Configure cgroups

This topic describes how to configure cgroups for OceanBase Database.

Background information

In the current version of OceanBase Database, worker threads and most background threads are distinguished based on the tenant, while network threads are shared threads. Therefore, you can control the CPU or IOPS usage of a tenant by configuring cgroups. Before you configure cgroups, we recommend that you learn about the concept of cgroups first. For more information, see Overview of resource isolation.

Precautions and limitations

• Resource isolation considerably compromises performance. We recommend that you do not use the cgroup feature to isolate tenant resources in the following scenarios:

  • Single-tenant scenarios that have only one tenant in the cluster.

  • Scenarios where tenants are associated with each other. For example, multiple tenants serve different microservices, resulting in an upstream and downstream relationship among the tenants.

  • Small-scale tenant scenarios where each tenant has two or four CPU cores.

• To use the cgroup feature, the Linux kernel version must be 5.10 or later.

• After upgrading OceanBase Database, you need to reconfigure cgroup.

Procedure

Step 1: Configure the cgroup system directory

This topic describes how to configure the cgroup system directory on one OBServer node. If the OceanBase cluster consists of multiple OBServer nodes, you must configure the cgroup system directory on each OBServer node.

1. Log in to the OBServer server as the admin user.

2. Run the following command to mount the /sys/fs/cgroup directory.

   Note

   If the /sys/fs/cgroup directory already exists, skip this step.

   [admin@xxx /]$ sudo mount -t tmpfs cgroups /sys/fs/cgroup
   

   Here, cgroups is a user-defined name for identification when you view the mount information.

   The mounting result is as follows:

   $df
   Filesystem      1K-blocks       Used Available Use% Mounted on
   /               293601280   28055472 265545808  10% /
   /dev/v01d      2348810240 2113955876 234854364  91% /data/1
   /dev/v02d      1300234240 1170211208 130023032  91% /data/log1
   shm              33554432          0  33554432   0% /dev/shm
   /dev/v04d       293601280   28055472 265545808  10% /home/admin/logs
   cgroups         395752136          0 395752136   0% /sys/fs/cgroup
   

3. Create a directory named /sys/fs/cgroup/cpu, change its owner, and mount the cpu subsystem.

   Note

   If the /sys/fs/cgroup/cpu directory already exists and is empty, skip this step.

   [admin@xxx /]$ sudo mkdir /sys/fs/cgroup/cpu
   
   [admin@xxx /]$ sudo chown admin:admin -R /sys/fs/cgroup/cpu
   

   Create a directory hierarchy named cpu, attach the cpu subsystem to this hierarchy, and mount this hierarchy to the /sys/fs/cgroup/cpu directory.

   [admin@xxx /]$ sudo mount -t cgroup -o cpu cpu /sys/fs/cgroup/cpu
   

4. Create a subdirectory named oceanbase and change its owner to admin.

   [admin@xxx /]$ sudo mkdir /sys/fs/cgroup/cpu/oceanbase
   
   [admin@xxx /]$ sudo chown admin:admin -R /sys/fs/cgroup/cpu/oceanbase
   

5. Allocate CPU and memory resources for the oceanbase directory.

   1. Execute the following command to check the mounting status of the cpu, cpuacct, and cpuset subsystems on your machine.

      [admin@xxx /]$ ll /sys/fs/cgroup
      

   2. Based on the subsystems' mounting status, proceed with the appropriate action:

      • The cpuset subsystem is mounted alongside cpu and cpuacct.

        In this case, typically all three subsystems are mounted under the same directory, as shown in the example below.

        drwxr-xr-x 3 root root 0 Jul 24 2020 blkio
        lrwxrwxrwx 1 root root 33 Jul 24 2020 cpu -> /sys/fs/cgroup/cpuset,cpu,cpuacct
        lrwxrwxrwx 1 root root 33 Jul 24 2020 cpuacct -> /sys/fs/cgroup/cpuset,cpu,cpuacct
        lrwxrwxrwx 1 root root 33 Jul 24 2020 cpuset -> /sys/fs/cgroup/cpuset,cpu,cpuacct
        drwxr-xr-x 4 root root 0  Jul 24 2020 cpuset,cpu,cpuacct
        

        For this setup, execute the following commands to allocate CPU and memory resources for the oceanbase directory.

        [admin@xxx /]$ sudo sh -c "echo `cat /sys/fs/cgroup/cpu/cpuset.cpus` > /sys/fs/cgroup/cpu/oceanbase/cpuset.cpus"
        
        [admin@xxx /]$ sudo sh -c "echo `cat /sys/fs/cgroup/cpu/cpuset.mems` > /sys/fs/cgroup/cpu/oceanbase/cpuset.mems"
        

      • The cpuset subsystem is mounted separately from cpu and cpuacct.

        In this case, the cpuset subsystem is independently mounted from cpu and cpuacct, a configuration frequently encountered in Elastic Compute Service (ECS) environments. The mounting result is as follows:

        drwxr-xr-x 2 root root 40 February 27 15:27 blkio
        lrwxrwxrwx 1 root root 11 February 27 15:27 cpu -> cpu,cpuacct
        lrwxrwxrwx 1 root root 11 February 27 15:27 cpuacct -> cpu,cpuacct
        drwxr-xr-x 2 root root 40 February 27 15:27 cpu,cpuacct
        drwxr-xr-x 2 root root 40 February 27 15:27 cpuset
        

        In this setup, no additional actions are needed. You can proceed to the next step.

6. Execute the following command to set the inheritance property for subdirectories in the oceanbase directory.

   [admin@xxx /]$ sudo sh -c "echo 1 > /sys/fs/cgroup/cpu/oceanbase/cgroup.clone_children"
   

   After the command executes successfully, any cgroup subdirectories created under the oceanbase directory will inherit the properties of the parent directory.

Step 2: Establish a soft link to OceanBase Database

After you configure the cgroup system directory, establish a soft link between the installation directory of OceanBase Database and the cgroup system directory.

1. Log in to the OBServer node as the admin user.

2. Manually establish a soft link between the installation directory of OceanBase Database and the cgroup system directory.

   [admin@xxx /home/admin]$ cd /home/admin/oceanbase/
   
   [admin@xxx /home/admin]
   $ ln -sf /sys/fs/cgroup/cpu/oceanbase/ cgroup
   

   Here, /home/admin/oceanbase/ is the installation directory of OceanBase Database.

   The execution result is as follows:

   [admin@xxx /home/admin/oceanbase]
   $ll cgroup
   lrwxrwxrwx 1 admin admin 29 Dec  8 11:09 cgroup -> /sys/fs/cgroup/cpu/oceanbase/
   lrwxrwxrwx 1 admin admin 29 Dec  8 11:09 cgroup -> /sys/fs/cgroup/blkio/oceanbase/
   

Step 3: Enable the cgroup feature

The cluster-level enable_cgroup parameter in OceanBase Database controls whether to enable the cgroup feature for the OBServer node. The default value is True, which means that the cgroup feature is enabled. After you establish the soft link and enable the cgroup feature, you do not need to restart the OBServer node. The cgroup feature will take effect automatically.

If the cgroup feature is disabled, you can perform the following steps to enable it.

1. Log in to the sys tenant of the cluster as the root user.

2. Execute the following statement to enable the cgroup feature:

   obclient> ALTER SYSTEM SET enable_cgroup = true;
   

   or

   obclient> ALTER SYSTEM SET enable_cgroup = 1;
   

   or

   obclient> ALTER SYSTEM SET enable_cgroup = ON;
   

What to do next

After you configure the cgroup system directory and enable the cgroup feature, in the case of emergencies, you can control the utilization of CPU resources in a tenant by using the cpu.cfs_period_us, cpu.cfs_quota_us, and cpu.shares files in the directory of the tenant. Generally, we recommend that you do not implement resource isolation in this way.

We recommend that you use the files in the cgroup system directory to call the CREATE_CONSUMER_GROUP subprogram in the DBMS_RESOURCE_MANAGER package to create resource groups for user-level or SQL statement-level resource isolation. For more information, see Configure resource isolation within a tenant.

References

Clear cgroup configurations