fix(SweepObjects): dedup backend checking

To prevent same backend from being checked multiple times

zstor/src/actors/repairer.rs

@@ -1,10 +1,14 @@
-use crate::actors::{
-    backends::{BackendManagerActor, RequestBackends, StateInterest},
-    meta::{MetaStoreActor, ObjectMetas},
-    zstor::{Rebuild, ZstorActor},
+use crate::{
+    actors::{
+        backends::{BackendManagerActor, RequestBackends, StateInterest},
+        meta::{MetaStoreActor, ObjectMetas},
+        zstor::{Rebuild, ZstorActor},
+    },
+    zdb::ZdbConnectionInfo,
 };
 use actix::prelude::*;
-use log::{error, warn};
+use log::{debug, error, warn};
+use std::collections::HashSet;
 use std::time::Duration;
 
 /// Amount of time between starting a new sweep of the backend objects.
@@ -79,13 +83,21 @@ impl Handler<SweepObjects> for RepairActor {
                 },
             };
 
+            // prevent same backend from being checked multiple times
+            let mut unique_zdbs = HashSet::new();
             for (key, metadata) in obj_metas.into_iter() {
-                let backend_requests = metadata
+                let backend_requests: Vec<ZdbConnectionInfo> = metadata
                     .shards()
                     .iter()
-                    .map(|shard_info| shard_info.zdb())
-                    .cloned()
-                    .collect::<Vec<_>>();
+                    .map(|shard_info| shard_info.zdb().clone())
+                    .filter(|zdb| unique_zdbs.insert(zdb.clone()))
+                    .collect();
+                if backend_requests.is_empty() {
+                    debug!("No unchecked backends found for object: {}", key);
+                    continue;
+                }
+                debug!("number of backends to check = {}", backend_requests.len());
+
                 let backends = match backend_manager
                     .send(RequestBackends {
                         backend_requests,