fix: fix read only store recovery, impl random drop (#16)

Signed-off-by: MrCroxx <mrcroxx@outlook.com>

foyer/Cargo.toml

@@ -21,6 +21,7 @@ nix = { version = "0.26", features = ["fs", "mman"] }
 parking_lot = "0.12"
 paste = "1.0"
 prometheus = "0.13"
+rand = "0.8.5"
 thiserror = "1"
 tokio = { version = "1", features = [
     "rt",
@@ -36,6 +37,5 @@ twox-hash = "1"
 bytesize = "1"
 clap = { version = "4", features = ["derive"] }
 hdrhistogram = "7"
-rand = "0.8.5"
 rand_mt = "4.2.1"
 tempfile = "3"

foyer/src/store/read_only_file_store.rs

@@ -23,7 +23,9 @@ use std::{collections::HashMap, marker::PhantomData};
 
 use async_trait::async_trait;
 
+use bytes::{Buf, BufMut};
 use itertools::Itertools;
+use rand::{thread_rng, Rng};
 use tokio::sync::{RwLock, RwLockWriteGuard};
 
 use crate::{Data, Index};
@@ -139,19 +141,18 @@ where
             let dir = config.dir.clone();
             move || {
                 create_dir_all(&dir)?;
-                let ids: Vec<FileId> = read_dir(dir)?
+
+                let mut ids: Vec<FileId> = read_dir(dir)?
                     .map(|entry| entry.unwrap())
                     .filter(|entry| {
-                        entry
-                            .file_name()
-                            .to_string_lossy()
-                            .is_prefix_of(META_FILE_PREFIX)
+                        META_FILE_PREFIX.is_prefix_of(&entry.file_name().to_string_lossy())
                     })
                     .map(|entry| {
                         entry.file_name().to_string_lossy()[META_FILE_PREFIX.len()..].to_string()
                     })
                     .map(|s| s.parse().unwrap())
                     .collect_vec();
+                ids.sort();
                 Ok(ids)
             }
         })
@@ -187,21 +188,35 @@ where
 
     #[allow(clippy::uninit_vec)]
     async fn store(&self, index: Self::I, data: Self::D) -> Result<()> {
-        let buf = data.into();
-        let len = buf.len();
-
         // append cache file and meta file
         let (fid, sid, location) = {
+            // randomly drop if size exceeds the threshold
+            if self.size.load(Ordering::Relaxed) as f64
+                >= self.config.capacity as f64 * self.config.trigger_random_drop_ratio
+            {
+                let mut rng = thread_rng();
+                if rng.gen_range(0.0..1.0) < self.config.random_drop_ratio {
+                    return Ok(());
+                }
+            }
+
+            let buf = data.into();
+
             let files = self.files.read().await;
 
             let fid = files.active.fid;
 
             let location = files.active.cache_file.append(buf).await?;
 
             let mut buf = Vec::with_capacity(Self::meta_entry_size());
+
+            let tags = Tags { valid: true };
+
             unsafe { buf.set_len(Self::meta_entry_size()) };
-            index.write(&mut buf[..]);
-            location.write(&mut buf[I::size()..]);
+            tags.write(&mut buf[..]);
+            index.write(&mut buf[Tags::size()..]);
+            location.write(&mut buf[Tags::size() + I::size()..]);
+
             let Location {
                 offset: meta_offset,
                 len: _,
@@ -219,7 +234,8 @@ where
             drop(indices);
         }
 
-        self.size.fetch_add(len, Ordering::Relaxed);
+        self.size
+            .fetch_add(location.len as usize, Ordering::Relaxed);
 
         if active_file_size >= self.config.max_file_size {
             let files = self.files.write().await;
@@ -434,8 +450,12 @@ where
         let buf = meta.read(0, size).await?;
         for sid in 0..slots {
             let slice = &buf[sid * Self::meta_entry_size()..(sid + 1) * Self::meta_entry_size()];
-            let index = I::read(slice);
-            let location = Location::read(&slice[I::size()..]);
+            let tags = Tags::read(slice);
+            if !tags.valid {
+                continue;
+            }
+            let index = I::read(&slice[Tags::size()..]);
+            let location = Location::read(&slice[Tags::size() + I::size()..]);
             indices.insert(index, (fid, sid as SlotId, location));
         }
         Ok(())
@@ -450,7 +470,29 @@ where
     }
 
     fn meta_entry_size() -> usize {
-        I::size() + Location::size()
+        I::size() + Location::size() + Tags::size()
+    }
+}
+
+struct Tags {
+    valid: bool,
+}
+
+impl Tags {
+    fn size() -> usize {
+        1
+    }
+
+    fn write(&self, mut buf: &mut [u8]) {
+        let mut val = 0;
+        val |= self.valid as u8;
+        buf.put_u8(val);
+    }
+
+    fn read(mut buf: &[u8]) -> Self {
+        let val = buf.get_u8();
+        let valid = (val & 1) != 0;
+        Self { valid }
     }
 }
 
@@ -514,4 +556,49 @@ mod tests {
 
         drop(dir);
     }
+
+    #[tokio::test]
+    async fn test_read_only_file_store_recovery() {
+        let dir = tempdir().unwrap();
+
+        let config = Config {
+            dir: dir.path().to_owned(),
+            max_file_size: 4 * 1024,
+            capacity: 16 * 1024,
+            trigger_reclaim_garbage_ratio: 0.0, // disabled
+            trigger_reclaim_capacity_ratio: 0.75,
+            trigger_random_drop_ratio: 0.0, // disabled
+            random_drop_ratio: 0.0,         // disabled
+        };
+
+        let store: ReadOnlyFileStore<u64, Vec<u8>> =
+            ReadOnlyFileStore::open(0, config.clone()).await.unwrap();
+
+        for i in 0..20 {
+            store.store(i, data(i as u8, 1024)).await.unwrap();
+        }
+
+        assert_eq!(store.files.read().await.frozens.len(), 2);
+        for i in 0..12 {
+            assert_eq!(store.load(&i).await.unwrap(), None);
+        }
+        for i in 12..20 {
+            assert_eq!(store.load(&i).await.unwrap(), Some(data(i as u8, 1024)));
+        }
+
+        drop(store);
+
+        let store: ReadOnlyFileStore<u64, Vec<u8>> =
+            ReadOnlyFileStore::open(0, config).await.unwrap();
+
+        assert_eq!(store.files.read().await.frozens.len(), 3);
+        for i in 0..12 {
+            assert_eq!(store.load(&i).await.unwrap(), None);
+        }
+        for i in 12..20 {
+            assert_eq!(store.load(&i).await.unwrap(), Some(data(i as u8, 1024)));
+        }
+
+        drop(dir);
+    }
 }