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From "Carl" <c...@etrak-plus.com>
Subject Re: Tomcat dies suddenly
Date Sun, 07 Feb 2010 12:02:48 GMT
Mark,

Thanks for your information.

I am not certain where the glibc versions I previously gave came from 
because... as you noted, they are not correct.  The correct glibc version is 
2.9 and the threading version (I hope I am stating this correctly) is NPTL 
2.9.

The kernel version is 2.6.29.6.  From the Slackware 13.0 release notes, 
'We've used the well-tested and recently patched 2.6.29.6 kernel'.  I 
assumed that was about as good a kernel as I could get... was I wrong?

I will try LD_ASSUME_KERNEL=2.4.1 (the Slackware site seems to indicate my 
version supports this setting) on one of the servers (so I can quickly 
revert to the other one if the setting doesn't work.)

I will add the 'XX:ParallelGCThreads=1 option to one of the servers and see 
how that works.

I am moving a litlle slowly because I don't want to make a nbad situation 
worse and want to be certain I can account for any improvements or screwups.

Thanks for your insights.

Carl


----- Original Message ----- 
From: "Mark Eggers" <its_toasted@yahoo.com>
To: "Tomcat Users List" <users@tomcat.apache.org>
Sent: Saturday, February 06, 2010 9:46 PM
Subject: Re: Tomcat dies suddenly


--- On Fri, 2/5/10, Carl <carl@etrak-plus.com> wrote:

Carl,

> 1. The application runs fine on an older system. Do we have
> the glibc and kernel versions for all systems?
>
> The old system: P4. 1GB memory, 1.3GB swap.
> Uses swap on a regular basis. kernel is 2.4.25.
> Java is 1.5.0_01-b08. Tomcat is 5.5.23. Glibc is
> version 2.3..1.
>
> New systems: Server A (Dell T110) is a Xeon 3440, sever B
> (Dell T105) is an AMD. A has 4GB memory and 19GB swap
> which is never used. B has 6GB memory and 10GB swap
> which is never used. A and B both use kernel version
> 2.6.29.6, Java 1.6.0_18-b07 and Tomcat 6.0.24.. Glibc
> version is 4.3.3 for both A and B.

A couple of observations here:

Both the old new kernels end in odd numbers. From memory, I thought the odd 
kernel numbers were experimental, while the even numbers were production or 
mainline. I don't remember when this numbering system took place, but 
certainly by the time the 2.6 kernels were released.

>From kernel.org, I didn't see a 2.6.29 release marked as stable.

The thread implementation has changed between the 2.4 and 2.6 kernels. You 
can see the thread implementation change by running:

getconf GNU_LIBPTHREAD_VERSION

I'd be interested in knowing the result of that and

getconf GNU_LIBC_VERSION

on both systems, since I don't recognize 4.3.3 as a glibc version (latest 
stable is 2.11.1, so I'm assuming 2.4.3.3?).

glibc has some thread bugs that were fixed, but not until 2.8 or 2.9. There 
was also a persistent bug for 32-bit systems that bites Java applications 
(not your concern since you're running 64-bit) that wasn't fixed until 
2.10.1.

So in short, I'm guessing this may be a glibc NPTL issue.

There are some observations that don't match, in that you're using Java 6 
(most problems are reported with Java 1.4 and Java 5), and that you've used 
OpenSuSE (kernel, glibc version?) with the same Tomcat failure.

However:

For some of the earlier 2.6 kernels, you could get around NPTL problems by 
setting this environment variable:

export LD_ASSUME_KERNEL=2.4.1

which forces the use of the old linuxthreads model. I don't know if that 
option is available with the 2.6 kernel that you are using.

Another work-around has been posted on the Java bugs forum, albeit for a 
different threading problem and Java 5:

-XX:ParallelGCThreads=1

sets GC to single threads. It's not fixed in the Java bugs database, because 
later versions of RedHat Linux don't exhibit the SIGSEGV problem.

Some people report that single-threading GC solves their problems, while 
other people report that it doesn't.

Some things to try I guess:

1. export LD_ASSUME_KERNEL=2.4.1 (maybe in startup.sh?) if your kernel 
supports this..

2. set -XX:ParallelGCThreads=1 in catalina.sh (JAVA_OPTS). This is an 
experimental switch, not documented here: 
http://java.sun.com/javase/technologies/hotspot/vmoptions.jsp, but 
documented here: 
http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html

3. Move to an even-numbered kernel with a glibc of 2.10.1 or better. 2.10 
might be OK for your environment since the bug fixed in 2.10.1 causes 
problems for 32-bit systems only.

just my two cents . . . .

/mde/





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