Database Management Systems Flashcards

Flashcards covering key vocabulary and concepts from the Database Management Systems lecture notes.

DBMS (Database Management System)

A software system that enables users to define, create, maintain, and control access to the database.

Parser

A component of the DBMS responsible for parsing and interpreting SQL commands.

Optimizer

A component of the DBMS that selects the most efficient execution strategy for a query.

Plan Executor

A component of the DBMS that handles the execution plan generated by the optimizer.

Recovery Manager

A component of the DBMS responsible for ensuring data consistency and reliability during system failures.

Files and Access Methods

A component of the DBMS that manages how data is accessed and stored on disk.

Buffer Manager

A component of the DBMS that manages the caching of data in memory to improve performance.

Disk Space Manager

A component of the DBMS that allocates and manages disk space for database objects.

Transaction Manager

A component of the DBMS that ensures that transactions are processed reliably and consistently.

Lock Manager

A component of the DBMS that manages locks to ensure concurrent access to data is handled correctly.

Query Evaluation Engine

The process of evaluating a query and producing the desired results.

Concurrency Control

Mechanism for managing concurrent access to the database to prevent inconsistencies.

Transaction

Any one execution of a program in a DBMS; a sequence of one or more operations on a database (read/write/commit/abort).

Read(T, I)

An operation in a transaction that retrieves data from the database.

Write(T, I)

An operation in a transaction that modifies data in the database.

Commit(T)

An operation that finalizes a transaction, making its changes permanent.

Abort(T)

An operation that undoes the changes made by a transaction.

ACID Properties

Atomicity, Consistency, Isolation, Durability - properties a DBMS must ensure for a transaction.

Atomicity

All operations in the transaction are executed, or none are (all-or-nothing).

Consistency

A transaction must preserve the consistency of the database after execution.

Isolation

A transaction is protected from the effects of concurrently scheduling other transactions.

Durability

The effects of a successfully completed transaction should persist even if a system crash occurs.

Crash Recovery

The DBMS logs all transaction writes, so it can undo them if necessary; guarantees atomicity in the presence of system crashes.

Integrity Constraints (ICs)

Transactions do not violate the integrity constraints specified on the database and enforced by the DBMS.

Write-Ahead Log

Changes are written to the log (on the disk) before being reflected in the database; ensures atomicity and durability.

Schedule

A list of operations (Read / Write / Commit / Abort) of a set of transactions with the order of operations in each individual transaction preserved.

Serial Schedule

A schedule in which the actions of different transactions are not interleaved.

Non-Serial Schedule

A schedule in which the actions of different transactions are interleaved.

Serializable Schedule

A schedule is serializable if its effect on a consistent database instance is identical to the effect of some serial schedule.

WR Conflict (Dirty Reads)

T2 is reading a data object previously written by T1.

RW Conflict (Unrepeatable Reads)

T2 is writing a data object previously read by T1.

WW Conflict (Overwriting Uncommitted Data)

T2 is writing a data object previously written by T1.