Rohit Jain created TRAFODION-1467:
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Summary: Update statistics does not generate multi-column key
stats on a salted table
Key: TRAFODION-1467
URL: https://issues.apache.org/jira/browse/TRAFODION-1467
Project: Apache Trafodion
Issue Type: Bug
Components: sql-cmu
Affects Versions: 1.1 (pre-incubation)
Reporter: Rohit Jain
Priority: Minor
The EVERY KEY or EVERY COLUMN option in update statistics generates
multi-column statistics for all the key columns. It does not do this if the
table is salted, potentially leading to poor plans.
Example of when it works:
create table t1 (a int NOT NULL NOT DROPPABLE, b int NOT NULL NOT DROPPABLE, c
int NOT NULL NOT DROPPABLE, primary key (a, b, c));
update statistics for table t1 on every key;
showstats for table t1 on existing columns;
Histogram data for Table TRAFODION.BCI.T1
Table ID: 7427073929238755441
Hist ID # Ints Rowcount UEC Colname(s)
========== ====== =========== =========== ===========================
868236218 1 0 0 C
868236223 1 0 0 B
868236228 1 0 0 A
868236233 1 0 0 A, B
868236238 1 0 0 A, B, C
Example of when it doesn't (salted table):
create table t1 (a int NOT NULL NOT DROPPABLE, b int NOT NULL NOT DROPPABLE,
c int NOT NULL NOT DROPPABLE, primary key (a, b, c)) salt using 4 partitions
on (a, b);
update statistics for table t1 on every key;
showstats for table t1 on existing columns;
Histogram data for Table TRAFODION.BCI.T1
Table ID: 7427073929238776270
Hist ID # Ints Rowcount UEC Colname(s)
========== ====== =========== =========== ===========================
998895314 1 0 0 C
998895319 1 0 0 B
998895324 1 0 0 A
998895329 1 0 0 "_SALT_"
998895334 1 0 0 "_SALT_", A, B, C
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