Deployment Considerations - Linux

When deploying Coherence on Linux please be aware of the following:

Native POSIX Thread Library (NPTL)

Early versions of the NPTL are prone to deadlock, especially when combined with 2.4 Linux Kernels. The kernel version and NPTL version can be obtained by executing the following commands:

uname -a

If running on a 2.4 kernel, it is recommended that you avoid using any version of the NPTL, and revert to using LinuxThreads. This can be done by setting the LD_ASSUME_KERNEL environment variable prior to launching Java.

export LD_ASSUME_KERNEL=2.4.19

If running on a 2.6 kernel, it is recommended that you use a 1.0 or higher version of NPTL. If upgrading the NPTL version is not possible then it is then recommended that you switch to LinuxThreads.

NPTL related issues are known to occur with Red Hat Linux 9 and Red Hat Enterprise Linux 3, and are also likely to effect any 2.4 based Linux distribution with a backported version of the NPTL. See for more details on this issue.

TSC High Resolution Timesource

Linux has a number of high resolution timesources to choose from, the fastest TSC (Time Stamp Counter) unfortunately is not always reliable. Linux chooses TSC by default, and during boot checks for inconsistencies, if found it switches to a slower safe timesource. The slower time sources can be 10 to 30 times more expensive to query then the TSC timesource, and may have a measurable impact on Coherence performance. Note that Coherence and the underlying JVM are not aware of the timesource which the OS is utilizing. It is suggested that you check your system logs (/var/log/dmesg) to verify that the following is not present.

kernel: Losing too many ticks!
kernel: TSC cannot be used as a timesource.
kernel: Possible reasons for this are:
kernel:   You're running with Speedstep,
kernel:   You don't have DMA enabled for your hard disk (see hdparm),
kernel:   Incorrect TSC synchronization on an SMP system (see dmesg).
kernel: Falling back to a sane timesource now.

As the log messages suggest, this can be caused by a variable rate CPU (SpeedStep), having DMA disabled, or incorrect TSC synchronization on multi CPU machines. If present it is suggested that you work with your system administrator to identify the cause and allow the TSC timesource to be utilized.