Implement opportunistic sync based on watch value, and use it

src/bayou.rs

@@ -19,12 +19,12 @@ use crate::k2v_util::k2v_wait_value_changed;
 use crate::login::Credentials;
 use crate::time::now_msec;
 
-const SAVE_STATE_EVERY: usize = 64;
+const KEEP_STATE_EVERY: usize = 64;
 
 // Checkpointing interval constants: a checkpoint is not made earlier
 // than CHECKPOINT_INTERVAL time after the last one, and is not made
 // if there are less than CHECKPOINT_MIN_OPS new operations since last one.
-const CHECKPOINT_INTERVAL: Duration = Duration::from_secs(3600);
+const CHECKPOINT_INTERVAL: Duration = Duration::from_secs(6 * 3600);
 const CHECKPOINT_MIN_OPS: usize = 16;
 // HYPOTHESIS: processes are able to communicate in a synchronous
 // fashion in times that are small compared to CHECKPOINT_INTERVAL.
@@ -89,6 +89,9 @@ impl<S: BayouState> Bayou<S> {
 
     /// Re-reads the state from persistent storage backend
     pub async fn sync(&mut self) -> Result<()> {
+        let new_last_sync = Some(Instant::now());
+        let new_last_sync_watch_ct = self.watch.rx.borrow().clone();
+
         // 1. List checkpoints
         let checkpoints = self.list_checkpoints().await?;
         debug!("(sync) listed checkpoints: {:?}", checkpoints);
@@ -225,7 +228,7 @@ impl<S: BayouState> Bayou<S> {
             // Now, apply all operations retrieved from storage after the common part
             for (ts, op) in ops.drain(i0..) {
                 state = state.apply(&op);
-                if (self.history.len() + 1) % SAVE_STATE_EVERY == 0 {
+                if (self.history.len() + 1) % KEEP_STATE_EVERY == 0 {
                     self.history.push((ts, op, Some(state.clone())));
                 } else {
                     self.history.push((ts, op, None));
@@ -236,22 +239,32 @@ impl<S: BayouState> Bayou<S> {
             self.history.last_mut().unwrap().2 = Some(state);
         }
 
-        self.last_sync = Some(Instant::now());
+        // Save info that sync has been done
+        self.last_sync = new_last_sync;
+        self.last_sync_watch_ct = new_last_sync_watch_ct;
         Ok(())
     }
 
-    async fn check_recent_sync(&mut self) -> Result<()> {
+    /// Does a sync() if either of the two conditions is met:
-        match self.last_sync {
+    /// - last sync was more than CHECKPOINT_INTERVAL/5 ago
-            Some(t) if (Instant::now() - t) < CHECKPOINT_INTERVAL / 10 => Ok(()),
+    /// - a change was detected
-            _ => self.sync().await,
+    pub async fn opportunistic_sync(&mut self) -> Result<()> {
+        let too_old = match self.last_sync {
+            Some(t) => Instant::now() > t + (CHECKPOINT_INTERVAL / 5),
+            _ => true,
+        };
+        let changed = self.last_sync_watch_ct != *self.watch.rx.borrow();
+        if too_old || changed {
+            self.sync().await?;
         }
+        Ok(())
     }
 
     /// Applies a new operation on the state. Once this function returns,
-    /// the option has been safely persisted to storage backend
+    /// the operation has been safely persisted to storage backend.
+    /// Make sure to call `.opportunistic_sync()` before doing this,
+    /// and even before calculating the `op` argument given here.
     pub async fn push(&mut self, op: S::Op) -> Result<()> {
-        self.check_recent_sync().await?;
-
         debug!("(push) add operation: {:?}", op);
 
         let ts = Timestamp::after(
@@ -276,7 +289,7 @@ impl<S: BayouState> Bayou<S> {
 
         // Clear previously saved state in history if not required
         let hlen = self.history.len();
-        if hlen >= 2 && (hlen - 1) % SAVE_STATE_EVERY != 0 {
+        if hlen >= 2 && (hlen - 1) % KEEP_STATE_EVERY != 0 {
             self.history[hlen - 2].2 = None;
         }
 
@@ -288,7 +301,7 @@ impl<S: BayouState> Bayou<S> {
     /// Save a new checkpoint if previous checkpoint is too old
     pub async fn checkpoint(&mut self) -> Result<()> {
         match self.last_try_checkpoint {
-            Some(ts) if Instant::now() - ts < CHECKPOINT_INTERVAL / 10 => Ok(()),
+            Some(ts) if Instant::now() - ts < CHECKPOINT_INTERVAL / 5 => Ok(()),
             _ => {
                 let res = self.checkpoint_internal().await;
                 if res.is_ok() {
@@ -300,7 +313,7 @@ impl<S: BayouState> Bayou<S> {
     }
 
     async fn checkpoint_internal(&mut self) -> Result<()> {
-        self.check_recent_sync().await?;
+        self.sync().await?;
 
         // Check what would be the possible time for a checkpoint in the history we have
         let now = now_msec() as i128;

src/imap/command/examined.rs

@@ -87,7 +87,9 @@ impl<'a> ExaminedContext<'a> {
     }
 
     pub async fn noop(self) -> Result<(Response, flow::Transition)> {
-        let updates = self.mailbox.sync_update().await?;
+        self.mailbox.mailbox.force_sync().await?;
+
+        let updates = self.mailbox.update().await?;
         Ok((
             Response::ok("NOOP completed.")?.with_body(updates),
             flow::Transition::None,

src/imap/mailbox_view.rs

@@ -68,16 +68,10 @@ impl MailboxView {
         Ok((new_view, data))
     }
 
-    /// Looks up state changes in the mailbox and produces a set of IMAP
-    /// responses describing the changes.
-    pub async fn sync_update(&mut self) -> Result<Vec<Body>> {
-        self.mailbox.sync().await?;
-
-        self.update().await
-    }
-
     /// Produces a set of IMAP responses describing the change between
     /// what the client knows and what is actually in the mailbox.
+    /// This does NOT trigger a sync, it bases itself on what is currently
+    /// loaded in RAM by Bayou.
     pub async fn update(&mut self) -> Result<Vec<Body>> {
         let new_view = MailboxView {
             mailbox: self.mailbox.clone(),
@@ -156,6 +150,8 @@ impl MailboxView {
         flags: &[Flag],
         uid: &bool,
     ) -> Result<Vec<Body>> {
+        self.mailbox.opportunistic_sync().await?;
+
         if *uid {
             bail!("UID STORE not implemented");
         }
@@ -181,9 +177,11 @@ impl MailboxView {
     }
 
     pub async fn expunge(&mut self) -> Result<Vec<Body>> {
+        self.mailbox.opportunistic_sync().await?;
+
         let deleted_flag = Flag::Deleted.to_string();
-        let msgs = self
+        let state = self.mailbox.current_uid_index().await;
-            .known_state
+        let msgs = state
             .table
             .iter()
             .filter(|(_uuid, (_uid, flags))| flags.iter().any(|x| *x == deleted_flag))

src/mail/mailbox.rs

@@ -60,8 +60,14 @@ impl Mailbox {
     }
 
     /// Sync data with backing store
-    pub async fn sync(&self) -> Result<()> {
+    pub async fn force_sync(&self) -> Result<()> {
-        self.mbox.write().await.sync().await
+        self.mbox.write().await.force_sync().await
+    }
+
+    /// Sync data with backing store only if changes are detected
+    /// or last sync is too old
+    pub async fn opportunistic_sync(&self) -> Result<()> {
+        self.mbox.write().await.opportunistic_sync().await
     }
 
     // ---- Functions for reading the mailbox ----
@@ -184,11 +190,16 @@ struct MailboxInternal {
 }
 
 impl MailboxInternal {
-    async fn sync(&mut self) -> Result<()> {
+    async fn force_sync(&mut self) -> Result<()> {
         self.uid_index.sync().await?;
         Ok(())
     }
 
+    async fn opportunistic_sync(&mut self) -> Result<()> {
+        self.uid_index.opportunistic_sync().await?;
+        Ok(())
+    }
+
     // ---- Functions for reading the mailbox ----
 
     async fn fetch_meta(&self, ids: &[UniqueIdent]) -> Result<Vec<MailMeta>> {
@@ -308,7 +319,8 @@ impl MailboxInternal {
                     .insert_item(&self.mail_path, &ident.to_string(), meta_blob, None)
                     .await?;
                 Ok::<_, anyhow::Error>(())
-            }
+            },
+            self.uid_index.opportunistic_sync()
         )?;
 
         // Add mail to Bayou mail index
@@ -357,7 +369,8 @@ impl MailboxInternal {
                     .insert_item(&self.mail_path, &ident.to_string(), meta_blob, None)
                     .await?;
                 Ok::<_, anyhow::Error>(())
-            }
+            },
+            self.uid_index.opportunistic_sync()
         )?;
 
         // Add mail to Bayou mail index
@@ -449,6 +462,7 @@ impl MailboxInternal {
                     .await?;
                 Ok::<_, anyhow::Error>(())
             },
+            self.uid_index.opportunistic_sync(),
         )?;
 
         // Add mail to Bayou mail index