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https://issues.apache.org/jira/browse/HIVE-26389?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stamatis Zampetakis reassigned HIVE-26389:
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> ALTER TABLE CASCADE is slow for tables with many partitions
> -----------------------------------------------------------
>
> Key: HIVE-26389
> URL: https://issues.apache.org/jira/browse/HIVE-26389
> Project: Hive
> Issue Type: Improvement
> Components: Metastore, Query Planning
> Affects Versions: 4.0.0-alpha-2
> Reporter: Stamatis Zampetakis
> Assignee: Stamatis Zampetakis
> Priority: Major
> Attachments: native_sql_queries.txt, per_partition_sql_queries.txt
>
>
> Consider the following simplified scenario with a table having two partitions.
> {code:sql}
> CREATE TABLE student (fname string, lname string) PARTITIONED BY (department
> string);
> INSERT INTO student VALUES ('Alex','Dumas', 'Computer Science');
> INSERT INTO student VALUES ('Victor','Hugo', 'Physics');
> {code}
> Altering a column of this table and propagating the changes to the partitions
> (using the CASCADE) syntax is slow.
> {code:sql}
> ALTER TABLE student CHANGE lname lastname STRING CASCADE;
> {code}
> The seemingly simple ALTER statement outlined above triggers roughly 136 SQL
> queries in the underlying DBMS of the metastore (see native_sql_queries.txt).
> We can observe that some of these queries are recurring and appear as many
> times as there are partitions in the table (see
> per_partition_sql_queries.txt).
> As the number of partitions grows so does the number of queries so if we
> manage to reduce the number of queries send per partition or make them more
> efficient this will have a positive impact on performance.
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