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CPU affinity

Kdb+ can be constrained to run on specific cores through the setting of CPU affinity.

Typically, you can set the CPU affinity for the shell you are in, and then processes started within that shell will inherit the affinity.

.Q.w (memory stats)
Basics: Command-line parameter -w, System command \w


Non-Uniform Access Memory (NUMA)

Detecting NUMA

The following commands will show if NUMA is active.

$ grep NUMA=y /boot/config-`uname -r`

Or test for the presence of NUMA maps.

$ find /proc -name numa_maps

Q and NUMA

Until Linux kernels 3.x, q and NUMA did not work well together.

When activating NUMA, substitute parameter settings according to the recommendations for different Linux kernels.

Activating NUMA

When NUMA is

  • not active, use the taskset command, e.g.

    taskset -c 0,1,2 q

    will run q on cores 0, 1 and 2. Or

    taskset -c 0,1,2 bash

    and then all processes started from within that new shell will automatically be restricted to those cores.

  • active, use numactl instead of taskset

    numactl --interleave=all --physcpubind=0,1,2 q

    and set

    echo 0 > /proc/sys/vm/zone_reclaim_mode

You can change zone_reclaim_mode without restarting q.

Other ways to limit resources

On Linux systems, administrators might prefer cgroups as a way of limiting resources.

On Unix systems, memory usage can be constrained using ulimit, e.g.

ulimit -v 262144

limits virtual address space to 256MB.


Use psrset

psrset -e 2 q

which will run q using processor set 2. Or, to start a shell restricted to those cores:

psrset -e 2 bash


Start q.exe with the OS command start with the /affinity flag set

start /affinity 3 c:\q\w64\q.exe 

will run q on core 0 and 1.

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