feat: Parallelize loading snapshots from storage (#25657)

influxdb3_write/src/persister.rs

@@ -32,6 +32,7 @@ use std::any::Any;
 use std::io::Write;
 use std::sync::Arc;
 use thiserror::Error;
+use tokio::task::JoinSet;
 use uuid::Uuid;
 
 #[derive(Debug, Error)]
@@ -187,7 +188,7 @@ impl Persister {
     ///
     /// This is intended to be used on server start.
     pub async fn load_snapshots(&self, mut most_recent_n: usize) -> Result<Vec<PersistedSnapshot>> {
-        let mut output = Vec::new();
+        let mut join_set = JoinSet::new();
         let mut offset: Option<ObjPath> = None;
         while most_recent_n > 0 {
             let count = if most_recent_n > 1000 {
@@ -228,9 +229,19 @@ impl Persister {
             let len = list.len();
             let end = if len <= count { len } else { count };
 
+            async fn get_snapshot(
+                location: ObjPath,
+                object_store: Arc<dyn ObjectStore>,
+            ) -> Result<PersistedSnapshot> {
+                let bytes = object_store.get(&location).await?.bytes().await?;
+                serde_json::from_slice(&bytes).map_err(Into::into)
+            }
+
             for item in &list[0..end] {
-                let bytes = self.object_store.get(&item.location).await?.bytes().await?;
-                output.push(serde_json::from_slice(&bytes)?);
+                join_set.spawn(get_snapshot(
+                    item.location.clone(),
+                    Arc::clone(&self.object_store),
+                ));
             }
 
             if end == 0 {
@@ -243,7 +254,8 @@ impl Persister {
             offset = Some(list[end - 1].location.clone());
         }
 
-        Ok(output)
+        // Returns an error if there is one and reuses the Vec's memory as well
+        join_set.join_all().await.into_iter().collect()
     }
 
     /// Loads a Parquet file from ObjectStore