Introduction — mnesia v4.25.2

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# Introduction

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The Mnesia application provides a heavy-duty real-time distributed database.

## Scope

This User's Guide describes how to build Mnesia-backed applications, and how to integrate and use the Mnesia database management system with OTP. Programming constructs are described, and numerous programming examples are included to illustrate the use of Mnesia.

This User's Guide is organized as follows:

- Mnesia provides an introduction to Mnesia.
- Getting Started introduces Mnesia with an example database. Examples are included on how to start an Erlang session, specify a Mnesia database directory, initialize a database schema, start Mnesia, and create tables. Initial prototyping of record definitions is also discussed.
- Build a Mnesia Database more formally describes the steps introduced in the previous section, namely the Mnesia functions that define a database schema, start Mnesia, and create the required tables.
- Transactions and Other Access Contexts describes the transactions properties that make Mnesia into a fault-tolerant, real-time distributed database management system. This section also describes the concept of locking to ensure consistency in tables, and "dirty operations", or shortcuts, which bypass the transaction system to improve speed and reduce overheads.
- Miscellaneous Mnesia Features describes features that enable the construction of more complex database applications. These features include indexing, checkpoints, distribution and fault tolerance, disc-less nodes, replica manipulation, local content tables, concurrency, and object-based programming in Mnesia.
- Mnesia System Information describes the files contained in the Mnesia database directory, database configuration data, core and table dumps, as well as the functions used for backup, restore, fallback, and disaster recovery.
- Combine Mnesia with SNMP is a short section that outlines the integration between Mnesia and SNMP.
- Appendix A: Backup Callback Interface is a program listing of the default implementation of this facility.
- Appendix B: Activity Access Callback Interface is a program outlining one possible implementation of this facility.
- Appendix C: Fragmented Table Hashing Callback Interface is a program outlining one possible implementation of this facility.

## Prerequisites

It is assumed that the reader is familiar with the Erlang programming language, system development principles, and database management systems.

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