Dynamic Resource Pools

Viewing Dynamic Resource Pool Configuration

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has a YARN service, the YARN > Resource Pools tab displays. If the cluster has an Impala service enabled as described in Enabling or Disabling Impala Admission Control in Cloudera Manager, the Impala Admission Control > Resource Pools tab displays.
2. Click the YARN or Impala Admission Control tab.

Creating a YARN Dynamic Resource Pool

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has a YARN service, the YARN > Resource Pools tab displays. If the cluster has an Impala service enabled as described in Enabling or Disabling Impala Admission Control in Cloudera Manager, the Impala Admission Control > Resource Pools tab displays.
2. Click the YARN tab.
3. Click Create Resource Pool. The Create Resource Pool dialog box displays, showing the Resource Limits tab.
4. Specify a name and resource limits for the pool:
   • In the Resource Pool Name field, specify a unique pool name containing only alphanumeric characters. If referencing a user or group name that contains a ".", replace the "." with "_dot_".
   • To make the pool a parent pool, select the Parent Pool checkbox.
   • Define a configuration set by assigning values to the listed properties. Specify a weight that indicates that pool's share of resources relative to other pools, minimum and maximum for virtual cores and memory, and a limit on the number of applications that can run simultaneously in the pool. If this is a parent pool, you can also set the maximum resources for undeclared children.
   • Click the Scheduling Policy tab and select a policy:
     • Dominant Resource Fairness (DRF) (default) - An extension of fair scheduling for more than one resource. DRF determines CPU and memory resource shares based on the availability of those resources and the job requirements.
     • Fair (FAIR) - Determines resource shares based on memory.
     • First-In, First-Out (FIFO) - Determines resource shares based on when a job was added.
   • If you have enabled Fair Scheduler preemption, click the Preemption tab and optionally set a preemption timeout to specify how long a job in this pool must wait before it can preempt resources from jobs in other pools. To enable preemption, follow the procedure in Enabling and Disabling Fair Scheduler Preemption.
   • If you have enabled ACLs and specified users or groups, optionally click the Submission and Administration Access Control tabs to specify which users and groups can submit applications and which users can view all and kill applications. By default, anyone can submit, view all, and kill applications. To restrict these permissions, select Allow these users and groups and provide a comma-delimited list of users and groups in the Users and Groups fields respectively.
5. Click Create.
6. Click Refresh Dynamic Resource Pools.

Enabling or Disabling Impala Admission Control in Cloudera Manager

We recommend enabling admission control on all production clusters to alleviate possible capacity issues. The capacity issues could be because of a high volume of concurrent queries, because of heavy-duty join and aggregation queries that require large amounts of memory, or because Impala is being used alongside other Hadoop data management components and the resource usage of Impala must be constrained to work well in a multitenant deployment.

1. Go to the Impala service.
2. In the Configuration tab, select Category > Admission Control.
3. Select or clear both the Enable Impala Admission Control checkbox and the Enable Dynamic Resource Pools checkbox.
4. Enter a Reason for change, and then click Save Changes to commit the changes.
5. Restart the Impala service.

After completing this task, for further configuration settings, customize the configuration settings for the dynamic resource pools, as described in below.

Creating an Impala Dynamic Resource Pool

There is always a resource pool designated as root.default. By default, all Impala queries run in this pool when the dynamic resource pool feature is enabled for Impala. You create additional pools when your workload includes identifiable groups of queries (such as from a particular application, or a particular group within your organization) that have their own requirements for concurrency, memory use, or service level agreement (SLA). Each pool has its own settings related to memory, number of queries, and timeout interval.

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has an Impala service, the Resource Pools tab displays under the Impala Admission Control tab.
2. Click the Impala Admission Control tab.
3. Click Create Resource Pool.
4. Specify a name and resource limits for the pool:
   • In the Resource Pool Name field, type a unique name containing only alphanumeric characters.
   • Optionally, click the Submission Access Control tab to specify which users and groups can submit queries. By default, anyone can submit queries. To restrict this permission, select the Allow these users and groups option and provide a comma-delimited list of users and groups in the Users and Groups fields respectively.
5. Click Create.
6. Click Refresh Dynamic Resource Pools.

Configuration Settings for Impala Dynamic Resource Pool

Max Memory

Maximum amount of aggregate memory available across the cluster to all queries executing in this pool. This should be a portion of the aggregate configured memory for Impala daemons, which will be shown in the settings dialog next to this option for convenience. Setting this to a non-zero value enables memory based admission control.

Impala determines the expected maximum memory used by all queries in the pool and holds back any further queries that would result in Max Memory being exceeded.

If you specify Max Memory, you should specify the amount of memory to allocate to each query in this pool. You can do this in two ways:

• By setting Maximum Query Memory Limit and Minimum Query Memory Limit. This is preferred in CDH 6.1 and higher and gives Impala flexibility to set aside more memory to queries that are expected to be memory-hungry.
• By setting Default Query Memory Limit to the exact amount of memory that Impala should set aside for queries in that pool.

Note that if you do not set any of the above options, or set Default Query Memory Limit to 0, Impala will rely entirely on memory estimates to determine how much memory to set aside for each query. This is not recommended because it can result in queries not running or being starved for memory if the estimates are inaccurate.

For example, consider the following scenario:

• The cluster is running impalad daemons on five hosts.
• A dynamic resource pool has Max Memory set to 100 GB.
• The Maximum Query Memory Limit for the pool is 10 GB and Minimum Query Memory Limit is 2 GB. Therefore, any query running in this pool could use up to 50 GB of memory (Maximum Query Memory Limit * number of Impala nodes).
• Impala will execute varying numbers of queries concurrently because queries may be given memory limits anywhere between 2 GB and 10 GB, depending on the estimated memory requirements. For example, Impala may execute up to 10 small queries with 2 GB memory limits or two large queries with 10 GB memory limits because that is what will fit in the 100 GB cluster-wide limit when executing on five hosts.
• The executing queries may use less memory than the per-host memory limit or the Max Memory cluster-wide limit if they do not need that much memory. In general this is not a problem so long as you are able to execute enough queries concurrently to meet your needs.

Minimum Query Memory Limit and Maximum Query Memory Limit

These two options determine the minimum and maximum per-host memory limit that will be chosen by Impala Admission control for queries in this resource pool. If set, Impala admission control will choose a memory limit between the minimum and maximum value based on the per-host memory estimate for the query. The memory limit chosen determines the amount of memory that Impala admission control will set aside for this query on each host that the query is running on. The aggregate memory across all of the hosts that the query is running on is counted against the pool’s Max Memory.

Minimum Query Memory Limit must be less than or equal to Maximum Query Memory Limit and Max Memory.

You can override Impala’s choice of memory limit by setting the MEM_LIMIT query option. If the Clamp MEM_LIMIT Query Option is selected and the user sets MEM_LIMIT to a value that is outside of the range specified by these two options, then the effective memory limit will be either the minimum or maximum, depending on whether MEM_LIMIT is lower than or higher than the range.

Default Query Memory Limit

The default memory limit applied to queries executing in this pool when no explicit MEM_LIMIT query option is set. The memory limit chosen determines the amount of memory that Impala Admission control will set aside for this query on each host that the query is running on. The aggregate memory across all of the hosts that the query is running on is counted against the pool’s Max Memory.

This option is deprecated from CDH 6.1 and higher and is replaced by Maximum Query Memory Limit and Minimum Query Memory Limit. Do not set this field if either Maximum Query Memory Limit or Minimum Query Memory Limit is set.

Max Running Queries

Maximum number of concurrently running queries in this pool. The default value is unlimited for CDH 5.7 or higher. (optional)

The maximum number of queries that can run concurrently in this pool. The default value is unlimited. Any queries for this pool that exceed Max Running Queries are added to the admission control queue until other queries finish. You can use Max Running Queries in the early stages of resource management, when you do not have extensive data about query memory usage, to determine if the cluster performs better overall if throttling is applied to Impala queries.

For a workload with many small queries, you typically specify a high value for this setting, or leave the default setting of "unlimited". For a workload with expensive queries, where some number of concurrent queries saturate the memory, I/O, CPU, or network capacity of the cluster, set the value low enough that the cluster resources are not overcommitted for Impala.

Once you have enabled memory-based admission control using other pool settings, you can still use Max Running Queries as a safeguard. If queries exceed either the total estimated memory or the maximum number of concurrent queries, they are added to the queue.

Max Queued Queries

Maximum number of queries that can be queued in this pool. The default value is 200 for CDH 5.3 or higher and 50 for previous versions of Impala. (optional)

Queue Timeout

The amount of time, in milliseconds, that a query waits in the admission control queue for this pool before being canceled. The default value is 60,000 milliseconds.

It the following cases, Queue Timeout is not significant, and you can specify a high value to avoid canceling queries unexpectedly:

• In a low-concurrency workload where few or no queries are queued
• In an environment without a strict SLA, where it does not matter if queries occasionally take longer than usual because they are held in admission control

You might also need to increase the value to use Impala with some business intelligence tools that have their own timeout intervals for queries.

In a high-concurrency workload, especially for queries with a tight SLA, long wait times in admission control can cause a serious problem. For example, if a query needs to run in 10 seconds, and you have tuned it so that it runs in 8 seconds, it violates its SLA if it waits in the admission control queue longer than 2 seconds. In a case like this, set a low timeout value and monitor how many queries are cancelled because of timeouts. This technique helps you to discover capacity, tuning, and scaling problems early, and helps avoid wasting resources by running expensive queries that have already missed their SLA.

If you identify some queries that can have a high timeout value, and others that benefit from a low timeout value, you can create separate pools with different values for this setting.

Clamp MEM_LIMIT Query Option

If this field is not selected, the MEM_LIMIT query option will not be bounded by the Maximum Query Memory Limit and the Minimum Query Memory Limit values specified for this resource pool. By default, this field is selected in CDH 6.1 and higher. The field is disabled if both Minimum Query Memory Limit and Maximum Query Memory Limit are not set.

Cloning a Resource Pool

Deleting a Resource Pool

Editing Dynamic Resource Pools

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has a YARN service, the YARN > Resource Pools tab displays. If the cluster has an Impala service enabled as described in Enabling or Disabling Impala Admission Control in Cloudera Manager, the Impala Admission Control > Resource Pools tab displays.
2. Click the YARN or Impala Admission Control tab.
3. Click Edit at the right of a resource pool row. Edit the properties.
4. If you have enabled ACLs and specified users or groups, optionally click the Submission and Administration Access Control tabs to specify which users and groups can submit applications and which users can view all and kill applications. By default, anyone can submit, view all, and kill applications. To restrict these permissions, select Allow these users and groups and provide a comma-delimited list of users and groups in the Users and Groups fields respectively.
5. Click Save.
6. Click Refresh Dynamic Resource Pools.

Viewing Dynamic Resource Pool Status

Configuring Default YARN Fair Scheduler Properties

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. The YARN > Resource Pools tab displays.
2. Click the YARN tab.
3. Click the Default Settings button.
4. Specify the default scheduling policy, maximum applications, and preemption timeout properties.
5. Click Save.
6. Click Refresh Dynamic Resource Pools.

Creating a Resource Subpool

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. The YARN > Resource Pools tab displays.
2. Click at the right of a resource pool row and select Create Subpool. Configure subpool properties.
3. Click Create.
4. Click Refresh Dynamic Resource Pools.

Setting YARN User Limits

Pool properties determine the maximum number of applications that can run in a pool. To limit the number of applications specific users can run at the same time:

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. The YARN > Resource Pools tab displays.
2. Click the User Limits tab. The table displays a list of users and the maximum number of jobs each user can submit.
3. Click Add User Limit.
4. Specify a username. containing only alphanumeric characters. If referencing a user or group name that contains a ".", replace the "." with "_dot_".
5. Specify the maximum number of running applications.
6. Click Create.
7. Click Refresh Dynamic Resource Pools.

Configuring ACLs

To configure which users and groups can submit and kill applications in any resource pool:

1. Enable ACLs.
2. In Cloudera Manager select the YARN service.
3. Click the Configuration tab.
4. Search for Admin ACL property, and specify which users and groups can submit and kill applications.
5. Enter a Reason for change, and then click Save Changes to commit the changes.
6. Return to the Home page by clicking the Cloudera Manager logo.
7. Click the icon that is next to any stale services to invoke the cluster restart wizard.
8. Click Restart Stale Services.
9. Click Restart Now.
10. Click Finish.

Enabling ACLs

To specify whether ACLs are checked:

1. In Cloudera Manager select the YARN service.
2. Click the Configuration tab.
3. Search for the Enable ResourceManager ACL property, and select the YARN service.
4. Enter a Reason for change, and then click Save Changes to commit the changes.
5. Return to the Home page by clicking the Cloudera Manager logo.
6. Click the icon that is next to any stale services to invoke the cluster restart wizard.
7. Click Restart Stale Services.
8. Click Restart Now.
9. Click Finish.

Specifying Resource Limit Properties

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has a YARN service, the YARN > Resource Pools tab displays. If the cluster has an Impala service enabled as described in Enabling or Disabling Impala Admission Control in Cloudera Manager, the Impala Admission Control > Resource Pools tab displays.
2. Click the Resource Pools tab.
3. For each resource pool, click Edit.
   1. Select a configuration set name.
   2. Edit the configuration set properties and click Save.
4. Click Refresh Dynamic Resource Pools.

Viewing the Properties of a Configuration Set

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has a YARN service, the YARN > Resource Pools tab displays. If the cluster has an Impala service enabled as described in Enabling or Disabling Impala Admission Control in Cloudera Manager, the Impala Admission Control > Resource Pools tab displays.
2. In the Configuration Sets drop-down list, select a configuration set. The properties of each pool for that configuration set display.

Adding a Scheduling Rule

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has a YARN service, the YARN > Resource Pools tab displays. If the cluster has an Impala service enabled as described in Enabling or Disabling Impala Admission Control in Cloudera Manager, the Impala Admission Control > Resource Pools tab displays.
2. Click the Scheduling Rules tab.
3. Click Create Scheduling Rule.
4. In the Configuration Set field, choose the configuration set to which the rule applies. Select Create New or Use Existing.
5. If you create a new configuration set, type a name in the Name field.

   If you use an existing configuration set, select one from the drop-down list.

6. Configure the rule to repeat or not:
   • To repeat the rule, keep the Repeat field selected and specify the repeat frequency. If the frequency is weekly, specify the repeat day or days.
   • If the rule does not repeat, clear the Repeat field, click the left side of the on field to display a drop-down calendar where you set the starting date and time. When you specify the date and time, a default time window of two hours is set in the right side of the on field. Click the right side to adjust the date and time.
7. Click Create.
8. Click Refresh Dynamic Resource Pools.

Reordering Scheduling Rules

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has a YARN service, the YARN > Resource Pools tab displays. If the cluster has an Impala service enabled as described in Enabling or Disabling Impala Admission Control in Cloudera Manager, the Impala Admission Control > Resource Pools tab displays.
2. Click the Scheduling Rules tab.
3. Click Reorder Scheduling Rules.
4. Click Move Up or Move Down in a rule row.
5. Click Save.
6. Click Refresh Dynamic Resource Pools.

Editing a Scheduling Rule

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has a YARN service, the YARN > Resource Pools tab displays. If the cluster has an Impala service enabled as described in Enabling or Disabling Impala Admission Control in Cloudera Manager, the Impala Admission Control > Resource Pools tab displays.
2. Click Scheduling Rules.
3. Click Edit at the right of a rule.
4. Edit the rule.
5. Click Save.
6. Click Refresh Dynamic Resource Pools.

Deleting a Scheduling Rule

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has a YARN service, the YARN > Resource Pools tab displays. If the cluster has an Impala service enabled as described in Enabling or Disabling Impala Admission Control in Cloudera Manager, the Impala Admission Control > Resource Pools tab displays.
2. Click Scheduling Rules.
3. Click at the right of a rule and select Delete.
4. Click OK.
5. Click Refresh Dynamic Resource Pools.

Placement Rule Ordering and Evaluation

Pool placement rules are evaluated in the order in which they appear in the placement rule list. When a job is submitted, the rules are evaluated, and the first matching rule is used to determine the pool in which the job is run.

If a rule is always satisfied, subsequent rules are not evaluated. Rules that are never evaluated appear in struck-though gray text. For an example see Example Placement Rules.

By default, pool placement rules are ordered in reverse order of when they were added; the last rule added appears first. You can easily reorder rules.

Creating Pool Placement Rules

Placement rules determine the pools to which applications and queries are assigned. At installation, Cloudera Manager provides a set of default rules and rule ordering.

Default Placement Rules and Order

Reordering Pool Placement Rules

To change the order in which pool placement rules are evaluated:

1. Select Clusters > Cluster name > Dynamic Resource Pool Configuration. If the cluster has a YARN service, the YARN > Resource Pools tab displays. If the cluster has an Impala service enabled as described in Enabling or Disabling Impala Admission Control in Cloudera Manager, the Impala Admission Control > Resource Pools tab displays.
2. Click the YARN or Impala Admission Control tab.
3. Click the Placement Rules tab.
4. Click Reorder Placement Rules.
5. Click Move Up or Move Down in a rule row.
6. Click Save.
7. Click Refresh Dynamic Resource Pools.