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https://issues.apache.org/jira/browse/TRAFODION-321?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14708685#comment-14708685
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Atanu Mishra commented on TRAFODION-321:
----------------------------------------
taoufik ben abdellatif (taoufik-abdellatif) wrote on 2014-06-13: #1
Changes were made to method HistogramCache::createColStatsList in
optimizer/NATable.cpp to look for columns that have unique indices specified on
them and flag them as unique. The FetchHistograms logic in hs_read.cpp uses
this flag to set the uec of the column to be the same as the table rowcount.
Changed in trafodion:
status: In Progress → Fix Committed
Julie Thai (julie-y-thai) wrote on 2014-08-12: #2
Verified on workstation, daily build 20140807_0830.
Verified cardinality of hybrid_hash_join reflects left child of the join.
>>control query shape hybrid_hash_join(scan(TABLE 'T', path
>>'TRAFODION."_MD_".TABLE_CONSTRAINTS', forward
, blocks_per_access 1 , mdam off),
scan(TABLE 'O', path 'TRAFODION."_MD_".OBJECTS_UNIQ_IDX', forward
, blocks_per_access 1 , mdam off));
+>+>+>
--- SQL operation complete.
>>prepare st1 from select T.CONSTRAINT_TYPE, o.OBJECT_NAME from
>>trafodion."_MD_".table_constraints T, trafodion."_MD_".objects O where
>>T.table_uid = o.object_uid;
--- SQL command prepared.
>>explain options 'f' st1;
LC RC OP OPERATOR OPT DESCRIPTION CARD
---- ---- ---- -------------------- -------- -------------------- ---------
3 . 4 root 1.00E+002
2 1 3 hybrid_hash_join u 1.00E+002
. . 2 trafodion_scan TABLE_CONSTRAINTS 1.00E+002
. . 1 trafodion_index_scan OBJECTS 1.00E+002
--- SQL operation complete.
Changed in trafodion:
status: Fix Committed → Fix Released
> LP Bug: 1324303 - bad cardinality estimates for metadata queries
> ----------------------------------------------------------------
>
> Key: TRAFODION-321
> URL: https://issues.apache.org/jira/browse/TRAFODION-321
> Project: Apache Trafodion
> Issue Type: Bug
> Components: sql-cmp
> Reporter: Apache Trafodion
> Assignee: Apache Trafodion
> Priority: Critical
>
> cardinality estimation for metadata queries is not correct. Specifically for
> the case of an index join and the join is on the index column. The
> cardinality of the join should reflect that of the left child of the join.
> Example of a metadata table that has the issue:
> prepare st1 from select T.CONSTRAINT_TYPE, o.OBJECT_NAME from
> trafodion."_MD_".table_constraints T, trafodion."_MD_".objects O where
> T.table_uid = o.object_uid;
> >>explain options 'f' st1;
> LC RC OP OPERATOR OPT DESCRIPTION CARD
> ---- ---- ---- -------------------- -------- -------------------- ---------
> 3 . 4 root 5.00E+003
> 2 1 3 hybrid_hash_join 5.00E+003
> . . 2 trafodion_index_scan OBJECTS 1.00E+002
> . . 1 trafodion_scan TABLE_CONSTRAINTS 1.00E+002
> --- SQL operation complete.
> >>
> Assigned to LaunchPad User taoufik ben abdellatif
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