IMPALA-5894: [DOCS] Clarify placement of STRAIGHT_JOIN hint "immediately after the SELECT keyword" was mentioned in a few places for STRAIGHT_JOIN. I reworded all instances to mention that [DISTINCT | ALL] can also come before the hint name.
Change-Id: I3cac1afccc132f389b2017ad217fdf7e7b04513a Reviewed-on: http://gerrit.cloudera.org:8080/8031 Reviewed-by: Alex Behm <[email protected]> Tested-by: Impala Public Jenkins Project: http://git-wip-us.apache.org/repos/asf/incubator-impala/repo Commit: http://git-wip-us.apache.org/repos/asf/incubator-impala/commit/03571788 Tree: http://git-wip-us.apache.org/repos/asf/incubator-impala/tree/03571788 Diff: http://git-wip-us.apache.org/repos/asf/incubator-impala/diff/03571788 Branch: refs/heads/master Commit: 03571788be44d903a81dc092a447c74ccb9bac76 Parents: 39f23bb Author: John Russell <[email protected]> Authored: Mon Sep 11 12:05:41 2017 -0700 Committer: Impala Public Jenkins <[email protected]> Committed: Tue Sep 12 07:02:09 2017 +0000 ---------------------------------------------------------------------- docs/shared/impala_common.xml | 2 +- docs/topics/impala_hints.xml | 3 ++- docs/topics/impala_perf_joins.xml | 12 +++++++++--- 3 files changed, 12 insertions(+), 5 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/incubator-impala/blob/03571788/docs/shared/impala_common.xml ---------------------------------------------------------------------- diff --git a/docs/shared/impala_common.xml b/docs/shared/impala_common.xml index 9d6f72b..f31bdf0 100644 --- a/docs/shared/impala_common.xml +++ b/docs/shared/impala_common.xml @@ -2722,7 +2722,7 @@ flight_num: INT32 SNAPPY DO:83456393 FPO:83488603 SZ:10216514/11474301 are supported in all Impala versions. The <codeph>CROSS JOIN</codeph> operator is available in Impala 1.2.2 and higher. During performance tuning, you can override the reordering of join clauses that Impala does internally by including the keyword <codeph>STRAIGHT_JOIN</codeph> immediately after the - <codeph>SELECT</codeph> keyword + <codeph>SELECT</codeph> and any <codeph>DISTINCT</codeph> or <codeph>ALL</codeph> keywords. </p> <p id="catalog_server_124"> http://git-wip-us.apache.org/repos/asf/incubator-impala/blob/03571788/docs/topics/impala_hints.xml ---------------------------------------------------------------------- diff --git a/docs/topics/impala_hints.xml b/docs/topics/impala_hints.xml index 18b0dc6..843d9be 100644 --- a/docs/topics/impala_hints.xml +++ b/docs/topics/impala_hints.xml @@ -131,7 +131,8 @@ INSERT <varname>insert_clauses</varname> <p> With both forms of hint syntax, include the <codeph>STRAIGHT_JOIN</codeph> - keyword immediately after the <codeph>SELECT</codeph> keyword to prevent Impala from + keyword immediately after the <codeph>SELECT</codeph> and any + <codeph>DISTINCT</codeph> or <codeph>ALL</codeph> keywords to prevent Impala from reordering the tables in a way that makes the join-related hints ineffective. </p> http://git-wip-us.apache.org/repos/asf/incubator-impala/blob/03571788/docs/topics/impala_perf_joins.xml ---------------------------------------------------------------------- diff --git a/docs/topics/impala_perf_joins.xml b/docs/topics/impala_perf_joins.xml index 116ba75..9cae4ef 100644 --- a/docs/topics/impala_perf_joins.xml +++ b/docs/topics/impala_perf_joins.xml @@ -57,8 +57,9 @@ under the License. <p> If statistics are not available for all the tables in the join query, or if Impala chooses a join order that is not the most efficient, you can override the automatic join order optimization by specifying the - <codeph>STRAIGHT_JOIN</codeph> keyword immediately after the <codeph>SELECT</codeph> keyword. In this case, - Impala uses the order the tables appear in the query to guide how the joins are processed. + <codeph>STRAIGHT_JOIN</codeph> keyword immediately after the <codeph>SELECT</codeph> and any <codeph>DISTINCT</codeph> + or <codeph>ALL</codeph> keywords. In this case, Impala uses the order the tables appear in the query to guide how the + joins are processed. </p> <p> @@ -149,7 +150,8 @@ under the License. <p> If an Impala join query is inefficient because of outdated statistics or unexpected data distribution, you can keep Impala from reordering the joined tables by using the <codeph>STRAIGHT_JOIN</codeph> keyword - immediately after the <codeph>SELECT</codeph> keyword. The <codeph>STRAIGHT_JOIN</codeph> keyword turns off + immediately after the <codeph>SELECT</codeph> and any <codeph>DISTINCT</codeph> or <codeph>ALL</codeph> + keywords. The <codeph>STRAIGHT_JOIN</codeph> keyword turns off the reordering of join clauses that Impala does internally, and produces a plan that relies on the join clauses being ordered optimally in the query text. In this case, rewrite the query so that the largest table is on the left, followed by the next largest, and so on until the smallest table is on the right. @@ -163,6 +165,10 @@ under the License. </p> <codeblock>select straight_join x from medium join small join (select * from big where c1 < 10) as big + where medium.id = small.id and small.id = big.id; + +-- If the query contains [DISTINCT | ALL], the hint goes after those keywords. +select distinct straight_join x from medium join small join (select * from big where c1 < 10) as big where medium.id = small.id and small.id = big.id;</codeblock> </conbody> </concept>
