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Workload Group

You can use Workload Groups to manage the CPU, memory, and I/O resources used by queries and imports in the Doris cluster, and to control the maximum concurrency of queries in the cluster. Permissions for Workload Groups can be granted to specific roles and users.

Workload Groups are particularly effective in the following scenarios:

  1. For scenarios where performance stability is preferred, and it is not required for query load to utilize all cluster resources, but stable query latency is desired. In such cases, you can set hard limits on CPU/I/O for Workload Groups.
  2. When overall cluster load is high and availability decreases, you can restore cluster availability by degrading Workload Groups that consume excessive resources. For example, reduce the maximum query concurrency and I/O throughput for these Workload Groups.

Using hard limits for resource management usually results in better stability and performance, such as configuring maximum concurrency for FE and setting hard limits on CPU. Soft limits on CPU typically only have an effect when the CPU is fully utilized, which can lead to increased latency due to resource contention with other Doris components (RPC) and the operating system. Configuring hard limits for Doris query loads can effectively mitigate this issue. Additionally, setting maximum concurrency and queuing can help prevent the exhaustion of all available cluster resources during peak times with continuous incoming queries.

Version Description​

Workload Group is a feature that has been supported since version 2.0. The main difference between version 2.0 and 2.1 is that the 2.0 version of Workload Group does not rely on CGroup, while the 2.1 version of Workload Group depends on CGroup. Therefore, when using the 2.1 version of Workload Group, the environment of CGroup needs to be configured.

Upgrade to version 2.0​

If upgrading from version 1.2 to version 2.0, it is recommended to enable the WorkloadGroup after the overall upgrade of the Doris cluster is completed. Because if you only upgrade a single Follower and enable this feature, as the FE code of the Master has not been updated yet, there is no metadata information for Workload Group in the Doris cluster, which may cause queries for the upgraded Follower nodes to fail. The recommended upgrade process is as follows:

  • First, upgrade the overall code of the Doris cluster to version 2.0.
  • Start using this feature according to the section Workload group usage in the following text.

Upgrade to version 2.1​

If the code version is upgraded from 2.0 to 2.1, there are two situations:

Scenario 1: In version 2.1, if the Workload Group has already been used, you only need to refer to the process of configuring cgroup v1 in the following text to use the new version of the Workload Group.

Scenario 2: If the Workload Group is not used in version 2.0, it is also necessary to upgrade the Doris cluster as a whole to version 2.1, and then start using this feature according to the section Workload group usage in the following text.

Workload group properties​

  • cpu_share: Optional, The default value is 1024, with a range of positive integers. used to set how much cpu time the workload group can acquire, which can achieve soft isolation of cpu resources. cpu_share is a relative value indicating the weight of cpu resources available to the running workload group. For example, if a user creates 3 workload groups rg-a, rg-b and rg-c with cpu_share of 10, 30 and 40 respectively, and at a certain moment rg-a and rg-b are running tasks while rg-c has no tasks, then rg-a can get 25% (10 / (10 + 30)) of the cpu resources while workload group rg-b can get 75% of the cpu resources. If the system has only one workload group running, it gets all the cpu resources regardless of the value of its cpu_share.

  • memory_limit: Optional, default value is 0% which means unlimited, range of values from 1% to 100%. set the percentage of be memory that can be used by the workload group. The absolute value of the workload group memory limit is: physical_memory * mem_limit * memory_limit, where mem_limit is a be configuration item. The total memory_limit of all workload groups in the system must not exceed 100%. Workload groups are guaranteed to use the memory_limit for the tasks in the group in most cases. When the workload group memory usage exceeds this limit, tasks in the group with larger memory usage may be canceled to release the excess memory, refer to enable_memory_overcommit.

  • enable_memory_overcommit: Optional, enable soft memory isolation for the workload group, default is true. if set to false, the workload group is hard memory isolated and the tasks with the largest memory usage will be canceled immediately after the workload group memory usage exceeds the limit to release the excess memory. if set to true, the workload group is hard memory isolated and the tasks with the largest memory usage will be canceled immediately after the workload group memory usage exceeds the limit to release the excess memory. if set to true, the workload group is softly isolated, if the system has free memory resources, the workload group can continue to use system memory after exceeding the memory_limit limit, and when the total system memory is tight, it will cancel several tasks in the group with the largest memory occupation, releasing part of the excess memory to relieve the system memory pressure. It is recommended that when this configuration is enabled for a workload group, the total memory_limit of all workload groups should be less than 100%, and the remaining portion should be used for workload group memory overcommit.

  • cpu_hard_limit: Optional, default value -1%, no limit. The range of values is from 1% to 100%. In CPU hard limit mode, the maximum available CPU percentage of Workload Group cannot exceed cpu_hard_limit value, regardless of whether the current machine's CPU resources are fully utilized. Sum of all Workload Groups's cpu_hard_limit cannot exceed 100%. This is a new property added since version 2.1.

  • max_concurrency: Optional, maximum query concurrency, default value is the maximum integer value, which means there is no concurrency limit. When the number of running queries reaches this value, new queries will being queued.

  • max_queue_size: Optional, length of the query queue. When the queue is full, new queries will be rejected. The default value is 0, which means no queuing.

  • queue_timeout: Optional, query the timeout time in the queue, measured in milliseconds. If the query exceeds this value, an exception will be thrown directly to the client. The default value is 0, which means no queuing.

  • scan_thread_num: Optional, the number of threads used for scanning in the current workload group. The default value is -1, which means it does not take effect, the number of scan threads in the be configuration shall prevail. The value is an integer greater than 0.

  • max_remote_scan_thread_num: Optional. The maximum number of threads in the scan thread pool for reading external data sources. The default value is -1, which means the actual number of threads is determined by the BE and is typically related to the number of cores.

  • min_remote_scan_thread_num: Optional. The minimum number of threads in the scan thread pool for reading external data sources. The default value is -1, which means the actual number of threads is determined by the BE and is typically related to the number of cores.

  • tag: Optional. Default is empty. Assigns a tag to the Workload Group. The sum of resources for Workload Groups with the same tag cannot exceed 100%. If multiple values are desired, they can be separated by commas. Detailed description of the tagging function will follow.

  • read_bytes_per_second: Optional. Specifies the maximum I/O throughput when reading internal tables in Doris. The default value is -1, which means there is no limit on I/O bandwidth. Note that this value is not bound to disks but to folders. For example, if Doris is configured with two folders for storing internal table data, the maximum read I/O for each folder will not exceed this value. If these two folders are configured on the same disk, the maximum throughput control will be twice the read_bytes_per_second. The directory where files are written is also subject to this value.

  • remote_read_bytes_per_second: Optional. Specifies the maximum I/O throughput when reading external tables in Doris. The default value is -1, which means there is no limit on I/O bandwidth.

Notes:

  1. At present, the simultaneous use of CPU's soft and hard limits is not supported. A cluster can only have soft or hard limits at a certain time. The switching method will be described in the following text.

  2. All properties are optional, but at least one property needs to be specified when creating a Workload Group.

  3. It is important to note that the default CPU soft limit values differ between cgroup v1 and cgroup v2. In cgroup v1, the default CPU soft limit value is 1024, with a range of 2 to 262144. In contrast, cgroup v2 has a default CPU soft limit value of 100, with a range of 1 to 10000.

If a value outside of this range is specified for the soft limit, it can lead to a failure in modifying the CPU soft limit in the backend. Additionally, if you set the default value of 100 in a cgroup v1 environment, it might cause the priority of this workload group to be the lowest on the machine.

Grouping Workload Group By Tag​

The Workload Group feature divides the resource usage of a single BE. When a user creates a Workload Group (Group A), its metadata is by default sent to all BEs and threads are started on each BE, leading to the following issues:

  1. Multiple Clusters Issue: In a production environment, a Doris cluster is typically divided into several smaller clusters, such as a local storage cluster and a cluster with Compute Nodes for querying external storage. These two clusters operate independently. If a user wants to use the Workload Group feature, it would lead to the issue where the mem_limit of Workload Groups for external storage and local storage cannot exceed 100%, even though these two types of load are on completely different machines, which is obviously unreasonable.
  2. Thread Resource Management: The number of threads itself is a resource. If a process's thread quota is exhausted, it will cause the process to crash. Therefore, sending the Workload Group metadata to all nodes by default is also unreasonable.

To address these issues, Doris implements a grouping feature for Workload Groups. The cumulative value of Workload Groups with the same tag cannot exceed 100%, but there can be multiple such tag groups within a cluster. When a BE node is tagged, it will match the corresponding Workload Groups based on specific rules.

Example:

  1. Create a Workload Group named tag_wg with the tag cn1. If none of the BEs in the cluster have been tagged, the metadata for this Workload Group will be sent to all BEs. The tag attribute can specify multiple values, separated by commas.
create workload group tag_wg properties('tag'='cn1');
  1. Modify the tag of a BE in the cluster to cn1. At this point, the tag_wg Workload Group will only be sent to this BE and any BE with no tag. The tag.workload_group attribute can specify multiple values, separated by commas.
alter system modify backend "localhost:9050" set ("tag.workload_group" = "cn1");

Workload Group and BE Matching Rules: If the Workload Group's tag is empty, the Workload Group can be sent to all BEs, regardless of whether the BE has a tag or not. If the Workload Group's tag is not empty, the Workload Group will only be sent to BEs with the same tag.

Configure cgroup​

Doris 2.0 version uses Doris scheduling to limit CPU resources, but since version 2.1, Doris defaults to using CGgroup v1 to limit CPU resources. Therefore, if CPU resources are expected to be limited in version 2.1, it is necessary to have CGgroup installed on the node where BE is located.

If users use the Workload Group software limit in version 2.0 and upgrade to version 2.1, they also need to configure CGroup, Otherwise, cpu soft limit may not work.

If using CGroup within a container, the container needs to have permission to operate the host.

Without configuring cgroup, users can use all functions of the workload group except for CPU limitations.

  1. Firstly, confirm that the CGgroup has been installed on the node where BE is located.
cat /proc/filesystems | grep cgroup
nodev   cgroup
nodev   cgroup2
nodev   cgroupfs
  1. Check the cgroup version.
If this path exists, it indicates that cgroup v1 is currently active.
/sys/fs/cgroup/cpu/


If this path exists, it indicates that cgroup v2 is currently active.
/sys/fs/cgroup/cgroup.controllers
  1. Create a new directory named doris in the CPU path of cgroup, user can specify their own directory name.

mkdir /sys/fs/cgroup/cpu/doris

  1. It is necessary to ensure that Doris's BE process has read/write/execute permissions for this directory
// Modify the permissions of this directory to read, write, and execute
chmod 770 /sys/fs/cgroup/cpu/doris

// Assign the ownership of this directory to Doris's account
chown -R doris:doris /sys/fs/cgroup/cpu/doris
  1. If cgroup v2 is being used in the current environment, the following actions need to be taken. This is because cgroup v2 has stricter permission controls, requiring write access to the cgroup.procs file in the root directory in order to move processes between groups.
chmod a+w /sys/fs/cgroup/cgroup.procs
  1. Modify the configuration of BE and specify the path to cgroup
doris_cgroup_cpu_path = /sys/fs/cgroup/cpu/doris
  1. restart BE, in the log (be. INFO), you can see the words "add thread xxx to group" indicating successful configuration.
tip

NOTE:

  1. The current workload group does not yet support the deployment of multiple BEs on a single machine.
  2. After the machine is restarted, the above cgroup configurations will be cleared. If you want the above configurations to take effect after a reboot, you can use systemd to set these operations as a custom system service, so that the creation and permission assignments are automatically completed each time the machine restarts.

Note for Using Workload Groups in K8S​

The CPU management for Workloads is implemented based on CGroup. To use Workload Groups within containers, you need to start the containers in privileged mode so that the Doris processes inside the container have permission to read and write CGroup files on the host.

When Doris runs inside a container, the CPU resources for Workload Groups are allocated based on the container's available resources. For example, if the host machine has 64 cores and the container is allocated 8 cores, with a CPU hard limit of 50% configured for the Workload Group, the actual number of usable cores for the Workload Group would be 4 (8 cores * 50%).

Memory and I/O management for Workload Groups are handled internally by Doris and do not rely on external components, so there is no difference in deployment between containers and physical machines.

If you want to use Doris on K8S, it is recommended to use the Doris Operator for deployment, as it can abstract away the underlying permission details.

Workload group usage​

  1. First, create a custom workload group. 
create workload group if not exists g1
properties (
    "cpu_share"="1024",
    "memory_limit"="30%",
    "enable_memory_overcommit"="true"
);

This is soft CPU limit. Since version 2.1, the system will automatically create a group named normal , which cannot be deleted.

For details on creating a workload group, see CREATE-WORKLOAD-GROUP, and to delete a workload group, refer to DROP-WORKLOAD-GROUP; to modify a workload group, refer to ALTER-WORKLOAD-GROUP; to view the workload group, you can visit doris system table information_schema.workload_groups or SHOW-WORKLOAD-GROUPS.

  1. Bind the workload group.
  • Bind the user to the workload group by default by setting the user property to normal.
set property 'default_workload_group' = 'g1'.

The current user's query will use 'g1' by default.

  • Specify the workload group via the session variable, which defaults to null.
set workload_group = 'g1'.

session variable workload_group takes precedence over user property default_workload_group, in case workload_group is empty, the query will be bound to default_workload_group, in case session variable workload_group is not empty, the query will be bound to workload_group.

If you are a non-admin user, you need to execute SHOW-WORKLOAD-GROUPS to check if the current user can see the workload group, if not, the workload group may not exist or the current user does not have permission to execute the query. If you cannot see the workload group, the workload group may not exist or the current user does not have privileges. To authorize the workload group, refer to: grant statement.

  1. Execute the query, which will be associated with the g1 workload group.

Query Queue​

create workload group if not exists queue_group
properties (
    "cpu_share"="10",
    "memory_limit"="30%",
    "max_concurrency" = "10",
    "max_queue_size" = "20",
    "queue_timeout" = "3000"
);

It should be noted that the current queuing design is not aware of the number of FEs, and the queuing parameters only works in a single FE, for example:

A Doris cluster is configured with a work load group and set max_concurrency=1, If there is only 1 FE in the cluster, then this workload group will only run one SQL at the same time from the Doris cluster perspective, If there are 3 FEs, the maximum number of query that can be run in Doris cluster is 3.

Configure CPU hard limits​

At present, Doris defaults to running the CPU's soft limit. If you want to use Workload Group's hard limit, you can do as follows.

1 Enable the cpu hard limit in FE. If there are multiple FE, the same operation needs to be performed on each FE.

1 modify fe.conf in disk
experimental_enable_cpu_hard_limit = true

2 modify conf in memory
ADMIN SET FRONTEND CONFIG ("enable_cpu_hard_limit" = "true");

2 modify cpu_hard_limit

alter workload group g1 properties ( 'cpu_hard_limit'='20%' );

3 Viewing the current configuration of the Workload Group, it can be seen that although the cpu_share may not be 0, but due to the hard limit mode being enabled, the query will also follow the CPU's hard limit during execution. That is to say, the switch of CPU software and hardware limits does not affect workload group modification.

mysql [information_schema]>select name, cpu_share,memory_limit,enable_memory_overcommit,cpu_hard_limit from information_schema.workload_groups where name='g1';
+------+-----------+--------------+--------------------------+----------------+
| name | cpu_share | memory_limit | enable_memory_overcommit | cpu_hard_limit |
+------+-----------+--------------+--------------------------+----------------+
| g1   |      1024 | 30%          | true                     | 20%            |
+------+-----------+--------------+--------------------------+----------------+
1 row in set (0.02 sec)

How to switch CPU limit node between soft limit and hard limit​

At present, Doris does not support running both the soft and hard limits of the CPU simultaneously. A Doris cluster can only have either the CPU soft limit or the CPU hard limit at any time.

Users can switch between two modes, and the main switching methods are as follows:

1 If the current cluster configuration is set to the default CPU soft limit and it is expected to be changed to the CPU hard limit, then cpu_hard_limit should be set to a valid value first.

alter workload group test_group properties ( 'cpu_hard_limit'='20%' );

It is necessary to modify cpu_hard_limit of all Workload Groups in the current cluster, sum of all Workload Group's cpu_hard_limit cannot exceed 100%. Due to the CPU's hard limit can not being able to provide a valid default value, if only the switch is turned on without modifying cpu_hard_limit, the CPU's hard limit will not work.

2 Turn on the CPU hard limit switch in all FEs.

1 modify fe.conf
experimental_enable_cpu_hard_limit = true

2 modify conf in memory
ADMIN SET FRONTEND CONFIG ("enable_cpu_hard_limit" = "true");

If user expects to switch back from cpu hard limit to cpu soft limit, then they only need to set enable_cpu_hard_limit=false. CPU Soft Limit property cpu_share will be filled with a valid value of 1024 by default(If the user has never set the cpu_share before), and users can adjust cpu_share based on the priority of Workload Group.

Workload Group Permissions Table

You can view the Workload Groups that users or roles have access to through the Workload Group privilege table. Authorization related usage can refer togrant statement.

This table currently has row level permission control. Root or admin accounts can view all data, while non root/admin accounts can only see data from Workload Groups that they have access to。

Schema of Workload Group privilege table is as follow：

mysql [information_schema]>desc information_schema.workload_group_privileges;
+---------------------+--------------+------+-------+---------+-------+
| Field               | Type         | Null | Key   | Default | Extra |
+---------------------+--------------+------+-------+---------+-------+
| GRANTEE             | varchar(64)  | Yes  | false | NULL    |       |
| WORKLOAD_GROUP_NAME | varchar(256) | Yes  | false | NULL    |       |
| PRIVILEGE_TYPE      | varchar(64)  | Yes  | false | NULL    |       |
| IS_GRANTABLE        | varchar(3)   | Yes  | false | NULL    |       |
+---------------------+--------------+------+-------+---------+-------+

Column Description：

  1. grantee, user or role.
  2. workload_group_name, value is the name of Workload Group or '%', where '%' represents all Workload Group.
  3. privilege_type, type of privilege, at present, the value of this column is only Usage_priv。
  4. is_grantable, value is YES or NO, it means whether the user can grant access privilege of Workload Group to other user.Only root/admin user has grant privilege.

Basic usage：

  1. Search for Workload Group with authorized access based on username.
mysql [information_schema]>select * from workload_group_privileges where GRANTEE like '%test_wlg_user%';
+---------------------+---------------------+----------------+--------------+
| GRANTEE             | WORKLOAD_GROUP_NAME | PRIVILEGE_TYPE | IS_GRANTABLE |
+---------------------+---------------------+----------------+--------------+
| 'test_wlg_user'@'%' | normal              | Usage_priv     | NO           |
| 'test_wlg_user'@'%' | test_group          | Usage_priv     | NO           |
+---------------------+---------------------+----------------+--------------+
2 rows in set (0.04 sec)
  1. Search for user which has access privilege by Workload Group name. 
mysql [information_schema]>select * from workload_group_privileges where WORKLOAD_GROUP_NAME='test_group';
+---------------------+---------------------+----------------+--------------+
| GRANTEE             | WORKLOAD_GROUP_NAME | PRIVILEGE_TYPE | IS_GRANTABLE |
+---------------------+---------------------+----------------+--------------+
| 'test_wlg_user'@'%' | test_group          | Usage_priv     | NO           |
+---------------------+---------------------+----------------+--------------+
1 row in set (0.03 sec)
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