vtexplain is a command line tool which provides information on how Vitess plans to execute a particular query. It can be used to validate queries for compatibility with Vitess.

For a user guide that describes how to use the vtexplain tool to explain how Vitess executes a particular SQL statement, see Analyzing a SQL statement.

Example Usage #

Explain how Vitess will execute the query SELECT * FROM users using the VSchema contained in vschemas.json and the database schema schema.sql:

vtexplain -- --vschema-file vschema.json --schema-file schema.sql --sql "SELECT * FROM users"

Explain how the example will execute on 128 shards using Row-based replication:

vtexplain -- -shards 128 --vschema-file vschema.json --schema-file schema.sql --replication-mode "ROW" --output-mode text --sql "INSERT INTO users (user_id, name) VALUES(1, 'john')"

Options #

The following parameters apply to mysqlctl:

Please note that -ks-shard-map and ks-shard-map-file will supercede --shards. If you attempt to vtexplain on a keyspace that is included in the keyspace shard map, the shards as defined in the mapping will be used and --shards will be ignored.

Limitations #

The VSchema must use a keyspace name. #

VTExplain requires a keyspace name for each keyspace in an input VSchema:

"keyspace_name": {
    "_comment": "Keyspace definition goes here."
}

If no keyspace name is present, VTExplain will return the following error:

ERROR: initVtgateExecutor: json: cannot unmarshal bool into Go value of type map[string]json.RawMessage