Description

psql2mysql provides some tooling for migrating data from PostgreSQL to MariaDB. It was main target for this tool is to migrate the databases of an OpenStack deployment from PostgreSQL to MariaDB. But it should work for other databases as well.

The tool itself is based on SQLalchemy and it's builtin type abstraction to handle some of the differences between both database.

Currently its focused on moving from PostgreSQL to MariaDB. Other MySQL like databases haven't been tested yet. Neither is the reverse direction of the migration (MariaDB to PostgreSQL) implemented. Both of these features should be easy to add however.

Usage

Installation

mkdir venv
virtualenv venv
. venv/bin/activate
pip install -r requirements.txt
python setup.py install

Prerequisites

• Before using psql2mysql for migration, the destination database and all its tables need to exist already.
• psql2mysql does not do any checks currently if the schema of the target and destination database are compatible. In the case of a migration of an OpenStack database it is assumed that the respective db_sync tool (e.g. keystone-manage db_sync) of the OpenStack service has been called before running psql2mysql.
• The identity provided for the source database needs to have enough privileges to read all data and schema in the specified database.
• Additionally to write access, the identity provided for the target database needs privileges to temporary disable constraints and foreign keys for the duration of the migration.

Commands

psql2mysql currenty provides two subcommands:

• precheck

  Runs a couple of checks on the tables of the source database. Currently only searches all text columns for characters that are not compatible with the "utf8" encoding of MariaDB. Prints out the rows (and affected columns) that contains incompatible strings.

• migrate

  Runs the acutal migration. Will go through, the database table by table and migrate all rows to the target database.

• purge-tables

  Purges all tables in the target database. Tables with names related to alembic and SQLalchemy-migrate are skipped and not purged. This subcommand can be executed optionally after a failed migration attempt. The migrate subcommand will also purge all tables in the target database in the same way before it starts to copy any data from the source database. But as that operation can take a significant amount of time it might make sense to run the purge-tables subcommand separately before migrate in order to reduce the overall downtime of the source database.

Options

• exclude-deleted

  When migrating the data from source to target database, exclude soft-deleted rows. Set to true by default.

• batch

  Process more databases in one run of psql2mysql. The argument for this option is a path to YML file that lists set of databases with their source and target connection strings. The format of YML file is:

  database1:
    source: source URI for database1
    target: target URI for database1
  database2:
    source: source URI for database2
    ...
  

• chunk-size

  By default table migrations are broken into chunks, a number of rows at a time. The default size is 10000. This option with change the chunk size.

  Breaking the migration into chunks improves RAM usage and allows the migration tool to work with larger databases.

  Setting chunk-size to 0 will disable chunking and the migration will migrate the whole table in one go. Be warned that this will use more RAM.

Examples

To check that it is actually possible to migrate run the precheck subcommand:

psql2mysql --source postgresql://neutron:[email protected]/neutron precheck

To check all databases in the batch file:

psql2mysql --batch databases.yml precheck

To do the actual migraton:

    psql2mysql \
        --source postgresql://neutron:[email protected]/neutron \
        --target mysql+pymysql://neutron:[email protected]/neutron?charset=utf8 \
        migrate

To migrate all databases in the batch file:

psql2mysql --batch databases.yml migrate

Testing

psql2mysql provides a test suite. To run the tests use:

nosetests