Buffer account's fields for hash (solana-labs#33788)

* buffer accounts field for hash

* use smallvec to allocate hash buffer on stack

* sort deps

* more opt

* clippy

---------

Co-authored-by: HaoranYi <haoran.yi@solana.com>

Cargo.toml

@@ -298,6 +298,7 @@ sha2 = "0.10.8"
 sha3 = "0.10.4"
 signal-hook = "0.3.17"
 siphasher = "0.3.11"
+smallvec = "1.11.1"
 smpl_jwt = "0.7.1"
 socket2 = "0.5.5"
 soketto = "0.7"

accounts-db/Cargo.toml

@@ -43,6 +43,7 @@ regex = { workspace = true }
 seqlock = { workspace = true }
 serde = { workspace = true, features = ["rc"] }
 serde_derive = { workspace = true }
+smallvec = { workspace = true }
 solana-bucket-map = { workspace = true }
 solana-config-program = { workspace = true }
 solana-frozen-abi = { workspace = true }

accounts-db/src/accounts_db.rs

@@ -79,6 +79,7 @@ use {
     rand::{thread_rng, Rng},
     rayon::{prelude::*, ThreadPool},
     serde::{Deserialize, Serialize},
+    smallvec::SmallVec,
     solana_measure::{measure::Measure, measure_us},
     solana_nohash_hasher::IntSet,
     solana_rayon_threadlimit::get_thread_count,
@@ -6274,31 +6275,49 @@ impl AccountsDb {
         }
         let mut hasher = blake3::Hasher::new();
 
-        hasher.update(&lamports.to_le_bytes());
+        // allocate 128 bytes buffer on the stack
+        const BUF_SIZE: usize = 128;
+        const TOTAL_FIELD_SIZE: usize = 8 /* lamports */ + 8 /* slot */ + 8 /* rent_epoch */ + 1 /* exec_flag */ + 32 /* owner_key */ + 32 /* pubkey */;
+        const DATA_SIZE_CAN_FIT: usize = BUF_SIZE - TOTAL_FIELD_SIZE;
+
+        let mut buffer = SmallVec::<[u8; BUF_SIZE]>::new();
+
+        // collect lamports, slot, rent_epoch into buffer to hash
+        buffer.extend_from_slice(&lamports.to_le_bytes());
 
         match include_slot {
             IncludeSlotInHash::IncludeSlot => {
                 // upon feature activation, stop including slot# in the account hash
-                hasher.update(&slot.to_le_bytes());
+                buffer.extend_from_slice(&slot.to_le_bytes());
             }
             IncludeSlotInHash::RemoveSlot => {}
             IncludeSlotInHash::IrrelevantAssertOnUse => {
                 panic!("IncludeSlotInHash is irrelevant, but we are calculating hash");
             }
         }
+        buffer.extend_from_slice(&rent_epoch.to_le_bytes());
 
-        hasher.update(&rent_epoch.to_le_bytes());
+        if data.len() > DATA_SIZE_CAN_FIT {
+            // For larger accounts whose data can't fit into the buffer, update the hash now.
+            hasher.update(&buffer);
+            buffer.clear();
 
-        hasher.update(data);
+            // hash account's data
+            hasher.update(data);
+        } else {
+            // For small accounts whose data can fit into the buffer, append it to the buffer.
+            buffer.extend_from_slice(data);
+        }
 
+        // collect exec_flag, owner, pubkey into buffer to hash
         if executable {
-            hasher.update(&[1u8; 1]);
+            buffer.push(1_u8);
         } else {
-            hasher.update(&[0u8; 1]);
+            buffer.push(0_u8);
         }
-
-        hasher.update(owner.as_ref());
-        hasher.update(pubkey.as_ref());
+        buffer.extend_from_slice(owner.as_ref());
+        buffer.extend_from_slice(pubkey.as_ref());
+        hasher.update(&buffer);
 
         AccountHash(Hash::new_from_array(hasher.finalize().into()))
     }