chore: typos & refine comments (#65)

* typo in  week2-01-compaction.md

* chroe: typos & add comments

* chore: more typos

* Update week2-01-compaction.md

---------

Co-authored-by: Alex Chi Z <iskyzh@gmail.com>

mini-lsm-book/src/week2-01-compaction.md

@@ -66,7 +66,7 @@ Because we always compact all SSTs, if we find multiple version of a key, we can
 
 There are some things that you might need to think about.
 
-* How does your implementation handle L0 flush in par with compaction? (Not taking the state lock when doing the compaction, and also need to consider new L0 files produced when compaction is going on.)
+* How does your implementation handle L0 flush in parallel with compaction? (Not taking the state lock when doing the compaction, and also need to consider new L0 files produced when compaction is going on.)
 * If your implementation removes the original SST files immediately after the compaction completes, will it cause problems in your system? (Generally no on macOS/Linux because the OS will not actually remove the file until no file handle is being held.)
 
 ## Task 2: Concat Iterator

mini-lsm-book/src/week2-04-leveled.md

@@ -63,7 +63,7 @@ In addition, at most *one* level can have a positive target size below `base_lev
 0 0 30MB 300MB 3GB 30GB
 ```
 
-Notice in this case L1 and L2 have target size of 0, and L3 is the only level with a postive target size below `base_level_size_mb`.
+Notice in this case L1 and L2 have target size of 0, and L3 is the only level with a positive target size below `base_level_size_mb`.
 
 ### Task 1.2: Decide Base Level
 

mini-lsm-mvcc/src/block/iterator.rs

@@ -15,7 +15,7 @@ pub struct BlockIterator {
     block: Arc<Block>,
     /// the current key at the iterator position
     key: KeyVec,
-    /// the value range from the block
+    /// the current value range in the block.data, corresponds to the current key
     value_range: (usize, usize),
     /// the current index at the iterator position
     idx: usize,

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

@@ -13,7 +13,7 @@ pub struct BlockIterator {
     block: Arc<Block>,
     /// The current key, empty represents the iterator is invalid
     key: KeyVec,
-    /// the value range from the block
+    /// the current value range in the block.data, corresponds to the current key
     value_range: (usize, usize),
     /// Current index of the key-value pair, should be in range of [0, num_of_elements)
     idx: usize,

mini-lsm/src/block/iterator.rs

@@ -15,7 +15,7 @@ pub struct BlockIterator {
     block: Arc<Block>,
     /// the current key at the iterator position
     key: KeyVec,
-    /// the value range from the block
+    /// the current value range in the block.data, corresponds to the current key
     value_range: (usize, usize),
     /// the current index at the iterator position
     idx: usize,