avoid copies when writing to an ancient append vec (solana-labs#28981)

* avoid copies when writing to an ancient append vec

* update comments

runtime/src/accounts_db.rs

@@ -4352,7 +4352,7 @@ impl AccountsDb {
     /// returns the pubkeys that are in 'accounts' that are already in 'existing_ancient_pubkeys'
     /// Also updated 'existing_ancient_pubkeys' to include all pubkeys in 'accounts' since they will soon be written into the ancient slot.
     fn get_keys_to_unref_ancient<'a>(
-        accounts: &'a [&StoredAccountMeta<'_>],
+        accounts: &'a [&FoundStoredAccount<'_>],
         existing_ancient_pubkeys: &mut HashSet<Pubkey>,
     ) -> HashSet<&'a Pubkey> {
         let mut unref = HashSet::<&Pubkey>::default();
@@ -4374,7 +4374,7 @@ impl AccountsDb {
     /// As a side effect, on exit, 'existing_ancient_pubkeys' will now contain all pubkeys in 'accounts'.
     fn unref_accounts_already_in_storage(
         &self,
-        accounts: &[&StoredAccountMeta<'_>],
+        accounts: &[&FoundStoredAccount<'_>],
         existing_ancient_pubkeys: &mut HashSet<Pubkey>,
     ) {
         let unref = Self::get_keys_to_unref_ancient(accounts, existing_ancient_pubkeys);
@@ -10106,8 +10106,25 @@ pub mod tests {
             stored_size,
             hash: &hash,
         };
+        let store_id = 0;
+        let found_account = FoundStoredAccount {
+            account: stored_account,
+            store_id,
+        };
+        let found_account2 = FoundStoredAccount {
+            account: stored_account2,
+            store_id,
+        };
+        let found_account3 = FoundStoredAccount {
+            account: stored_account3,
+            store_id,
+        };
+        let found_account4 = FoundStoredAccount {
+            account: stored_account4,
+            store_id,
+        };
         let mut existing_ancient_pubkeys = HashSet::default();
-        let accounts = [&stored_account];
+        let accounts = [&found_account];
         // pubkey NOT in existing_ancient_pubkeys, so do NOT unref, but add to existing_ancient_pubkeys
         let unrefs =
             AccountsDb::get_keys_to_unref_ancient(&accounts, &mut existing_ancient_pubkeys);
@@ -10125,7 +10142,7 @@ pub mod tests {
         );
         assert_eq!(unrefs.iter().cloned().collect::<Vec<_>>(), vec![&pubkey]);
         // pubkey2 NOT in existing_ancient_pubkeys, so do NOT unref, but add to existing_ancient_pubkeys
-        let accounts = [&stored_account2];
+        let accounts = [&found_account2];
         let unrefs =
             AccountsDb::get_keys_to_unref_ancient(&accounts, &mut existing_ancient_pubkeys);
         assert!(unrefs.is_empty());
@@ -10148,7 +10165,7 @@ pub mod tests {
         );
         assert_eq!(unrefs.iter().cloned().collect::<Vec<_>>(), vec![&pubkey2]);
         // pubkey3/4 NOT in existing_ancient_pubkeys, so do NOT unref, but add to existing_ancient_pubkeys
-        let accounts = [&stored_account3, &stored_account4];
+        let accounts = [&found_account3, &found_account4];
         let unrefs =
             AccountsDb::get_keys_to_unref_ancient(&accounts, &mut existing_ancient_pubkeys);
         assert!(unrefs.is_empty());

runtime/src/ancient_append_vecs.rs

@@ -4,10 +4,7 @@
 //! 2. multiple 'slots' squashed into a single older (ie. ancient) slot for convenience and performance
 //! Otherwise, an ancient append vec is the same as any other append vec
 use {
-    crate::{
-        accounts_db::FoundStoredAccount,
-        append_vec::{AppendVec, StoredAccountMeta},
-    },
+    crate::{accounts_db::FoundStoredAccount, append_vec::AppendVec},
     solana_sdk::clock::Slot,
 };
 
@@ -25,7 +22,7 @@ pub enum StorageSelector {
 /// We need 1-2 of these slices constructed based on available bytes and individual account sizes.
 /// The slice arithmetic accross both hashes and account data gets messy. So, this struct abstracts that.
 pub struct AccountsToStore<'a> {
-    accounts: Vec<&'a StoredAccountMeta<'a>>,
+    accounts: &'a [&'a FoundStoredAccount<'a>],
     /// if 'accounts' contains more items than can be contained in the primary storage, then we have to split these accounts.
     /// 'index_first_item_overflow' specifies the index of the first item in 'accounts' that will go into the overflow storage
     index_first_item_overflow: usize,
@@ -37,26 +34,22 @@ impl<'a> AccountsToStore<'a> {
     /// available_bytes: how many bytes remain in the primary storage. Excess accounts will be directed to an overflow storage
     pub fn new(
         mut available_bytes: u64,
-        stored_accounts: &'a [&'a FoundStoredAccount<'a>],
+        accounts: &'a [&'a FoundStoredAccount<'a>],
         slot: Slot,
     ) -> Self {
-        let num_accounts = stored_accounts.len();
-        let mut accounts = Vec::with_capacity(num_accounts);
+        let num_accounts = accounts.len();
         // index of the first account that doesn't fit in the current append vec
         let mut index_first_item_overflow = num_accounts; // assume all fit
-        stored_accounts.iter().for_each(|account| {
+        for (i, account) in accounts.iter().enumerate() {
             let account_size = account.account.stored_size as u64;
             if available_bytes >= account_size {
                 available_bytes = available_bytes.saturating_sub(account_size);
             } else if index_first_item_overflow == num_accounts {
-                available_bytes = 0;
                 // the # of accounts we have so far seen is the most that will fit in the current ancient append vec
-                index_first_item_overflow = accounts.len();
+                index_first_item_overflow = i;
+                break;
             }
-            // we have to specify 'slot' here because we are writing to an ancient append vec and squashing slots,
-            // so we need to update the previous accounts index entry for this account from 'slot' to 'ancient_slot'
-            accounts.push(&account.account);
-        });
+        }
         Self {
             accounts,
             index_first_item_overflow,
@@ -70,7 +63,7 @@ impl<'a> AccountsToStore<'a> {
     }
 
     /// get the accounts to store in the given 'storage'
-    pub fn get(&self, storage: StorageSelector) -> &[&'a StoredAccountMeta<'a>] {
+    pub fn get(&self, storage: StorageSelector) -> &[&'a FoundStoredAccount<'a>] {
         let range = match storage {
             StorageSelector::Primary => 0..self.index_first_item_overflow,
             StorageSelector::Overflow => self.index_first_item_overflow..self.accounts.len(),
@@ -99,7 +92,7 @@ pub mod tests {
         super::*,
         crate::{
             accounts_db::{get_temp_accounts_paths, AppendVecId},
-            append_vec::{AccountMeta, StoredMeta},
+            append_vec::{AccountMeta, StoredAccountMeta, StoredMeta},
         },
         solana_sdk::{
             account::{AccountSharedData, ReadableAccount},
@@ -162,7 +155,7 @@ pub mod tests {
             let accounts_to_store = AccountsToStore::new(available_bytes as u64, &map, slot);
             let accounts = accounts_to_store.get(selector);
             assert_eq!(
-                accounts,
+                accounts.iter().map(|b| &b.account).collect::<Vec<_>>(),
                 map.iter().map(|b| &b.account).collect::<Vec<_>>(),
                 "mismatch"
             );

runtime/src/storable_accounts.rs

@@ -1,6 +1,9 @@
 //! trait for abstracting underlying storage of pubkey and account pairs to be written
 use {
-    crate::{accounts_db::IncludeSlotInHash, append_vec::StoredAccountMeta},
+    crate::{
+        accounts_db::{FoundStoredAccount, IncludeSlotInHash},
+        append_vec::StoredAccountMeta,
+    },
     solana_sdk::{account::ReadableAccount, clock::Slot, hash::Hash, pubkey::Pubkey},
 };
 
@@ -154,6 +157,7 @@ impl<'a> StorableAccounts<'a, StoredAccountMeta<'a>>
 }
 
 /// this tuple contains a single different source slot that applies to all accounts
+/// accounts are StoredAccountMeta
 impl<'a> StorableAccounts<'a, StoredAccountMeta<'a>>
     for (
         Slot,
@@ -194,6 +198,49 @@ impl<'a> StorableAccounts<'a, StoredAccountMeta<'a>>
         self.1[index].meta.write_version
     }
 }
+
+/// this tuple contains a single different source slot that applies to all accounts
+/// accounts are FoundStoredAccount
+impl<'a> StorableAccounts<'a, StoredAccountMeta<'a>>
+    for (
+        Slot,
+        &'a [&'a FoundStoredAccount<'a>],
+        IncludeSlotInHash,
+        Slot,
+    )
+{
+    fn pubkey(&self, index: usize) -> &Pubkey {
+        self.1[index].pubkey()
+    }
+    fn account(&self, index: usize) -> &StoredAccountMeta<'a> {
+        &self.1[index].account
+    }
+    fn slot(&self, _index: usize) -> Slot {
+        // same other slot for all accounts
+        self.3
+    }
+    fn target_slot(&self) -> Slot {
+        self.0
+    }
+    fn len(&self) -> usize {
+        self.1.len()
+    }
+    fn contains_multiple_slots(&self) -> bool {
+        false
+    }
+    fn include_slot_in_hash(&self) -> IncludeSlotInHash {
+        self.2
+    }
+    fn has_hash_and_write_version(&self) -> bool {
+        true
+    }
+    fn hash(&self, index: usize) -> &Hash {
+        self.1[index].account.hash
+    }
+    fn write_version(&self, index: usize) -> u64 {
+        self.1[index].account.meta.write_version
+    }
+}
 #[cfg(test)]
 pub mod tests {
     use {