code: func (builder *RequestBuilder) SetFromSessionVars(sv *variable.SessionVars) *RequestBuilder {
  	builder.Request.Concurrency = sv.DistSQLScanConcurrency
  	builder.Request.IsolationLevel = builder.getIsolationLevel()
  	builder.Request.NotFillCache = sv.StmtCtx.NotFillCache
  	builder.Request.Priority = builder.getKVPriority(sv)
  	return builder
  }
docs: // SetFromSessionVars sets the following fields for "kv.Request" from session variables:
  // "Concurrency", "IsolationLevel", "NotFillCache".