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| <h1 class="title topictitle1" id="ariaid-title1">Controlling Impala Resource Usage</h1> |
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| 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 <span class="keyword"></span> |
| cluster: |
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| 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 <a class="xref" href="impala_admission.html#admission_control">Admission Control and Query Queuing</a> for details. |
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| You can restrict the amount of memory Impala reserves during query execution by specifying the |
| <code class="ph codeph">-mem_limit</code> option for the <code class="ph codeph">impalad</code> daemon. See |
| <a class="xref" href="impala_config_options.html#config_options">Modifying Impala Startup Options</a> 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. |
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| For production deployments, implement resource isolation using your cluster management |
| tool. |
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| <div class="related-links"> |
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| <div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_performance.html">Tuning Impala for Performance</a></div> |
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