SingleStore DB

Migrating Data with mysqldump

mysqldump is a popular tool packaged with the MySQL client infrastructure. It queries the database to produce a series of CREATE TABLE and INSERT statements that can be replayed to restore the database.

Find the mysqldump reference page here.

While moving your data from MySQL to SingleStore DB, there are a few considerations to keep in mind:

  • For most MySQL storage engines (MyISAM, InnoDB, etc), indexes are stored as B-trees. In SingleStore DB, indexes can be unidirectional lock-free skip lists (ascending or descending) or lock-free hash tables. Picking the right data structure for your index can have a significant impact on the performance of your application. While hash tables are optimized for key-value look ups, skip lists are extremely flexible for complex range scans and sorts (ORDER BY). While transferring your schema, you should audit your table definitions and investigate whether your indexes can be optimized for SingleStore DB. The default BTREE notation is converted into a skip list (see Skip List Indexes) .

  • mysqldump will generate a few queries that are unsupported by SingleStore DB. For example, SingleStore DB does not support disabling UNIQUE_CHECKS. To make it easier to work with mysqldump, unsupported features are by default reported as warnings instead of errors. This functionality can be controlled by adjusting the warn_level variable. See Unsupported MySQL Features for more details. Some components of a CREATE TABLE statement might be blocked completely. If you run into this issue while loading a schema into SingleStore DB, you can manually massage the schema definition into something supported by SingleStore DB.

  • If the machine running SingleStore DB does not have enough memory to support the data you’re loading, the server will issue an error on offending INSERT statements indicating its out-of-memory state. In this case, you should upgrade your machine to one with more memory. If you copy your existing memsqlbin directory to the new machine, SingleStore DB will be able to reuse the schema definitions and INSERT statements that have already compiled.

You should separate your schema and data into separate files, so that you can easily review and modify your schema if necessary. To produce a dump of your database, run something like:

mysqldump -h 127.0.0.1 -u root -B [database name] --no-data -r schema.sql
mysqldump -h 127.0.0.1 -u root -B [database name] --no-create-info -r data.sql

You can then replay these files directly into SingleStore DB by running:

mysql -h 127.0.0.1 -u root -P 3307 < schema.sql
mysql -h 127.0.0.1 -u root -P 3307 < data.sql

While this step runs, you can observe the memsql.log file to see which unsupported features have been ignored. After the import is completed, you can connect to SingleStore DB and start querying the tables directly.