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From "Alex Behm (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] [DOCS] Tighten up advice about first COMPUTE INCREMENTAL STATS
Date Fri, 06 Oct 2017 17:34:31 GMT
Alex Behm has posted comments on this change. ( http://gerrit.cloudera.org:8080/7999 )

Change subject: [DOCS] Tighten up advice about first COMPUTE INCREMENTAL STATS
......................................................................


Patch Set 2:

(4 comments)

http://gerrit.cloudera.org:8080/#/c/7999/2/docs/shared/impala_common.xml
File docs/shared/impala_common.xml:

http://gerrit.cloudera.org:8080/#/c/7999/2/docs/shared/impala_common.xml@1228
PS2, Line 1228: DROP STATS</codeph> and
              :         <codeph>DROP INCREMENTAL STATS</codeph>)
> are these drops required?
They are not required if you *exactly* what you are doing, but that does not apply to most
people. Dropping first is always safe and definitely the recommended practice.

If you do not drop and switch back-and-forth between compute stats and compute incremental
sats, then you may end up with "unexpected" table metadata.


http://gerrit.cloudera.org:8080/#/c/7999/2/docs/shared/impala_common.xml@1243
PS2, Line 1243:         be cached on every <cmdname>impalad</cmdname> host. If
this metadata for a table exceeds
> more specifically, impalads that are also coordinators?
Yes


http://gerrit.cloudera.org:8080/#/c/7999/2/docs/shared/impala_common.xml@1243
PS2, Line 1243: metadata for a table exceeds
              :         2 GB
> is there a diagnostic page that we can point to here that explains how to f
This is a longer story. I asked Bharath to help here.


http://gerrit.cloudera.org:8080/#/c/7999/2/docs/shared/impala_common.xml@1247
PS2, Line 1247: does not affect
> does that mean lack of stats has not affect on optimization or something el
Please see my explanation on what "incremental" stats is in previous patch sets. Dropping
*incremental* stats has no effect on the row counts and NDVs used in query optimization.



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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: Ia53a6518ce5541e5c9a2cd896856ce042a599b03
Gerrit-Change-Number: 7999
Gerrit-PatchSet: 2
Gerrit-Owner: John Russell <jrussell@cloudera.com>
Gerrit-Reviewer: Alex Behm <alex.behm@cloudera.com>
Gerrit-Reviewer: Greg Rahn <grahn@cloudera.com>
Gerrit-Reviewer: John Russell <jrussell@cloudera.com>
Gerrit-Reviewer: Mostafa Mokhtar <mmokhtar@cloudera.com>
Gerrit-Reviewer: Silvius Rus <srus@cloudera.com>
Gerrit-Reviewer: Vuk Ercegovac <vercegovac@cloudera.com>
Gerrit-Comment-Date: Fri, 06 Oct 2017 17:34:31 +0000
Gerrit-HasComments: Yes

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