use symlink when possible

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

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)
+    }
+}