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https://issues.apache.org/jira/browse/TRAFODION-2037?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Wayne Birdsall resolved TRAFODION-2037.
---------------------------------------------
Resolution: Fixed
Fix Version/s: 2.1-incubating
> 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
> Fix For: 2.1-incubating
>
>
> 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.
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