Include some entropy when choosing the storage bucket for a file (#7048)

open-chat-labs · Dec 12, 2024 · 5e27262 · 5e27262
1 parent af9a4fc
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Showing 3 changed files with 7 additions and 5 deletions.
diff --git a/backend/canisters/storage_index/CHANGELOG.md b/backend/canisters/storage_index/CHANGELOG.md
@@ -11,6 +11,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Update the canister creation fee to 0.5T ([#6700](https://github.com/open-chat-labs/open-chat/pull/6700))
 - Expose size of each virtual stable memory in metrics ([#6981](https://github.com/open-chat-labs/open-chat/pull/6981))
 - Use `GroupedTimerJobQueue` to sync events to storage buckets ([#7045](https://github.com/open-chat-labs/open-chat/pull/7045))
+- Include some entropy when choosing the storage bucket for a file ([#7048](https://github.com/open-chat-labs/open-chat/pull/7048))
 
 ## [[2.0.1419](https://github.com/open-chat-labs/open-chat/releases/tag/v2.0.1419-storage_index)] - 2024-10-28
 

diff --git a/backend/canisters/storage_index/impl/src/model/buckets.rs b/backend/canisters/storage_index/impl/src/model/buckets.rs
@@ -49,12 +49,14 @@ impl Buckets {
         }
     }
 
-    pub fn allocate(&self, blob_hash: Hash) -> Option<CanisterId> {
+    pub fn allocate(&self, blob_hash: Hash, entropy: u64) -> Option<CanisterId> {
         let bucket_count = self.active_buckets.len();
         if bucket_count == 0 {
             None
         } else {
-            let usize_from_hash = u64::from_le_bytes(blob_hash[..8].try_into().unwrap()) as usize;
+            let mut bucket_allocation_hash = blob_hash;
+            bucket_allocation_hash.rotate_left((entropy % 32) as usize);
+            let usize_from_hash = u64::from_le_bytes(bucket_allocation_hash[..8].try_into().unwrap()) as usize;
 
             // Use a modified modulo of the hash to slightly favour the first bucket
             // so that they don't all run out of space at the same time

diff --git a/backend/canisters/storage_index/impl/src/queries/allocated_bucket.rs b/backend/canisters/storage_index/impl/src/queries/allocated_bucket.rs
@@ -33,15 +33,14 @@ fn allocated_bucket_impl(args: Args, state: &RuntimeState) -> Response {
             });
         }
 
+        let now = state.env.now();
         let bucket = state
             .data
             .files
             .bucket_for_blob(args.file_hash)
-            .or_else(|| state.data.buckets.allocate(args.file_hash));
+            .or_else(|| state.data.buckets.allocate(args.file_hash, now));
 
         if let Some(canister_id) = bucket {
-            let now = state.env.now();
-
             Success(SuccessResult {
                 canister_id,
                 file_id: generate_file_id(