Wednesday, November 13, 2013

On to the Lucky Number...

Do you remember last October? The rsyslog mailing list got very busy with things like output load balancing, global variables, and a lot of technical details of the rsyslog engine. I don't intend to reproduce all of this here. The interested reader may simply review the rsyslog mailing list archives, starting at October 2013.

Most of these discussions focused on the evolution of the rsyslog engine. Essentially, the v7 engine brought many new things, but was constraint due to a lot of legacy, for example the output module interface which originally (roughly 8 years ago) was designed to keep it very simple to use, especially for developers who did not know about threading (which was uncommon to know at that time). Also, the engine gained lot's of speeds by a special SIMD-like execution mode (details in mailing list archive), but that mode was counter-productive for some of the newer features. An ultimate problem were global variables, which were very hard to implement with the v7 engine. I even proposed a complete shadow variable system to make them fit into the framework, but this was -thankfully- not well received by the community at large.

Note that I wanted to re-write at least part of the core engine for quite some while, but it sounded like a task so large that I deferred it one time after another. However, seeing all the time going into the discussion, potential work-arounds (like shadow variables) and the then still-nonoptimal state I very strongly considered if it may be time for a radical change. Better spend the time on cool new things than investing that time into some "work-around" type of implementations.

With that on my mind, I had a couple of days of drafting and some talks with my peers. It turned out that we wanted to at least give this a try and see how (and if;)) things would evolve. So I did a week of test implementation, mostly focused on a new, highly concurrent output module interface. That did work out rather well, so we finally decided to go for the full length. I started rewriting the complete core rule execution engine.

And this brings us to the lucky number: let's welcome rsyslog v8, as the new version will be named. I thought for a short moment to stick with v7, but the changes are really, really big and quite a bit of legacy and upward compatibility has been lost. For example, all output modules need to be rewritten. So while v8 may not be a great marketing tool to get it quickly into the distros, it correctly flags that some bigger changes are to be anticipated (but as usual we were very conservative with breaking existing configurations ;)).

I did not announce this effort any sooner as until now I wasn't sure if it would really work out. Obviously, I now think thinks look sufficiently well ;-). It's not yet deployable, but we are getting closer.

Expect a 8.1.0 release within the next couple of days. We are working on the final finishing touches, many of which involve testing. Note that 8.1.0 will be highly experimental and really is for folks who would like to get an impression of its new capabilities ... and those trying to help find bugs.

There are some restrictions on supported modules and features, and some upgrades may run into trouble with that (details will be available together with the release). Also note that the rewrite is not yet 100% complete. Some of the finer details still need to be advanced, e.g. a new, higher performance and easier to use interface for output transactions. Or some aspects of message error processing ... and so on. This follows our usual pattern that in a new development branch we bring in new features gradually, until we have reached the final goal. In any case, we are now pretty confident that we will reach this goal. If all goes exceptionally well, a v8-stable may come up in March 2014 (and free support for v7 will be available for another month or two so that there is time to migrate).

To facilitate this move, git branches will change. Yesterday's master branch will become available as v7-devel (now in place) and the master branch will hold the new v8 code. Follow this blog post and the rsyslog mailing list to be sure to see exciting new versions when they become available.

Version 7-devel will get kind of a beta status, where mostly bug fixes are applied. However, some non-bugfix changes will also happen, but only after careful consideration. The focus obviously is now on v8 and this is where we will do the "cool" stuff in the future.

Note that the average user will possibly not notice much difference between v7 and v8 initially. The new engine will be most useful for power users and installations with complex rules and/or a high log volume.

I am very excited about this new branch of development and hope you'll also be excited as it unrolls. Also my sincere thanks to everyone who waits patiently for v7 related work. I was too busy to look a that the past few weeks and will probably be occupied with v8 for a quite a bit longer.

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