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<ol class="chapter"><li class="chapter-item expanded "><a href="index.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="installation_features.html"><strong aria-hidden="true">2.</strong> Installation and Features</a></li><li class="chapter-item expanded "><a href="connecting.html"><strong aria-hidden="true">3.</strong> Connecting to the Database</a></li><li class="chapter-item expanded "><a href="reading.html"><strong aria-hidden="true">4.</strong> Reading From the Database</a></li><li class="chapter-item expanded "><div><strong aria-hidden="true">5.</strong> Writing To the Database</div></li><li class="chapter-item expanded "><a href="performance.html"><strong aria-hidden="true">6.</strong> Performance</a></li><li class="chapter-item expanded "><div><strong aria-hidden="true">7.</strong> Serde Integration</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">8.</strong> Sessions and Transactions</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">9.</strong> Change Streams</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">10.</strong> Monitoring</div></li><li class="chapter-item expanded "><a href="tracing.html" class="active"><strong aria-hidden="true">11.</strong> Tracing and Logging</a></li><li class="chapter-item expanded "><a href="web_framework_examples.html"><strong aria-hidden="true">12.</strong> Web Framework Examples</a></li><li class="chapter-item expanded "><a href="encryption.html"><strong aria-hidden="true">13.</strong> Encryption</a></li><li class="chapter-item expanded affix "><li class="part-title">Development</li><li class="chapter-item expanded "><div><strong aria-hidden="true">14.</strong> Writing Tests</div></li></ol>
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<h1 class="menu-title">MongoDB Rust Driver</h1>
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<h1 id="tracing-and-logging"><a class="header" href="#tracing-and-logging">Tracing and Logging</a></h1>
<p>The driver utilizes the <a href="https://crates.io/crates/tracing"><code>tracing</code></a> crate to emit events at points of interest. To enable this, you must turn on the <code>tracing-unstable</code> feature flag.</p>
<h2 id="stability-guarantees"><a class="header" href="#stability-guarantees">Stability Guarantees</a></h2>
<p>This functionality is considered unstable as the <code>tracing</code> crate has not reached 1.0 yet. Future minor versions of the driver may upgrade the <code>tracing</code> dependency
to a new version which is not backwards-compatible with <code>Subscriber</code>s that depend on older versions of <code>tracing</code>.
Additionally, future minor releases may make changes such as:</p>
<ul>
<li>add or remove tracing events</li>
<li>add or remove values attached to tracing events</li>
<li>change the types and/or names of values attached to tracing events</li>
<li>add or remove driver-defined tracing spans</li>
<li>change the severity level of tracing events</li>
</ul>
<p>Such changes will be called out in release notes.</p>
<h2 id="event-targets"><a class="header" href="#event-targets">Event Targets</a></h2>
<p>Currently, events are emitted under the following targets:</p>
<div class="table-wrapper"><table><thead><tr><th>Target</th><th>Description</th></tr></thead><tbody>
<tr><td><code>mongodb::command</code></td><td>Events describing commands sent to the database and their success or failure.</td></tr>
<tr><td><code>mongodb::server_selection</code></td><td>Events describing the driver's process of selecting a server in the database deployment to send a command to.</td></tr>
<tr><td><code>mongodb::connection</code></td><td>Events describing the behavior of driver connection pools and the connections they contain.</td></tr>
</tbody></table>
</div>
<h2 id="consuming-events"><a class="header" href="#consuming-events">Consuming Events</a></h2>
<p>To consume events in your application, in addition to enabling the <code>tracing-unstable</code> feature flag, you must either register a <code>tracing</code>-compatible subscriber or a <code>log</code>-compatible logger, as detailed in the following sections.</p>
<h3 id="consuming-events-with-tracing"><a class="header" href="#consuming-events-with-tracing">Consuming Events with <code>tracing</code></a></h3>
<p>To consume events with <code>tracing</code>, you will need to register a type implementing the <code>tracing::Subscriber</code> trait in your application, as <a href="https://docs.rs/tracing/latest/tracing/#in-executables">discussed in the <code>tracing</code> docs</a>.</p>
<p>Here's a minimal example of a program using the driver which uses a tracing subscriber.</p>
<p>First, add the following to <code>Cargo.toml</code>:</p>
<pre><code class="language-toml no_run">tracing = "LATEST_VERSION_HERE"
tracing-subscriber = "LATEST_VERSION_HERE"
mongodb = { version = "LATEST_VERSION_HERE", features = ["tracing-unstable"] }
</code></pre>
<p>And then in <code>main.rs</code>:</p>
<pre><pre class="playground"><code class="language-rust no_run edition2021"><span class="boring">extern crate mongodb;
</span><span class="boring">extern crate tokio;
</span><span class="boring">extern crate tracing_subscriber;
</span><span class="boring">use std::env;
</span>use mongodb::{bson::doc, error::Result, Client};
#[tokio::main]
async fn main() -> Result<()> {
// Register a global tracing subscriber which will obey the RUST_LOG environment variable
// config.
tracing_subscriber::fmt::init();
// Create a MongoDB client.
let mongodb_uri =
env::var("MONGODB_URI").expect("The MONGODB_URI environment variable was not set.");
let client = Client::with_uri_str(mongodb_uri).await?;
// Insert a document.
let coll = client.database("test").collection("test_coll");
coll.insert_one(doc! { "x" : 1 }, None).await?;
Ok(())
}</code></pre></pre>
<p>This program can be run from the command line as follows, using the <a href="https://docs.rs/tracing-subscriber/0.3.16/tracing_subscriber/fmt/index.html#filtering-events-with-environment-variables"><code>RUST_LOG</code></a> environment variable to configure verbosity levels and observe command-related events with severity debug or higher:</p>
<pre><code class="language-sh no_run">RUST_LOG='mongodb::command=debug' MONGODB_URI='YOUR_URI_HERE' cargo run
</code></pre>
<p>The output will look something like the following:</p>
<pre><code class="language-text">2023-02-03T19:20:16.091822Z DEBUG mongodb::command: Command started topologyId="63dd5e706af9908fc834fd94" command="{\"insert\":\"test_coll\",\"ordered\":true,\"$db\":\"test\",\"lsid\":{\"id\":{\"$binary\":{\"base64\":\"y/v7PiLaRwOhT0RBFRDtNw==\",\"subType\":\"04\"}}},\"documents\":[{\"_id\":{\"$oid\":\"63dd5e706af9908fc834fd95\"},\"x\":1}]}" databaseName="test" commandName="insert" requestId=4 driverConnectionId=1 serverConnectionId=16 serverHost="localhost" serverPort=27017
2023-02-03T19:20:16.092700Z DEBUG mongodb::command: Command succeeded topologyId="63dd5e706af9908fc834fd94" reply="{\"n\":1,\"ok\":1.0}" commandName="insert" requestId=4 driverConnectionId=1 serverConnectionId=16 serverHost="localhost" serverPort=27017 durationMS=0
</code></pre>
<h3 id="consuming-events-with-log"><a class="header" href="#consuming-events-with-log">Consuming Events with <code>log</code></a></h3>
<p>Alternatively, to consume events with <code>log</code>, you will need to add <code>tracing</code> as a dependency of your application, and enable either its <code>log</code> or <code>log-always</code> feature.
Those features are described in detail <a href="https://docs.rs/tracing/latest/tracing/#log-compatibility">here</a>. </p>
<p>Here's a minimal example of a program using the driver which uses <a href="https://crates.io/crates/env_logger"><code>env_logger</code></a>.</p>
<p>In <code>Cargo.toml</code>:</p>
<pre><code class="language-toml no_run">tracing = { version = "LATEST_VERSION_HERE", features = ["log"] }
mongodb = { version = "LATEST_VERSION_HERE", features = ["tracing-unstable"] }
env_logger = "LATEST_VERSION_HERE"
</code></pre>
<p>And in <code>main.rs</code>:</p>
<pre><pre class="playground"><code class="language-rust no_run edition2021"><span class="boring">extern crate mongodb;
</span><span class="boring">extern crate tokio;
</span><span class="boring">extern crate env_logger;
</span>use std::env;
use mongodb::{bson::doc, error::Result, Client};
#[tokio::main]
async fn main() -> Result<()> {
// Register a global logger.
env_logger::init();
// Create a MongoDB client.
let mongodb_uri =
env::var("MONGODB_URI").expect("The MONGODB_URI environment variable was not set.");
let client = Client::with_uri_str(mongodb_uri).await?;
// Insert a document.
let coll = client.database("test").collection("test_coll");
coll.insert_one(doc! { "x" : 1 }, None).await?;
Ok(())
}</code></pre></pre>
<p>This program can be run from the command line as follows, using the <a href="https://docs.rs/env_logger/latest/env_logger/#enabling-logging"><code>RUST_LOG</code></a> environment variable to configure verbosity levels and observe command-related messages with severity debug or higher:</p>
<pre><code class="language-sh no_run">RUST_LOG='mongodb::command=debug' MONGODB_URI='YOUR_URI_HERE' cargo run
</code></pre>
<p>The output will look something like the following:</p>
<pre><code class="language-text">2023-02-03T19:20:16.091822Z DEBUG mongodb::command: Command started topologyId="63dd5e706af9908fc834fd94" command="{\"insert\":\"test_coll\",\"ordered\":true,\"$db\":\"test\",\"lsid\":{\"id\":{\"$binary\":{\"base64\":\"y/v7PiLaRwOhT0RBFRDtNw==\",\"subType\":\"04\"}}},\"documents\":[{\"_id\":{\"$oid\":\"63dd5e706af9908fc834fd95\"},\"x\":1}]}" databaseName="test" commandName="insert" requestId=4 driverConnectionId=1 serverConnectionId=16 serverHost="localhost" serverPort=27017
2023-02-03T19:20:16.092700Z DEBUG mongodb::command: Command succeeded topologyId="63dd5e706af9908fc834fd94" reply="{\"n\":1,\"ok\":1.0}" commandName="insert" requestId=4 driverConnectionId=1 serverConnectionId=16 serverHost="localhost" serverPort=27017 durationMS=0
</code></pre>
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