BAD_INPUT is returned when an end-user either sends SQL that couldn't be parsed correctly, or tries a query that isn't supported by Vitess.

CANCELLED means that the context was cancelled (and noticed in the app layer, as opposed to the RPC layer).

DEADLINE_EXCEEDED is returned when an action is taking longer than a given timeout.

INTEGRITY_ERROR is returned on integrity error from MySQL, usually due to duplicate primary keys.

INTERNAL_ERRORs are problems that only the server can fix, not the client.

NOT_IN_TX means that we're not currently in a transaction, but we should be.

PERMISSION_DENIED errors are returned when a user requests access to something that they don't have permissions for.

QUERY_NOT_SERVED means that a query could not be served right now.

RESOURCE_EXHAUSTED is returned when a query exceeds its quota in some dimension and can't be completed due to that.

SUCCESS is returned from a successful call.

TRANSIENT_ERROR is used for when there is some error that we expect we can recover from automatically - often due to a resource limit temporarily being reached.

UNAUTHENTICATED errors are returned when a user requests access to something, and we're unable to verify the user's authentication.

UNKNOWN_ERROR includes: 1.

CallerID is passed along RPCs to identify the originating client for a request.

RPCError is an application-level error structure returned by VtTablet (and passed along by VtGate if appropriate).

ErrorCode is the enum values for Errors.