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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="kudu_read_mode" rev="3.1.0 IMPALA-6812"> |
| |
| <title>KUDU_READ_MODE Query Option (<keyword keyref="impala31"/> or higher only)</title> |
| |
| <titlealts audience="PDF"> |
| |
| <navtitle>KUDU_READ_MODE</navtitle> |
| |
| </titlealts> |
| |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Impala Query Options"/> |
| <data name="Category" value="Performance"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p rev="3.1.0 IMPALA-6812"> |
| The <codeph>KUDU_READ_MODE</codeph> query option allows you to set a desired consistency |
| level for scans of Kudu tables. |
| </p> |
| |
| <p> |
| <b>Type:</b> String |
| </p> |
| |
| <p> |
| <b>Default:</b> <codeph>"DEFAULT"</codeph> |
| </p> |
| |
| <p> |
| <b>Added in:</b> <keyword keyref="impala31"/> |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| |
| <p> |
| The following values are supported for the query option: |
| <ul> |
| <li> |
| <codeph>"DEFAULT"</codeph>: The value of the startup flag, |
| <codeph>‑‑kudu_read_mode</codeph>, is used. </li> |
| |
| <li> |
| <codeph>"READ_LATEST"</codeph>: Commonly known as the Read Committed isolation mode, |
| in this mode, Kudu provides no consistency guarantees for this mode, except that all |
| returned rows were committed at some point. |
| </li> |
| |
| <li> |
| <codeph>"READ_AT_SNAPSHOT"</codeph>: Kudu will take a snapshot of the current state of |
| the data and perform the scan over the snapshot, possibly after briefly waiting for |
| ongoing writes to complete. This provides "Read Your Writes" consistency within a |
| single Impala session, except in the case of a Kudu leader change. See the Kudu |
| documentation for more details. |
| </li> |
| </ul> |
| </p> |
| |
| </conbody> |
| |
| </concept> |