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| <meta name="DC.Title" content="THREAD_RESERVATION_AGGREGATE_LIMIT Query Option (Impala 3.1 or higher only)" /> |
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| <title>THREAD_RESERVATION_AGGREGATE_LIMIT Query Option (Impala 3.1 or higher only)</title> |
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| <h1 class="title topictitle1" id="ariaid-title1">THREAD_RESERVATION_AGGREGATE_LIMIT Query Option (<span class="keyword">Impala 3.1</span> or higher only)</h1> |
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| <p class="p"> |
| The <code class="ph codeph">THREAD_RESERVATION_AGGREGATE_LIMIT</code> query option limits the number of |
| reserved threads for a query across all nodes on which it is executing. The option is |
| intended to prevent execution of complex queries that can consume excessive CPU or |
| operating system resources on a cluster. Queries that have more threads than this |
| threshold are rejected by Impala’s admission controller before they start executing. |
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| For example, an Impala administrator could set a default value of |
| <code class="ph codeph">THREAD_RESERVATION_AGGREGATE_LIMIT=2000</code> for a resource pool on a 100 node |
| where they expect only relatively simple queries with less than 20 threads per node to |
| run. This will reject queries that require more than 2000 reserved threads across all |
| nodes, for example a query with 21 fragments running on all 100 nodes of the cluster. |
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| You can override the default value per-query or per-session, in the same way as other |
| query options, if you do not want the default |
| <code class="ph codeph">THREAD_RESERVATION_AGGREGATE_LIMIT</code> value to apply to a specific query or |
| session. |
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| <p class="p"> |
| <strong class="ph b">Syntax:</strong> <code class="ph codeph">SET THREAD_RESERVATION_AGGREGATE_LIMIT=number;</code> |
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| <strong class="ph b">Type:</strong> numeric |
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| <strong class="ph b">Default:</strong> 0 (no limit) |
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| <strong class="ph b">Added in:</strong> <span class="keyword">Impala 3.1</span> |
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| <div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_query_options.html">Query Options for the SET Statement</a></div> |
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