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Hive MetaStore Upgrade HowTo ============================ This document describes how to upgrade the schema of a PostgreSQL backed Hive MetaStore instance from one release version of Hive to another release version of Hive. For example, by following the steps listed below it is possible to upgrade a Hive 0.5.0 MetaStore schema to a Hive 0.7.0 MetaStore schema. Before attempting this project we strongly recommend that you read through all of the steps in this document and familiarize yourself with the required tools. MetaStore Upgrade Steps ======================= 1) Shutdown your MetaStore instance and restrict access to the MetaStore's PostgreSQL database. It is very important that no one else accesses or modifies the contents of database while you are performing the schema upgrade. 2) Create a backup of your PostgreSQL metastore database. This will allow you to revert any changes made during the upgrade process if something goes wrong. The pg_dump utility is the easiest way to create a backup of a PostgreSQL database: % pg_dump --opt <metastore_db_name> > metastore_backup.sql Note that you may need also need to specify a hostname and username using the --host and --username command line switches. 3) Dump your metastore database schema to a file. We use the pg_dump utility again, but this time with a command line option that specifies we are only interested in dumping the DDL statements required to create the schema: % pg_dump --schema-only <metastore_db_name> > my-schema-x.y.z.postgres.sql 4) The schema upgrade scripts assume that the schema you are upgrading closely matches the official schema for your particular version of Hive. The files in this directory with names like "hive-schema-x.y.z.postgres.sql" contain dumps of the official schemas corresponding to each of the released versions of Hive. You can determine differences between your schema and the official schema by diffing the contents of the official dump with the schema dump you created in the previous step. Some differences are acceptable and will not interfere with the upgrade process, but others need to be resolved manually or the upgrade scripts will fail to complete. * Missing Tables: Hive's default configuration causes the MetaStore to create schema elements only when they are needed. Some tables may be missing from your MetaStore schema if you have not created the corresponding Hive catalog objects, e.g. the PARTITIONS table will probably not exist if you have not created any table partitions in your MetaStore. You MUST create these missing tables before running the upgrade scripts. The easiest way to do this is by executing the official schema DDL script against your schema. Each of the CREATE TABLE statements in the schema script include an IF NOT EXISTS clause, so tables which already exist in your schema will be ignored, and those which don't exist will get created. * Extra Tables: Your schema may include a table named NUCLEUS_TABLES or a table named SEQUENCE_TABLE. These tables are managed by the DataNucleus ORM layer and will be created automatically if they don't exist. No action on your part is required. * Reversed Column Constraint Names in the Same Table: Tables with multiple constraints may have the names of the constraints reversed. For example, the PARTITIONS table contains two foreign key constraints named PARTITIONS_FK1 and PARTITIONS_FK2 which reference SDS.SD_ID and TBLS.TBL_ID respectively. However, in your schema you may find that PARTITIONS_FK1 references TBLS.TBL_ID and PARTITIONS_FK2 references SDS.SD_ID. Either version is acceptable -- the only requirement is that these constraints actually exist. * Differences in Column/Constraint Names: Your schema may contain tables with columns named "IDX" or unique keys named "UNIQUE<tab_name>". If you find either of these in your schema you will need to change the names to "INTEGER_IDX" and "UNIQUE_<tab_name>" before running the upgrade scripts. For more background on this issue please refer to HIVE-1435. 5) You are now ready to run the schema upgrade scripts. If you are upgrading from Hive 0.5.0 to Hive 0.6.0 you need to run the upgrade-0.5.0-to-0.6.0.postgres.sql script, but if you are upgrading from 0.5.0 to 0.7.0 you will need to run the 0.5.0 to 0.6.0 upgrade script followed by the 0.6.0 to 0.7.0 upgrade script. # su postgres $ psql -f <loc>/upgrade-0.5.0-to-0.6.0.postgres.sql -d <metastore_db_name> $ psql -f <loc>/upgrade-0.6.0-to-0.7.0.postgres.sql -d <metastore_db_name> These scripts should run to completion without any errors. If you do encounter errors you need to analyze the cause and attempt to trace it back to one of the preceding steps. 6) The final step of the upgrade process is validating your freshly upgraded schema against the official schema for your particular version of Hive. This is accomplished by repeating steps (3) and (4), but this time comparing against the official version of the upgraded schema, e.g. if you upgraded the schema to Hive 0.7.0 then you will want to compare your schema dump against the contents of hive-schema-0.7.0.postgres.sql