feat(code): part 3 iterators

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

Cargo.lock

@@ -8,6 +8,18 @@ version = "1.0.68"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2cb2f989d18dd141ab8ae82f64d1a8cdd37e0840f73a406896cf5e99502fab61"
 
+[[package]]
+name = "arc-swap"
+version = "1.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "983cd8b9d4b02a6dc6ffa557262eb5858a27a0038ffffe21a0f133eaa819a164"
+
+[[package]]
+name = "autocfg"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
+
 [[package]]
 name = "bitflags"
 version = "1.3.2"
@@ -26,6 +38,12 @@ version = "1.0.78"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a20104e2335ce8a659d6dd92a51a767a0c062599c73b343fd152cb401e828c3d"
 
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
 [[package]]
 name = "clap"
 version = "4.0.32"
@@ -77,6 +95,40 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "crossbeam-epoch"
+version = "0.9.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "01a9af1f4c2ef74bb8aa1f7e19706bc72d03598c8a570bb5de72243c7a9d9d5a"
+dependencies = [
+ "autocfg",
+ "cfg-if",
+ "crossbeam-utils",
+ "memoffset",
+ "scopeguard",
+]
+
+[[package]]
+name = "crossbeam-skiplist"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "af28cff91e276c27eb739e14b0dda13dfd4cbab8364ebdb8d517a4c5454a227a"
+dependencies = [
+ "cfg-if",
+ "crossbeam-epoch",
+ "crossbeam-utils",
+ "scopeguard",
+]
+
+[[package]]
+name = "crossbeam-utils"
+version = "0.8.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4fb766fa798726286dbbb842f174001dab8abc7b627a1dd86e0b7222a95d929f"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "duct"
 version = "0.13.6"
@@ -171,12 +223,34 @@ version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f051f77a7c8e6957c0696eac88f26b0117e54f52d3fc682ab19397a8812846a4"
 
+[[package]]
+name = "lock_api"
+version = "0.4.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "435011366fe56583b16cf956f9df0095b405b82d76425bc8981c0e22e60ec4df"
+dependencies = [
+ "autocfg",
+ "scopeguard",
+]
+
+[[package]]
+name = "memoffset"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5de893c32cde5f383baa4c04c5d6dbdd735cfd4a794b0debdb2bb1b421da5ff4"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "mini-lsm"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "arc-swap",
  "bytes",
+ "crossbeam-skiplist",
+ "parking_lot",
 ]
 
 [[package]]
@@ -184,7 +258,10 @@ name = "mini-lsm-starter"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "arc-swap",
  "bytes",
+ "crossbeam-skiplist",
+ "parking_lot",
 ]
 
 [[package]]
@@ -219,6 +296,29 @@ version = "6.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9b7820b9daea5457c9f21c69448905d723fbd21136ccf521748f23fd49e723ee"
 
+[[package]]
+name = "parking_lot"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3742b2c103b9f06bc9fff0a37ff4912935851bee6d36f3c02bcc755bcfec228f"
+dependencies = [
+ "lock_api",
+ "parking_lot_core",
+]
+
+[[package]]
+name = "parking_lot_core"
+version = "0.9.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7ff9f3fef3968a3ec5945535ed654cb38ff72d7495a25619e2247fb15a2ed9ba"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "redox_syscall",
+ "smallvec",
+ "windows-sys",
+]
+
 [[package]]
 name = "proc-macro-error"
 version = "1.0.4"
@@ -261,6 +361,15 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "redox_syscall"
+version = "0.2.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fb5a58c1855b4b6819d59012155603f0b22ad30cad752600aadfcb695265519a"
+dependencies = [
+ "bitflags",
+]
+
 [[package]]
 name = "rustix"
 version = "0.36.5"
@@ -275,6 +384,12 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "scopeguard"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
+
 [[package]]
 name = "shared_child"
 version = "1.0.0"
@@ -285,6 +400,12 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "smallvec"
+version = "1.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a507befe795404456341dfab10cef66ead4c041f62b8b11bbb92bffe5d0953e0"
+
 [[package]]
 name = "strsim"
 version = "0.10.0"

mini-lsm-book/src/00-overview.md

@@ -42,6 +42,7 @@ The storage engine generally provides the following interfaces:
 * `Put(key, value)`: store a key-value pair in the LSM tree.
 * `Delete(key)`: remove a key and its corresponding value.
 * `Get(key)`: get the value corresponding to a key.
+* `Scan(range)`: get a range of key-value pairs.
 
 To ensure persistence,
 

mini-lsm-starter/Cargo.toml

@@ -6,4 +6,7 @@ publish = false
 
 [dependencies]
 anyhow = "1"
+arc-swap = "1"
 bytes = "1"
+crossbeam-skiplist = "0.1"
+parking_lot = "0.12"

mini-lsm-starter/src/block.rs

@@ -4,12 +4,12 @@
 mod builder;
 mod iterator;
 
-use bytes::Bytes;
-
 pub use builder::BlockBuilder;
+use bytes::Bytes;
 pub use iterator::BlockIterator;
 
-/// A block is the smallest unit of read and caching in LSM tree. It is a collection of sorted key-value pairs.
+/// A block is the smallest unit of read and caching in LSM tree. It is a collection of sorted
+/// key-value pairs.
 pub struct Block {
     data: Vec<u8>,
     offsets: Vec<u16>,

mini-lsm-starter/src/iterators.rs

@@ -0,0 +1,6 @@
+pub mod impls;
+pub mod merge_iterator;
+pub mod two_merge_iterator;
+
+#[cfg(test)]
+mod tests;

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

@@ -0,0 +1,15 @@
+use anyhow::Result;
+
+pub trait StorageIterator {
+    /// Get the current value.
+    fn value(&self) -> &[u8];
+
+    /// Get the current key.
+    fn key(&self) -> &[u8];
+
+    /// Check if the current iterator is valid.
+    fn is_valid(&self) -> bool;
+
+    /// Move to the next position.
+    fn next(&mut self) -> Result<()>;
+}

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

@@ -0,0 +1,67 @@
+#![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::cmp::{self};
+use std::collections::BinaryHeap;
+
+use anyhow::Result;
+
+use super::impls::StorageIterator;
+
+struct HeapWrapper<I: StorageIterator>(pub usize, pub Box<I>);
+
+impl<I: StorageIterator> PartialEq for HeapWrapper<I> {
+    fn eq(&self, other: &Self) -> bool {
+        self.partial_cmp(other).unwrap() == cmp::Ordering::Equal
+    }
+}
+
+impl<I: StorageIterator> Eq for HeapWrapper<I> {}
+
+impl<I: StorageIterator> PartialOrd for HeapWrapper<I> {
+    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
+        match self.1.key().cmp(other.1.key()) {
+            cmp::Ordering::Greater => Some(cmp::Ordering::Greater),
+            cmp::Ordering::Less => Some(cmp::Ordering::Less),
+            cmp::Ordering::Equal => self.0.partial_cmp(&other.0),
+        }
+        .map(|x| x.reverse())
+    }
+}
+
+impl<I: StorageIterator> Ord for HeapWrapper<I> {
+    fn cmp(&self, other: &Self) -> cmp::Ordering {
+        self.partial_cmp(other).unwrap()
+    }
+}
+
+/// Merge multiple iterators of the same type. If the same key occurs multiple times in some
+/// iterators, perfer the one with smaller index.
+pub struct MergeIterator<I: StorageIterator> {
+    iters: BinaryHeap<HeapWrapper<I>>,
+    current: HeapWrapper<I>,
+}
+
+impl<I: StorageIterator> MergeIterator<I> {
+    pub fn create(iters: Vec<Box<I>>) -> Self {
+        unimplemented!()
+    }
+}
+
+impl<I: StorageIterator> StorageIterator for MergeIterator<I> {
+    fn key(&self) -> &[u8] {
+        unimplemented!()
+    }
+
+    fn value(&self) -> &[u8] {
+        unimplemented!()
+    }
+
+    fn is_valid(&self) -> bool {
+        unimplemented!()
+    }
+
+    fn next(&mut self) -> Result<()> {
+        unimplemented!()
+    }
+}

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

@@ -0,0 +1,4 @@
+//! Please copy `mini-lsm/src/iterators/tests.rs` here so that you can run tests.
+
+pub mod merge_iterator_test;
+pub mod two_merge_iterator_test;

mini-lsm-starter/src/iterators/tests/merge_iterator_test.rs

@@ -0,0 +1,2 @@
+//! Please copy `mini-lsm/src/iterators/tests/merge_iterator_test.rs` here so that you can run
+//! tests.

mini-lsm-starter/src/iterators/tests/two_merge_iterator_test.rs

@@ -0,0 +1,2 @@
+//! Please copy `mini-lsm/src/iterators/tests/two_merge_iterator_test.rs` here so that you can run
+//! tests.

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

@@ -0,0 +1,38 @@
+#![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 anyhow::Result;
+
+use super::impls::StorageIterator;
+
+/// Merges two iterators of different types into one. If the two iterators have the same key, only
+/// produce the key once and prefer the entry from A.
+pub struct TwoMergeIterator<A: StorageIterator, B: StorageIterator> {
+    a: A,
+    b: B,
+    // Add fields as need
+}
+
+impl<A: StorageIterator, B: StorageIterator> TwoMergeIterator<A, B> {
+    pub fn create(a: A, b: B) -> Result<Self> {
+        unimplemented!()
+    }
+}
+
+impl<A: StorageIterator, B: StorageIterator> StorageIterator for TwoMergeIterator<A, B> {
+    fn key(&self) -> &[u8] {
+        unimplemented!()
+    }
+
+    fn value(&self) -> &[u8] {
+        unimplemented!()
+    }
+
+    fn is_valid(&self) -> bool {
+        unimplemented!()
+    }
+
+    fn next(&mut self) -> Result<()> {
+        unimplemented!()
+    }
+}

mini-lsm-starter/src/lib.rs

@@ -1,3 +1,6 @@
 pub mod block;
-pub mod storage;
+pub mod iterators;
+pub mod lsm_iterator;
+pub mod lsm_storage;
+pub mod mem_table;
 pub mod table;

mini-lsm-starter/src/lsm_iterator.rs

@@ -0,0 +1 @@
+pub struct LsmIterator {}

mini-lsm-starter/src/lsm_storage.rs

@@ -0,0 +1,75 @@
+use std::ops::Bound;
+use std::path::Path;
+use std::sync::Arc;
+
+use anyhow::Result;
+use arc_swap::ArcSwap;
+use bytes::Bytes;
+
+use crate::lsm_iterator::LsmIterator;
+use crate::mem_table::MemTable;
+use crate::table::{SsTable, SsTableIterator};
+
+pub struct LsmStorageInner {
+    memtables: Vec<Arc<MemTable>>,
+    sstables: Vec<Arc<SsTable>>,
+}
+
+impl LsmStorageInner {
+    fn create() -> Self {
+        Self {
+            memtables: vec![Arc::new(MemTable::create())],
+            sstables: vec![],
+        }
+    }
+}
+
+/// The storage interface of the LSM tree.
+pub struct LsmStorage {
+    inner: ArcSwap<LsmStorageInner>,
+}
+
+impl LsmStorage {
+    pub fn open(_path: &Path) -> Result<Self> {
+        Ok(Self {
+            inner: ArcSwap::from_pointee(LsmStorageInner::create()),
+        })
+    }
+
+    pub fn get(&self, key: &[u8]) -> Result<Option<Bytes>> {
+        let snapshot = self.inner.load();
+        for memtable in &snapshot.memtables {
+            if let Some(value) = memtable.get(key)? {
+                if value.is_empty() {
+                    // found tomestone, return key not exists
+                    return Ok(None);
+                }
+                return Ok(Some(value));
+            }
+        }
+        let mut iters = Vec::new();
+        iters.reserve(snapshot.sstables.len());
+        for table in snapshot.sstables.iter().rev() {
+            iters.push(SsTableIterator::create_and_seek_to_key(table.clone(), key)?);
+        }
+        Ok(None)
+    }
+
+    pub fn put(&mut self, key: &[u8], value: &[u8]) -> Result<()> {
+        assert!(!value.is_empty(), "value cannot be empty");
+        assert!(!key.is_empty(), "key cannot be empty");
+        unimplemented!()
+    }
+
+    pub fn delete(&mut self, _key: &[u8]) -> Result<()> {
+        unimplemented!()
+    }
+
+    pub fn sync(&mut self) -> Result<()> {
+        unimplemented!()
+    }
+
+    pub fn scan(&self, _lower: Bound<&[u8]>, _upper: Bound<&[u8]>) -> Result<LsmIterator> {
+        unimplemented!()
+    }
+}

mini-lsm-starter/src/mem_table.rs

@@ -0,0 +1,79 @@
+#![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::ops::Bound;
+
+use anyhow::Result;
+use bytes::Bytes;
+use crossbeam_skiplist::SkipMap;
+
+use crate::iterators::impls::StorageIterator;
+use crate::table::SsTableBuilder;
+
+/// A basic mem-table based on crossbeam-skiplist
+pub struct MemTable {
+    map: SkipMap<Bytes, Bytes>,
+}
+
+impl MemTable {
+    /// Create a new mem-table.
+    pub fn create() -> Self {
+        unimplemented!()
+    }
+
+    /// Get a value by key.
+    pub fn get(&self, key: &[u8]) -> Result<Option<Bytes>> {
+        unimplemented!()
+    }
+
+    /// Put a key-value pair into the mem-table.
+    pub fn put(&self, key: &[u8], value: &[u8]) -> Result<()> {
+        unimplemented!()
+    }
+
+    /// Get an iterator over a range of keys.
+    pub fn scan(&self, lower: Bound<&[u8]>, upper: Bound<&[u8]>) -> Result<MemTableIterator> {
+        unimplemented!()
+    }
+
+    /// Flush the mem-table to SSTable.
+    pub fn flush(&self, builder: &mut SsTableBuilder) -> Result<()> {
+        unimplemented!()
+    }
+}
+
+type SkipMapRangeIter<'a> =
+    crossbeam_skiplist::map::Range<'a, Bytes, (Bound<Bytes>, Bound<Bytes>), Bytes, Bytes>;
+
+/// An iterator over a range of `SkipMap`.
+pub struct MemTableIterator<'a> {
+    _phantom: std::marker::PhantomData<&'a ()>,
+}
+
+impl<'a> MemTableIterator<'a> {
+    fn new(iter: SkipMapRangeIter<'a>) -> Self {
+        unimplemented!()
+    }
+}
+
+impl StorageIterator for MemTableIterator<'_> {
+    fn value(&self) -> &[u8] {
+        unimplemented!()
+    }
+
+    fn key(&self) -> &[u8] {
+        unimplemented!()
+    }
+
+    fn is_valid(&self) -> bool {
+        unimplemented!()
+    }
+
+    fn next(&mut self) -> Result<()> {
+        unimplemented!()
+    }
+}
+
+#[cfg(test)]
+#[path = "mem_table_test.rs"]
+mod tests;

mini-lsm-starter/src/mem_table_test.rs

@@ -0,0 +1 @@
+//! Please copy `mini-lsm/src/mem_table_test.rs` here so that you can run tests.

mini-lsm-starter/src/table.rs

@@ -4,14 +4,15 @@
 mod builder;
 mod iterator;
 
-use std::{path::Path, sync::Arc};
+use std::path::Path;
+use std::sync::Arc;
 
+use anyhow::Result;
 pub use builder::SsTableBuilder;
 use bytes::{Buf, Bytes};
 pub use iterator::SsTableIterator;
 
 use crate::block::Block;
-use anyhow::Result;
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct BlockMeta {
@@ -25,7 +26,8 @@ impl BlockMeta {
     /// Encode block meta to a buffer.
     pub fn encode_block_meta(
         block_meta: &[BlockMeta],
-        #[allow(clippy::ptr_arg)] /* remove this allow after you finish */ buf: &mut Vec<u8>,
+        #[allow(clippy::ptr_arg)] // remove this allow after you finish
+        buf: &mut Vec<u8>,
     ) {
         unimplemented!()
     }

mini-lsm-starter/src/table/builder.rs

@@ -1,9 +1,10 @@
 #![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 anyhow::Result;
 use std::path::Path;
 
+use anyhow::Result;
+
 use super::{BlockMeta, SsTable};
 
 /// Builds an SSTable from key-value pairs.
@@ -14,17 +15,22 @@ pub struct SsTableBuilder {
 
 impl SsTableBuilder {
     /// Create a builder based on target SST size and target block size.
-    pub fn new(target_size: usize, block_size: usize) -> Self {
+    pub fn new(block_size: usize) -> Self {
         unimplemented!()
     }
 
-    /// Adds a key-value pair to SSTable, return false when SST full.
-    #[must_use]
-    pub fn add(&mut self, key: &[u8], value: &[u8]) -> bool {
+    /// Adds a key-value pair to SSTable
+    pub fn add(&mut self, key: &[u8], value: &[u8]) {
         unimplemented!()
     }
 
-    /// Builds the SSTable and writes it to the given path. No need to actually write to disk until chapter 4 block cache.
+    /// Get the estimated size of the SSTable.
+    pub fn estimated_size(&self) -> usize {
+        unimplemented!()
+    }
+
+    /// Builds the SSTable and writes it to the given path. No need to actually write to disk until
+    /// chapter 4 block cache.
     pub fn build(self, path: impl AsRef<Path>) -> Result<SsTable> {
         unimplemented!()
     }

mini-lsm-starter/src/table/iterator.rs

@@ -1,9 +1,10 @@
 #![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 anyhow::Result;
 use std::sync::Arc;
 
+use anyhow::Result;
+
 use super::SsTable;
 
 /// An iterator over the contents of an SSTable.

mini-lsm/Cargo.toml

@@ -12,4 +12,7 @@ description = "A tutorial for building an LSM tree storage engine in a week."
 
 [dependencies]
 anyhow = "1"
+arc-swap = "1"
 bytes = "1"
+crossbeam-skiplist = "0.1"
+parking_lot = "0.12"

mini-lsm/src/block.rs

@@ -1,14 +1,14 @@
 mod builder;
 mod iterator;
 
-use bytes::{Buf, BufMut, Bytes};
-
 pub use builder::BlockBuilder;
+use bytes::{Buf, BufMut, Bytes};
 pub use iterator::BlockIterator;
 
 pub const SIZEOF_U16: usize = std::mem::size_of::<u16>();
 
-/// A block is the smallest unit of read and caching in LSM tree. It is a collection of sorted key-value pairs.
+/// A block is the smallest unit of read and caching in LSM tree. It is a collection of sorted
+/// key-value pairs.
 pub struct Block {
     data: Vec<u8>,
     offsets: Vec<u16>,

mini-lsm/src/block/tests.rs

@@ -1,6 +1,8 @@
 use std::sync::Arc;
 
-use super::{builder::BlockBuilder, iterator::BlockIterator, *};
+use super::builder::BlockBuilder;
+use super::iterator::BlockIterator;
+use super::*;
 
 #[test]
 fn test_block_build_single_key() {

mini-lsm/src/iterators.rs

@@ -0,0 +1,6 @@
+pub mod impls;
+pub mod merge_iterator;
+pub mod two_merge_iterator;
+
+#[cfg(test)]
+mod tests;

mini-lsm/src/iterators/impls.rs

@@ -0,0 +1,15 @@
+use anyhow::Result;
+
+pub trait StorageIterator {
+    /// Get the current value.
+    fn value(&self) -> &[u8];
+
+    /// Get the current key.
+    fn key(&self) -> &[u8];
+
+    /// Check if the current iterator is valid.
+    fn is_valid(&self) -> bool;
+
+    /// Move to the next position.
+    fn next(&mut self) -> Result<()>;
+}

mini-lsm/src/iterators/merge_iterator.rs

@@ -0,0 +1,127 @@
+use std::cmp::{self};
+use std::collections::binary_heap::PeekMut;
+use std::collections::BinaryHeap;
+
+use anyhow::Result;
+
+use super::impls::StorageIterator;
+
+struct HeapWrapper<I: StorageIterator>(pub usize, pub Box<I>);
+
+impl<I: StorageIterator> PartialEq for HeapWrapper<I> {
+    fn eq(&self, other: &Self) -> bool {
+        self.partial_cmp(other).unwrap() == cmp::Ordering::Equal
+    }
+}
+
+impl<I: StorageIterator> Eq for HeapWrapper<I> {}
+
+impl<I: StorageIterator> PartialOrd for HeapWrapper<I> {
+    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
+        match self.1.key().cmp(other.1.key()) {
+            cmp::Ordering::Greater => Some(cmp::Ordering::Greater),
+            cmp::Ordering::Less => Some(cmp::Ordering::Less),
+            cmp::Ordering::Equal => self.0.partial_cmp(&other.0),
+        }
+        .map(|x| x.reverse())
+    }
+}
+
+impl<I: StorageIterator> Ord for HeapWrapper<I> {
+    fn cmp(&self, other: &Self) -> cmp::Ordering {
+        self.partial_cmp(other).unwrap()
+    }
+}
+
+/// Merge multiple iterators of the same type. If the same key occurs multiple times in some
+/// iterators, perfer the one with smaller index.
+pub struct MergeIterator<I: StorageIterator> {
+    iters: BinaryHeap<HeapWrapper<I>>,
+    current: HeapWrapper<I>,
+}
+
+impl<I: StorageIterator> MergeIterator<I> {
+    pub fn create(iters: Vec<Box<I>>) -> Self {
+        assert!(!iters.is_empty());
+
+        let mut heap = BinaryHeap::new();
+
+        if iters.iter().all(|x| !x.is_valid()) {
+            // All invalid, select the last one as the current.
+            let mut iters = iters;
+            return Self {
+                iters: heap,
+                current: HeapWrapper(0, iters.pop().unwrap()),
+            };
+        }
+
+        for (idx, iter) in iters.into_iter().enumerate() {
+            if iter.is_valid() {
+                heap.push(HeapWrapper(idx, iter));
+            }
+        }
+
+        let current = heap.pop().unwrap();
+        Self {
+            iters: heap,
+            current,
+        }
+    }
+}
+
+impl<I: StorageIterator> StorageIterator for MergeIterator<I> {
+    fn key(&self) -> &[u8] {
+        self.current.1.key()
+    }
+
+    fn value(&self) -> &[u8] {
+        self.current.1.value()
+    }
+
+    fn is_valid(&self) -> bool {
+        self.current.1.is_valid()
+    }
+
+    fn next(&mut self) -> Result<()> {
+        // Pop the item out of the heap if they have the same value.
+        while let Some(mut inner_iter) = self.iters.peek_mut() {
+            debug_assert!(
+                inner_iter.1.key() >= self.current.1.key(),
+                "heap invariant violated"
+            );
+            if inner_iter.1.key() == self.current.1.key() {
+                // Case 1: an error occurred when calling `next`.
+                if let e @ Err(_) = inner_iter.1.next() {
+                    PeekMut::pop(inner_iter);
+                    return e;
+                }
+
+                // Case 2: iter is no longer valid.
+                if !inner_iter.1.is_valid() {
+                    PeekMut::pop(inner_iter);
+                }
+            } else {
+                break;
+            }
+        }
+
+        self.current.1.next()?;
+
+        // If the current iterator is invalid, pop it out of the heap and select the next one.
+        if !self.current.1.is_valid() {
+            if let Some(iter) = self.iters.pop() {
+                self.current = iter;
+            }
+            return Ok(());
+        }
+
+        // Otherwise, compare with heap top and swap if necessary.
+        if let Some(mut inner_iter) = self.iters.peek_mut() {
+            if self.current < *inner_iter {
+                std::mem::swap(&mut *inner_iter, &mut self.current);
+            }
+        }
+
+        Ok(())
+    }
+}

mini-lsm/src/iterators/tests.rs

@@ -0,0 +1,40 @@
+use anyhow::Result;
+use bytes::Bytes;
+
+use super::impls::StorageIterator;
+
+pub mod merge_iterator_test;
+pub mod two_merge_iterator_test;
+
+#[derive(Clone)]
+pub struct MockIterator {
+    pub data: Vec<(Bytes, Bytes)>,
+    pub index: usize,
+}
+
+impl MockIterator {
+    pub fn new(data: Vec<(Bytes, Bytes)>) -> Self {
+        Self { data, index: 0 }
+    }
+}
+
+impl StorageIterator for MockIterator {
+    fn next(&mut self) -> Result<()> {
+        if self.index < self.data.len() {
+            self.index += 1;
+        }
+        Ok(())
+    }
+
+    fn key(&self) -> &[u8] {
+        self.data[self.index].0.as_ref()
+    }
+
+    fn value(&self) -> &[u8] {
+        self.data[self.index].1.as_ref()
+    }
+
+    fn is_valid(&self) -> bool {
+        self.index < self.data.len()
+    }
+}

mini-lsm/src/iterators/tests/merge_iterator_test.rs

@@ -0,0 +1,131 @@
+use super::*;
+use crate::iterators::merge_iterator::MergeIterator;
+
+fn as_bytes(x: &[u8]) -> Bytes {
+    Bytes::copy_from_slice(x)
+}
+
+fn check_iter_result(iter: impl StorageIterator, expected: Vec<(Bytes, Bytes)>) {
+    let mut iter = iter;
+    for (k, v) in expected {
+        assert!(iter.is_valid());
+        assert_eq!(
+            k,
+            iter.key(),
+            "expected key: {:?}, actual key: {:?}",
+            k,
+            as_bytes(iter.key()),
+        );
+        assert_eq!(
+            v,
+            iter.value(),
+            "expected value: {:?}, actual value: {:?}",
+            v,
+            as_bytes(iter.value()),
+        );
+        iter.next().unwrap();
+    }
+    assert!(!iter.is_valid());
+}
+
+#[test]
+fn test_merge_1() {
+    let i1 = MockIterator::new(vec![
+        (Bytes::from("a"), Bytes::from("1.1")),
+        (Bytes::from("b"), Bytes::from("2.1")),
+        (Bytes::from("c"), Bytes::from("3.1")),
+    ]);
+    let i2 = MockIterator::new(vec![
+        (Bytes::from("a"), Bytes::from("1.2")),
+        (Bytes::from("b"), Bytes::from("2.2")),
+        (Bytes::from("c"), Bytes::from("3.2")),
+        (Bytes::from("d"), Bytes::from("4.2")),
+    ]);
+    let i3 = MockIterator::new(vec![
+        (Bytes::from("b"), Bytes::from("2.3")),
+        (Bytes::from("c"), Bytes::from("3.3")),
+        (Bytes::from("d"), Bytes::from("4.3")),
+    ]);
+
+    let iter = MergeIterator::create(vec![
+        Box::new(i1.clone()),
+        Box::new(i2.clone()),
+        Box::new(i3.clone()),
+    ]);
+
+    check_iter_result(
+        iter,
+        vec![
+            (Bytes::from("a"), Bytes::from("1.1")),
+            (Bytes::from("b"), Bytes::from("2.1")),
+            (Bytes::from("c"), Bytes::from("3.1")),
+            (Bytes::from("d"), Bytes::from("4.2")),
+        ],
+    );
+
+    let iter = MergeIterator::create(vec![Box::new(i3), Box::new(i1), Box::new(i2)]);
+
+    check_iter_result(
+        iter,
+        vec![
+            (Bytes::from("a"), Bytes::from("1.1")),
+            (Bytes::from("b"), Bytes::from("2.3")),
+            (Bytes::from("c"), Bytes::from("3.3")),
+            (Bytes::from("d"), Bytes::from("4.3")),
+        ],
+    );
+}
+
+#[test]
+fn test_merge_2() {
+    let i1 = MockIterator::new(vec![
+        (Bytes::from("a"), Bytes::from("1.1")),
+        (Bytes::from("b"), Bytes::from("2.1")),
+        (Bytes::from("c"), Bytes::from("3.1")),
+    ]);
+    let i2 = MockIterator::new(vec![
+        (Bytes::from("d"), Bytes::from("1.2")),
+        (Bytes::from("e"), Bytes::from("2.2")),
+        (Bytes::from("f"), Bytes::from("3.2")),
+        (Bytes::from("g"), Bytes::from("4.2")),
+    ]);
+    let i3 = MockIterator::new(vec![
+        (Bytes::from("h"), Bytes::from("1.3")),
+        (Bytes::from("i"), Bytes::from("2.3")),
+        (Bytes::from("j"), Bytes::from("3.3")),
+        (Bytes::from("k"), Bytes::from("4.3")),
+    ]);
+    let i4 = MockIterator::new(vec![]);
+    let result = vec![
+        (Bytes::from("a"), Bytes::from("1.1")),
+        (Bytes::from("b"), Bytes::from("2.1")),
+        (Bytes::from("c"), Bytes::from("3.1")),
+        (Bytes::from("d"), Bytes::from("1.2")),
+        (Bytes::from("e"), Bytes::from("2.2")),
+        (Bytes::from("f"), Bytes::from("3.2")),
+        (Bytes::from("g"), Bytes::from("4.2")),
+        (Bytes::from("h"), Bytes::from("1.3")),
+        (Bytes::from("i"), Bytes::from("2.3")),
+        (Bytes::from("j"), Bytes::from("3.3")),
+        (Bytes::from("k"), Bytes::from("4.3")),
+    ];
+
+    let iter = MergeIterator::create(vec![
+        Box::new(i1.clone()),
+        Box::new(i2.clone()),
+        Box::new(i3.clone()),
+        Box::new(i4.clone()),
+    ]);
+    check_iter_result(iter, result.clone());
+
+    let iter = MergeIterator::create(vec![
+        Box::new(i2.clone()),
+        Box::new(i4.clone()),
+        Box::new(i3.clone()),
+        Box::new(i1.clone()),
+    ]);
+    check_iter_result(iter, result.clone());
+
+    let iter = MergeIterator::create(vec![Box::new(i4), Box::new(i3), Box::new(i2), Box::new(i1)]);
+    check_iter_result(iter, result);
+}

mini-lsm/src/iterators/tests/two_merge_iterator_test.rs

@@ -0,0 +1,129 @@
+use super::*;
+use crate::iterators::two_merge_iterator::TwoMergeIterator;
+
+fn check_iter_result(iter: impl StorageIterator, expected: Vec<(Bytes, Bytes)>) {
+    let mut iter = iter;
+    for (k, v) in expected {
+        assert!(iter.is_valid());
+        assert_eq!(iter.key(), k.as_ref());
+        assert_eq!(iter.value(), v.as_ref());
+        iter.next().unwrap();
+    }
+    assert!(!iter.is_valid());
+}
+
+#[test]
+fn test_merge_1() {
+    let i1 = MockIterator::new(vec![
+        (Bytes::from("a"), Bytes::from("1.1")),
+        (Bytes::from("b"), Bytes::from("2.1")),
+        (Bytes::from("c"), Bytes::from("3.1")),
+    ]);
+    let i2 = MockIterator::new(vec![
+        (Bytes::from("a"), Bytes::from("1.2")),
+        (Bytes::from("b"), Bytes::from("2.2")),
+        (Bytes::from("c"), Bytes::from("3.2")),
+        (Bytes::from("d"), Bytes::from("4.2")),
+    ]);
+    let iter = TwoMergeIterator::create(i1, i2).unwrap();
+    check_iter_result(
+        iter,
+        vec![
+            (Bytes::from("a"), Bytes::from("1.1")),
+            (Bytes::from("b"), Bytes::from("2.1")),
+            (Bytes::from("c"), Bytes::from("3.1")),
+            (Bytes::from("d"), Bytes::from("4.2")),
+        ],
+    )
+}
+
+#[test]
+fn test_merge_2() {
+    let i2 = MockIterator::new(vec![
+        (Bytes::from("a"), Bytes::from("1.1")),
+        (Bytes::from("b"), Bytes::from("2.1")),
+        (Bytes::from("c"), Bytes::from("3.1")),
+    ]);
+    let i1 = MockIterator::new(vec![
+        (Bytes::from("a"), Bytes::from("1.2")),
+        (Bytes::from("b"), Bytes::from("2.2")),
+        (Bytes::from("c"), Bytes::from("3.2")),
+        (Bytes::from("d"), Bytes::from("4.2")),
+    ]);
+    let iter = TwoMergeIterator::create(i1, i2).unwrap();
+    check_iter_result(
+        iter,
+        vec![
+            (Bytes::from("a"), Bytes::from("1.2")),
+            (Bytes::from("b"), Bytes::from("2.2")),
+            (Bytes::from("c"), Bytes::from("3.2")),
+            (Bytes::from("d"), Bytes::from("4.2")),
+        ],
+    )
+}
+
+#[test]
+fn test_merge_3() {
+    let i2 = MockIterator::new(vec![
+        (Bytes::from("a"), Bytes::from("1.1")),
+        (Bytes::from("b"), Bytes::from("2.1")),
+        (Bytes::from("c"), Bytes::from("3.1")),
+    ]);
+    let i1 = MockIterator::new(vec![
+        (Bytes::from("b"), Bytes::from("2.2")),
+        (Bytes::from("c"), Bytes::from("3.2")),
+        (Bytes::from("d"), Bytes::from("4.2")),
+    ]);
+    let iter = TwoMergeIterator::create(i1, i2).unwrap();
+    check_iter_result(
+        iter,
+        vec![
+            (Bytes::from("a"), Bytes::from("1.1")),
+            (Bytes::from("b"), Bytes::from("2.2")),
+            (Bytes::from("c"), Bytes::from("3.2")),
+            (Bytes::from("d"), Bytes::from("4.2")),
+        ],
+    )
+}
+
+#[test]
+fn test_merge_4() {
+    let i2 = MockIterator::new(vec![]);
+    let i1 = MockIterator::new(vec![
+        (Bytes::from("b"), Bytes::from("2.2")),
+        (Bytes::from("c"), Bytes::from("3.2")),
+        (Bytes::from("d"), Bytes::from("4.2")),
+    ]);
+    let iter = TwoMergeIterator::create(i1, i2).unwrap();
+    check_iter_result(
+        iter,
+        vec![
+            (Bytes::from("b"), Bytes::from("2.2")),
+            (Bytes::from("c"), Bytes::from("3.2")),
+            (Bytes::from("d"), Bytes::from("4.2")),
+        ],
+    );
+    let i1 = MockIterator::new(vec![]);
+    let i2 = MockIterator::new(vec![
+        (Bytes::from("b"), Bytes::from("2.2")),
+        (Bytes::from("c"), Bytes::from("3.2")),
+        (Bytes::from("d"), Bytes::from("4.2")),
+    ]);
+    let iter = TwoMergeIterator::create(i1, i2).unwrap();
+    check_iter_result(
+        iter,
+        vec![
+            (Bytes::from("b"), Bytes::from("2.2")),
+            (Bytes::from("c"), Bytes::from("3.2")),
+            (Bytes::from("d"), Bytes::from("4.2")),
+        ],
+    );
+}
+
+#[test]
+fn test_merge_5() {
+    let i2 = MockIterator::new(vec![]);
+    let i1 = MockIterator::new(vec![]);
+    let iter = TwoMergeIterator::create(i1, i2).unwrap();
+    check_iter_result(iter, vec![])
+}

mini-lsm/src/iterators/two_merge_iterator.rs

@@ -0,0 +1,80 @@
+use anyhow::Result;
+
+use super::impls::StorageIterator;
+
+/// Merges two iterators of different types into one. If the two iterators have the same key, only
+/// produce the key once and prefer the entry from A.
+pub struct TwoMergeIterator<A: StorageIterator, B: StorageIterator> {
+    a: A,
+    b: B,
+    choose_a: bool,
+}
+
+impl<A: StorageIterator, B: StorageIterator> TwoMergeIterator<A, B> {
+    fn choose_a(a: &A, b: &B) -> bool {
+        if !a.is_valid() {
+            return false;
+        }
+        if !b.is_valid() {
+            return true;
+        }
+        a.key() < b.key()
+    }
+
+    fn skip_b(&mut self) -> Result<()> {
+        if self.a.is_valid() {
+            while self.b.is_valid() && self.b.key() == self.a.key() {
+                self.b.next()?;
+            }
+        }
+        Ok(())
+    }
+
+    pub fn create(a: A, b: B) -> Result<Self> {
+        let mut iter = Self {
+            choose_a: false,
+            a,
+            b,
+        };
+        iter.skip_b()?;
+        iter.choose_a = Self::choose_a(&iter.a, &iter.b);
+        Ok(iter)
+    }
+}
+
+impl<A: StorageIterator, B: StorageIterator> StorageIterator for TwoMergeIterator<A, B> {
+    fn key(&self) -> &[u8] {
+        if self.choose_a {
+            self.a.key()
+        } else {
+            self.b.key()
+        }
+    }
+
+    fn value(&self) -> &[u8] {
+        if self.choose_a {
+            self.a.value()
+        } else {
+            self.b.value()
+        }
+    }
+
+    fn is_valid(&self) -> bool {
+        if self.choose_a {
+            self.a.is_valid()
+        } else {
+            self.b.is_valid()
+        }
+    }
+
+    fn next(&mut self) -> Result<()> {
+        if self.choose_a {
+            self.a.next()?;
+        } else {
+            self.b.next()?;
+        }
+        self.skip_b()?;
+        self.choose_a = Self::choose_a(&self.a, &self.b);
+        Ok(())
+    }
+}

mini-lsm/src/lib.rs

@@ -1,3 +1,6 @@
 pub mod block;
-pub mod storage;
+pub mod iterators;
+pub mod lsm_iterator;
+pub mod lsm_storage;
+pub mod mem_table;
 pub mod table;

mini-lsm/src/lsm_iterator.rs

@@ -0,0 +1 @@
+pub struct LsmIterator {}

mini-lsm/src/lsm_storage.rs

@@ -0,0 +1,75 @@
+use std::ops::Bound;
+use std::path::Path;
+use std::sync::Arc;
+
+use anyhow::Result;
+use arc_swap::ArcSwap;
+use bytes::Bytes;
+
+use crate::lsm_iterator::LsmIterator;
+use crate::mem_table::MemTable;
+use crate::table::{SsTable, SsTableIterator};
+
+pub struct LsmStorageInner {
+    memtables: Vec<Arc<MemTable>>,
+    sstables: Vec<Arc<SsTable>>,
+}
+
+impl LsmStorageInner {
+    fn create() -> Self {
+        Self {
+            memtables: vec![Arc::new(MemTable::create())],
+            sstables: vec![],
+        }
+    }
+}
+
+/// The storage interface of the LSM tree.
+pub struct LsmStorage {
+    inner: ArcSwap<LsmStorageInner>,
+}
+
+impl LsmStorage {
+    pub fn open(_path: &Path) -> Result<Self> {
+        Ok(Self {
+            inner: ArcSwap::from_pointee(LsmStorageInner::create()),
+        })
+    }
+
+    pub fn get(&self, key: &[u8]) -> Result<Option<Bytes>> {
+        let snapshot = self.inner.load();
+        for memtable in &snapshot.memtables {
+            if let Some(value) = memtable.get(key)? {
+                if value.is_empty() {
+                    // found tomestone, return key not exists
+                    return Ok(None);
+                }
+                return Ok(Some(value));
+            }
+        }
+        let mut iters = Vec::new();
+        iters.reserve(snapshot.sstables.len());
+        for table in snapshot.sstables.iter().rev() {
+            iters.push(SsTableIterator::create_and_seek_to_key(table.clone(), key)?);
+        }
+        Ok(None)
+    }
+
+    pub fn put(&mut self, key: &[u8], value: &[u8]) -> Result<()> {
+        assert!(!value.is_empty(), "value cannot be empty");
+        assert!(!key.is_empty(), "key cannot be empty");
+        unimplemented!()
+    }
+
+    pub fn delete(&mut self, _key: &[u8]) -> Result<()> {
+        unimplemented!()
+    }
+
+    pub fn sync(&mut self) -> Result<()> {
+        unimplemented!()
+    }
+
+    pub fn scan(&self, _lower: Bound<&[u8]>, _upper: Bound<&[u8]>) -> Result<LsmIterator> {
+        unimplemented!()
+    }
+}

mini-lsm/src/mem_table.rs

@@ -0,0 +1,110 @@
+use std::ops::Bound;
+
+use anyhow::Result;
+use bytes::Bytes;
+use crossbeam_skiplist::map::Entry;
+use crossbeam_skiplist::SkipMap;
+
+use crate::iterators::impls::StorageIterator;
+use crate::table::SsTableBuilder;
+
+/// A basic mem-table based on crossbeam-skiplist
+pub struct MemTable {
+    map: SkipMap<Bytes, Bytes>,
+}
+
+impl MemTable {
+    /// Create a new mem-table.
+    pub fn create() -> Self {
+        Self {
+            map: SkipMap::new(),
+        }
+    }
+
+    /// Get a value by key.
+    pub fn get(&self, key: &[u8]) -> Result<Option<Bytes>> {
+        let entry = self.map.get(key).map(|e| e.value().clone());
+        Ok(entry)
+    }
+
+    /// Put a key-value pair into the mem-table.
+    pub fn put(&self, key: &[u8], value: &[u8]) -> Result<()> {
+        self.map
+            .insert(Bytes::copy_from_slice(key), Bytes::copy_from_slice(value));
+        Ok(())
+    }
+
+    fn map_bound(bound: Bound<&[u8]>) -> Bound<Bytes> {
+        match bound {
+            Bound::Included(x) => Bound::Included(Bytes::copy_from_slice(x)),
+            Bound::Excluded(x) => Bound::Excluded(Bytes::copy_from_slice(x)),
+            Bound::Unbounded => Bound::Unbounded,
+        }
+    }
+
+    /// Get an iterator over a range of keys.
+    pub fn scan(&self, lower: Bound<&[u8]>, upper: Bound<&[u8]>) -> Result<MemTableIterator> {
+        let iter = self
+            .map
+            .range((Self::map_bound(lower), Self::map_bound(upper)));
+        Ok(MemTableIterator::new(iter))
+    }
+
+    /// Flush the mem-table to SSTable.
+    pub fn flush(&self, builder: &mut SsTableBuilder) -> Result<()> {
+        for entry in self.map.iter() {
+            builder.add(&entry.key()[..], &entry.value()[..]);
+        }
+        Ok(())
+    }
+}
+
+type SkipMapRangeIter<'a> =
+    crossbeam_skiplist::map::Range<'a, Bytes, (Bound<Bytes>, Bound<Bytes>), Bytes, Bytes>;
+
+/// An iterator over a range of `SkipMap`.
+pub struct MemTableIterator<'a> {
+    iter: SkipMapRangeIter<'a>,
+    item: (Bytes, Bytes),
+}
+
+impl<'a> MemTableIterator<'a> {
+    fn entry_to_item(entry: Option<Entry<'a, Bytes, Bytes>>) -> (Bytes, Bytes) {
+        entry
+            .map(|x| (x.key().clone(), x.value().clone()))
+            .unwrap_or_else(|| (Bytes::from_static(&[]), Bytes::from_static(&[])))
+    }
+
+    fn new(mut iter: SkipMapRangeIter<'a>) -> Self {
+        let entry = iter.next();
+
+        Self {
+            item: Self::entry_to_item(entry),
+            iter,
+        }
+    }
+}
+
+impl StorageIterator for MemTableIterator<'_> {
+    fn value(&self) -> &[u8] {
+        &self.item.1[..]
+    }
+
+    fn key(&self) -> &[u8] {
+        &self.item.0[..]
+    }
+
+    fn is_valid(&self) -> bool {
+        !self.item.0.is_empty()
+    }
+
+    fn next(&mut self) -> Result<()> {
+        let entry = self.iter.next();
+        self.item = Self::entry_to_item(entry);
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+#[path = "mem_table_test.rs"]
+mod tests;

mini-lsm/src/mem_table_test.rs

@@ -0,0 +1,96 @@
+use super::MemTable;
+use crate::iterators::impls::StorageIterator;
+use crate::table::{SsTableBuilder, SsTableIterator};
+
+#[test]
+fn test_memtable_get() {
+    let memtable = MemTable::create();
+    memtable.put(b"key1", b"value1").unwrap();
+    memtable.put(b"key2", b"value2").unwrap();
+    memtable.put(b"key3", b"value3").unwrap();
+    assert_eq!(&memtable.get(b"key1").unwrap().unwrap()[..], b"value1");
+    assert_eq!(&memtable.get(b"key2").unwrap().unwrap()[..], b"value2");
+    assert_eq!(&memtable.get(b"key3").unwrap().unwrap()[..], b"value3");
+}
+
+#[test]
+fn test_memtable_overwrite() {
+    let memtable = MemTable::create();
+    memtable.put(b"key1", b"value1").unwrap();
+    memtable.put(b"key2", b"value2").unwrap();
+    memtable.put(b"key3", b"value3").unwrap();
+    memtable.put(b"key1", b"value11").unwrap();
+    memtable.put(b"key2", b"value22").unwrap();
+    memtable.put(b"key3", b"value33").unwrap();
+    assert_eq!(&memtable.get(b"key1").unwrap().unwrap()[..], b"value11");
+    assert_eq!(&memtable.get(b"key2").unwrap().unwrap()[..], b"value22");
+    assert_eq!(&memtable.get(b"key3").unwrap().unwrap()[..], b"value33");
+}
+
+#[test]
+fn test_memtable_flush() {
+    let memtable = MemTable::create();
+    memtable.put(b"key1", b"value1").unwrap();
+    memtable.put(b"key2", b"value2").unwrap();
+    memtable.put(b"key3", b"value3").unwrap();
+    let mut builder = SsTableBuilder::new(128);
+    memtable.flush(&mut builder).unwrap();
+    let sst = builder.build("").unwrap();
+    let mut iter = SsTableIterator::create_and_seek_to_first(sst.into()).unwrap();
+    assert_eq!(iter.key(), b"key1");
+    assert_eq!(iter.value(), b"value1");
+    iter.next().unwrap();
+    assert_eq!(iter.key(), b"key2");
+    assert_eq!(iter.value(), b"value2");
+    iter.next().unwrap();
+    assert_eq!(iter.key(), b"key3");
+    assert_eq!(iter.value(), b"value3");
+    iter.next().unwrap();
+    assert!(!iter.is_valid());
+}
+
+#[test]
+fn test_memtable_iter() {
+    use std::ops::Bound;
+    let memtable = MemTable::create();
+    memtable.put(b"key1", b"value1").unwrap();
+    memtable.put(b"key2", b"value2").unwrap();
+    memtable.put(b"key3", b"value3").unwrap();
+
+    {
+        let mut iter = memtable.scan(Bound::Unbounded, Bound::Unbounded).unwrap();
+        assert_eq!(iter.key(), b"key1");
+        assert_eq!(iter.value(), b"value1");
+        iter.next().unwrap();
+        assert_eq!(iter.key(), b"key2");
+        assert_eq!(iter.value(), b"value2");
+        iter.next().unwrap();
+        assert_eq!(iter.key(), b"key3");
+        assert_eq!(iter.value(), b"value3");
+        iter.next().unwrap();
+        assert!(!iter.is_valid());
+    }
+
+    {
+        let mut iter = memtable
+            .scan(Bound::Included(b"key1"), Bound::Included(b"key2"))
+            .unwrap();
+        assert_eq!(iter.key(), b"key1");
+        assert_eq!(iter.value(), b"value1");
+        iter.next().unwrap();
+        assert_eq!(iter.key(), b"key2");
+        assert_eq!(iter.value(), b"value2");
+        iter.next().unwrap();
+        assert!(!iter.is_valid());
+    }
+
+    {
+        let mut iter = memtable
+            .scan(Bound::Excluded(b"key1"), Bound::Excluded(b"key3"))
+            .unwrap();
+        assert_eq!(iter.key(), b"key2");
+        assert_eq!(iter.value(), b"value2");
+        iter.next().unwrap();
+        assert!(!iter.is_valid());
+    }
+}

mini-lsm/src/storage.rs

@@ -1 +0,0 @@
-pub struct Storage {}

mini-lsm/src/table.rs

@@ -1,14 +1,15 @@
 mod builder;
 mod iterator;
 
-use std::{path::Path, sync::Arc};
+use std::path::Path;
+use std::sync::Arc;
 
+use anyhow::Result;
 pub use builder::SsTableBuilder;
 use bytes::{Buf, BufMut, Bytes};
 pub use iterator::SsTableIterator;
 
 use crate::block::Block;
-use anyhow::Result;
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct BlockMeta {

mini-lsm/src/table/builder.rs

@@ -1,6 +1,7 @@
+use std::path::Path;
+
 use anyhow::Result;
 use bytes::BufMut;
-use std::path::Path;
 
 use super::{BlockMeta, FileObject, SsTable};
 use crate::block::BlockBuilder;
@@ -11,36 +12,29 @@ pub struct SsTableBuilder {
     first_key: Vec<u8>,
     data: Vec<u8>,
     pub(super) meta: Vec<BlockMeta>,
-    target_size: usize,
     block_size: usize,
 }
 
 impl SsTableBuilder {
     /// Create a builder based on target SST size and target block size.
-    pub fn new(target_size: usize, block_size: usize) -> Self {
+    pub fn new(block_size: usize) -> Self {
         Self {
             data: Vec::new(),
             meta: Vec::new(),
             first_key: Vec::new(),
-            target_size,
             block_size,
             builder: BlockBuilder::new(block_size),
         }
     }
 
-    /// Adds a key-value pair to SSTable, return false when SST full.
-    #[must_use]
-    pub fn add(&mut self, key: &[u8], value: &[u8]) -> bool {
-        if self.data.len() > self.target_size {
-            return false;
-        }
-
+    /// Adds a key-value pair to SSTable
+    pub fn add(&mut self, key: &[u8], value: &[u8]) {
         if self.first_key.is_empty() {
             self.first_key = key.to_vec();
         }
 
         if self.builder.add(key, value) {
-            return true;
+            return;
         }
         // create a new block builder and append block data
         self.finish_block();
@@ -48,8 +42,11 @@ impl SsTableBuilder {
         // add the key-value pair to the next block
         assert!(self.builder.add(key, value));
         self.first_key = key.to_vec();
+    }
 
-        true
+    /// Get the estimated size of the SSTable.
+    pub fn estimated_size(&self) -> usize {
+        self.data.len()
     }
 
     fn finish_block(&mut self) {
@@ -62,7 +59,8 @@ impl SsTableBuilder {
         self.data.extend(encoded_block);
     }
 
-    /// Builds the SSTable and writes it to the given path. No need to actually write to disk until chapter 4 block cache.
+    /// Builds the SSTable and writes it to the given path. No need to actually write to disk until
+    /// chapter 4 block cache.
     pub fn build(mut self, path: impl AsRef<Path>) -> Result<SsTable> {
         self.finish_block();
         let mut buf = self.data;

mini-lsm/src/table/iterator.rs

@@ -1,8 +1,10 @@
-use anyhow::Result;
 use std::sync::Arc;
 
+use anyhow::Result;
+
 use super::SsTable;
 use crate::block::BlockIterator;
+use crate::iterators::impls::StorageIterator;
 
 /// An iterator over the contents of an SSTable.
 pub struct SsTableIterator {
@@ -68,25 +70,22 @@ impl SsTableIterator {
         self.blk_idx = blk_idx;
         Ok(())
     }
-
-    /// Get the current key.
-    pub fn key(&self) -> &[u8] {
-        self.blk_iter.key()
 }
 
-    /// Get the current value.
-    pub fn value(&self) -> &[u8] {
+impl StorageIterator for SsTableIterator {
+    fn value(&self) -> &[u8] {
         self.blk_iter.value()
     }
 
-    /// Check if the iterator is valid.
-    pub fn is_valid(&self) -> bool {
+    fn key(&self) -> &[u8] {
+        self.blk_iter.key()
+    }
+
+    fn is_valid(&self) -> bool {
         self.blk_iter.is_valid()
     }
 
-    /// Move to the next key-value pair.
-    #[allow(clippy::should_implement_trait)]
-    pub fn next(&mut self) -> Result<()> {
+    fn next(&mut self) -> Result<()> {
         self.blk_iter.next();
         if !self.blk_iter.is_valid() {
             self.blk_idx += 1;

mini-lsm/src/table/tests.rs

@@ -2,41 +2,30 @@ use std::sync::Arc;
 
 use bytes::Bytes;
 
+use super::*;
+use crate::iterators::impls::StorageIterator;
 use crate::table::SsTableBuilder;
 
-use super::{SsTable, SsTableIterator};
-
 #[test]
 fn test_sst_build_single_key() {
-    let mut builder = SsTableBuilder::new(16, 16);
-    assert!(builder.add(b"233", b"233333"));
+    let mut builder = SsTableBuilder::new(16);
+    builder.add(b"233", b"233333");
     builder.build("").unwrap();
 }
 
 #[test]
 fn test_sst_build_two_blocks() {
-    let mut builder = SsTableBuilder::new(1024, 16);
-    assert!(builder.add(b"11", b"11"));
-    assert!(builder.add(b"22", b"22"));
-    assert!(builder.add(b"33", b"11"));
-    assert!(builder.add(b"44", b"22"));
-    assert!(builder.add(b"55", b"11"));
-    assert!(builder.add(b"66", b"22"));
+    let mut builder = SsTableBuilder::new(16);
+    builder.add(b"11", b"11");
+    builder.add(b"22", b"22");
+    builder.add(b"33", b"11");
+    builder.add(b"44", b"22");
+    builder.add(b"55", b"11");
+    builder.add(b"66", b"22");
     assert!(builder.meta.len() >= 2);
     builder.build("").unwrap();
 }
 
-#[test]
-fn test_sst_build_full() {
-    let mut builder = SsTableBuilder::new(32, 16);
-    assert!(builder.add(b"11", b"11"));
-    assert!(builder.add(b"22", b"22"));
-    assert!(builder.add(b"33", b"11"));
-    assert!(builder.add(b"44", b"22"));
-    assert!(!builder.add(b"55", b"11"));
-    builder.build("").unwrap();
-}
-
 fn key_of(idx: usize) -> Vec<u8> {
     format!("key_{:03}", idx * 5).into_bytes()
 }
@@ -50,11 +39,11 @@ fn num_of_keys() -> usize {
 }
 
 fn generate_sst() -> SsTable {
-    let mut builder = SsTableBuilder::new(65536, 128);
+    let mut builder = SsTableBuilder::new(128);
     for idx in 0..num_of_keys() {
         let key = key_of(idx);
         let value = value_of(idx);
-        assert!(builder.add(&key[..], &value[..]));
+        builder.add(&key[..], &value[..]);
     }
     builder.build("").unwrap()
 }