David Wayne Birdsall created TRAFODION-2037:
-----------------------------------------------
Summary: Improve DDL concurrency
Key: TRAFODION-2037
URL: https://issues.apache.org/jira/browse/TRAFODION-2037
Project: Apache Trafodion
Issue Type: Improvement
Components: sql-cmu
Affects Versions: 2.1-incubating
Environment: All
Reporter: David Wayne Birdsall
Assignee: David Wayne Birdsall
In CmpSeabaseDDL::getSeabaseUserTableDesc
(core/sql/sqlcomp/CmpSeabaseDDLtable.cpp), the code executes the following
query:
select trim(O.catalog_name || '.' || '\"' || O.schema_name || '\"' || '.' ||
'\"' || O.object_name || '\"' ) constr_name, trim(O2.catalog_name || '.' ||
'\"' || O2.schema_name || '\"' || '.' || '\"' || O2.object_name || '\"' )
table_name from %s.\"%s\".%s U, %s.\"%s\".%s O, %s.\"%s\".%s O2, %s.\"%s\".%s T
where O.object_uid = U.foreign_constraint_uid and O2.object_uid = T.table_uid
and T.constraint_uid = U.foreign_constraint_uid and U.unique_constraint_uid =
%Ld order by 2, 1
The plan for this query does a full scan of TABLE_CONSTRAINTS, and joins that
to OBJECTS_UNIQ_IDX. So all rows of TABLE_CONSTRAINTS are read, and many if not
most rows of OBJECTS_UNIQ_IDX.
Analyzing the query plan, the full scan is inherent. The only known information
we have for TABLE_CONSTRAINTS is CONSTRAINT_UID, which is the second column of
the key. The first column has high UEC so MDAM is not a possibility.
Creating this large read set conflicts with many write transactions to
metadata, decreasing DDL concurrency.
As an experiment, I added an index to the metadata on
TABLE_CONSTRAINTS(CONSTRAINT_UID). I found I had to add a CQS as well to force
it to avoid a full scan. With this change, I found that DDL concurrency was
much improved. So, the proposal in this JIRA is to add this index and CQS.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
