Migration steps

This page describes the steps to perform and verify a successful migration to YugabyteDB. Before proceeding with migration, ensure that you have completed the following steps:

Install yb-voyager.
Check the unsupported features and known issues.
Review data modeling strategies.
Prepare the source database.
Prepare the target database.

Prepare the source database

Prepare your source database by creating a new database user, and provide it with READ access to all the resources which need to be migrated.

Create a database user and provide the user with READ access to all the resources which need to be migrated. Run the following commands in a psql session:

Create a new user named ybvoyager.

CREATE USER ybvoyager PASSWORD 'password';

Switch to the database that you want to migrate.
```
\c <database_name>
```
Grant the USAGE permission to the ybvoyager user on all schemas of the database.
```
SELECT 'GRANT USAGE ON SCHEMA ' || schema_name || ' TO ybvoyager;' FROM information_schema.schemata; \gexec
```
The above SELECT statement generates a list of GRANT USAGE statements which are then executed by psql because of the \gexec switch. The \gexec switch works for PostgreSQL v9.6 and later. For older versions, you'll have to manually execute the GRANT USAGE ON SCHEMA schema_name TO ybvoyager statement, for each schema in the source PostgreSQL database.

Grant SELECT permission on all the tables and sequences.

SELECT 'GRANT SELECT ON ALL TABLES IN SCHEMA ' || schema_name || ' TO ybvoyager;' FROM information_schema.schemata; \gexec

SELECT 'GRANT SELECT ON ALL SEQUENCES IN SCHEMA ' || schema_name || ' TO ybvoyager;' FROM information_schema.schemata; \gexec

The ybvoyager user can now be used for migration.

Create a database user and provide the user with READ access to all the resources which need to be migrated. Replace 'localhost' from the following commands with an appropriate hostname in your setup.

Create a new user ybvoyager.

CREATE USER 'ybvoyager'@'<client_IP>' IDENTIFIED WITH  mysql_native_password BY 'Password#123';

Grant the global PROCESS permission.

GRANT PROCESS ON *.* TO 'ybvoyager'@'<client_IP>';

Grant the SELECT, SHOW VIEW, and TRIGGER permissions on the source database:

GRANT SELECT ON source_db_name.* TO 'ybvoyager'@'<client_IP>';
GRANT SHOW VIEW ON source_db_name.* TO 'ybvoyager'@'<client_IP>';
GRANT TRIGGER ON source_db_name.* TO 'ybvoyager'@'<client_IP>';

Note that if you want to accelerate data export, include the following grants additionally as follows:

For MYSQL

GRANT FLUSH_TABLES ON *.* TO 'ybvoyager'@'<client_IP>';
GRANT REPLICATION CLIENT ON *.* TO 'ybvoyager'@'<client_IP>';

For MYSQL RDS

GRANT FLUSH_TABLES ON *.* TO 'ybvoyager'@'<client_IP>';
GRANT REPLICATION CLIENT ON *.* TO 'ybvoyager'@'<client_IP>';
GRANT LOCK TABLES ON <source_db_name>.* TO 'ybvoyager'@'<client_IP>';

If you are running MySQL version 8.0.20 or later, grant the global SHOW_ROUTINE permission. For older versions, grant the global SELECT permission. These permissions are necessary to dump stored procedure/function definitions.
```
--For MySQL >= 8.0.20
GRANT SHOW_ROUTINE  ON *.* TO 'ybvoyager'@'<client_IP>';
```
```
--For older versions
GRANT SELECT ON *.* TO 'ybvoyager'@'<client_IP>';
```
The ybvoyager user can now be used for migration.

Create a role and a database user, and provide the user with READ access to all the resources which need to be migrated.

Create a role that has the privileges as listed in the following table:

Permission	Object type in the source schema
`SELECT`	VIEW, SEQUENCE, TABLE PARTITION, TABLE, SYNONYM, MATERIALIZED VIEW
`EXECUTE`	TYPE

Change the <SCHEMA_NAME> appropriately in the following snippets, and run the following steps as a privileged user.

CREATE ROLE <SCHEMA_NAME>_reader_role;

BEGIN
    FOR R IN (SELECT owner, object_name FROM all_objects WHERE owner=UPPER('<SCHEMA_NAME>') and object_type in ('VIEW','SEQUENCE','TABLE PARTITION','SYNONYM','MATERIALIZED VIEW'))
    LOOP
       EXECUTE IMMEDIATE 'grant select on '||R.owner||'."'||R.object_name||'" to <SCHEMA_NAME>_reader_role';
    END LOOP;
END;
/

BEGIN
    FOR R IN (SELECT owner, object_name FROM all_objects WHERE owner=UPPER('<SCHEMA_NAME>') and object_type ='TABLE' MINUS SELECT owner, table_name from all_nested_tables where owner = UPPER('<SCHEMA_NAME>'))
    LOOP
       EXECUTE IMMEDIATE 'grant select on '||R.owner||'."'||R.object_name||'" to  <SCHEMA_NAME>_reader_role';
    END LOOP;
END;
/

BEGIN
    FOR R IN (SELECT owner, object_name FROM all_objects WHERE owner=UPPER('<SCHEMA_NAME>') and object_type = 'TYPE')
    LOOP
       EXECUTE IMMEDIATE 'grant execute on '||R.owner||'."'||R.object_name||'" to <SCHEMA_NAME>_reader_role';
    END LOOP;
END;
/

GRANT SELECT_CATALOG_ROLE TO <SCHEMA_NAME>_reader_role;
GRANT SELECT ANY DICTIONARY TO <SCHEMA_NAME>_reader_role;
GRANT SELECT ON SYS.ARGUMENT$ TO <SCHEMA_NAME>_reader_role;

Create a user ybvoyager and grant CONNECT and <SCHEMA_NAME>_reader_role to the user:

CREATE USER ybvoyager IDENTIFIED BY password;
GRANT CONNECT TO ybvoyager;
GRANT <SCHEMA_NAME>_reader_role TO ybvoyager;

If you're using accelerated data export, run the additional grant as follows:

GRANT FLASHBACK ANY TABLE TO ybvoyager;

If you're using accelerated data export, the log_mode should be archivelog.

Check the value for log_mode using the following command for Oracle/Oracle RDS:
```
SELECT LOG_MODE FROM V$DATABASE;
```

If the log_mode value is NOARCHIVELOG, run the following commands:

For Oracle

sqlplus /nolog
SQL>alter system set db_recovery_file_dest_size = 10G;
SQL>alter system set db_recovery_file_dest = '<oracle_path>/oradata/recovery_area' scope=spfile;
SQL> connect / as sysdba
SQL> Shutdown immediate
SQL> Startup mount
SQL> Alter database archivelog;
SQL> Alter database open;

For Oracle RDS

exec rdsadmin.rdsadmin_util.set_configuration('archivelog retention hours',24);

Verify using archive log list.

If you want yb-voyager to connect to the source database over SSL, refer to SSL Connectivity.

Connecting to Oracle instances

You can use only one of the following arguments to connect to your Oracle instance.

Prepare the target database

Prepare your target YugabyteDB cluster by creating a database, and a user for your cluster.

Create the target database

Create the target database in your YugabyteDB cluster. The database name can be the same or different from the source database name. If the target database name is not provided, yb-voyager assumes the target database name to be yugabyte. If you do not want to import in the default yugabyte database, specify the name of the target database name using the --target-db-name argument to the yb-voyager import commands.

CREATE DATABASE target_db_name;

Create a user

Create a user with SUPERUSER role.

For a local YugabyteDB cluster or YugabyteDB Anywhere, create a user and role with the superuser privileges using the following command:
```
CREATE USER ybvoyager SUPERUSER PASSWORD 'password';
```
For YugabyteDB Managed, create a user with yb_superuser role using the following command:
```
CREATE USER ybvoyager PASSWORD 'password';
GRANT yb_superuser TO ybvoyager;
```

If you want yb-voyager to connect to the target database over SSL, refer to SSL Connectivity.

Deleting the ybvoyager user

After migration, all the migrated objects (tables, views, and so on) are owned by the ybvoyager user. You should transfer the ownership of the objects to some other user (for example, yugabyte) and then delete the ybvoyager user. Example steps to delete the user are:

REASSIGN OWNED BY ybvoyager TO yugabyte;
DROP OWNED BY ybvoyager;
DROP USER ybvoyager;

Create an export directory

yb-voyager keeps all of its migration state, including exported schema and data, in a local directory called the export directory.

Before starting migration, you should create the export directory on a file system that has enough space to keep the entire source database. Next, you should provide the path of the export directory as a mandatory argument (--export-dir) to each invocation of the yb-voyager command in an environment variable.

mkdir $HOME/export-dir
export EXPORT_DIR=$HOME/export-dir

The export directory has the following sub-directories and files:

reports directory contains the generated Schema Analysis Report.
schema directory contains the source database schema translated to PostgreSQL. The schema is partitioned into smaller files by the schema object type such as tables, views, and so on.
data directory contains TSV (Tab Separated Values) files that are passed to the COPY command on the target database.
metainfo and temp directories are used by yb-voyager for internal bookkeeping.
yb-voyager.log contains log messages.

Migrate your database to YugabyteDB

Proceed with schema and data migration using the following steps:

Export and analyze schema

To begin, export the schema from the source database. Once exported, analyze the schema and apply any necessary manual changes.

Export schema

The yb-voyager export schema command extracts the schema from the source database, converts it into PostgreSQL format (if the source database is Oracle or MySQL), and dumps the SQL DDL files in the EXPORT_DIR/schema/* directories.

Renaming index names for MySQL

YugabyteDB Voyager renames the indexes for MySQL migrations while exporting the schema. MySQL supports two or more indexes to have the same name in the same database, provided they are for different tables. Similarly to PostgreSQL, YugabyteDB does not support duplicate index names in the same schema. To avoid index name conflicts during export schema, yb-voyager prefixes each index name with the associated table name.

Usage for source_db_schema

The source_db_schema argument specifies the schema of the source database.

For MySQL, currently the source-db-schema argument is not applicable.
For PostgreSQL, source-db-schema can take one or more schema names separated by comma.
For Oracle, source-db-schema can take only one schema name and you can migrate only one schema at a time.

An example invocation of the command is as follows:

# Replace the argument values with those applicable for your migration.
yb-voyager export schema --export-dir <EXPORT_DIR> \
        --source-db-type <SOURCE_DB_TYPE> \
        --source-db-host <SOURCE_DB_HOST> \
        --source-db-user <SOURCE_DB_USER> \
        --source-db-password <SOURCE_DB_PASSWORD> \ # Enclose the password in single quotes if it contains special characters.
        --source-db-name <SOURCE_DB_NAME> \
        --source-db-schema <SOURCE_DB_SCHEMA> # Not applicable for MySQL

Refer to export schema for details about the arguments.

Analyze schema

The schema exported in the previous step may not yet be suitable for importing into YugabyteDB. Even though YugabyteDB is PostgreSQL compatible, given its distributed nature, you may need to make minor manual changes to the schema.

The yb-voyager analyze-schema command analyses the PostgreSQL schema dumped in the export schema step, and prepares a report that lists the DDL statements which need manual changes. An example invocation of the command is as follows:

# Replace the argument values with those applicable for your migration.
yb-voyager analyze-schema --export-dir <EXPORT_DIR> --output-format <FORMAT>

The above command generates a report file under the EXPORT_DIR/reports/ directory.

Refer to analyze schema for details about the arguments.

Manually edit the schema

Fix all the issues listed in the generated schema analysis report by manually editing the SQL DDL files from the EXPORT_DIR/schema/*.

After making the manual changes, re-run the yb-voyager analyze-schema command. This generates a fresh report using your changes. Repeat these steps until the generated report contains no issues.

To learn more about modelling strategies using YugabyteDB, refer to Data modeling.

Manual schema changes

CREATE INDEX CONCURRENTLY is not currently supported in YugabyteDB. You should remove the CONCURRENTLY clause before trying to import the schema.
Include the primary key definition in the CREATE TABLE statement. Primary Key cannot be added to a partitioned table using the ALTER TABLE statement.

Export data

Dump the source data into the EXPORT_DIR/data directory using the yb-voyager export data command as follows:

# Replace the argument values with those applicable for your migration.
yb-voyager export data --export-dir <EXPORT_DIR> \
        --source-db-type <SOURCE_DB_TYPE> \
        --source-db-host <SOURCE_DB_HOST> \
        --source-db-user <SOURCE_DB_USER> \
        --source-db-password <SOURCE_DB_PASSWORD> \ # Enclose the password in single quotes if it contains special characters.
        --source-db-name <SOURCE_DB_NAME> \
        --source-db-schema <SOURCE_DB_SCHEMA> # Not applicable for MySQL

Note that the source-db-schema argument is required for PostgreSQL and Oracle, and is not applicable for MySQL. Refer to export data for details about the arguments, and export data status to track the status of an export operation.

The options passed to the command are similar to the yb-voyager export schema command. To export only a subset of the tables, pass a comma-separated list of table names in the --table-list argument.

Sequence migration considerations

Sequence migration consists of two steps: sequence creation and setting resume value (resume value refers to the NEXTVAL of a sequence on a source database). A sequence object is generated during export schema and the resume values for sequences are generated during export data. These resume values are then set on the target database just after the data is imported for all tables.

Note that there are some special cases involving sequences such as the following:

In MySQL, auto-increment column is migrated to YugbayteDB as a normal column with a sequence attached to it.
For PostgreSQL, SERIAL datatype and GENERATED AS IDENTITY columns use sequence object internally, so resume values for them are also generated during data export.

Accelerate data export for MySQL and Oracle

For MySQL and Oracle, you can optionally speed up data export by setting the environment variable BETA_FAST_DATA_EXPORT=1 when you run export data using yb-voyager.

Consider the following caveats before using the feature:

You need to perform additional steps when you prepare the source database.
Some data types are unsupported. For a detailed list, refer to datatype mappings.
--parallel-jobs argument will have no effect.
SSL is unsupported.
In MySQL RDS, writes are not allowed during the data export process.
For Oracle where sequences are not attached to a column, resume value generation is unsupported.

Import schema

Import the schema using the yb-voyager import schema command.

Usage for target_db_schema

The target_db_schema argument specifies the schema of the target database and is applicable only for MySQL and Oracle. yb-voyager imports the source database into the public schema of the target database. By specifying --target-db-schema argument during import, you can instruct yb-voyager to create a non-public schema and use it for the schema/data import.

An example invocation of the command is as follows:

# Replace the argument values with those applicable for your migration.
yb-voyager import schema --export-dir <EXPORT_DIR> \
        --target-db-host <TARGET_DB_HOST> \
        --target-db-user <TARGET_DB_USER> \
        --target-db-password <TARGET_DB_PASSWORD> \ # Enclose the password in single quotes if it contains special characters..
        --target-db-name <TARGET_DB_NAME> \
        --target-db-schema <TARGET_DB_SCHEMA> # MySQL and Oracle only

Refer to import schema for details about the arguments.

yb-voyager applies the DDL SQL files located in the $EXPORT_DIR/schema directory to the target database. If yb-voyager terminates before it imports the entire schema, you can rerun it by adding the --ignore-exist option.

Importing indexes and triggers

Because the presence of indexes and triggers can slow down the rate at which data is imported, by default import schema does not import indexes and triggers. You should complete the data import without creating indexes and triggers. Only after data import is complete, create indexes and triggers using the import schema command with an additional --post-import-data flag.

Import data

After you have successfully exported the source data and imported the schema in the target database, you can import the data using the yb-voyager import data command as follows:

# Replace the argument values with those applicable for your migration.
yb-voyager import data --export-dir <EXPORT_DIR> \
        --target-db-host <TARGET_DB_HOST> \
        --target-db-user <TARGET_DB_USER> \
        --target-db-password <TARGET_DB_PASSWORD> \ # Enclose the password in single quotes if it contains special characters.
        --target-db-name <TARGET_DB_NAME> \
        --target-db-schema <TARGET_DB_SCHEMA> \ # MySQL and Oracle only.
        --parallel-jobs <NUMBER_OF_JOBS>

By default, yb-voyager creates C/2 connections where C is the total number of cores in the cluster. You can change the default number of connections using the --parallel-jobs argument. If yb-voyager fails to determine the number of cores in the cluster, it defaults to 2 connections per node.

Refer to import data for details about the arguments.

yb-voyager splits the data dump files (from the $EXPORT_DIR/data directory) into smaller batches. yb-voyager concurrently ingests the batches such that all nodes of the target YugabyteDB cluster are used. This phase is designed to be restartable if yb-voyager terminates while the data import is in progress. After restarting, the data import resumes from its current state.

Importing large datasets

When importing a very large database, run the import data command in a screen session, so that the import is not terminated when the terminal session stops.

If the yb-voyager import data command terminates before completing the data ingestion, you can re-run it with the same arguments and the command will resume the data import operation.

Import data status

Run the yb-voyager import data status --export-dir <EXPORT_DIR> command to get an overall progress of the data import operation.

Import data file

If all your data files are in CSV format and you have already created a schema in your target YugabyteDB, you can use the yb-voyager import data file command to load the data into the target table directly from the CSV file(s). This command doesn't require performing other migration steps (export and analyze schema, export data, or import schema prior to import. It only requires a table present in the target database to perform the import.

# Replace the argument values with those applicable for your migration.
yb-voyager import data file --export-dir <EXPORT_DIR> \
        --target-db-host <TARGET_DB_HOST> \
        --target-db-user <TARGET_DB_USER> \
        --target-db-password <TARGET_DB_PASSWORD> \ # Enclose the password in single quotes if it contains special characters.
        --target-db-name <TARGET_DB_NAME> \
        --target-db-schema <TARGET_DB_SCHEMA> \ # MySQL and Oracle only
        –-data-dir </path/to/files/dir/> \
        --file-table-map <filename1:table1,filename2:table2> \
        --delimiter <DELIMITER> \
        –-has-header \
        --null-string "<NULL_STRING>"

Refer to import data file for details about the arguments.

Import data file from AWS S3

Import data file also allows you to load directly from your data files stored on AWS S3. The S3 bucket URI can be provided to the data-dir flag as follows:

yb-voyager import data file .... \
        --data-dir s3://voyager-data

Refer to import data file for additional details to set up your S3 bucket with yb-voyager.

Import indexes and triggers

Import indexes and triggers using the import schema command with an additional --post-import-data flag as follows:

# Replace the argument values with those applicable for your migration.
yb-voyager import schema --export-dir <EXPORT_DIR> \
        --target-db-host <TARGET_DB_HOST> \
        --target-db-user <TARGET_DB_USER> \
        --target-db-password <TARGET_DB_PASSWORD> \ # Enclose the password in single quotes if it contains special characters.
        --target-db-name <TARGET_DB_NAME> \
        --target-db-user <TARGET_DB_USER> \
        --target-db-schema <TARGET_DB_SCHEMA> \ # MySQL and Oracle only
        --post-import-data

Refer to import schema for details about the arguments.

Verify migration

After the schema and data import is complete, the automated part of the database migration process is considered complete. You should manually run validation queries on both the source and target database to ensure that the data is correctly migrated. A sample query to validate the databases can include checking the row count of each table.

Caveat associated with rows reported by import data status

Suppose you have a scenario where,

import data or import data file command fails.
To resolve this issue, you delete some of the rows from the split files.
After retrying, the import data command completes successfully.

In this scenario, import data status command reports incorrect imported row count; because it doesn't take into account the deleted rows.

For more details, refer to the GitHub issue #360.