MoveTables

Move tables between keyspaces without downtime

Command

MoveTables  [-cells=<cells>] [-tablet_types=<source_tablet_types>] -workflow=<workflow>
                                      <source_keyspace> <target_keyspace> <table_specs>

Description

MoveTables is used to start a workflow to move one or more tables from an external database or an existing Vitess keyspace into a new Vitess keyspace. The target keyspace can be unsharded or sharded.

MoveTables is used typically for migrating data into Vitess or to implement vertical sharding. You might use the former when you first start using Vitess and the latter if you want to distribute your load across servers.

Parameters

-cells

optional
default local cell

A comma separated list of cell names or cell aliases. This list is used by VReplication to determine which cells should be used to pick a tablet for selecting data from the source keyspace.

Uses
  • Improve performance by using picking a tablet in cells in network proximity with the target
  • To reduce bandwidth costs by skipping cells which are in different availability zones
  • Select cells where replica lags are lower

-tablet_types

optional
default replica

A comma separated list of tablet types that are used while picking a tablet for sourcing data. One or more from MASTER, REPLICA, RDONLY.

Uses
  • To reduce load on master tablets by using REPLICAs or RDONLYs
  • Reducing lags by pointing to MASTER

workflow

mandatory

Unique name for the MoveTables-initiated workflow, used in later commands to refer back to this workflow

source_keyspace

mandatory

Name of existing keyspace that contains the tables to be moved

target_keyspace

mandatory

Name of existing keyspace to which the tables will be moved

table_specs

mandatory

One of
  • comma separated list of tables (if vschema has been already specified for all the tables)
  • JSON table section of the vschema for associated tables in case vschema is not yet specified

A MoveTables Workflow

Once you select the set of tables to move from one keyspace to another you need to initiate a VReplication workflow as follows:

  1. Initiate the migration using MoveTables
  2. Monitor the workflow using Workflow or VExec
  3. Confirm that data has been copied over correctly using VDiff
  4. Start the cutover by routing all reads from your application to those tables using SwitchReads
  5. Complete the cutover by routing all writes using SwitchWrites
  6. Optionally cleanup the source tables using DropSources

Common use cases for MoveTables

Adopting Vitess

For those wanting to try out Vitess for the first time MoveTables provides an easy way to route part of their workload to Vitess with the ability of migrating back at any time without any risk. You point a vttablet to your existing MySQL installation, spin up a unsharded Vitess cluster and use a MoveTables workflow to start serving some tables from Vitess. You can also go further and use a Reshard workflow to experiment with a sharded version of a part of your database.

See user guide for detailed steps

Horizontal Sharding

For existing Vitess users you can easily move one or more tables to another keyspace, either for balancing load or as a preparation to sharding your tables.

See user guide which describes how MoveTables works in the local example provided in the Vitess repo.

More Reading