BuzzDB with Multi-Version Concurrency Control (MVCC)

BuzzDB is a lightweight database built to support Multi-Version Concurrency Control (MVCC). It efficiently handles concurrent transactions and ensures data consistency through versioned tuple management.

Supported Concurrency Control Protocols

1. MVOCC (Multi-Version Optimistic Concurrency Control)

• Assumes conflicts are rare and only checks for conflicts at commit time.
• If a conflict is detected during commit, the transaction is aborted and restarted.

2. MV2PL (Multi-Version Two-Phase Locking)

• Transactions acquire locks on all tuples they read or write, preventing changes by other transactions during the lock period.
• Ensures serializability by preventing conflicting operations from occurring concurrently.
• Eliminates conflict checks at commit time as locks safeguard against concurrent conflicts.

Running BuzzDB

Run with MV2PL Concurrency Protocol:

./buzzdb 2PL

Run with MVOCC Concurrency Protocol:

./buzzdb OCC

Key Features

Tuple Metadata

Each tuple includes the following metadata:

• Creation Timestamp: Timestamp when the version was created.
• Expiration Timestamp: Timestamp when the version was superseded or expired.
• Previous Version Metadata: Metadata (page number and slot number) of the previous version, if applicable.

Version Manager

The Version Manager is a centralized structure that:

• Maintains the latest committed version of each tuple.
• Enables traversal through the version chain for historical data.
• Facilitates scan operations to locate the correct tuple version based on transaction timestamps.

Transactions

A Transaction in BuzzDB:

• Represents a set of isolated queries.
• Tracks tuples updated or written during execution.
• Includes a Commit Method that:
  • Safely commits changes by acquiring necessary locks.
  • Updates the Transaction Manager to reflect committed changes.
  • Makes changes visible to other transactions.

Transaction Manager

The Transaction Manager:

• Tracks active and committed transactions.
• Maintains a mapping of committed transactions and their updates to ensure consistency.

Locking Mechanism

Lock

• Locks prevent concurrent access to specific memory locations.
• In BuzzDB, locks are held on (pageNumber + slotId) combinations.

Lock Manager

• Manages acquisition and release of locks.
• Maps locks to memory locations for efficient transaction handling.

Setup and Usage

1. Clone the repository:

   git clone https://github.com/your-username/mvcc_buzzdb.git
   cd mvcc_buzzdb

2. Compile the code:

   make

3. Run the database with the desired concurrency protocol:

   ./buzzdb <concurrency_protocol>

Overview of Changes Made

1. Tuple Metadata Enhancements

• Added creation and expiration timestamps.
• Included metadata for previous tuple versions.

2. Version Manager Implementation

• Centralized management of tuple versions.
• Support for version traversal and scans.

3. Transaction Improvements

• Enhanced commit process with safe locking and visibility updates.
• Conflict detection for MVOCC at commit.

4. Locking Enhancements

• Locks applied to (pageNumber + slotId) for fine-grained control.
• Centralized management through Lock Manager.

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