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VTGate

How does VTGate know which shard to route a query to? #

VTGate knows both the Vschema and the schema of your tables in the backing MySQL databases.

This enables VTGate to look at the WHERE clause of the query and then route the queries to the correct shards. VTGate is also aware of the sharding metadata, cluster state, and availability of tables, so it will only scatter the query across the shards it needs to use.

How do you use gRPC with VTGate? #

To do this you will need to use the Vitess MySQL Go client. We have a Golang compatible gRPC driver and a Java driver.

Once you have the appropriate driver you will need to add the --service_map grpc-vtgateservice VTGate flag and set the port --grpc_port.

This runs on a standard gRPC interface, so if you want to directly use it you can follow the example below:

#!/usr/bin/env node
import Debug from "debug";
import * as grpc from "grpc";
import {CallerID} from './proto/vitess/vtrpc_pb';
import {BoundQuery} from './proto/vitess/query_pb';
import {Session,ExecuteRequest,ExecuteResponse} from './proto/vitess/vtgate_pb';
import {VitessClient} from  './proto/vitess/vtgateservice_grpc_pb';
const log = Debug("VtgateClient");
const client = new VitessClient("139.178.90.99:15306",grpc.credentials.createInsecure());
const SingleQuery = async () => {
   return new Promise((resolve,reject) => {
       const caller = new CallerID();
       caller.setPrincipal("nodejs");
       const session = new Session();
       session.setTargetString("main");
       const query = new BoundQuery();
       query.setSql("SELECT * from main.sbtest1 where id=10");
       const request = new ExecuteRequest()
       request.setSession(session);
       request.setQuery(query);
       request.setCallerId(caller);
       client.execute(request, (err: grpc.ServiceError | null, response: ExecuteResponse ) => {
           if( err != null ){
               console.log(`[SingleQuery] Error: ${err.message}`)
               reject(err); return;
           }
           console.log(`[SingleQuery] Response: ${JSON.stringify(response.toObject())}`)
           resolve(response);
       });
   });
}
async function main() {
   client.
   console.log(`[main] Starting`);
   await SingleQuery();
}
main().then((_) => _);
VTGate