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Comparison of MySQL clients
This page aims at comparing some different MySQL clients/drivers for Erlang.
Here is a benchmark: https://tjheeta.github.io/2015/05/31/elixir-and-erlang-mysql-drivers/
TODO: Update (e.g. the compared versions) and add more modern drivers, e.g. mariaex.
This chart was made in 2015 and compares MySQL/OTP to the most used ones. More are listed in less detail below.
|Compared version||0.7.1||0.4.1||? (updated 2007)||?|
|Binary protocol for prepared statements||yes||no||no||no|
|Transactions||yes||no||yes, problematic ||no|
|Query timeouts without reconnect||yes||no||no||no|
|Connection pool||3rd party||build-in||built-in||simple round-robin|
|Usable without connection pool||yes||?||?||yes|
|Records in public API||no||yes||yes||yes|
|Auth method "native"||yes||yes||yes||yes|
|Auth method "old"||no||yes||yes||yes|
|Other auth methods||no||no||no||no|
|Old handshake (MySQL < 4.1)||no||yes||yes||yes|
|New handshake (MySQL >= 4.1)||yes||yes||yes||yes|
|Code coverage of tests||97%||some||none||none|
|Values converted to Erlang terms||yes||yes||yes||no |
|DECIMAL without precision loss||yes ||no, float||?||N/A|
|Microseconds in TIME and DATETIME
|License||LGPLv3+||Expat||3-clause BSD||3-clause BSD|
- Uncaught exceptions such as
throw(foo)don't cause the transaction to rollback.
- All values are returned as binary or string (option) except NULL which is returned as an atom.
- DECIMAL values are represented as integers or floats when possible whithout precision loss. High precision decimals are returned as binaries on the form
<<"3.120000000000000000000000042">>. This representation of DECIMALs is inspired by the odbc OTP application. (Emysql converts these to floats which results in precision loss.)
Emysql is a rewrite of the older erlang-mysql-driver. It works with Erlang/OTP 7.1 with warnings for deprecated types.
Architecture: The application supervises a "connection manager" which is a gen_server that manages multiple connection pools. A connection is not a process but just a record in the state of the connection manager. When a query is executed, a process is spawned to execute the query and error handling is done by monitoring this process. Instead of a timeout on the recv calls from the socket, the process is killed after a certain time if a query takes too long to execute, whereafter a new connection is opened and returned to the connection pool. This design makes error handling very messy and transactions not feasible to implement. Therefore, Emysql still as of 2014-12-24 lacks transaction support.
There are multiple forks of this historic driver. It shares much of the design with Emysql and thus many of Emysql's problems. The source code at https://code.google.com/p/erlang-mysql-driver/ has not been updated since 2007. This is the driver listed by Oracle on the page https://dev.mysql.com/doc/refman/5.7/en/connectors-apis.html (2014-12-30).
The queries are executed in the caller's process. The process dictionary of caller's process is used for things such as transaction state. There is transaction handling but it is not bomb-proof. (Exceptions such as
throw(foo) that doesn't always cause the transaction to rollback.)
Description from the project:
This MySQL driver for Erlang is based on the Yxa driver obtained from Process One (at https://support.process-one.net/doc/display/CONTRIBS/Yxa). It includes several new features such as prepared statements, transactions, binary queries, type-converted query results, more efficient logging and a new connection pooling mechanism.
The first MySQL native driver seems to be this one, written by Magnus Ahltorp at KTH in 2002 for the YXA SIP software. Source code: https://github.com/fredrikt/yxa/tree/master/src/mysql.
ProcessOne seem to be using this driver in ejabberd with only minor modifications. It appears to be in use and has commits from 2014. Source code: https://github.com/processone/mysql.
Emysql and erlang-mysql-driver are based on an early version of this one.
This is a port driver using one OS process per connection. This is not what you usually want. "ODBC compatible MySQL Erlang port driver, using libmysqlclient." Source code: https://github.com/bjc/mysqlerl.
This client by Alexei Krasnopolski is said to be modelled after MySQL Connector/C, the main C client library. It has implemented many features such as the binary protocol for prepared statements. It is unknown whether this client is actually in use. The library contains multiple unprefixed modules with general names such as "connection" and "helper_common". The source code is available at http://sourceforge.net/p/erlmysql/code/HEAD/tree/source/trunk/ and generated EDoc at http://erlmysql.sourceforge.net/.