![]() ![]() In addition there are also in-memory alternatives, although these lose the durability property of ACID. These compromise the atomicity and the isolation properties of ACID, but offer around 10× more throughput. For performance reasons, it also supports deliberate " dirty operations" which avoid transactions. General coding style for Mnesia will always use transactions. The semantics of using transactions in this way remains consistent, making it easy to write library code that works equally in either context. ![]() It's also possible to distribute transactions across multiple nodes (i.e. This can lead to clearer source code than the paired BEGIN / COMMIT syntax of SQL, and so avoids its problem of unclosed transactions within a procedure.Īgain as a result of the functional nature of Erlang, nesting transactions is simple. The functional block which is run as a transaction is a commonplace Erlang construct called a Functional Object (or Fun) and is called by the single Mnesia statement mnesia:transaction(F). ![]() Mnesia builds on this to obtain ACID transaction support. It permits easy representation of transactions as a natural feature of Erlang by allowing developers to utilize a single language throughout an application.Įrlang is a functional language. The query language of Mnesia is Erlang itself, rather than SQL. Ī key feature of Mnesia's high-availability approach is that tables can be reconfigured within a schema and relocated between nodes, not only while the database is still running, but even while write operations are still going on. Relationships between them are modelled as other tables. The database model is relational, but isn't what someone familiar with SQL might expect. Klarna added the LevelDB backend plugin while Aeternity added the RocksDB backend plugin. Backend plugins ĭue to limits imposed by Dets, support for other backend plugins was suggested by Ulf Wiger and these were added to Mnesia. Dets file format uses signed 32-bit integers for file offsets and has a limit of 2GB so do disc_only_copies. Disc_only_copies ĭata resides only on disc and are backed by Dets (disk version of ETS). Disc_copies were backed by Dets tables until 30th September 2001 with the release of Erlang R7B-4. Mnesia has three inbuilt table types: ram_copies, disc_copies and disc_only_copies.ĭata resides in memory and table size is limited by available memory and are backed by ETS (erlang term storage) table.ĭata resides in memory but is also persisted on disk backed by disk_log. This data field may in turn be a tuple containing an Erlang data structure of any complexity. "Rows" in tables are represented as records that contain a key value and a data field. It has more in common with embeddable DBMS such as Berkeley DB than with any SQL database server. Instead Mnesia exists to support Erlang, where DBMS-like persistence is required. It was not intended as a general office-based data processing database management system, nor to replace SQL-based systems. It is distributed as part of the Open Telecom Platform.Īs with Erlang, Mnesia was developed by Ericsson for soft real-time distributed and high-availability computing work related to telecoms. Mnesia is a distributed, soft real-time database management system written in the Erlang programming language. It is entirely composed of free and open-source software LYME (software bundle) is based on Erlang and comprises Mnesia. ![]()
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