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commit 99e2d5056c977ed6d9c4b2f65febd183b3b0e64c Author: Alex Rodoni <arod...@cloudera.com> AuthorDate: Thu Feb 14 18:04:53 2019 -0800 IMPALA-8203: [DOCS] Clarified a few points in DISABLE_CODEGEN Change-Id: Ic10fd66d8a83d10c0900e93a00241d532902a759 Reviewed-on: http://gerrit.cloudera.org:8080/12496 Tested-by: Impala Public Jenkins <impala-public-jenk...@cloudera.com> Reviewed-by: Alex Rodoni <arod...@cloudera.com> --- docs/topics/impala_disable_codegen.xml | 50 ++++++++++++++++++++++++++-------- 1 file changed, 38 insertions(+), 12 deletions(-) diff --git a/docs/topics/impala_disable_codegen.xml b/docs/topics/impala_disable_codegen.xml index 82add52..7410b6c 100644 --- a/docs/topics/impala_disable_codegen.xml +++ b/docs/topics/impala_disable_codegen.xml @@ -21,7 +21,13 @@ under the License. <concept id="disable_codegen"> <title>DISABLE_CODEGEN Query Option</title> - <titlealts audience="PDF"><navtitle>DISABLE_CODEGEN</navtitle></titlealts> + + <titlealts audience="PDF"> + + <navtitle>DISABLE_CODEGEN</navtitle> + + </titlealts> + <prolog> <metadata> <data name="Category" value="Impala"/> @@ -34,23 +40,43 @@ under the License. <conbody> <p> - <indexterm audience="hidden">DISABLE_CODEGEN query option</indexterm> - This is a debug option, intended for diagnosing and working around issues that cause crashes. If a query - fails with an <q>illegal instruction</q> or other hardware-specific message, try setting - <codeph>DISABLE_CODEGEN=true</codeph> and running the query again. If the query succeeds only when the - <codeph>DISABLE_CODEGEN</codeph> option is turned on, submit the problem to <keyword keyref="support_org"/> and include that - detail in the problem report. Do not otherwise run with this setting turned on, because it results in lower - overall performance. + The <codeph>DISABLE_CODEGEN</codeph> is a debug option, and it's used to work around any + issues with Impala's runtime code generation. If a query fails with an <q>illegal + instruction</q> or other hardware-specific message, try setting + <codeph>DISABLE_CODEGEN=true</codeph> and running the query again. If the query succeeds + only when the <codeph>DISABLE_CODEGEN</codeph> option is turned on, submit the problem to + <keyword keyref="support_org"> </keyword> and include that detail in the problem report. </p> <p> - Because the code generation phase adds a small amount of overhead for each query, you might turn on the - <codeph>DISABLE_CODEGEN</codeph> option to achieve maximum throughput when running many short-lived queries - against small tables. + Most queries will run significantly slower with <codeph>DISABLE_CODEGEN=true</codeph>. + </p> + + <p> + In Impala 2.10 and higher, the <codeph>DISABLE_CODEGEN_ROWS_THRESHOLD</codeph> + optimisation automatically disables codegen for small queries because short-running + queries may run faster without the overhead of codegen. + </p> + + <p> + The following values are supported: + <ul> + <li> + <codeph>TRUE</codeph> or <codeph>1</codeph>: Disables codegen. + </li> + + <li> + <codeph>FALSE</codeph> or <codeph>0</codeph>: Enables codegen. + </li> + </ul> + </p> + + <p> + <b>Type:</b> Boolean </p> - <p conref="../shared/impala_common.xml#common/type_boolean"/> <p conref="../shared/impala_common.xml#common/default_false_0"/> </conbody> + </concept>