Clear dead feeds from the Directory once a day, not before every scan (#193)

stale_unsubscribed takes the newest item of every unsubscribed feed, 2-5 s
warm and up to 12 s in production, and reap ran it before each scan, every
few minutes, holding up the sequential worker's scans and downloads. Its
thresholds are a month dead and a year quiet, so a day is plenty. Kept in
memory: a restart looks again at once.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.rs

@@ -156,6 +156,9 @@ pub struct Ctx {
     /// Wakes DeadAir's maker when a show is turned on, so its copies start at once instead of
     /// at the next pass (#171).
     pub deadair: tokio::sync::Notify,
+    /// When the Directory was last cleared of dead feeds (`clean_directory`), 0 for not since
+    /// starting.
+    pub directory_cleaned: std::sync::atomic::AtomicI64,
 }
 
 /// A copy of the config to change, holding off every other change until `store_cfg` keeps it.
@@ -348,6 +351,7 @@ async fn main() -> Result<()> {
         detach_torrents: is_daemon,
         retry: Default::default(),
         cfg_write: Default::default(),
+        directory_cleaned: Default::default(),
         deadair: Default::default(),
     });
 
@@ -1118,6 +1122,13 @@ async fn clean_directory(ctx: &Ctx) -> Result<()> {
     const DEAD: i64 = 30 * 86_400;
     const QUIET: i64 = 365 * 86_400;
     let now = db::now();
+    // Once a day, for feeds dead a month or quiet a year: before every scan, its query took 1 to
+    // 12 s every few minutes, and the scans and downloads waited behind it (#193).
+    use std::sync::atomic::Ordering::Relaxed;
+    if now - ctx.directory_cleaned.load(Relaxed) < 86_400 {
+        return Ok(());
+    }
+    ctx.directory_cleaned.store(now, Relaxed);
     let stale = ctx.db.stale_unsubscribed(now - DEAD, now - QUIET).await?;
     if stale.is_empty() {
         return Ok(());
@@ -2467,9 +2478,26 @@ mod tests {
             retry: Default::default(),
             cfg_write: Default::default(),
             deadair: Default::default(),
+            directory_cleaned: Default::default(),
         }
     }
 
+    #[tokio::test]
+    async fn dead_feeds_leave_the_directory_once_a_day_not_before_every_scan() {
+        let ctx = test_ctx(config::Config::default()).await;
+        let dead = |id: &str| format!("INSERT INTO feeds (id, url, error_since, managed) VALUES ('{id}', 'u-{id}', 100, false)");
+        let listed = async || ctx.db.feed_urls().await.unwrap().into_iter().map(|(id, _)| id).collect::<Vec<_>>();
+        ctx.db.sql(&dead("a")).await.unwrap();
+        clean_directory(&ctx).await.unwrap();
+        assert!(listed().await.is_empty(), "the first pass since starting looks");
+        ctx.db.sql(&dead("b")).await.unwrap();
+        clean_directory(&ctx).await.unwrap();
+        assert_eq!(listed().await, ["b"], "not again the same day (#193)");
+        ctx.directory_cleaned.store(db::now() - 86_401, std::sync::atomic::Ordering::Relaxed);
+        clean_directory(&ctx).await.unwrap();
+        assert!(listed().await.is_empty(), "a day on, it looks again");
+    }
+
     #[tokio::test]
     async fn a_removed_account_takes_the_feeds_only_it_read_with_it() {
         let ctx = test_ctx(config::Config::default()).await;