Opslagengine

Opslagengine, or storage engine, is a modular component of a database management system (DBMS) responsible for how data is stored, indexed, and accessed on disk. It provides the data structures and algorithms for persisting tables, handling transactions, and implementing features such as indexing, locking, and recovery. In many DBMSs, storage engines are pluggable, allowing administrators to choose an engine that best fits workload and reliability requirements, often without changing SQL queries.

A storage engine sits below the SQL layer and abstracts the details of disk layout, file organization, and memory usage. It handles writing data to disk, maintaining data integrity through logs or redo/undo information, and reading pages into memory. It may support row-oriented storage, which stores one row per record, or columnar storage, which stores values by column to improve analytical workloads. It can implement transactional behavior (ACID) with techniques such as multi-version concurrency control (MVCC) or two-phase locking, and may offer features like data compression, encryption, and online backups. Some engines provide specialized capabilities, such as full-text indexing or columnar analytics.

Common examples include InnoDB, a transactional storage engine for MySQL that supports foreign keys and MVCC; MyISAM, a non-transactional engine for MySQL; WiredTiger, the default storage engine for MongoDB in recent versions; and Aria or ColumnStore in MariaDB. PostgreSQL uses a unified storage subsystem rather than pluggable engines but still exposes different access methods.

Choosing a storage engine involves balancing durability, performance, concurrency, and feature needs, and can significantly impact scalability and maintenance.