System configuration

Perform the following configuration on each node in the cluster:

• set up time synchronization
• set ulimits
• enable transparent hugepages

Keep in mind that, although YugabyteDB is PostgreSQL compatible and runs a postgres process, it is not a PostgreSQL distribution. The PostgreSQL it runs doesn't need the same OS and system resources that open source PostgreSQL requires. For this reason, the kernel configuration requirements are different.

In particular, the main YugabyteDB process, the YB-TServer, is multi-threaded. As a result, you don't need to modify settings for shared memory and inter-process communication (IPC), because there is no inter-process communication or shared memory in a multi-threaded process model (all memory is shared by the same process).

Set up time synchronization

YugabyteDB relies on clock synchronization to guarantee consistency in distributed transactions. chrony is the preferred NTP implementation for clock synchronization.

To install chrony, run:

$ sudo yum install -y chrony

Set ulimits

In Linux, ulimit is used to limit and control the usage of system resources (threads, files, and network connections) on a per-process or per-user basis.

Check ulimits

Run the following command to check the ulimit settings.

$ ulimit -a

The following settings are recommended when running YugabyteDB.

core file size          (blocks, -c) unlimited
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 119934
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1048576
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 12000
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

Set system-wide ulimits

You can change values by substituting the -n option for any possible value in the output of ulimit -a. Issue a command in the following form to change a ulimit setting.

$ ulimit -n <value>

-f (file size): unlimited
-t (cpu time): unlimited
-v (virtual memory): unlimited [1]
-l (locked-in-memory size): unlimited
-n (open files): 64000
-m (memory size): unlimited [1] [2]
-u (processes/threads): 64000

{{< note title="Restart servers" >}}

If you change a ulimit setting on a node where the YB-Master and YB-TServer servers are already running, you must restart the servers for the new settings to take effect. Check the yb-tserver.INFO file to verify that the ulimits are applied. You can also check the /proc/<process pid> file to see the current settings.

{{< /note >}}

Changes made using ulimit may revert following a system restart depending on the system configuration. These settings should be applied permanently by adding the following in /etc/security/limits.conf:

*                -       core            unlimited
*                -       data            unlimited
*                -       fsize           unlimited
*                -       sigpending      119934
*                -       memlock         64
*                -       rss             unlimited
*                -       nofile          1048576
*                -       msgqueue        819200
*                -       stack           8192
*                -       cpu             unlimited
*                -       nproc           12000
*                -       locks           unlimited

On CentOS, /etc/security/limits.d/20-nproc.conf must also be configured to match.

*          soft    nproc     12000

After changing a ulimit setting in /etc/security/limits.conf, you will need to log out and back in. To update system processes, you may need to restart.

{{< note title="Using other distributions" >}} If you're using a desktop-distribution, such as ubuntu-desktop, the preceding settings may not suffice. The operating system needs additional steps to change ulimit for GUI login.

In the case of ubuntu-desktop, in /etc/systemd/user.conf and /etc/systemd/system.conf, add DefaultLimitNOFILE=64000 at the end of file.

Something similar may be needed for other distributions. {{< /note >}}

Kernel settings

If running on a virtual machine, execute the following to tune kernel settings:

1. Configure the parameter vm.swappiness as follows:

   shCopy

   sudo bash -c 'sysctl vm.swappiness=0 >> /etc/sysctl.conf'
   

2. Setup path for core files as follows:

   shCopy

   sudo sysctl kernel.core_pattern=/home/yugabyte/cores/core_%p_%t_%E
   

3. Configure the parameter vm.max_map_count as follows:

   shCopy

   sudo sysctl -w vm.max_map_count=262144
   sudo bash -c 'sysctl vm.max_map_count=262144 >> /etc/sysctl.conf'
   

4. Validate the change as follows:

   shCopy

   sysctl vm.max_map_count
   

Using systemd

If you're using systemd to start the processes, and the ulimits are not propagated, add the ulimits in the Service section of the systemd configuration file:

[Unit]
.....

[Service]
.....
ulimits options here

[Install]
.....

For more details, see the systemd example configuration for yb-master.service, and yb-tserver.service.

The mappings of ulimit options with values are:

If a ulimit is set to unlimited, set it to infinity in the systemd configuration file.

Enable transparent hugepages

Transparent hugepages should be enabled for optimal performance. By default, they are enabled.

You can check with the following command:

$ cat /sys/kernel/mm/transparent_hugepage/enabled

You should see the following output:

[always] madvise never

In addition, you should verify that transparent hugepages use the following settings:

/sys/kernel/mm/transparent_hugepage/defrag:
    always defer [defer+madvise] madvise never

/sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_none:
    0

If any of these values are not set as shown, you should modify your kernel command line to match. Consult your operating system documentation to determine the best way to modify a kernel command line argument for your operating system.

For example, on RHEL or CentOS 7 or 8, using grub2, you can use the following steps to enable transparent hugepages:

1. Append "transparent_hugepage=always" to GRUB_CMDLINE_LINUX in /etc/default/grub.

   shCopy

   GRUB_CMDLINE_LINUX="rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap ... transparent_hugepage=always"
   

2. Rebuild /boot/grub2/grub.cfg using grub2-mkconfig.

   Be sure to take a backup of the existing /boot/grub2/grub.cfg before rebuilding.

   On BIOS-based machines:

   shCopy

   grub2-mkconfig -o /boot/grub2/grub.cfg
   

   On UEFI-based machines:

   shCopy

   grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
   

3. Reboot the system.