update lru for read only cache if it has been long enough since last …

…access

runtime/src/accounts_db.rs

@@ -2364,6 +2364,8 @@ impl AccountsDb {
     ) -> Self {
         let num_threads = get_thread_count();
         const MAX_READ_ONLY_CACHE_DATA_SIZE: usize = 400_000_000; // 400M bytes
+        // read only cache does not update lru on read of an entry unless it has been at least this many ms since the last lru update
+        const READ_ONLY_CACHE_MS_TO_SKIP_LRU_UPDATE: u32 = 100;
 
         let mut temp_accounts_hash_cache_path = None;
         let accounts_hash_cache_path = accounts_hash_cache_path.unwrap_or_else(|| {
@@ -2395,7 +2397,10 @@ impl AccountsDb {
             storage: AccountStorage::default(),
             accounts_cache: AccountsCache::default(),
             sender_bg_hasher: None,
-            read_only_accounts_cache: ReadOnlyAccountsCache::new(MAX_READ_ONLY_CACHE_DATA_SIZE),
+            read_only_accounts_cache: ReadOnlyAccountsCache::new(
+                MAX_READ_ONLY_CACHE_DATA_SIZE,
+                READ_ONLY_CACHE_MS_TO_SKIP_LRU_UPDATE,
+            ),
             recycle_stores: RwLock::new(RecycleStores::default()),
             uncleaned_pubkeys: DashMap::new(),
             next_id: AtomicAppendVecId::new(0),

runtime/src/read_only_accounts_cache.rs

@@ -8,6 +8,7 @@ use {
         account::{AccountSharedData, ReadableAccount},
         clock::Slot,
         pubkey::Pubkey,
+        timing::timestamp,
     },
     std::sync::{
         atomic::{AtomicU64, AtomicUsize, Ordering},
@@ -23,33 +24,59 @@ type ReadOnlyCacheKey = (Pubkey, Slot);
 #[derive(Debug)]
 struct ReadOnlyAccountCacheEntry {
     account: AccountSharedData,
-    index: Index, // Index of the entry in the eviction queue.
+    /// Index of the entry in the eviction queue.
+    index: Index,
+    /// lower bits of last timestamp when eviction queue was updated
+    last_time: u32,
+}
+
+impl ReadOnlyAccountCacheEntry {
+    fn new(account: AccountSharedData, index: Index) -> Self {
+        Self {
+            account,
+            index,
+            last_time: Self::timestamp(),
+        }
+    }
+    /// lower bits of current timestamp. We don't need higher bits and u32 fits with Index u32
+    fn timestamp() -> u32 {
+        (timestamp() % (u32::MAX as u64 + 1)) as u32
+    }
+    /// ms since `last_time` timestamp
+    fn ms_since_last_time(&self) -> u32 {
+        Self::timestamp().wrapping_sub(self.last_time)
+    }
 }
 
 #[derive(Debug)]
 pub(crate) struct ReadOnlyAccountsCache {
     cache: DashMap<ReadOnlyCacheKey, ReadOnlyAccountCacheEntry>,
-    // When an item is first entered into the cache, it is added to the end of
-    // the queue. Also each time an entry is looked up from the cache it is
-    // moved to the end of the queue. As a result, items in the queue are
-    // always sorted in the order that they have last been accessed. When doing
-    // LRU eviction, cache entries are evicted from the front of the queue.
+    /// When an item is first entered into the cache, it is added to the end of
+    /// the queue. Also each time an entry is looked up from the cache it is
+    /// moved to the end of the queue. As a result, items in the queue are
+    /// always sorted in the order that they have last been accessed. When doing
+    /// LRU eviction, cache entries are evicted from the front of the queue.
     queue: Mutex<IndexList<ReadOnlyCacheKey>>,
     max_data_size: usize,
     data_size: AtomicUsize,
+    // read only cache does not update lru on read of an entry unless it has been at least this many ms since the last lru update
+    ms_to_skip_lru_update: u32,
+
+    /// stats
     hits: AtomicU64,
     misses: AtomicU64,
     evicts: AtomicU64,
     load_us: AtomicU64,
 }
 
 impl ReadOnlyAccountsCache {
-    pub(crate) fn new(max_data_size: usize) -> Self {
+    pub(crate) fn new(max_data_size: usize, ms_to_skip_lru_update: u32) -> Self {
         Self {
             max_data_size,
             cache: DashMap::default(),
             queue: Mutex::<IndexList<ReadOnlyCacheKey>>::default(),
             data_size: AtomicUsize::default(),
+            ms_to_skip_lru_update,
             hits: AtomicU64::default(),
             misses: AtomicU64::default(),
             evicts: AtomicU64::default(),
@@ -84,10 +111,13 @@ impl ReadOnlyAccountsCache {
             // Move the entry to the end of the queue.
             // self.queue is modified while holding a reference to the cache entry;
             // so that another thread cannot write to the same key.
-            {
+            // If we updated the eviction queue within this much time, then leave it where it is. We're likely to hit it again.
+            let update_lru = entry.ms_since_last_time() >= self.ms_to_skip_lru_update;
+            if update_lru {
                 let mut queue = self.queue.lock().unwrap();
                 queue.remove(entry.index);
                 entry.index = queue.insert_last(key);
+                entry.last_time = ReadOnlyAccountCacheEntry::timestamp();
             }
             let account = entry.account.clone();
             drop(entry);
@@ -113,7 +143,7 @@ impl ReadOnlyAccountsCache {
                 // Insert the entry at the end of the queue.
                 let mut queue = self.queue.lock().unwrap();
                 let index = queue.insert_last(key);
-                entry.insert(ReadOnlyAccountCacheEntry { account, index });
+                entry.insert(ReadOnlyAccountCacheEntry::new(account, index));
             }
             Entry::Occupied(mut entry) => {
                 let entry = entry.get_mut();
@@ -192,7 +222,8 @@ mod tests {
         let per_account_size = CACHE_ENTRY_SIZE;
         let data_size = 100;
         let max = data_size + per_account_size;
-        let cache = ReadOnlyAccountsCache::new(max);
+        let cache =
+            ReadOnlyAccountsCache::new(max, READ_ONLY_CACHE_MS_TO_SKIP_LRU_UPDATE_FOR_TESTS);
         let slot = 0;
         assert!(cache.load(Pubkey::default(), slot).is_none());
         assert_eq!(0, cache.cache_len());
@@ -227,7 +258,8 @@ mod tests {
 
         // can store 2 items, 3rd item kicks oldest item out
         let max = (data_size + per_account_size) * 2;
-        let cache = ReadOnlyAccountsCache::new(max);
+        let cache =
+            ReadOnlyAccountsCache::new(max, READ_ONLY_CACHE_MS_TO_SKIP_LRU_UPDATE_FOR_TESTS);
         cache.store(key1, slot, account1.clone());
         assert_eq!(100 + per_account_size, cache.data_size());
         assert!(accounts_equal(&cache.load(key1, slot).unwrap(), &account1));
@@ -250,13 +282,19 @@ mod tests {
         assert_eq!(2, cache.cache_len());
     }
 
+    /// tests like to deterministically update lru always
+    const READ_ONLY_CACHE_MS_TO_SKIP_LRU_UPDATE_FOR_TESTS: u32 = 0;
+
     #[test]
     fn test_read_only_accounts_cache_random() {
         const SEED: [u8; 32] = [0xdb; 32];
         const DATA_SIZE: usize = 19;
         const MAX_CACHE_SIZE: usize = 17 * (CACHE_ENTRY_SIZE + DATA_SIZE);
         let mut rng = ChaChaRng::from_seed(SEED);
-        let cache = ReadOnlyAccountsCache::new(MAX_CACHE_SIZE);
+        let cache = ReadOnlyAccountsCache::new(
+            MAX_CACHE_SIZE,
+            READ_ONLY_CACHE_MS_TO_SKIP_LRU_UPDATE_FOR_TESTS,
+        );
         let slots: Vec<Slot> = repeat_with(|| rng.gen_range(0, 1000)).take(5).collect();
         let pubkeys: Vec<Pubkey> = repeat_with(|| {
             let mut arr = [0u8; 32];