[impala] 02/03: IMPALA-9586: update query option docs for mt_dop

[ta...@apache.org]

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commit 8551805875fcd2c701d988df887c1173520fca12
Author: Tim Armstrong <ta...@cloudera.com>
AuthorDate: Mon Feb 8 20:44:16 2021 -0800

    IMPALA-9586: update query option docs for mt_dop
    
    There are interactions between mt_dop and num_nodes and
    num_scanner_threads. Mention these in the docs.
    
    Change-Id: I3d9a6f56ffaf211d7d3ca1fad506ee83d516ccbd
    Reviewed-on: http://gerrit.cloudera.org:8080/17043
    Tested-by: Impala Public Jenkins <im...@cloudera.com>
    Reviewed-by: Joe McDonnell <jo...@cloudera.com>
---
 docs/topics/impala_num_nodes.xml           | 5 +++++
 docs/topics/impala_num_scanner_threads.xml | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/docs/topics/impala_num_nodes.xml b/docs/topics/impala_num_nodes.xml
index f885124..0bbf782 100644
--- a/docs/topics/impala_num_nodes.xml
+++ b/docs/topics/impala_num_nodes.xml
@@ -55,6 +55,11 @@ under the License.
      <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
 
      <p>
+     Setting <codeph>NUM_NODES</codeph> to 1 disables multithreading, i.e. if
+     <codeph>MT_DOP</codeph> is greater than 1, it is effectively reduced to 1.
+     </p>
+
+     <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.
diff --git a/docs/topics/impala_num_scanner_threads.xml b/docs/topics/impala_num_scanner_threads.xml
index b7a47ae..dd111da 100644
--- a/docs/topics/impala_num_scanner_threads.xml
+++ b/docs/topics/impala_num_scanner_threads.xml
@@ -42,6 +42,10 @@ under the License.
     </p>
 
     <p>
+      Has no effect if multi-threaded query execution is enabled, i.e.
+      <codeph>MT_DOP</codeph> is greater than 0.
+    </p>
+    <p>
       <b>Type:</b> numeric
     </p>