web: add metrics for the rustdoc rendering times

Author: pietroalbini

src/web/metrics.rs

@@ -72,6 +72,13 @@ lazy_static::lazy_static! {
     )
     .unwrap();
 
+    pub static ref RUSTDOC_RENDERING_TIMES: HistogramVec = register_histogram_vec!(
+        "docsrs_rustdoc_rendering_time",
+        "The time it takes to render a rustdoc page",
+        &["step"]
+    )
+    .unwrap();
+
     pub static ref FAILED_DB_CONNECTIONS: IntCounter = register_int_counter!(
         "docsrs_failed_db_connections",
         "Number of attempted and failed connections to the database"
@@ -197,6 +204,47 @@ impl iron::Handler for RequestRecorder {
     }
 }
 
+struct RenderingTime {
+    start: Instant,
+    step: &'static str,
+}
+
+pub(crate) struct RenderingTimesRecorder {
+    metric: &'static HistogramVec,
+    current: Option<RenderingTime>,
+}
+
+impl RenderingTimesRecorder {
+    pub(crate) fn new(metric: &'static HistogramVec) -> Self {
+        Self {
+            metric,
+            current: None,
+        }
+    }
+
+    pub(crate) fn step(&mut self, step: &'static str) {
+        self.record_current();
+        self.current = Some(RenderingTime {
+            start: Instant::now(),
+            step,
+        });
+    }
+
+    fn record_current(&mut self) {
+        if let Some(current) = self.current.take() {
+            self.metric
+                .with_label_values(&[current.step])
+                .observe(duration_to_seconds(current.start.elapsed()));
+        }
+    }
+}
+
+impl Drop for RenderingTimesRecorder {
+    fn drop(&mut self) {
+        self.record_current();
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::test::{assert_success, wrapper};

src/web/rustdoc.rs

@@ -3,6 +3,7 @@
 use super::crate_details::CrateDetails;
 use super::error::Nope;
 use super::file::File;
+use super::metrics;
 use super::page::Page;
 use super::pool::Pool;
 use super::redirect_base;
@@ -215,6 +216,9 @@ pub fn rustdoc_redirector_handler(req: &mut Request) -> IronResult<Response> {
 /// This includes all HTML files for an individual crate, as well as the `search-index.js`, which is
 /// also crate-specific.
 pub fn rustdoc_html_server_handler(req: &mut Request) -> IronResult<Response> {
+    let mut rendering_time =
+        metrics::RenderingTimesRecorder::new(&metrics::RUSTDOC_RENDERING_TIMES);
+
     // Get the request parameters
     let router = extension!(req, Router);
 
@@ -246,6 +250,8 @@ pub fn rustdoc_html_server_handler(req: &mut Request) -> IronResult<Response> {
         Ok(super::redirect(url))
     };
 
+    rendering_time.step("match version");
+
     // Check the database for releases with the requested version while doing the following:
     // * If both the name and the version are an exact match, return the version of the crate.
     // * If there is an exact match, but the requested crate name was corrected (dashes vs. underscores), redirect to the corrected name.
@@ -275,6 +281,8 @@ pub fn rustdoc_html_server_handler(req: &mut Request) -> IronResult<Response> {
         return Err(IronError::new(Nope::ResourceNotFound, status::NotFound));
     };
 
+    rendering_time.step("crate details");
+
     // Get the crate's details from the database
     let crate_details = cexpect!(CrateDetails::new(&conn, &name, &version));
 
@@ -284,6 +292,8 @@ pub fn rustdoc_html_server_handler(req: &mut Request) -> IronResult<Response> {
         return redirect(&name, &version, &req_path[1..]);
     }
 
+    rendering_time.step("fetch from storage");
+
     // Add rustdoc prefix, name and version to the path for accessing the file stored in the database
     req_path.insert(0, "rustdoc");
     req_path.insert(1, &name);
@@ -311,9 +321,12 @@ pub fn rustdoc_html_server_handler(req: &mut Request) -> IronResult<Response> {
 
     // Serve non-html files directly
     if !path.ends_with(".html") {
+        rendering_time.step("serve asset");
         return Ok(file.serve());
     }
 
+    rendering_time.step("parse html");
+
     let file_content = ctry!(String::from_utf8(file.0.content));
     // Extract the head and body of the rustdoc file so that we can insert it into our own html
     let (head, body, mut body_class) = ctry!(utils::extract_head_and_body(&file_content));
@@ -326,6 +339,8 @@ pub fn rustdoc_html_server_handler(req: &mut Request) -> IronResult<Response> {
         body_class.push_str(" container-rustdoc");
     }
 
+    rendering_time.step("serve html");
+
     let latest_release = crate_details.latest_release();
 
     // Get the latest version of the crate