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commit 8551805875fcd2c701d988df887c1173520fca12
Author: Tim Armstrong <tarmstr...@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 <impala-public-jenk...@cloudera.com>
Reviewed-by: Joe McDonnell <joemcdonn...@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>
