Reshard
split or merge shards in a keyspace
Starting with Vitess 11.0 you should use the VReplication v2 commands
Command #
Reshard -v1 [-cells=<cells>] [-tablet_types=<source_tablet_types>] [-skip_schema_copy] [-auto_start] [-stop_after_copy] <keyspace.workflow> <source_shards> <target_shards>
Description #
Reshard support horizontal sharding by letting you change the sharding ranges of your existing keyspace.
Parameters #
-cells #
optional\
Comma separated Cell(s) or CellAlias(es) to replicate from.
-tablet_types #
optional
default empty
Source Vitess tablet_type, or comma separated list of tablet types, that should be used for choosing source tablet(s) for the reshard.
Note: If replicating from primary, you must explicitly use -tablet_types=primary. If not specified, it defaults to the tablet type(s) specified by the -vreplication_tablet_type VTTablet command line flag. -vreplication_tablet_type defaults to "PRIMARY,REPLICA".
-skip_schema_copy #
optional
default false
If true the source schema is copied to the target shards. If false, you need to create the tables
before calling reshard.
-auto_start #
optional
default true
If false, streams will start in the Stopped state and will need to be explicitly started (default true).
-stop_after_copy #
optional
default false
Streams will be stopped once the copy phase is completed.
keyspace.workflow #
mandatory
Name of keyspace being sharded and the associated workflow name, used in later commands to refer back to this reshard.
source_shards #
mandatory
Comma separated shard names to reshard from.
target_shards #
mandatory
Comma separated shard names to reshard to.
A Reshard Workflow #
Once you decide on the new resharding strategy for a keyspace, you need to initiate a VReplication workflow as follows:
- Initiate the migration using Reshard
- Monitor the workflow using Workflow or VExec
- Confirm that data has been copied over correctly using VDiff
- Start the cutover by routing all reads from your application to those tables using SwitchReads
- Complete the cutover by routing all writes using SwitchWrites
- Optionally cleanup the source tables using DropSources
Reshard