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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="thread_reservation_aggregate_limit"> |
| |
| <title>THREAD_RESERVATION_AGGREGATE_LIMIT Query Option (<keyword |
| keyref="impala31"/> or higher only)</title> |
| |
| <titlealts audience="PDF"> |
| |
| <navtitle>THREAD RESERVATION AGGREGATE LIMIT</navtitle> |
| |
| </titlealts> |
| |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Impala Query Options"/> |
| <data name="Category" value="Scalability"/> |
| <data name="Category" value="Memory"/> |
| <data name="Category" value="Troubleshooting"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| The <codeph>THREAD_RESERVATION_AGGREGATE_LIMIT</codeph> 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. |
| </p> |
| |
| <p> |
| For example, an Impala administrator could set a default value of |
| <codeph>THREAD_RESERVATION_AGGREGATE_LIMIT=2000</codeph> 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. |
| </p> |
| |
| <p> |
| 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 |
| <codeph>THREAD_RESERVATION_AGGREGATE_LIMIT</codeph> value to apply to a specific query or |
| session. |
| </p> |
| |
| <p> |
| <b>Syntax:</b> <codeph>SET THREAD_RESERVATION_AGGREGATE_LIMIT=number;</codeph> |
| </p> |
| |
| <p> |
| <b>Type:</b> numeric |
| </p> |
| |
| <p> |
| <b>Default:</b> 0 (no limit) |
| </p> |
| |
| <p> |
| <b>Added in:</b> <keyword keyref="impala31"/> |
| </p> |
| |
| </conbody> |
| |
| </concept> |