# phpman > perldoc > MongoDB::Monitoring ## NAME [MongoDB::Monitoring](https://www.chedong.com/phpMan.php/perldoc/MongoDB%3A%3AMonitoring/markdown) - Internal event monitoring API for instrumentation ## VERSION version v2.2.2 ## DESCRIPTION The [MongoDB::MongoClient](https://www.chedong.com/phpMan.php/perldoc/MongoDB%3A%3AMongoClient/markdown) takes an optional "monitoring_callback" attribute, which can be used to monitor events that occur during the operation of the driver. The API is very simple: given a code reference, a hashref for each event is passed to the code reference. Here is a simple example that just accumulates events in an array: our @events; my $cb = sub { push @events, $_[0] }; MongoDB->connect( $uri, { monitoring_callback => $cb } ); ## EVENT TYPES Every event is a hash reference, with a "type" field indicating the type, e.g. "command_started". Each type is described below. ### Command Monitoring These events are fired for commands directly to the wire and the response. command_started This event is sent just before a command is put one the wire. It will be followed by either a "command_succeeded" or "command_failed" event. Fields: * type: "command_started" * databaseName: the name of the database to which the command applies * commandName: the name of the command being executed; for legacy operations that don't use commands, the driver will convert them to appear as if they are in command form. * command: a hash reference representing the full command to be sent * requestId: the request identifier sent to the server * connectionId: address and port of the destination server command_succeeded This event is sent just after a command reply is received, but only if the database reply document contains a non-false "ok" field. NOTE: write errors will have "ok:1" even though they have write errors; for writes, success indicates that the write attempt was valid, not that the write succeeded. Fields: * type: "command_succeeded" * commandName: the name of the command being executed * durationSecs: the elapsed time in seconds since the "command_started" event. * reply: a hash reference representing the full database reply * requestId: the request identifier sent to the server * connectionId: address and port of the destination server command_failed This event is sent just after a command reply is received, but only if the database reply document contains a false "ok" field or if an exception occurred during send or receive operations. Fields: * type: "command_failed" * commandName: the name of the command being executed * durationSecs: the elapsed time in seconds since the "command_started" event. * failure: a string with a error message about the failure * eval_error: if an exception occurs, this contains the value of $@ when the exception was caught * reply: a hash reference representing the full database reply or an empty hashref if the failure is due to an exception * requestId: the request identifier sent to the server * connectionId: address and port of the destination server ### Server Discovery and Monitoring These events are fired when servers and topology are amended. server_opening_event This event is sent when a new server is added to the topology. Fields: * type: "server_opening_event" * topologyId: The topology refaddr * address: address of the server server_closed_event This event is sent when a server is removed from the topology. Fields: * type: "server_closed_event" * topologyId: The topology refaddr * address: address of the server server_description_changed_event This event is sent when the server description changes, but does not include changes to the RTT. Fields: * type: "server_description_changed_event" * address: address of the server * topologyId: The topology refaddr * previousDescription: Server Description before the change * newDescription: Server Description after the change topology_opening_event This event is sent when the topology is created. Fields: * type: "topology_opening_event" * topologyId: The topology refaddr topology_closed_event This event is sent when the topology is closed. Fields: * type: "topology_closed_event" * topologyId: The topology refaddr topology_description_changed_event This event is sent when the topology description changes. Fields: * type: "topology_description_changed_event" * topologyId: The topology refaddr * previousDescription: Topology Description before the change * newDescription: Topology Description after the change server_heartbeat_started_event This event is sent before the ismaster command is sent to the server. Fields: * type: "server_heartbeat_started_event" * connectionId: address of the link to connect to server_heartbeat_succeeded_event This event is sent after the reply from the ismaster command arrives from a successful reply. Fields: * type: "server_heartbeat_succeeded_event" * duration: time it took to send and receive a reply * reply: the ismaster command reply * connectionId: address of the server server_heartbeat_failed_event This event is sent if there is a failure from the ismaster command, which returns an error string of some sort. Fields: * type: "server_heartbeat_failed_event" * duration: time it took to send and receive a reply * failure: Returns an error string of the failure * connectionId: address of the server ## REDACTION Certain commands are considered sensitive. When any of the following commands are seen in monitoring, the command body and database reply body are replaced with an empty document: * authenticate * saslStart * saslContinue * getnonce * createUser * updateUser * copydbgetnonce * copydbsaslstart ## AUTHORS * David Golden <> * Rassi <> * Mike Friedman <> * Kristina Chodorow <> * Florian Ragwitz <> ## COPYRIGHT AND LICENSE This software is Copyright (c) 2020 by MongoDB, Inc. This is free software, licensed under: The Apache License, Version 2.0, January 2004