vttablet

A VTTablet server controls a running MySQL server. VTTablet supports two primary types of deployments:

• Managed MySQL (most common)
• External MySQL

In addition to these deployment types, a partially managed VTTablet is also possible by setting --disable_active_reparents.

Example Usage

Managed MySQL

In this mode, Vitess actively manages MySQL:

export TOPOLOGY_FLAGS="--topo_implementation etcd2 --topo_global_server_address localhost:2379 --topo_global_root /vitess/global"
export VTDATAROOT="/tmp"
vttablet \
$TOPOLOGY_FLAGS
--tablet-path $alias
--init_keyspace $keyspace
--init_shard $shard
--init_tablet_type $tablet_type
--port $port
--grpc_port $grpc_port
--service_map 'grpc-queryservice,grpc-tabletmanager,grpc-updatestream'

$alias needs to be of the form: <cell>-id, and the cell should match one of the local cells that was created in the topology. The id can be left padded with zeroes: cell-100 and cell-000000100 are synonymous.

External MySQL

In this mode, an external MySQL can be used such as AWS RDS, AWS Aurora, Google CloudSQL; or just an existing (vanilla) MySQL installation.

See Unmanaged Tablet for the full guide.

Even if a MySQL is external, you can still make vttablet perform some management functions. They are as follows:

• --disable_active_reparents: If this flag is set, then any reparent or replica commands will not be allowed. These are InitShardPrimary, PlannedReparentShard, EmergencyReparentShard, and ReparentTablet. In this mode, you should use the TabletExternallyReparented command to inform vitess of the current primary.
• --replication_connect_retry: This value is give to mysql when it connects a replica to the primary as the retry duration parameter.
• --enable_replication_reporter: If this flag is set, then vttablet will transmit replica lag related information to the vtgates, which will allow it to balance load better. Additionally, enabling this will also cause vttablet to restart replication if it was stopped. However, it will do this only if —disable_active_reparents was not turned on.
• --heartbeat_enable and --heartbeat_interval duration: cause vttablet to write heartbeats to the sidecar database. This information is also used by the replication reporter to assess replica lag.

Options

The following global options apply to vttablet:

Key Options

• --restore_from_backup: The default value for this flag is false. If set to true, and the my.cnf file was successfully loaded, then vttablet can perform automatic restores as follows:

  • If started against a mysql instance that has no data files, it will search the list of backups for the latest one, and initiate a restore. After this, it will point the mysql to the current primary and wait for replication to catch up. Once replication is caught up to the specified tolerance limit, it will advertise itself as serving. This will cause the vtgates to add it to the list of healthy tablets to serve queries from.
  • If this flag is true, but my.cnf was not loaded, then vttablet will fatally exit with an error message.
  • You can additionally control the level of concurrency for a restore with the --restore_concurrency flag. This is typically useful in cloud environments to prevent the restore process from becoming a ‘noisy’ neighbor by consuming all available disk IOPS.