mysqld

mysqld is the server component of the MySQL relational database management system. It runs as the MySQL daemon and is responsible for handling client connections, parsing and executing SQL statements, enforcing access control, managing transactions, and storing and retrieving data. It can run as a system daemon on Unix-like systems or as a background service on Windows. By default it listens on port 3306 and can also communicate over a Unix socket or Windows named pipe.

Architecture and operation: mysqld is multithreaded and supports multiple storage engines, with InnoDB as the default transactional engine and MyISAM (historical) as a non-transactional option. It uses a pluggable storage engine interface and applies SQL parsing, optimization, and execution steps. It implements client authentication and authorization via the mysql user tables and can be configured with resource limits, caching, and pluggable authentication plugins. It supports replication features through the binary log, enabling master-slave setups, or more complex topologies.

Configuration and data: the server data directory contains databases and system tables. Configuration is typically read from my.cnf or my.ini and can be specified on the command line; options cover network settings, memory usage, logging, and performance parameters. Data writes are persisted to the configured data directory; the server maintains logs such as error logs, general query log, slow query log, and performance_schema data.

Administration and monitoring: common tools include MySQL Shell, mysql, mysqladmin, mysqldump, and mysqlbinlog. The server's status can be inspected via INFORMATION_SCHEMA, PERFORMANCE_SCHEMA, PROCESSLIST, and status variables. Security features include TLS encryption for client connections, plugin-based authentication, and fine-grained privileges.