more bonus tasks

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

mini-lsm-book/src/week1-05-read-path.md

@@ -81,4 +81,8 @@ For get requests, it will be processed as lookups in the memtables, and then sca
 
 We do not provide reference answers to the questions, and feel free to discuss about them in the Discord community.
 
+## Bonus Tasks
+
+* **The Cost of Dynamic Dispatch.** Implement a `Box<dyn StorageIterator>` version of merge iterators and benchmark to see the performance differences.
+
 {{#include copyright.md}}

mini-lsm-book/src/week1-06-write-path.md

@@ -122,4 +122,8 @@ You can implement helper functions like `range_overlap` and `key_within` to simp
 
 We do not provide reference answers to the questions, and feel free to discuss about them in the Discord community.
 
+## Bonus Tasks
+
+* **Implement Write Stall.** When the number of memtables exceed the maximum number too much, you can stop users from writing to the storage engine. You may also implement write stall for L0 tables in week 2 after you have implemented compactions.
+
 {{#include copyright.md}}

mini-lsm-book/src/week1-07-sst-optimizations.md

@@ -1,4 +1,4 @@
-# SST Optimizations
+# Snack Time: SST Optimizations
 
 ![Chapter Overview](./lsm-tutorial/week1-07-overview.svg)
 

mini-lsm-book/src/week2-overview.md

@@ -1,4 +1,4 @@
-# Overview
+# Week 2 Overview: Compaction and Persistence
 
 ![Chapter Overview](./lsm-tutorial/week2-overview.svg)