v2.1: Refactors get_snapshot_storages() (backport of #3760)

accounts-db/src/account_storage.rs

@@ -200,6 +200,29 @@ impl AccountStorage {
     pub(crate) fn len(&self) -> usize {
         self.map.len()
     }
+
+    /// Returns the (slot, storage) tuples where `predicate` returns `true`
+    ///
+    /// This function is useful when not all storages are desired,
+    /// as storages are only Arc::cloned if they pass the predicate.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `shrink` is in progress.
+    pub fn get_if(
+        &self,
+        predicate: impl Fn(&Slot, &AccountStorageEntry) -> bool,
+    ) -> Box<[(Slot, Arc<AccountStorageEntry>)]> {
+        assert!(self.no_shrink_in_progress());
+        self.map
+            .iter()
+            .filter_map(|entry| {
+                let slot = entry.key();
+                let storage = &entry.value().storage;
+                predicate(slot, storage).then(|| (*slot, Arc::clone(storage)))
+            })
+            .collect()
+    }
 }
 
 /// iterate contents of AccountStorage without exposing internals
@@ -291,7 +314,11 @@ impl Default for AccountStorageStatus {
 
 #[cfg(test)]
 pub(crate) mod tests {
-    use {super::*, crate::accounts_file::AccountsFileProvider, std::path::Path};
+    use {
+        super::*,
+        crate::accounts_file::AccountsFileProvider,
+        std::{iter, path::Path},
+    };
 
     #[test]
     fn test_shrink_in_progress() {
@@ -568,4 +595,52 @@ pub(crate) mod tests {
             .is_none());
         assert!(storage.get_account_storage_entry(slot, id).is_some());
     }
+
+    #[test]
+    fn test_get_if() {
+        let storage = AccountStorage::default();
+        assert!(storage.get_if(|_, _| true).is_empty());
+
+        // add some entries
+        let ids = [123, 456, 789];
+        for id in ids {
+            let slot = id as Slot;
+            let entry = AccountStorageEntry::new(
+                Path::new(""),
+                slot,
+                id,
+                5000,
+                AccountsFileProvider::AppendVec,
+            );
+            storage.map.insert(
+                slot,
+                AccountStorageReference {
+                    id,
+                    storage: entry.into(),
+                },
+            );
+        }
+
+        // look 'em up
+        for id in ids {
+            let found = storage.get_if(|slot, _| *slot == id as Slot);
+            assert!(found
+                .iter()
+                .map(|(slot, _)| *slot)
+                .eq(iter::once(id as Slot)));
+        }
+
+        assert!(storage.get_if(|_, _| false).is_empty());
+        assert_eq!(storage.get_if(|_, _| true).len(), ids.len());
+    }
+
+    #[test]
+    #[should_panic(expected = "self.no_shrink_in_progress()")]
+    fn test_get_if_fail() {
+        let storage = AccountStorage::default();
+        storage
+            .shrink_in_progress_map
+            .insert(0, storage.get_test_storage());
+        storage.get_if(|_, _| true);
+    }
 }

accounts-db/src/accounts_db.rs

@@ -8278,44 +8278,27 @@ impl AccountsDb {
         &self,
         requested_slots: impl RangeBounds<Slot> + Sync,
     ) -> (Vec<Arc<AccountStorageEntry>>, Vec<Slot>) {
-        let mut m = Measure::start("get slots");
-        let mut slots_and_storages = self
+        let start = Instant::now();
+        let max_alive_root_exclusive = self
+            .accounts_index
+            .roots_tracker
+            .read()
+            .unwrap()
+            .alive_roots
+            .max_exclusive();
+        let (slots, storages) = self
             .storage
-            .iter()
-            .filter_map(|(slot, store)| {
-                requested_slots
-                    .contains(&slot)
-                    .then_some((slot, Some(store)))
+            .get_if(|slot, storage| {
+                (*slot < max_alive_root_exclusive)
+                    && requested_slots.contains(slot)
+                    && storage.has_accounts()
             })
-            .collect::<Vec<_>>();
-        m.stop();
-        let mut m2 = Measure::start("filter");
-        let chunk_size = 5_000;
-        let (result, slots): (Vec<_>, Vec<_>) = self.thread_pool_clean.install(|| {
-            slots_and_storages
-                .par_chunks_mut(chunk_size)
-                .map(|slots_and_storages| {
-                    slots_and_storages
-                        .iter_mut()
-                        .filter(|(slot, _)| self.accounts_index.is_alive_root(*slot))
-                        .filter_map(|(slot, store)| {
-                            let store = std::mem::take(store).unwrap();
-                            store.has_accounts().then_some((store, *slot))
-                        })
-                        .collect::<Vec<(Arc<AccountStorageEntry>, Slot)>>()
-                })
-                .flatten()
-                .unzip()
-        });
-
-        m2.stop();
-
-        debug!(
-            "hash_total: get slots: {}, filter: {}",
-            m.as_us(),
-            m2.as_us(),
-        );
-        (result, slots)
+            .into_vec()
+            .into_iter()
+            .unzip();
+        let duration = start.elapsed();
+        debug!("get_snapshot_storages: {duration:?}");
+        (storages, slots)
     }
 
     /// Returns the latest full snapshot slot