Eric Day: Drizzle Protocol Changes
On an entirely unrelated note to the MySQL protocol discussions happening yesterday, the MySQL protocol is now the default protocol in Drizzle as of Monday’s tarball (3/15). Drizzle supports a limited version of the MySQL protocol, only supporting the subset of commands Drizzle cares about (no server-side prepared statements, replication, or deprecated commands due to SQL query equivalents). Not all MySQL clients have been fully tested with it, but our entire test suite is using it now with the libdrizzle MySQL implementation. The latest release of libdrizzle also includes defaulting to the MySQL protocol and port for Drizzle connections.
There has been some debate about this change, even amongst some of the core developers. The current Drizzle protocol is a slight modification of the MySQL protocol. It has been running on the IANA assigned Drizzle port (4427) by default since the beginning. We are developing a new Drizzle protocol which will have a number of new features, as well as being more extensible than the old protocol. It may be some time before this protocol is stable and tested well enough to make it the default. Thinking into the future, there are a couple upgrade paths to consider when it is ready:
The first option is to declare a certain release the “new protocol release” and clients talking to it would need to be upgraded at the same time. This would switch the line-level protocol on port 4427 from the old Drizzle protocol to the new. Clients would be required to upgrade because those using the old protocol would break when trying to connect to the new server-side protocol module (there are no clever, efficient hacks here because different sides send the first byte for each protocol). This option doesn’t involve any dependencies on the MySQL protocol module or APIs at all, but does make a forced upgrade situation in the future for clients tools and APIs.
The second option is to make the MySQL protocol the default protocol now, and when the new Drizzle protocol module is ready and available, tell folks they can start using it. Those people using libdrizzle or it’s derived APIs will have an easy transition because a libdrizzle release can change the default as well. This allows us to put the Drizzle protocol module (port 4427) in an experimental mode that changes between releases as we develop it. This introduces a required dependency to the MySQL protocol module for the time being, and possible confusion when we make the switch back.
Both approaches have pros and cons, and for better or for worse, it has been decided to take the latter approach. If you start running the drizzle tarball being released today, the client tools will speak MySQL to port 3306 by default, and the latest libdrizzle release defaults to this as well. If you are running Drizzle on the same machine as MySQL/MariaDB and you get a port conflict on 3306 when starting, be sure to start drizzled with –mysql-protocol-port=X to bind to a different port (you’ll of course need to use the same port in the client utils/APIs when connecting).
URL: http://oddments.org/?p=307
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