by Mara Bos — At Topic: Chapter 4. A Safe Interface Using a Lock Guard Recommendation: Start reading from the beginning of the chapter to get the full picture Prerequisites Lifetime Annotations in Struct Definitions Eg. Struct ImportantExcerpt has the single field part that holds a string slice, which is a reference. …

By Triton Ho — At Lesson 2: Page 28 — End Notes Nature Key: Eg. 身份證號碼, Email, 航班日期 + 航班編號 Surrogate Key: no specific meaning key, Eg. auto increment, UUID 一般商業系統(不考慮報表的部份)，90%的資料讀取/改動都是基於 PK 的 同一時期建立 …

By Triton Ho — At Lesson 2: Page 13 — Page 27 Notes B+ Tree 主流的 RDBMS eg. PostgreSQL, MariaDB, Oracle 用來實現 Indexing 的方式 Primary key, Unique Constraint 背後也是 index Height of B+ Tree is O(log n), and …

By Triton Ho — At Lesson 2: Page 1 — Page 12 Notes File System Normally, Most file systems will divide the hard disk into blocks (aka. pages). Even if a file is only 1 bytes, it will still occupy 4 KB of space at file system based on 4 KB block size. 硬體操作是以區塊為單位 每個 page 在同一時間只能被一個 TX 改動 把性質相近的 Record 物理性放到一起會提高 cache hit rate ，但是更容易發生 Contention => 就是說:單一 page 能儲存越多的東西，READ的效能會越好，但是 WRITE 效能會越差 How RDBMS Saves Data?

By Triton Ho — At Lesson 1: Page 28 — End Notes 4 levels: Read Uncommitted Read Committed: Prevent Dirty Read Repeatable Read: Prevent Dirty Read and Non-Repeatable Read Serializable: Prevent Dirty Read, Non-Repeatable Read and Phantom Read Read Committed SX Lock: 「改動」前，為 Record 加上 X LOCK ，直到 TX 完結 「讀取」(Read) 前，為 Record 加上 S…

By Triton Ho — At Lesson 1: Page 23 — Page 27 Notes SX Lock and MVCC SX lock: Shared-exclusive Lock 用途: 達到 isoliation 避免 race condition Oracle 和 PostgreSQL 使用 MVCC ，而 MySQL 和 MSSQL 使用 SX lock 就單一 …

By Triton Ho — At Lesson 1: Page 14 — Page 22 Notes Three types: dirty read, non-reapeatable read, phantom read Dirty Read 能讀取其他還未 committed 的 TX 的資料改動 在還未 Commit 之前， database 是處於 inconsistent state (不應該被其他人看到) 任何情況下， Dirty Read 在 RDBMS 都應該避免的 MySQL, Oracle, PostgreSQL default dirty read will never happen Non-repeatable read 讀取的資料包含其他已經 committed TX 的 update ，而這些 TX 的 commit 時間發生在此 TX 的開始之後 (同一個 TX ，同一筆資料在第一次讀取和第二次讀取出現不同結果)

Subtypes must be substitutable (without breaking the program) for their base (parent) types Important: OOP focuses on behavior rather than properties Use Cases Update an algorithm without bothering the user using our interface Examples A square should not be a subclass of a rectangle It might not be intuitive, but it applies to…

By Mara Bos — At Topic: Chapter 4. An Unsafe Spin Lock Unsafe: compiler is not validating for you no more, It is user’s responsibility now Prerequisites Interior Mutability Recall What is spin lock? Instead of putting the thread to sleep, the thread will continuously attempt to lock the locked lock When to use spin lock? …