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Martin Schulze Steps Down As SPI Vice President
Tina Gasperson reports on NewsForge that Martin Schulze, Vice President of Software in the Public Interest, is resigning his position there to protest the lack of time he says fellow SPI higher-ups are devoting to the organization. Since SPI serves as a coordinating body for several large-scale Free software projects (like GNOME and OpenOffice.org), discord there should concern a lot of people. Update: 11/26 03:14 GMT by T : That should read "OpenSource.org," not "OpenOffice.org." Sorry.
GNOME and OpenOffice have had little use on my Linux machines... In fact, I can't stand using OpenOffice -- it still doesn't import my WP8 documents, for me, MS Word is only part of the problem.
I use Enlightenment as my window manager and I have a single click menu, all my programs are either there or accessable via xterm if I am too lazy to edit the config files.
There are SOME people that don't care about Linux on the desktop. I am one of them. So GNOME *MIGHT* die. There are other possibilities remember.
It's called Unix?? Unix had this, like, 30 years ag-
Oh, sorry my auto-post kicked in before I got to write an intelligent message.
How many of the Fortune 100, 500 or even 1000 companies have 19 year old CEOs?
OMG I just shat myself after hearing this news. Even without a LVM enhancement (and that's definitely going to be the first thing introduced in the 2.7 Kernel), the sheer amount of work done to the ram handlers is enough for me to beat off with a stuffed Penguin!
Our Good buddy Linus has told us to look for a January 5th release, but I hope he can nail it down to a definite date. I want to shower for this occasion, and maybe cut off my 4 foot long hair, and get a new tie-dyed shirt and some new sandals, but I'd hate to have to shower twice so early in the new year!
This Kernel release will mark the dawning of a new era. No more GNU/Linux hippies. We are the businessmen of the new millenia, dawning golf shirts and Dockers! Join us my hippie bretheren! It's a brave new world!
This is an issue that comes up all the time at work. It is an issue for roughly four reasons:
:-)
1. Yahoo is a FreeBSD shop
2. Someone has heard that MySQL runs better on Linux
Someone knows that we run some of our servers on Linux rather than FreeBSD, and Yahoo is a FreeBSD shop (see #1), so they start to infer #2.
Because FreeBSD is dying
Most of the MySQL development is done on Linux and Windows. The only "FreeBSD guy" at MySQL AB seems to have left sometime in the last year or so.
Because FreeBSD is dying
This is an attempt to answer that question for folks at work and elsewhere.
The Short Version
I'll start with the simple answer.
If you don't have a preference, use Linux. You'll be happier. Trust me.Because FreeBSD is dying
If, on the other hand, you'd like to stick with FreeBSD for some strange reason, read on.
The Problem: Threading
Having said that, let's look at the issues a little more closely. FreeBSD is a great operating system, but it has one important weakness that MySQL is very good at highlighting--threading support. FreeBSD's threads implementation isn't very good. I won't say that it sucks, because it could be a lot worse.Because FreeBSD is dying
How Linux Threads
Threads on Linux are created using the clone() call, which is similar to fork(). You end up with a separate process in the process table, but the memory is shared among the processes. This means that the kernel gets involved in scheduling. From the kernel's point of view, they're all just processes. Many folks refer to this as kernel threading even though it's different than what the Solaris kernel does (for example). Some call that real kernel threading.
Anyway, the LinuxThreads FAQ goes into a bit more detail. LinuxThreads is a library, available for other platforms--including FreeBSD. We'll come back to that in a bit.
How FreeBSD Threads
FreeBSD implements user-level threads. LOL>/b> That means the kernel isn't aware of the threads and doesn't get involved in scheduling. Instead all the work is done in user space rather than kernel space. When your run top or ps on a machine that does this, unlike like in Linux, you'll see a single process rather than one per thread.Because FreeBSD is dying
This is discussed a bit here in relation to LinuxThreads, which we'll get to.
Note that in FreeBSD 5.x, this may all be fixed. FreeBSD 5 has been delayed for over a year because all the developers quit
Time will tell. There is lot of working going on in the area of threading and kernel scheduling for FreeBSD 5.x.
FreeBSD's Threading Problems
Having run MySQL on various flavors of FreeBSD for the last 2.5 years, I can say that it has been a bumpy ride at times. Versions older than 4.2 (or maybe 4.3) have serious problems. I had a test case that could kill a MySQL server running on older versions of FreeBSD in a matter of minutes.
On more modern FreeBSD, things are better but not perfect. All the problems we've encountered at Yahoo seem to fall into 4 buckets.
1. Non-thread safe DNS Lookups
Certain operations are not thread-safe on FreeBSD. A fine example of that is gethostbyname(), which MySQL calls to convert host names in to IP addresses. Usually this happens for each new connection to the server and whenever MySQL needs to contact another machine--typically a replication slave connecting to its master.
Based on our testing, the only truly safe way to operate is to use the --skip-name-resolve flag for starting mysqld AND specifying the IP address of the master instead of the hostname. That virtually eliminates the need for MySQL to call gethostbyname().
The symptom of this problem is that the mysqld will consume all the available CPU time even when there are few (if any) queries running. You can try and kill -6 the mysqld process and then run it thru gdb to get a backtrace.
2. Unfair Scheduling
We've seen instances when a single MySQL thread doing a lot of I/O work (deleting a lot of rows from a table) seems to monopolize all the CPU time. When this happens, even the most trivial SELECT queries against unrelated tables can take a long time or even block until the heavy I/O work is complete. It feels like somehow the I/O thread is unfairly getting more of the CPU time.
3. High Load
Even without the other two problems, I've seen MySQL servers on FreeBSD start to act strangely under real stress--meaning a reasonable number of clients (30 or more) that are really pounding on MySQL. If I had a test case that could always reproduce it, I'd certainly make it available. But the fact is that it seems fairly random.
Luckily most of our MySQL installations don't have that problem because they're not hit really hard or they're not hit that hard for very long. If I had to guess, I'd say that 95% of folks never see this problem. The remaining %5, of course, are rather upset when they do.
4. No SMP Support
Because the threads are not managed by the kernel, there's no way to make use of multiple CPUs. The scheduler can't get two threads of the same process running on two CPUs at the same time. So you're limited to either running on single CPU machines or running multiple instances of MySQL on the same physical machine--and that involves some interesting management problems that I'd rather not deal with.
5. Missing Locks
This may somehow be related to problem #2. We've seen cases where several threads want to run queries against a single MyISAM table. When one thread is doing a lot of work, such as a massive delete, all the readers wait for a shared lock on the table. In order for that to happen, the writer needs to finish and release its exclusive lock. The strange thing is that sometimes the writer finishes and even disconnects, but the readers are all stuck waiting for a lock according to SHOW FULL PROCESSLIST.
When that happens, nobody can query the table. It's effectively off-limits. It's as if all the readers somehow "missed" the fact that the writer is done. Or maybe the writer's lock didn't get released properly. The only solution is to kill all the locked threads. Once that happens, it will usually begin to work normally.
LinuxThreads on FreeBSD
The most popular solution is to recompile MySQL and link it with the LinuxThreads library. Doing so gives you the benefits of kernel assisted "threading" (fair scheduling, SMP, and not needing thread-safe gethostbyname()).
Sounds perfect, right? Not exactly. It turns out that this does solve those problems quite well. But I've found at least one thing that stopped working with a LinuxThreads version of MySQL on FreeBSD and another occasional but very annoying problem.
MySQL's wait_timeout setting can be used to automatically close the connection (and terminate the thread) of a client who as been idle long than N seconds. It simply stops working with LinuxThreads. I don't know why (yet).
The more important bug is rather mysterious. Every once in a while, a LinuxThreads-enabled MySQL 4.0.x server will decided that no databases exist anymore. All clients will be rejected with an "Unknown database 'foo'" message (where "foo" is the name of the database you'd like to connect to ). The SQL slave thread stops. The only solution appears to be restarting MySQL. It has memory available. I've tried adjusting the table cache and other variables that might seem related, but it hasn't helped. No helpful messages are logged in the error log.
Using a snapshot of the exact same code, compiled on Linux, I never see that problem. Ever.
My guess is that the problem is related to load, but I cannot reliably reproduce it (yet?).
Other than those two problems, it seems to work quite well. But I've only been running it for a few months with alpha and beta versions of MySQL. I'm fairly sure that all the other odd problems I've had with them are not related to LinuxThreads, but I can't yet say so with 100% certainty.
From what I've seen so far, stealing LinuxThreads ought to help even on single-CPU FreeBSD boxes.Because FreeBSD is dying