Improve persistence logic

Cargo.lock

@@ -1067,6 +1067,7 @@ dependencies = [
  "operational-transform",
  "parking_lot",
  "pretty_env_logger",
+ "rand 0.8.3",
  "serde",
  "serde_json",
  "sqlx",

rustpad-server/Cargo.toml

@@ -20,6 +20,7 @@ sqlx = { version = "0.5.9", features = ["runtime-tokio-rustls", "sqlite"] }
 tokio = { version = "1.6.1", features = ["full", "test-util"] }
 tokio-stream = "0.1.6"
 warp = "0.3.1"
+rand = "0.8"
 
 [dev-dependencies]
 tempfile = "3.2.0"

rustpad-server/src/lib.rs

@@ -8,6 +8,7 @@ use std::time::{Duration, SystemTime};
 
 use dashmap::DashMap;
 use log::{error, info};
+use rand::Rng;
 use serde::Serialize;
 use tokio::time::{self, Instant};
 use warp::{filters::BoxedFilter, ws::Ws, Filter, Rejection, Reply};
@@ -208,19 +209,25 @@ async fn cleaner(state: ServerState, expiry_days: u32) {
 }
 
 const PERSIST_INTERVAL: Duration = Duration::from_secs(3);
+const PERSIST_INTERVAL_JITTER: Duration = Duration::from_secs(1);
 
 /// Persists changed documents after a fixed time interval.
 async fn persister(id: String, rustpad: Arc<Rustpad>, db: Database) {
     let mut last_revision = 0;
     while !rustpad.killed() {
-        time::sleep(PERSIST_INTERVAL).await;
+        let interval = PERSIST_INTERVAL
+            + Duration::from_millis(
+                rand::thread_rng().gen_range(0..=PERSIST_INTERVAL_JITTER.as_millis() as u64),
+            );
+        time::sleep(interval).await;
         let revision = rustpad.revision();
         if revision > last_revision {
             info!("persisting revision {} for id = {}", revision, id);
             if let Err(e) = db.store(&id, &rustpad.snapshot()).await {
                 error!("when persisting document {}: {}", id, e);
+            } else {
+                last_revision = revision;
             }
-            last_revision = revision;
         }
     }
 }