refactor: move iterator trait to parent mod

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

mini-lsm-book/src/04-engine.md

@@ -1 +1,25 @@
 # Storage Engine and Block Cache
+
+
+<!-- toc -->
+
+In this part, you will need to modify:
+
+* `src/lsm_iterator.rs`
+* `src/lsm_storage.rs`
+* Other parts that use `SsTable::read_block`
+
+You can use `cargo x copy-test day4` to copy our provided test cases to the starter code directory. After you have
+finished this part, use `cargo x scheck` to check the style and run all test cases. If you want to write your own
+test cases, write a new module `#[cfg(test)] mod user_tests { /* your test cases */ }` in `table.rs`. Remember to remove
+`#![allow(...)]` at the top of the modules you modified so that cargo clippy can actually check the styles.
+
+## Task 1 - Put and Delete
+
+## Task 2 - Get
+
+## Task 3 - Scan
+
+## Task 4 - Sync
+
+## Task 5 - Block Cache

mini-lsm-book/src/SUMMARY.md

@@ -6,8 +6,8 @@
 
 - [Store key-value pairs in little blocks](./01-block.md)
 - [And make them into an SST](./02-sst.md)
-- [Now it's time for merging everything](./03-memtable.md)
+- [Now it's time to merge everything](./03-memtable.md)
-- [Block cache, the good way](./04-engine.md)
+- [The engine starts](./04-engine.md)
 - [Let's do something in the background](./05-compaction.md)
 - [Be careful when the system crashes](./06-recovery.md)
 - [A good bloom filter makes life easier](./07-bloom-filter.md)

mini-lsm-starter/src/iterators.rs

@@ -1,6 +1,19 @@
-pub mod impls;
 pub mod merge_iterator;
 pub mod two_merge_iterator;
 
+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) -> anyhow::Result<()>;
+}
+
 #[cfg(test)]
 mod tests;

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

@@ -1,15 +0,0 @@
-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

@@ -6,7 +6,7 @@ use std::collections::BinaryHeap;
 
 use anyhow::Result;
 
-use super::impls::StorageIterator;
+use super::StorageIterator;
 
 struct HeapWrapper<I: StorageIterator>(pub usize, pub Box<I>);
 

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

@@ -3,7 +3,7 @@
 
 use anyhow::Result;
 
-use super::impls::StorageIterator;
+use super::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.

mini-lsm-starter/src/lsm_iterator.rs

@@ -3,7 +3,7 @@
 
 use anyhow::Result;
 
-use crate::iterators::impls::StorageIterator;
+use crate::iterators::StorageIterator;
 
 pub struct LsmIterator {}
 

mini-lsm-starter/src/lsm_storage.rs

@@ -45,24 +45,32 @@ impl LsmStorage {
         })
     }
 
+    /// Get a key from the storage. In day 7, this can be further optimized by using a bloom filter.
     pub fn get(&self, key: &[u8]) -> Result<Option<Bytes>> {
         unimplemented!()
     }
 
+    /// Put a key-value pair into the storage by writing into the current memtable.
     pub fn put(&self, key: &[u8], value: &[u8]) -> Result<()> {
         assert!(!value.is_empty(), "value cannot be empty");
         assert!(!key.is_empty(), "key cannot be empty");
         unimplemented!()
     }
 
+    /// Remove a key from the storage by writing an empty value.
     pub fn delete(&self, _key: &[u8]) -> Result<()> {
         unimplemented!()
     }
 
+    /// Persist data to disk.
+    ///
+    /// In day 3: flush the current memtable to disk as L0 SST.
+    /// In day 6: call `fsync` on WAL.
     pub fn sync(&self) -> Result<()> {
         unimplemented!()
     }
 
+    /// Create an iterator over a range of keys.
     pub fn scan(
         &self,
         _lower: Bound<&[u8]>,

mini-lsm-starter/src/mem_table.rs

@@ -9,7 +9,7 @@ use bytes::Bytes;
 use crossbeam_skiplist::SkipMap;
 use ouroboros::self_referencing;
 
-use crate::iterators::impls::StorageIterator;
+use crate::iterators::StorageIterator;
 use crate::table::SsTableBuilder;
 
 /// A basic mem-table based on crossbeam-skiplist

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

@@ -6,7 +6,7 @@ use std::sync::Arc;
 use anyhow::Result;
 
 use super::SsTable;
-use crate::iterators::impls::StorageIterator;
+use crate::iterators::StorageIterator;
 
 /// An iterator over the contents of an SSTable.
 pub struct SsTableIterator {}

mini-lsm/src/iterators.rs

@@ -1,6 +1,19 @@
-pub mod impls;
 pub mod merge_iterator;
 pub mod two_merge_iterator;
 
+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) -> anyhow::Result<()>;
+}
+
 #[cfg(test)]
 mod tests;

mini-lsm/src/iterators/impls.rs

@@ -1,15 +0,0 @@
-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

@@ -4,7 +4,7 @@ use std::collections::BinaryHeap;
 
 use anyhow::Result;
 
-use super::impls::StorageIterator;
+use super::StorageIterator;
 
 struct HeapWrapper<I: StorageIterator>(pub usize, pub Box<I>);
 

mini-lsm/src/iterators/tests.rs

@@ -1,7 +1,7 @@
 use anyhow::Result;
 use bytes::Bytes;
 
-use super::impls::StorageIterator;
+use super::StorageIterator;
 
 pub mod merge_iterator_test;
 pub mod two_merge_iterator_test;

mini-lsm/src/iterators/two_merge_iterator.rs

@@ -1,6 +1,6 @@
 use anyhow::Result;
 
-use super::impls::StorageIterator;
+use super::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.

mini-lsm/src/lsm_iterator.rs

@@ -3,9 +3,9 @@ use std::ops::Bound;
 use anyhow::Result;
 use bytes::Bytes;
 
-use crate::iterators::impls::StorageIterator;
 use crate::iterators::merge_iterator::MergeIterator;
 use crate::iterators::two_merge_iterator::TwoMergeIterator;
+use crate::iterators::StorageIterator;
 use crate::mem_table::MemTableIterator;
 use crate::table::SsTableIterator;
 

mini-lsm/src/lsm_storage.rs

@@ -7,9 +7,9 @@ use bytes::Bytes;
 use parking_lot::{Mutex, RwLock};
 
 use crate::block::Block;
-use crate::iterators::impls::StorageIterator;
 use crate::iterators::merge_iterator::MergeIterator;
 use crate::iterators::two_merge_iterator::TwoMergeIterator;
+use crate::iterators::StorageIterator;
 use crate::lsm_iterator::{FusedIterator, LsmIterator};
 use crate::mem_table::{map_bound, MemTable};
 use crate::table::{SsTable, SsTableBuilder, SsTableIterator};
@@ -126,6 +126,8 @@ impl LsmStorage {
         self.path.join(format!("{:05}.sst", id))
     }
 
+    /// Persist data to disk.
+    ///
     /// In day 3: flush the current memtable to disk as L0 SST.
     /// In day 6: call `fsync` on WAL.
     pub fn sync(&self) -> Result<()> {

mini-lsm/src/mem_table.rs

@@ -7,7 +7,7 @@ use crossbeam_skiplist::map::Entry;
 use crossbeam_skiplist::SkipMap;
 use ouroboros::self_referencing;
 
-use crate::iterators::impls::StorageIterator;
+use crate::iterators::StorageIterator;
 use crate::table::SsTableBuilder;
 
 /// A basic mem-table based on crossbeam-skiplist

mini-lsm/src/mem_table/tests.rs

@@ -1,7 +1,7 @@
 use tempfile::tempdir;
 
 use super::MemTable;
-use crate::iterators::impls::StorageIterator;
+use crate::iterators::StorageIterator;
 use crate::table::{SsTableBuilder, SsTableIterator};
 
 #[test]

mini-lsm/src/table/iterator.rs

@@ -4,7 +4,7 @@ use anyhow::Result;
 
 use super::SsTable;
 use crate::block::BlockIterator;
-use crate::iterators::impls::StorageIterator;
+use crate::iterators::StorageIterator;
 
 /// An iterator over the contents of an SSTable.
 pub struct SsTableIterator {

mini-lsm/src/table/tests.rs

@@ -4,7 +4,7 @@ use bytes::Bytes;
 use tempfile::{tempdir, TempDir};
 
 use super::*;
-use crate::iterators::impls::StorageIterator;
+use crate::iterators::StorageIterator;
 use crate::table::SsTableBuilder;
 
 #[test]

mini-lsm/src/tests/day4_tests.rs

@@ -3,7 +3,7 @@ use std::ops::Bound;
 use bytes::Bytes;
 use tempfile::tempdir;
 
-use crate::iterators::impls::StorageIterator;
+use crate::iterators::StorageIterator;
 
 fn as_bytes(x: &[u8]) -> Bytes {
     Bytes::copy_from_slice(x)