[TRAFODION-321] LP Bug: 1324303 - bad cardinality estimates for metadata queries

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Fix Version/s: 0.8 (pre-incubation)
• Component/s: sql-cmp
• External issue URL: https://bugs.launchpad.net/bugs/1324303
• Assignee: Unassigned
• Reporter: Apache Trafodion
• Created: 22/Jul/15 18:15
• Updated: 24/Aug/15 02:21
• Resolved: 24/Aug/15 02:21

Description

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