separated	by a comma.  If	": or "," appear in a
       key or value, they must be URL encoded.	The "readPreferenceTags"
       option may appear more than once, in which case each document will be
       added to	the tag	set list.

   replica_set_name
       Specifies the replica set name to connect to.  If this string is	non-
       empty, then the topology	is treated as a	replica	set and	all server
       replica set names must match this or they will be removed from the
       topology.

       This may	be set in a connection string with the "replicaSet" option.

   server_selection_timeout_ms
       This attribute specifies	the amount of time in milliseconds to wait for
       a suitable server to be available for a read or write operation.	 If no
       server is available within this time period, an exception will be
       thrown.

       The default is 30,000 ms.

       See "SERVER SELECTION" for more details.

       This may	be set in a connection string with the
       "serverSelectionTimeoutMS" option.

   server_selection_try_once
       This attribute controls whether the client will make only a single
       attempt to find a suitable server for a read or write operation.	 The
       default is true.

       When true, the client will not use the "server_selection_timeout_ms".
       Instead,	if the topology	information is stale and needs to be checked
       or if no	suitable server	is available, the client will make a single
       scan of all known servers to try	to find	a suitable one.

       When false, the client will continually scan known servers until	a
       suitable	server is found	or the "serverSelectionTimeoutMS" is reached.

       See "SERVER SELECTION" for more details.

       This may	be set in a connection string with the
       "serverSelectionTryOnce"	option.

   socket_check_interval_ms
       If a socket to a	server has not been used in this many milliseconds, an
       "ismaster" command will be issued to check the status of	the server
       before issuing any reads	or writes. Must	be non-negative.

       The default is 5,000 ms.

       This may	be set in a connection string with the "socketCheckIntervalMS"
       option.

   socket_timeout_ms
       This attribute specifies	the amount of time in milliseconds to wait for
       a reply from the	server before issuing a	network	exception.

       The default is 30,000 ms.

       If set to a negative value, socket operations will block	indefinitely
       until the server	replies	or until the operating system TCP/IP stack
       gives up.

       A zero value polls the socket for available data	and is thus likely to
       fail except when	talking	to a local process (and	perhaps	even then).

       This may	be set in a connection string with the "socketTimeoutMS"
       option.

   ssl
	   ssl => 1
	   ssl => \%ssl_options

       This tells the driver that you are connecting to	an SSL mongodb
       instance.

       You must	have IO::Socket::SSL 1.42+ and Net::SSLeay 1.49+ installed for
       SSL support.

       The "ssl" attribute takes either	a boolean value	or a hash reference of
       options to pass to IO::Socket::SSL.  For	example, to set	a CA file to
       validate	the server certificate and set a client	certificate for	the
       server to validate, you could set the attribute like this:

	   ssl => {
	       SSL_ca_file   =>	"/path/to/ca.pem",
	       SSL_cert_file =>	"/path/to/client.pem",
	   }

       If "SSL_ca_file"	is not provided, server	certificates are verified
       against a default list of CAs, either Mozilla::CA or an operating-
       system-specific default CA file.	 To disable verification, you can use
       "SSL_verify_mode	=> 0x00".

       You are strongly	encouraged to use your own CA file for increased
       security.

       Server hostnames	are also validated against the CN name in the server
       certificate using "SSL_verifycn_scheme => 'http'".  You can use the
       scheme 'none' to	disable	this check.

       Disabling certificate or	hostname verification is a security risk and
       is not recommended.

       This may	be set to the string 'true' or 'false' in a connection string
       with the	"ssl" option, which will enable	ssl with default
       configuration.  (A future version of the	driver may support customizing
       ssl via the connection string.)

   username
       Optional	username for this client connection.  If this field is set,
       the client will attempt to authenticate when connecting to servers.
       Depending on the	"auth_mechanism", the "password" field or other
       attributes will need to be set for authentication to succeed.

       This may	be provided in the connection string URI as a
       "username:password" pair	in the leading portion of the authority
       section before a	"@" character.	For example, to	authenticate as	user
       "mulder"	with password "trustno1":

	   mongodb://mulder:trustno1@localhost

       If the username or password have	a ":" or "@" in	it, they must be URL
       encoded.	 An empty password still requires a ":"	character.

   w
       The client write	concern.

       o   0 Unacknowledged. MongoClient will NOT wait for an acknowledgment
	   that	the server has received	and processed the request. Older
	   documentation may refer to this as "fire-and-forget"	mode.  This
	   option is not recommended.

       o   1 Acknowledged. This	is the default.	MongoClient will wait until
	   the primary MongoDB acknowledges the	write.

       o   2 Replica acknowledged. MongoClient will wait until at least	two
	   replicas (primary and one secondary)	acknowledge the	write. You can
	   set a higher	number for more	replicas.

       o   "all" All replicas acknowledged.

       o   "majority" A	majority of replicas acknowledged.

       In MongoDB v2.0+, you can "tag" replica members.	With "tagging" you can
       specify a custom	write concern For more information see Data Center
       Awareness <http://docs.mongodb.org/manual/data-center-awareness/>

       This may	be set in a connection string with the "w" option.

   wtimeout
       The number of milliseconds an operation should wait for "w" secondaries
       to replicate it.

       Defaults	to 1000	(1 second).

       See "w" above for more information.

       This may	be set in a connection string with the "wTimeoutMS" option.

   read_concern_level
       The read	concern	level determines the consistency level required	of
       data being read.

       The default level is "undef", which means the server will use its
       configured default.

       If the level is set to "local", reads will return the latest data a
       server has locally.

       Additional levels are storage engine specific.  See Read	Concern
       <http://docs.mongodb.org/manual/search/?query=readConcern> in the
       MongoDB documentation for more details.

       This may	be set in a connection string with the the "readConcernLevel"
       option.

   dt_type (DEPRECATED AND READ-ONLY)
       Sets the	type of	object which is	returned for DateTime fields. The
       default is DateTime. Other acceptable values are	DateTime::Tiny,
       Time::Moment and	"undef". The latter will give you the raw epoch	value
       (possibly as a floating point value) rather than	an object.

       This will be used to construct "bson_codec" object if one is not
       provided.

       As this has a one-time effect, it is now	read-only to help you detect
       code that was trying to change after the	fact during program execution.

       For temporary or	localized changes, look	into overriding	the
       "bson_codec" object for a database or collection	object.

   query_timeout (DEPRECATED AND READ-ONLY)
	   # set query timeout to 1 second
	   my $client =	MongoDB::MongoClient->new(query_timeout	=> 1000);

       This option has been renamed as "socket_timeout_ms".  If	this option is
       set and that one	is not,	this will be used.

       This value is in	milliseconds and defaults to 30000.

   sasl	(DEPRECATED)
       If true,	the driver will	set the	authentication mechanism based on the
       "sasl_mechanism"	property.

   sasl_mechanism (DEPRECATED)
       This specifies the SASL mechanism to use	for authentication with	a
       MongoDB server.	It has the same	valid values as	"auth_mechanism".  The
       default is GSSAPI.

   timeout (DEPRECATED AND READ-ONLY)
       This option has been renamed as "connect_timeout_ms".  If this option
       is set and that one is not, this	will be	used.

       Connection timeout is in	milliseconds. Defaults to 10000.

METHODS
   read_preference
       Returns a MongoDB::ReadPreference object	constructed from
       "read_pref_mode"	and "read_pref_tag_sets"

       The use of "read_preference" as a mutator has been removed.  Read
       preference is read-only.	 If you	need a different read preference for a
       database	or collection, you can specify that in "get_database" or
       "get_collection".

   write_concern
       Returns a MongoDB::WriteConcern object constructed from "w",
       "write_concern" and "j".

   read_concern
       Returns a MongoDB::ReadConcern object constructed from
       "read_concern_level".

   topology_type
       Returns an enumerated topology type.  If	the "replica_set_name" is set,
       the value will be either	'ReplicaSetWithPrimary'	or
       'ReplicaSetNoPrimary' (if the primary is	down or	not yet	discovered).
       Without "replica_set_name", the type will be 'Single' if	there is only
       one server in the list of hosts,	and 'Sharded' if there are more	than
       one.

       N.B. A single mongos will have a	topology type of 'Single', as that
       mongos will be used for all reads and writes, just like a standalone
       mongod.	The 'Sharded' type indicates a sharded cluster with multiple
       mongos servers, and reads/writes	will be	distributed acc

   connect
	   $client->connect;

       Calling this method is unnecessary, as connections are established
       automatically as	needed.	 It is kept for	backwards compatibility.
       Calling it will check all servers in the	deployment which ensures a
       connection to any that are available.

       See "reconnect" for a method that is useful when	using forks or
       threads.

   disconnect
	   $client->disconnect;

       Drops all connections to	servers.

   reconnect
	   $client->reconnect;

       This method closes all connections to the server, as if "disconnect"
       were called, and	then immediately reconnects.  Use this after forking
       or spawning off a new thread.

   topology_status
	   $client->topology_status;
	   $client->topology_status( refresh =>	1 );

       Returns a hash reference	with server topology information like this:

	   {
	       'topology_type' => 'ReplicaSetWithPrimary'
	       'replica_set_name' => 'foo',
	       'last_scan_time'	  => '1433766895.183241',
	       'servers'	  => [
		   {
		       'address'     =>	'localhost:50003',
		       'ewma_rtt_ms' =>	'0.223462326',
		       'type'	     =>	'RSSecondary'
		   },
		   {
		       'address'     =>	'localhost:50437',
		       'ewma_rtt_ms' =>	'0.268435456',
		       'type'	     =>	'RSArbiter'
		   },
		   {
		       'address'     =>	'localhost:50829',
		       'ewma_rtt_ms' =>	'0.737782272',
		       'type'	     =>	'RSPrimary'
		   }
	       },
	   }

       If the 'refresh'	argument is true, then the topology will be scanned to
       update server data before returning the hash reference.

   database_names
	   my @dbs = $client->database_names;

       Lists all databases on the MongoDB server.

   get_database, db
	   my $database	= $client->get_database('foo');
	   my $database	= $client->get_database('foo', $options);
	   my $database	= $client->db('foo', $options);

       Returns a MongoDB::Database instance for	the database with the given
       $name.

       It takes	an optional hash reference of options that are passed to the
       MongoDB::Database constructor.

       The "db"	method is an alias for "get_database".

   get_namespace, ns
	   my $collection = $client->get_namespace('test.foo');
	   my $collection = $client->get_namespace('test.foo', $options);
	   my $collection = $client->ns('test.foo', $options);

       Returns a MongoDB::Collection instance for the given namespace.	The
       namespace has both the database name and	the collection name separated
       with a dot character.

       This is a quick way to get a collection object if you don't need	the
       database	object separately.

       It takes	an optional hash reference of options that are passed to the
       MongoDB::Collection constructor.	 The intermediate MongoDB::Database
       object will be created with default options.

       The "ns"	method is an alias for "get_namespace".

   fsync(\%args)
	   $client->fsync();

       A function that will forces the server to flush all pending writes to
       the storage layer.

       The fsync operation is synchronous by default, to run fsync
       asynchronously, use the following form:

	   $client->fsync({async => 1});

       The primary use of fsync	is to lock the database	during backup
       operations. This	will flush all data to the data	storage	layer and
       block all write operations until	you unlock the database. Note: you can
       still read while	the database is	locked.

	   $conn->fsync({lock => 1});

   fsync_unlock
	   $conn->fsync_unlock();

       Unlocks a database server to allow writes and reverses the operation of
       a $conn->fsync({lock => 1}); operation.

DEPLOYMENT TOPOLOGY
       MongoDB can operate as a	single server or as a distributed system.  One
       or more servers that collectively provide access	to a single logical
       set of MongoDB databases	are referred to	as a "deployment".

       There are three types of	deployments:

       o   Single server a a stand-alone mongod	database

       o   Replica set a a set of mongod databases with	data replication and
	   fail-over capability

       o   Sharded cluster aA a	distributed deployment that spreads data
	   across one or more shards, each of which can	be a replica set.
	   Clients communicate with a mongos process that routes operations to
	   the correct share.

       The state of a deployment, including its	type, which servers are
       members,	the server types of members and	the round-trip network latency
       to members is referred to as the	"topology" of the deployment.

       To the greatest extent possible,	the MongoDB driver abstracts away the
       details of communicating	with different deployment types.  It
       determines the deployment topology through a combination	of the
       connection string, configuration	options	and direct discovery
       communicating with servers in the deployment.

CONNECTION STRING URI
       MongoDB uses a pseudo-URI connection string to specify one or more
       servers to connect to, along with configuration options.

       To connect to more than one database server, provide host or host:port
       pairs as	a comma	separated list:

	   mongodb://host1[:port1][,host2[:port2],...[,hostN[:portN]]]

       This list is referred to	as the "seed list".  An	arbitrary number of
       hosts can be specified.	If a port is not specified for a given host,
       it will default to 27017.

       If multiple hosts are given in the seed list or discovered by talking
       to servers in the seed list, they must all be replica set members or
       must all	be mongos servers for a	sharded	cluster.

       A replica set MUST have the "replicaSet"	option set to the replica set
       name.

       If there	is only	single host in the seed	list and "replicaSet" is not
       provided, the deployment	is treated as a	single server deployment and
       all reads and writes will be sent to that host.

       Providing a replica set member as a single host without the set name is
       the way to get a	"direct	connection" for	carrying out administrative
       activities on that server.

       The connection string may also have a username and password:

	   mongodb://username:password@host1:port1,host2:port2

       The username and	password must be URL-escaped.

       A optional database name	for authentication may be given:

	   mongodb://username:password@host1:port1,host2:port2/my_database

       Finally,	connection string options may be given as URI attribute	pairs
       in a query string:

	   mongodb://host1:port1,host2:port2/?ssl=1&wtimeoutMS=1000
	   mongodb://username:password@host1:port1,host2:port2/my_database?ssl=1&wtimeoutMS=1000

       The currently supported connection string options are:

	   *appName *authMechanism *authMechanism.SERVICE_NAME
	   *connectTimeoutMS *journal *readPreference *readPreferenceTags
	   *replicaSet *ssl *w *wtimeoutMS

       See the official	MongoDB	documentation on connection strings for	more
       on the URI format and connection	string options:
       <http://docs.mongodb.org/manual/reference/connection-string/>.

SERVER SELECTION
       For a single server deployment or a direct connection to	a mongod or
       mongos, all reads and writes and	sent to	that server.  Any read-
       preference is ignored.

       When connected to a deployment with multiple servers, such as a replica
       set or sharded cluster, the driver chooses a server for operations
       based on	the type of operation (read or write), the types of servers
       available and a read preference.

       For a replica set deployment, writes are	sent to	the primary (if
       available) and reads are	sent to	a server based on the
       "read_preference" attribute, which defaults to sending reads to the
       primary.	 See MongoDB::ReadPreference for more.

       For a sharded cluster reads and writes are distributed across mongos
       servers in the seed list.  Any read preference is passed	through	to the
       mongos and used by it when executing reads against shards.

       If multiple servers can service an operation (e.g. multiple mongos
       servers,	or multiple replica set	members), one is chosen	at random from
       within the "latency window".  The server	with the shortest average
       round-trip time (RTT) is	always in the window.  Any servers with	an
       average round-trip time less than or equal to the shortest RTT plus the
       "local_threshold_ms" are	also in	the latency window.

       If a suitable server is not immediately available, what happens next
       depends on the "server_selection_try_once" option.

       If that option is true, a single	topology scan will be performed.
       Afterwards if a suitable	server is available, it	will be	returned;
       otherwise, an exception is thrown.

       If that option is false,	the driver will	do topology scans repeatedly
       looking for a suitable server.  When more than
       "server_selection_timeout_ms" milliseconds have elapsed since the start
       of server selection without a suitable server being found, an exception
       is thrown.

       Note: the actual	maximum	wait time for server selection could be	as
       long "server_selection_timeout_ms" plus the amount of time required to
       do a topology scan.

SERVER MONITORING AND FAILOVER
       When the	client first needs to find a server for	a database operation,
       all servers from	the "host" attribute are scanned to determine which
       servers to monitor.  If the deployment is a replica set,	additional
       hosts may be discovered in this process.	 Invalid hosts are dropped.

       After the initial scan, whenever	the servers have not been checked in
       "heartbeat_frequency_ms"	milliseconds, the scan will be repeated.  This
       amortizes monitoring time over many of operations.  Additionally, if a
       socket has been idle for	a while, it will be checked before being used
       for an operation.

       If a server operation fails because of a	"not master" or	"node is
       recovering" error, or if	there is a network error or timeout, then the
       server is flagged as unavailable	and exception will be thrown.  See
       MongoDB::Errors for exception types.

       If the error is caught and handled, the next operation will rescan all
       servers immediately to update its view of the topology.	The driver can
       continue	to function as long as servers are suitable per	"SERVER
       SELECTION".

       When catching an	exception, users must determine	whether	or not their
       application should retry	an operation based on the specific operation
       attempted and other use-case-specific considerations.  For automating
       retries despite exceptions, consider using the Try::Tiny::Retry module.

AUTHENTICATION
       The MongoDB server provides several authentication mechanisms, though
       some are	only available in the Enterprise edition.

       MongoDB client authentication is	controlled via the "auth_mechanism"
       attribute, which	takes one of the following values:

       o   MONGODB-CR -- legacy	username-password challenge-response

       o   SCRAM-SHA-1 -- secure username-password challenge-response (3.0+)

       o   MONGODB-X509	-- SSL client certificate authentication (2.6+)

       o   PLAIN -- LDAP authentication	via SASL PLAIN (Enterprise only)

       o   GSSAPI -- Kerberos authentication (Enterprise only)

       The mechanism to	use depends on the authentication configuration	of the
       server.	See the	core documentation on authentication:
       <http://docs.mongodb.org/manual/core/access-control/>.

       Usage information for each mechanism is given below.

   MONGODB-CR and SCRAM-SHA-1 (for username/password)
       These mechnisms require a username and password,	given either as
       constructor attributes or in the	"host" connection string.

       If a username is	provided and an	authentication mechanism is not
       specified, the client will use SCRAM-SHA-1 for version 3.0 or later
       servers and will	fall back to MONGODB-CR	for older servers.

	   my $mc = MongoDB::MongoClient->new(
	       host => "mongodb://mongo.example.com/",
	       username	=> "johndoe",
	       password	=> "trustno1",
	   );

	   my $mc = MongoDB::MongoClient->new(
	       host => "mongodb://johndoe:trustno1@mongo.example.com/",
	   );

       Usernames and passwords will be UTF-8 encoded before use.  The password
       is never	sent over the wire -- only a secure digest is used.  The
       SCRAM-SHA-1 mechanism is	the Salted Challenge Response Authentication
       Mechanism definedin RFC 5802 <http://tools.ietf.org/html/rfc5802>.

       The default database for	authentication is 'admin'.  If another
       database	name should be used, specify it	with the "db_name" attribute
       or via the connection string.

	   db_name => auth_db

	   mongodb://johndoe:trustno1@mongo.example.com/auth_db

   MONGODB-X509	(for SSL client	certificate)
       X509 authentication requires SSL	support	(IO::Socket::SSL), requires
       that a client certificate be configured in the ssl parameters, and
       requires	specifying the "MONGODB-X509" authentication mechanism.

	   my $mc = MongoDB::MongoClient->new(
	       host => "mongodb://sslmongo.example.com/",
	       ssl => {
		   SSL_ca_file	 => "certs/ca.pem",
		   SSL_cert_file => "certs/client.pem",
	       },
	       auth_mechanism => "MONGODB-X509",
	   );

   PLAIN (for LDAP)
       This mechanism requires a username and password,	which will be UTF-8
       encoded before use.  The	"auth_mechanism" parameter must	be given as a
       constructor attribute or	in the "host" connection string:

	   my $mc = MongoDB::MongoClient->new(
	       host => "mongodb://mongo.example.com/",
	       username	=> "johndoe",
	       password	=> "trustno1",
	       auth_mechanism => "PLAIN",
	   );

	   my $mc = MongoDB::MongoClient->new(
	       host => "mongodb://johndoe:trustno1@mongo.example.com/authMechanism=PLAIN",
	   );

   GSSAPI (for Kerberos)
       Kerberos	authentication requires	the CPAN module	Authen::SASL and a
       GSSAPI-capable backend.

       On Debian systems, Authen::SASL may be available	as
       "libauthen-sasl-perl"; on RHEL systems, it may be available as
       "perl-Authen-SASL".

       The Authen::SASL::Perl backend comes with Authen::SASL and requires the
       GSSAPI CPAN module for GSSAPI support.  On Debian systems, this may be
       available as "libgssapi-perl"; on RHEL systems, it may be available as
       "perl-GSSAPI".

       Installing the GSSAPI module from CPAN rather than an OS	package
       requires	"libkrb5" and the "krb5-config"	utility	(available for
       Debian/RHEL systems in the "libkrb5-dev"	package).

       Alternatively, the Authen::SASL::XS or Authen::SASL::Cyrus modules may
       be used.	 Both rely on Cyrus "libsasl".	Authen::SASL::XS is preferred,
       but not yet available as	an OS package.	Authen::SASL::Cyrus is
       available on Debian as "libauthen-sasl-cyrus-perl" and on RHEL as
       "perl-Authen-SASL-Cyrus".

       Installing Authen::SASL::XS or Authen::SASL::Cyrus from CPAN requires
       "libsasl".  On Debian systems, it is available from "libsasl2-dev"; on
       RHEL, it	is available in	"cyrus-sasl-devel".

       To use the GSSAPI mechanism, first run "kinit" to authenticate with the
       ticket granting service:

	   $ kinit johndoe@EXAMPLE.COM

       Configure MongoDB::MongoClient with the principal name as the
       "username" parameter and	specify	'GSSAPI' as the	"auth_mechanism":

	   my $mc = MongoDB::MongoClient->new(
	       host => 'mongodb://mongo.example.com',
	       username	=> 'johndoe@EXAMPLE.COM',
	       auth_mechanism => 'GSSAPI',
	   );

       Both can	be specified in	the "host" connection string, keeping in mind
       that the	'@' in the principal name must be encoded as "%40":

	   my $mc = MongoDB::MongoClient->new(
	       host =>
		 'mongodb://johndoe%40EXAMPLE.COM@mongo.examplecom/?authMechanism=GSSAPI',
	   );

       The default service name	is 'mongodb'.  It can be changed with the
       "auth_mechanism_properties" attribute or	in the connection string.

	   auth_mechanism_properties =>	{ SERVICE_NAME => 'other_service' }

	   mongodb://.../?authMechanism=GSSAPI&authMechanismProperties=SERVICE_NAME:other_service

THREAD-SAFETY AND FORK-SAFETY
       You MUST	call the "reconnect" method on any MongoDB::MongoClient
       objects after forking or	spawning a thread.

AUTHORS
       o   David Golden	<david@mongodb.com>

       o   Rassi <rassi@mongodb.com>

       o   Mike	Friedman <friedo@friedo.com>

       o   Kristina Chodorow <k.chodorow@gmail.com>

       o   Florian Ragwitz <rafl@debian.org>

COPYRIGHT AND LICENSE
       This software is	Copyright (c) 2017 by MongoDB, Inc.

       This is free software, licensed under:

	 The Apache License, Version 2.0, January 2004

perl v5.24.1			  2017-04-10	       MongoDB::MongoClient(3)

NAME | VERSION | SYNOPSIS | DESCRIPTION | ATTRIBUTES | METHODS | DEPLOYMENT TOPOLOGY | CONNECTION STRING URI | SERVER SELECTION | SERVER MONITORING AND FAILOVER | AUTHENTICATION | THREAD-SAFETY AND FORK-SAFETY | AUTHORS | COPYRIGHT AND LICENSE

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