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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="mem_limits"> |
| |
| <title>Controlling Impala Resource Usage</title> |
| <titlealts audience="PDF"><navtitle>Controlling Resource Usage</navtitle></titlealts> |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Performance"/> |
| <data name="Category" value="Memory"/> |
| <data name="Category" value="Scalability"/> |
| <data name="Category" value="Resource Management"/> |
| <data name="Category" value="Administrators"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| Sometimes, balancing raw query performance against scalability requires limiting the amount of resources, |
| such as memory or CPU, used by a single query or group of queries. Impala can use several mechanisms that |
| help to smooth out the load during heavy concurrent usage, resulting in faster overall query times and |
| sharing of resources across Impala queries, MapReduce jobs, and other kinds of workloads across a <keyword keyref="distro"/> |
| cluster: |
| </p> |
| |
| <ul> |
| <li> |
| The Impala admission control feature uses a fast, distributed mechanism to hold back queries that exceed |
| limits on the number of concurrent queries or the amount of memory used. The queries are queued, and |
| executed as other queries finish and resources become available. You can control the concurrency limits, |
| and specify different limits for different groups of users to divide cluster resources according to the |
| priorities of different classes of users. This feature is new in Impala 1.3. |
| See <xref href="impala_admission.xml#admission_control"/> for details. |
| </li> |
| |
| <li> |
| <p> |
| You can restrict the amount of memory Impala reserves during query execution by specifying the |
| <codeph>-mem_limit</codeph> option for the <codeph>impalad</codeph> daemon. See |
| <xref href="impala_config_options.xml#config_options"/> for details. This limit applies only to the |
| memory that is directly consumed by queries; Impala reserves additional memory at startup, for example to |
| hold cached metadata. |
| </p> |
| </li> |
| |
| <li> |
| <p> |
| For production deployments, implement resource isolation using your cluster management |
| tool. |
| </p> |
| </li> |
| </ul> |
| </conbody> |
| </concept> |