~drizzle-trunk/drizzle/development : revision 1984

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Notable MySQL Differences

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=========================

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Drizzle was forked from the (now defunct) MySQL 6.0 tree. Since then there

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have been a lot of changes. Some areas are similar, others unrecognisable.

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This section aims to explore some of the notable differences between MySQL

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and Drizzle.

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This section was originally adapted from the Drizzle Wiki.

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Drizzle was forked from the (now defunct) MySQL 6.0 tree in 2008. Since then there have been a lot of changes. Drizzle is in some ways similar to MySQL, and in other ways, unrecognizable.

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This section of documentation aims to explore some of the notable differences between MySQL and Drizzle, and has been modified from its original state on the Drizzle Wiki.

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Usage

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* Drizzle is optimized for massively concurrent environments. If we have the

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choice of improving performance for 1024 simultaneous connections to the

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detriment of performance with only 64 connections, we will take that choice.

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* Designed for modern POSIX systems

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* It is designed for modern POSIX systems

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* Microsoft Windows is not a supported platform (neither is HP-UX or IRIX).

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* No timezones. Everything is UTC.

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* Drizzle doesn't use timezones. Everything is UTC.

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Installation

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* No scripts/mysql_install_db or similar. A "just works" installation

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mentality without administrative overhead.

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* No scripts/mysql_install_db or similar. Drizzle aims for a "just works" installation, without administrative overhead.

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* No system database that needs upgrading between versions.

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* Drizzle can listen on the Drizzle port (4427) and/or MySQL port (3306)

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and speak the respective protocols.

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Architecture

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------------

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Drizzle is designed around the concept of being a micro-kernel. There should

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Drizzle is designed around the concept of being a microkernel. There should

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be a small core of the server with most functionality being provided through

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small, efficient and hard to misuse plugin interfaces. The goal is a small,

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light weight kernel which is easy to maintain, understand and extend.

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light weight kernel that is easy to maintain, understand and extend.

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Drizzle is written in C++ making use of the Standard Template Library (STL)

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Drizzle is written in C++ and makes use of the Standard Template Library (STL)

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and Boost. Only where performance or correctness proves to be inadequate will

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we consider rolling our own, and our preference is to fix the upstream library

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we consider rolling our own; our preference is to fix the upstream library

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instead.

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Network protocol

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Pluggable network protocols allow Drizzle to speak one (or more) of several

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protocols. Currently we support the MySQL protocol (compatible with existing

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MySQL client libraries) and the Drizzle protocol which is still under

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development but aims for several important differences:

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development.

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The Drizzle protocol embodies several important differences from MySQL:

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* Client sends first packet instead of server

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* built in sharding

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* multi statement support (without using a semicolon to separate them)

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* room for expansion to include NoSQL type commands inline with SQL.

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* Built in sharding

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* Multi statement support (without using a semicolon to separate them)

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* Room for expansion to include NoSQL type commands inline with SQL.

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There is also a console plugin that instead of providing access over a network

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socket, allows access from the current tty.

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There is also a console plugin -- instead of providing access over a network

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socket, this plugin allows access from the current tty.

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Plugin API

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Existing plugin APIs inherited from MySQL have been reworked.

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The existing plugin APIs that Drizzle inherited from MySQL have been reworked.

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* User Defined Functions (UDFs) now follow the same API as within the

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* User Defined Functions (UDFs) now follow the same API as a given

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server instead of a different C API. This means that UDFs are on the

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exact same level as builtin functions.

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exact same level as built-in functions.

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* Storage Engine API has had some parts extensively reworked, especially

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around transactions and DDL.

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* Logging is now pluggable

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Stored Procedures

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-----------------

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Drizzle does not currently have any plugins implement stored procedures. We

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Drizzle does not currently have any plugins that implement stored procedures. We

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viewed the implementation in MySQL to be non-optimal, bloating the parser

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and only supporting one language (SQL2003 stored procedures) which was not

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and only supporting one language (SQL2003 stored procedures), which was not

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well known.

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Fundamentally, stored procedures usually are not the correct architectural

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decision for applications that need to scale. Pushing more computation down

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into the database (which is the trickiest layer to scale) isn't a good idea.

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We do recognise that the ability to reduce the time row locks are held

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by using stored procedures is valuable, but think the same advantage can

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be gotten with improved batching of commands over the wire instead of adding

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We do recognize that the ability to reduce the time row locks are held

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by using stored procedures is valuable, but think we can achieve the same

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advantage by improved batching of commands over the wire instead of adding and

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administering stored procedures to the list of things that can go wrong in

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admisistering the database.

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administering the database.

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Triggers

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--------

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SQL Views are not currently supported in Drizzle. We believe they should be

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implemented via a query rewrite plugin. See the `Query Rewrite Blueprint <https://blueprints.launchpad.net/drizzle/+spec/query-rewrite>`_ on launchpad.

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implemented via a query rewrite plugin. See the `Query Rewrite Blueprint <https://blueprints.launchpad.net/Drizzle/+spec/query-rewrite>`_ on launchpad.

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Partitioning

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INFORMATION_SCHEMA

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The INFORMATION_SCHEMA provides access to database metadata.

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The INFORMATION_SCHEMA in Drizzle is strictly ANSI compliant. If you write

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a query to any of the tables in the INFORMATION_SCHEMA in Drizzle, you can

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Authentication, Authorization and Access

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Plugins. Currently there are PAM and HTTP AUTH plugins for authentication.

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Authentication lies in Drizzle plugins. Currently there are PAM and HTTP AUTH plugins for authentication.

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Through the PAM plugin, you can use any PAM module (such as LDAP).

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Command line clients

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No gotcha of using the unix socket when localhost is specified and then

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connecting you to the wrong database server.

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There is no drizzleadmin command.

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There is no Drizzle admin command.

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Storage Engines

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There are no FRM files in Drizzle. Engines now own their own metadata.

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Some choose to still store these in files on disk. These are now in a

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Some still choose to store these in files on disk. These are now in a

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documented file format (using the google protobuf library).

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SHOW commands