The DBMS can almost always manage memory better than the OS.

<aside> 💡 Two types of contol we care about

1. Spatial Control
2. Temporal Contorl </aside>

1. Buffer Pool Manager

Memory region organized as an array of fixed-size pages.

An array entry is called a frame.

When the DBMS requests a page, an exact copy is placed into one of these frames.

1.1 Metadata

The page table keeps track of pages that are currently in memory.

Also maintains additional meta-data per page:

• Dirty Flag
• Pin/Reference Counter

1.2 Locks & Latches

<aside> 💡 Locks

• Protects the database's logical contents from other transactions.
• Held for transaction duration.
• Need to be able to rollback changes. </aside>

<aside> 💡 Latches

• Protects the critical sections of the DBMS's internal data structure from other threads.
• Held for operation duration.
• Do not need to be able to rollback changes. </aside>

1.3 Page Directory & Page Table

• Page directory

  the mapping from page ids to page locations in the database files.

  All changes must be recorded on disk to allow the DBMS to find on restart.

• Page table

  the mapping from page ids to a copy of the page in buffer pool frames.

  This is an in-memory data structure that does not need to be stored on disk.

  Care about thread-safety, not scalability

1.4 Optimizations

1. Global Policies:

   Make decisions for all active txns.

2. Local Policies

   Allocate frames to a specific txn without considering the behavior of concurrent txns. Still need to support sharing pages.

1.4.1 Multiple Buffer Pools

The DBMS not always have a single buffer pool for the entire system