THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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About
Schema tool helps to initialise and upgrade metastore database and hive sys schema.
Metastore Schema Verification
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Hive now records the schema version in the metastore database and verifies that the metastore schema version is compatible with Hive binaries that are going to accesss access the metastore. Note that the Hive properties to implicitly create or alter the existing schema are disabled by default. Hive will not attempt to change the metastore schema implicitly. When you execute a Hive query against an old schema, it will fail to access the metastore:
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By default the configuration property hive.metastore.schema.verification is false and metastore to implicitly write true. If we set it false, metastore implicitly writes the schema version if it's not matching. To enable disable the strict schema verification, you need to set this property to true false in hive-site.xml.
See Hive Metastore Administration for general information about the metastore.
The Hive Schema Tool
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The Hive distribution now includes an offline tool for Hive metastore schema manipulation. This tool can be used to initialize the metastore schema for the current Hive version. It can also handle upgrading the schema from an older version to current. It tries to find the current schema from the metastore if it is available. This will be applicable to future upgrades like 0.12.0 to 0.13.0. In case of upgrades from older releases like 0.7.0 or 0.10.0, you can specify the schema version of the existing metastore as a command line option to the tool.
The schematool figures out the SQL scripts required to initialize or upgrade the schema and then executes those scripts against the backend database. The metastore DB connection information like JDBC URL, JDBC driver and DB credentials are extracted from the Hive configuration. You can provide alternate DB credentials if needed.
Warning: You should always initialize the metastore schema first and the Hive schema second. The Hive schema initialization checks the metastore database schema and if it is not initialized, it puts some objects into the metastore database as well to make sure hive schema is running. That also means if you want to run the metastore schema initialization after the hive one, it will fail as it finds a database that already contains some objects.
The schematool Command
The schematool command invokes the Hive schema tool with these options:
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