vtexplain
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:
| Name | Type | Definition |
|---|---|---|
| -output-mode | string | Output in human-friendly text or JSON (default "text") |
| -planner-version | string | Sets the query planner version to use when generating the explain output. Valid values are V3 and Gen4 (default "V3") |
| -normalize | boolean | Whether to enable vtgate normalization (default false) |
| -shards | int | Number of shards per keyspace, passing -ks-shard-map/-ks-shard-map-file causes this flag to be ignored (default 2) |
| -replication-mode | string | The replication mode to simulate -- must be set to either ROW or STATEMENT (default "ROW") |
| -schema | string | The SQL table schema (default "") |
| -schema-file | string | Identifies the file that contains the SQL table schema (default "") |
| -sql | string | A list of semicolon-delimited SQL commands to analyze (default "") |
| -sql-file | string | Identifies the file that contains the SQL commands to analyze (default "") |
| -vschema | string | Identifies the VTGate routing schema (default "") |
| -vschema-file | string | Identifies the VTGate routing schema file (default "") |
| -ks-shard-map | string | JSON map of keyspace name -> shard name -> ShardReference object. The inner map should be the same as the output of FindAllShardsInKeyspace (default "") |
| -ks-shard-map-file | string | File containing JSON blob of keyspace name -> shard name -> ShardReference object (default "") |
| -dbname | string | Optional database target to override normal routing (default "") |
| -queryserver-config-passthrough-dmls | boolean | Query server pass through all dml statements without rewriting (default false) |
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