Move tasks over to rayon thread pool + adjust db connection pool

The rayon threadpool alone was not enough to solve perf problems with
offloading these tasks. I had thought it was related to queuing or too
much parallelism and it (kinda) was but really it was exhaustion of
the db connection pool (default 10) with a high timeout (30s).

These two adjustments combined now at least prevent the server from
going unresponsive when I hit it with 5000 rps. The server _before_
any offloading (just running all this on the Tokio runtime threads)
is still lower latency. It's probable that this "blocking/CPU work"
is just still so little the thread coordination overhead is higher
than the work at hand.

Cargo.toml

@@ -36,3 +36,4 @@ http = "0.2"
 toml = "0.5.10"
 tracing = "0.1.40"
 tracing-subscriber = { version = "0.3.18", features = ["env-filter", "tracing-log"] }
+tokio-rayon = "2.1.0"

src/handler.rs

@@ -30,7 +30,7 @@ pub trait WithDB {
     #[tracing::instrument(level = "debug", skip(self))]
     fn dbconn(&self) -> Result<PooledConnection<ConnectionManager<SqliteConnection>>, DBError> {
         self.dbpool().get().map_err(|e| {
-            error!("{:?}", e);
+            error!("error getting connection: {:?}", e);
             DBError::new()
         })
     }

src/handlers/fetch.rs

@@ -31,18 +31,18 @@ pub async fn get_post_handler(
     let slug_clone = url_slug.clone();
     let mut slug_conn = db.dbconn()?;
     let mut post: Post = 
-        tokio::task::spawn_blocking(move || {
+        tokio_rayon::spawn_fifo(move || {
             Post::by_slug(&slug_clone)
                 .first::<Post>(&mut slug_conn)
                 .map_err(|e| handle_db_errors(e))
         })
         .instrument(debug_span!("post_by_slug"))
-        .await.map_err(|e| Into::<ServerError>::into(e))??;
+        .await?;
 
     let post_id = post.id;
     let mut tags_conn = db.dbconn()?;
     let tags_fut =
-        tokio::task::spawn_blocking(move || {
+        tokio_rayon::spawn_fifo(move || {
             use crate::schema::categories::dsl as category_dsl;
              category_dsl::categories
                 .select(category_dsl::category)
@@ -53,7 +53,7 @@ pub async fn get_post_handler(
         .instrument(debug_span!("tags_by_post_id"));
 
     let photos_fut =
-        tokio::task::spawn_blocking(move || {
+        tokio_rayon::spawn_fifo(move || {
             use crate::schema::photos::dsl as photos_dsl;
             photos_dsl::photos
                 .select((photos_dsl::url, photos_dsl::alt))
@@ -64,8 +64,8 @@ pub async fn get_post_handler(
         .instrument(debug_span!("photos_by_post_id"));
 
     let (tags_result, photos_result)= join!(tags_fut, photos_fut);
-    let tags = tags_result.map_err(|e| Into::<ServerError>::into(e))??;
-    let photos = photos_result.map_err(|e| Into::<ServerError>::into(e))??;
+    let tags = tags_result?;
+    let photos = photos_result?;
 
     debug!("input datetime: {:?}", post.created_at);
     let datetime = post_util::get_local_datetime(&post.created_at, &site_config.micropub.current_timezone_offset).map_err(|e| {
@@ -77,11 +77,11 @@ pub async fn get_post_handler(
     post.created_at = datetime.to_rfc3339();
 
     let post_view =
-        tokio::task::spawn_blocking(move || {
+        tokio_rayon::spawn_fifo(move || {
             PostView::new_from(post, tags, DateView::from(&datetime), photos)
         })
         .instrument(debug_span!("create post view model"))
-        .await.map_err(|e| Into::<ServerError>::into(e))?;
+        .await;
 
     let _templates = debug_span!("template_render");
     _templates.in_scope(|| {

src/lib.rs

@@ -7,6 +7,8 @@ extern crate diesel;
 #[macro_use]
 extern crate serde_json;
 
+use std::time::Duration;
+
 use diesel::prelude::SqliteConnection;
 use diesel::r2d2;
 
@@ -29,5 +31,9 @@ pub fn new_dbconn_pool(
     db_file: &str,
 ) -> Result<r2d2::Pool<r2d2::ConnectionManager<SqliteConnection>>, anyhow::Error> {
     let manager = r2d2::ConnectionManager::<SqliteConnection>::new(db_file);
-    Ok(r2d2::Pool::new(manager)?)
+    let pool = r2d2::Builder::new()
+        .max_size(36)
+        .connection_timeout(Duration::new(5, 0))
+        .build(manager)?;
+    Ok(pool)
 }