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IMPALA-11987: [DOCS] Document the mem_limit_executors query option

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Document the difference between mem_limit and mem_limit_executors
query options.

Change-Id: Ibce8347d564afde0f9b9e83df560454f4b8b5c9d
Reviewed-on: http://gerrit.cloudera.org:8080/19604
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Reviewed-by: Daniel Becker <daniel.becker@cloudera.com>
Reviewed-by: Wenzhe Zhou <wzhou@cloudera.com>
This commit is contained in:
Shajini Thayasingh
2023-03-08 11:20:23 -08:00
committed by Wenzhe Zhou
parent 65ae5febee
commit 19b5d781f4
1 changed files with 20 additions and 1 deletions
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21
docs/topics/impala_mem_limit.xml
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@@ -209,5 +209,24 @@ for buffer reservations. Memory reservation needed given the current plan: 38.00
or the pool config (max-query-mem-limit, min-query-mem-limit) for the query to allow the query memory limit to be
at least 70.00 MB. Note that changing the mem_limit may also change the plan. See the query profile for more
information about the per-node memory requirements.</codeblock>
</conbody>
</conbody>
<concept id="mem_limit_executors">
<title>MEM_LIMIT_EXECUTORS Query Option</title>
<conbody>
<note>This is a developer-only query option. Setting this query option is not recommended
unless specifically advised.</note>
<p>The existing <codeph>MEM_LIMIT</codeph> query option applies to all impala coordinators and
executors. This means that the same amount of memory gets reserved but coordinators
typically just do the job of coordinating the query and thus do not necessarily need all the
estimated memory. Blocking the estimated memory on coordinators blocks the memory to be used
for other queries.</p>
<p>The new <codeph>MEM_LIMIT_EXECUTORS</codeph> query option functions similarly to the
<codeph>MEM_LIMIT</codeph> option but sets the query memory limit only on executors. This
new option addresses the issue related to <codeph>MEM_LIMIT</codeph> and is recommended in
scenarios where the query needs much higher memory on executors compared with
coordinators.</p>
<p>Note that the <codeph>MEM_LIMIT_EXECUTORS</codeph> option does not work with
<codeph>MEM_LIMIT</codeph>. If you set both, only <codeph>MEM_LIMIT</codeph> applies.</p>
</conbody>
</concept>
</concept>