[jira] [Commented] (HIVE-27755) Quote identifiers in SQL emitted by SchemaTool for MySQL

["Stamatis Zampetakis (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-27755?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17770042#comment-17770042 ] 

Stamatis Zampetakis commented on HIVE-27755:
--------------------------------------------

For testing the changes, I enabled the general_log for MySQL (https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_general_log) and run the following tests before and after the changes in PR#4757:

{noformat}
cd standalone-metastore/metastore-server
mvn test -Dtest=TestMysql#upgrade -Dtest.groups=""
mvn test -Dtest=TestSchemaToolForMetastore#testValidateSchemaTables*Mysql* -Dtest.groups="" (requires patch in #4754)
mvn test -Dtest=TestSchemaToolForMetastore#testValidateSequences*Mysql* -Dtest.groups="" (requires patch in #4754)
{noformat}

I monitored the general_log output generated by the aforementioned tests and I compared before and after files for each test verifying that table and column names are quoted as expected.

The before and after files from the general_log are attached in this JIRA.

> Quote identifiers in SQL emitted by SchemaTool for MySQL
> --------------------------------------------------------
>
>                 Key: HIVE-27755
>                 URL: https://issues.apache.org/jira/browse/HIVE-27755
>             Project: Hive
>          Issue Type: Improvement
>          Components: Standalone Metastore
>    Affects Versions: 4.0.0-beta-1
>            Reporter: Stamatis Zampetakis
>            Assignee: Stamatis Zampetakis
>            Priority: Major
>              Labels: pull-request-available
>         Attachments: TestMysql-upgrade-after.txt, TestMysql-upgrade-before.txt, TestSchemaToolForMetastore-validateSequences-after.txt, TestSchemaToolForMetastore-validateSequences-before.txt, TestSchemaToolForMetastore-validateTables-after.txt, TestSchemaToolForMetastore-validateTables-before.txt
>
>
> Various SchemaTool options/tasks (e.g., "validate") generate and run SQL statements on the underlying database. Depending on the database identifiers in the SQL statements may be quoted (see [https://github.com/apache/hive/blob/2dbfbeefc1a73d6a50f1c829658846fc827fc780/standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/tools/schematool/HiveSchemaHelper.java#L173]).
> Currently, all identifiers are quoted when the database is Postgres and this tickets aims to do the same for MySQL/MariaDB.
> The main motivation behind this change is to avoid unexpected surprises and query failures when/if the database decides to turn some of the tables/columns we are using internally to reserved keywords.
> As a concrete example, the Percona fork of MySQL recently turned SEQUENCE_TABLE into a reserved keyword ([https://docs.percona.com/percona-server/8.0/flexibility/sequence_table.html]) and this comes in conflict with our internal metastore table.
> The installation scripts do not fail since in that case SEQUENCE_TABLE is quoted ([https://github.com/apache/hive/blob/2dbfbeefc1a73d6a50f1c829658846fc827fc780/standalone-metastore/metastore-server/src/main/sql/mysql/hive-schema-4.0.0-beta-2.mysql.sql#L447]) but validation queries emitted by the SchemaTool will fail ([https://github.com/apache/hive/blob/2dbfbeefc1a73d6a50f1c829658846fc827fc780/standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/tools/schematool/SchemaToolTaskValidate.java#L117]) if we don't use quoted identifiers.



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