| <?xml version="1.0" encoding="UTF-8"?> |
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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="num_nodes"> |
| |
| <title>NUM_NODES Query Option</title> |
| <titlealts audience="PDF"><navtitle>NUM_NODES</navtitle></titlealts> |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Impala Query Options"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| <data name="Category" value="Troubleshooting"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| <indexterm audience="hidden">NUM_NODES query option</indexterm> |
| Limit the number of nodes that process a query, typically during debugging. |
| </p> |
| |
| <p> |
| <b>Type:</b> numeric |
| </p> |
| |
| <p> |
| <b>Allowed values:</b> Only accepts the values 0 |
| (meaning all nodes) or 1 (meaning all work is done on the coordinator node). |
| </p> |
| |
| <p> |
| <b>Default:</b> 0 |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| |
| <p> |
| If you are diagnosing a problem that you suspect is due to a timing issue due to |
| distributed query processing, you can set <codeph>NUM_NODES=1</codeph> to verify |
| if the problem still occurs when all the work is done on a single node. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/num_nodes_tip"/> |
| |
| <note type="warning" rev="DOCS-1161"> |
| <p> |
| Because this option results in increased resource utilization on a single host, |
| it could cause problems due to contention with other Impala statements or |
| high resource usage. Symptoms could include queries running slowly, exceeding the memory limit, |
| or appearing to hang. Use it only in a single-user development/test environment; |
| <b>do not</b> use it in a production environment or in a cluster with a high-concurrency |
| or high-volume or performance-critical workload. |
| </p> |
| </note> |
| |
| |
| </conbody> |
| </concept> |