use symlink when possible

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-starter/src/debug.rs

@@ -1,8 +1,8 @@
-use crate::lsm_storage::MiniLsm;
+use crate::lsm_storage::{LsmStorageInner, MiniLsm};
 
-impl MiniLsm {
+impl LsmStorageInner {
     pub fn dump_structure(&self) {
-        let snapshot = self.inner.state.read();
+        let snapshot = self.state.read();
         if !snapshot.l0_sstables.is_empty() {
             println!(
                 "L0 ({}): {:?}",
@@ -15,3 +15,9 @@ impl MiniLsm {
         }
     }
 }
+
+impl MiniLsm {
+    pub fn dump_structure(&self) {
+        self.inner.dump_structure()
+    }
+}

mini-lsm-starter/src/iterators/two_merge_iterator.rs

@@ -3,8 +3,6 @@
 
 use anyhow::Result;
 
-use crate::key::KeySlice;
-
 use super::StorageIterator;
 
 /// Merges two iterators of different types into one. If the two iterators have the same key, only
@@ -16,8 +14,8 @@ pub struct TwoMergeIterator<A: StorageIterator, B: StorageIterator> {
 }
 
 impl<
-        A: 'static + for<'a> StorageIterator<KeyType<'a> = KeySlice<'a>>,
-        B: 'static + for<'a> StorageIterator<KeyType<'a> = KeySlice<'a>>,
+        A: 'static + StorageIterator,
+        B: 'static + for<'a> StorageIterator<KeyType<'a> = A::KeyType<'a>>,
     > TwoMergeIterator<A, B>
 {
     pub fn create(a: A, b: B) -> Result<Self> {
@@ -26,13 +24,13 @@ impl<
 }
 
 impl<
-        A: 'static + for<'a> StorageIterator<KeyType<'a> = KeySlice<'a>>,
-        B: 'static + for<'a> StorageIterator<KeyType<'a> = KeySlice<'a>>,
+        A: 'static + StorageIterator,
+        B: 'static + for<'a> StorageIterator<KeyType<'a> = A::KeyType<'a>>,
     > StorageIterator for TwoMergeIterator<A, B>
 {
-    type KeyType<'a> = KeySlice<'a>;
+    type KeyType<'a> = A::KeyType<'a>;
 
-    fn key(&self) -> KeySlice {
+    fn key(&self) -> Self::KeyType<'_> {
         unimplemented!()
     }
 

mini-lsm-starter/src/lib.rs

@@ -7,6 +7,7 @@ pub mod lsm_iterator;
 pub mod lsm_storage;
 pub mod manifest;
 pub mod mem_table;
+pub mod mvcc;
 pub mod table;
 pub mod wal;
 

mini-lsm-starter/src/lsm_storage.rs

@@ -18,6 +18,7 @@ use crate::compact::{
 use crate::lsm_iterator::{FusedIterator, LsmIterator};
 use crate::manifest::Manifest;
 use crate::mem_table::MemTable;
+use crate::mvcc::LsmMvccInner;
 use crate::table::SsTable;
 
 pub type BlockCache = moka::sync::Cache<(usize, usize), Arc<Block>>;
@@ -122,6 +123,7 @@ pub(crate) struct LsmStorageInner {
     pub(crate) options: Arc<LsmStorageOptions>,
     pub(crate) compaction_controller: CompactionController,
     pub(crate) manifest: Option<Manifest>,
+    pub(crate) mvcc: Option<LsmMvccInner>,
 }
 
 /// A thin wrapper for `LsmStorageInner` and the user interface for MiniLSM.
@@ -249,6 +251,7 @@ impl LsmStorageInner {
             compaction_controller,
             manifest: None,
             options: options.into(),
+            mvcc: None,
         };
 
         Ok(storage)

mini-lsm-starter/src/mvcc.rs

@@ -0,0 +1,58 @@
+#![allow(unused_variables)] // TODO(you): remove this lint after implementing this mod
+#![allow(dead_code)] // TODO(you): remove this lint after implementing this mod
+
+pub mod txn;
+mod watermark;
+
+use std::{
+    collections::{BTreeMap, HashSet},
+    sync::Arc,
+};
+
+use parking_lot::Mutex;
+
+use crate::lsm_storage::LsmStorageInner;
+
+use self::{txn::Transaction, watermark::Watermark};
+
+pub(crate) struct CommittedTxnData {
+    pub(crate) key_hashes: HashSet<u32>,
+    #[allow(dead_code)]
+    pub(crate) read_ts: u64,
+    #[allow(dead_code)]
+    pub(crate) commit_ts: u64,
+}
+
+pub(crate) struct LsmMvccInner {
+    pub(crate) write_lock: Mutex<()>,
+    pub(crate) ts: Arc<Mutex<(u64, Watermark)>>,
+    pub(crate) committed_txns: Arc<Mutex<BTreeMap<u64, CommittedTxnData>>>,
+}
+
+impl LsmMvccInner {
+    pub fn new(initial_ts: u64) -> Self {
+        Self {
+            write_lock: Mutex::new(()),
+            ts: Arc::new(Mutex::new((initial_ts, Watermark::new()))),
+            committed_txns: Arc::new(Mutex::new(BTreeMap::new())),
+        }
+    }
+
+    pub fn latest_commit_ts(&self) -> u64 {
+        self.ts.lock().0
+    }
+
+    pub fn update_commit_ts(&self, ts: u64) {
+        self.ts.lock().0 = ts;
+    }
+
+    /// All ts (strictly) below this ts can be garbage collected.
+    pub fn watermark(&self) -> u64 {
+        let ts = self.ts.lock();
+        ts.1.watermark().unwrap_or(ts.0)
+    }
+
+    pub fn new_txn(&self, inner: Arc<LsmStorageInner>, serializable: bool) -> Arc<Transaction> {
+        unimplemented!()
+    }
+}

mini-lsm-starter/src/mvcc/txn.rs

@@ -0,0 +1,128 @@
+#![allow(unused_variables)] // TODO(you): remove this lint after implementing this mod
+#![allow(dead_code)] // TODO(you): remove this lint after implementing this mod
+
+use std::{
+    collections::HashSet,
+    ops::Bound,
+    sync::{atomic::AtomicBool, Arc},
+};
+
+use anyhow::Result;
+use bytes::Bytes;
+use crossbeam_skiplist::SkipMap;
+use ouroboros::self_referencing;
+use parking_lot::Mutex;
+
+use crate::{
+    iterators::{two_merge_iterator::TwoMergeIterator, StorageIterator},
+    lsm_iterator::{FusedIterator, LsmIterator},
+    lsm_storage::LsmStorageInner,
+};
+
+pub struct Transaction {
+    pub(crate) read_ts: u64,
+    pub(crate) inner: Arc<LsmStorageInner>,
+    pub(crate) local_storage: Arc<SkipMap<Bytes, Bytes>>,
+    pub(crate) committed: Arc<AtomicBool>,
+    /// Write set and read set
+    pub(crate) key_hashes: Option<Mutex<(HashSet<u32>, HashSet<u32>)>>,
+}
+
+impl Transaction {
+    pub fn get(&self, key: &[u8]) -> Result<Option<Bytes>> {
+        unimplemented!()
+    }
+
+    pub fn scan(self: &Arc<Self>, lower: Bound<&[u8]>, upper: Bound<&[u8]>) -> Result<TxnIterator> {
+        unimplemented!()
+    }
+
+    pub fn put(&self, key: &[u8], value: &[u8]) {
+        unimplemented!()
+    }
+
+    pub fn delete(&self, key: &[u8]) {
+        unimplemented!()
+    }
+
+    pub fn commit(&self) -> Result<()> {
+        unimplemented!()
+    }
+}
+
+impl Drop for Transaction {
+    fn drop(&mut self) {}
+}
+
+type SkipMapRangeIter<'a> =
+    crossbeam_skiplist::map::Range<'a, Bytes, (Bound<Bytes>, Bound<Bytes>), Bytes, Bytes>;
+
+#[self_referencing]
+pub struct TxnLocalIterator {
+    /// Stores a reference to the skipmap.
+    map: Arc<SkipMap<Bytes, Bytes>>,
+    /// Stores a skipmap iterator that refers to the lifetime of `MemTableIterator` itself.
+    #[borrows(map)]
+    #[not_covariant]
+    iter: SkipMapRangeIter<'this>,
+    /// Stores the current key-value pair.
+    item: (Bytes, Bytes),
+}
+
+impl StorageIterator for TxnLocalIterator {
+    type KeyType<'a> = &'a [u8];
+
+    fn value(&self) -> &[u8] {
+        unimplemented!()
+    }
+
+    fn key(&self) -> &[u8] {
+        unimplemented!()
+    }
+
+    fn is_valid(&self) -> bool {
+        unimplemented!()
+    }
+
+    fn next(&mut self) -> Result<()> {
+        unimplemented!()
+    }
+}
+
+pub struct TxnIterator {
+    _txn: Arc<Transaction>,
+    iter: TwoMergeIterator<TxnLocalIterator, FusedIterator<LsmIterator>>,
+}
+
+impl TxnIterator {
+    pub fn create(
+        txn: Arc<Transaction>,
+        iter: TwoMergeIterator<TxnLocalIterator, FusedIterator<LsmIterator>>,
+    ) -> Result<Self> {
+        unimplemented!()
+    }
+}
+
+impl StorageIterator for TxnIterator {
+    type KeyType<'a> = &'a [u8] where Self: 'a;
+
+    fn value(&self) -> &[u8] {
+        self.iter.value()
+    }
+
+    fn key(&self) -> Self::KeyType<'_> {
+        self.iter.key()
+    }
+
+    fn is_valid(&self) -> bool {
+        self.iter.is_valid()
+    }
+
+    fn next(&mut self) -> Result<()> {
+        unimplemented!()
+    }
+
+    fn num_active_iterators(&self) -> usize {
+        self.iter.num_active_iterators()
+    }
+}

mini-lsm-starter/src/mvcc/watermark.rs

@@ -0,0 +1,24 @@
+#![allow(unused_variables)] // TODO(you): remove this lint after implementing this mod
+#![allow(dead_code)] // TODO(you): remove this lint after implementing this mod
+
+use std::collections::BTreeMap;
+
+pub struct Watermark {
+    readers: BTreeMap<u64, usize>,
+}
+
+impl Watermark {
+    pub fn new() -> Self {
+        Self {
+            readers: BTreeMap::new(),
+        }
+    }
+
+    pub fn add_reader(&mut self, ts: u64) {}
+
+    pub fn remove_reader(&mut self, ts: u64) {}
+
+    pub fn watermark(&self) -> Option<u64> {
+        Some(0)
+    }
+}