Migrate from MySQL

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This page has instructions for migrating data from MySQL to CockroachDB using IMPORT's support for reading mysqldump files.

The examples use the employees data set that is also used in the MySQL docs.

Considerations

In addition to the general considerations listed in the Migration Overview, there is also the following MySQL-specific information to consider as you prepare your migration.

String case sensitivity

MySQL strings are case-insensitive by default, but strings in CockroachDB are case-sensitive. This means that you may need to edit your MySQL dump file to get the results you expect from CockroachDB. For example, you may have been doing string comparisons in MySQL that will need to be changed to work with CockroachDB.

For more information about the case sensitivity of strings in MySQL, see Case Sensitivity in String Searches from the MySQL documentation. For more information about CockroachDB strings, see STRING.

FIELD function

The MYSQL FIELD function is not supported in CockroachDB. Instead, you can use the array_position function, which returns the index of the first occurrence of element in the array.

Example usage:

> SELECT array_position(ARRAY[4,1,3,2],1);

  array_position
------------------
               2
(1 row)

While MYSQL returns 0 when the element is not found, CockroachDB returns NULL. So if you are using the ORDER BY clause in a statement with the array_position function, the caveat is that sort is applied even when the element is not found. As a workaround, you can use the COALESCE operator.

> SELECT * FROM table_a ORDER BY COALESCE(array_position(ARRAY[4,1,3,2],5),999);

Step 1. Dump the MySQL database

There are several ways to dump data from MySQL to be imported into CockroachDB:

• Dump the entire database
• Dump one table at a time

Dump the entire database

Most users will want to import their entire MySQL database all at once, as shown below in Import a full database dump. To dump the entire database, run the mysqldump command shown below:

$ mysqldump -uroot employees > /tmp/employees-full.sql

If you only want to import one table from a database dump, see Import a table from a full database dump below.

Dump one table at a time

To dump the employees table from a MySQL database also named employees, run the mysqldump command shown below. You can import this table using the instructions in Import a table from a table dump below.

$ mysqldump -uroot employees employees > employees.sql

Step 2. Host the files where the cluster can access them

Each node in the CockroachDB cluster needs to have access to the files being imported. There are several ways for the cluster to access the data; for more information on the types of storage IMPORT can pull from, see the following:

• Use Cloud Storage for Bulk Operations
• Use a Local File Server for Bulk Operations

Step 3. Import the MySQL dump file

You can choose from several variants of the IMPORT statement, depending on whether you want to import an entire database or just one table:

• Import a full database dump
• Import a table from a full database dump
• Import a table from a table dump

All of the IMPORT statements in this section pull real data from Amazon S3 and will kick off background import jobs that you can monitor with SHOW JOBS.

Import a full database dump

This example assumes you dumped the entire database.

The IMPORT statement below reads the data and DDL statements (including CREATE TABLE and foreign key constraints) from the full database dump.

> CREATE DATABASE IF NOT EXISTS employees;
> USE employees;
> IMPORT MYSQLDUMP 'https://s3-us-west-1.amazonaws.com/cockroachdb-movr/datasets/employees-db/mysqldump/employees-full.sql.gz';

       job_id       |  status   | fraction_completed |  rows   | index_entries | system_records |   bytes
--------------------+-----------+--------------------+---------+---------------+----------------+-----------
 382716507639906305 | succeeded |                  1 | 3919015 |        331636 |              0 | 110104816
(1 row)

Import a table from a full database dump

This example assumes you dumped the entire database.

IMPORT can import one table's data from a full database dump. It reads the data and applies any CREATE TABLE statements from the dump file.

> CREATE DATABASE IF NOT EXISTS employees;
> USE employees;
> IMPORT TABLE employees FROM MYSQLDUMP 'https://s3-us-west-1.amazonaws.com/cockroachdb-movr/datasets/employees-db/mysqldump/employees.sql.gz';

       job_id       |  status   | fraction_completed |  rows  | index_entries | system_records |  bytes
--------------------+-----------+--------------------+--------+---------------+----------------+----------
 383839294913871873 | succeeded |                  1 | 300024 |             0 |              0 | 11534293
(1 row)

Import a table from a table dump

The following examples assume you dumped one table.

The simplest way to import a table dump is to run IMPORT. It reads the table data and any CREATE TABLE statements from the file:

> CREATE DATABASE IF NOT EXISTS employees;
> USE employees;
> IMPORT TABLE employees FROM MYSQLDUMP 'https://s3-us-west-1.amazonaws.com/cockroachdb-movr/datasets/employees-db/mysqldump/employees.sql.gz';

       job_id       |  status   | fraction_completed |  rows  | index_entries | system_records |  bytes
--------------------+-----------+--------------------+--------+---------------+----------------+----------
 383855569817436161 | succeeded |                  1 | 300024 |             0 |              0 | 11534293
(1 row)

Configuration Options

The following options are available to IMPORT ... MYSQLDUMP:

• Row limit
• Skip foreign keys

Row limit

The row_limit option determines the number of rows to import. If you are importing one table, setting row_limit = 'n' will import the first n rows of the table. If you are importing an entire database, this option will import the first n rows from each table in the dump file. It is useful for finding errors quickly before executing a more time- and resource-consuming import.

Example usage:

> IMPORT MYSQLDUMP 's3://your-external-storage/employees.sql?AWS_ACCESS_KEY_ID=123&AWS_SECRET_ACCESS_KEY=456' WITH row_limit = '10';

Skip foreign keys

By default, IMPORT ... MYSQLDUMP supports foreign keys. Default: false. Add the skip_foreign_keys option to speed up data import by ignoring foreign key constraints in the dump file's DDL. It will also enable you to import individual tables that would otherwise fail due to dependencies on other tables.

Example usage:

> IMPORT MYSQLDUMP 's3://your-external-storage/employees.sql?AWS_ACCESS_KEY_ID=123&AWS_SECRET_ACCESS_KEY=456' WITH skip_foreign_keys;

Foreign key constraints can be added by using ALTER TABLE ... ADD CONSTRAINT commands after importing the data.

See also

• IMPORT
• Import Performance Best Practices
• Migrate from CSV
• Migrate from PostgreSQL
• Can a PostgreSQL or MySQL application be migrated to CockroachDB?
• Back up Data
• Restore Data
• Use the Built-in SQL Client
• cockroach Commands Overview

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