// TableStats is an endpoint that returns columns, indices, and other
// relevant details for the specified table.
func (s *adminServer) TableStats(
	ctx context.Context, req *serverpb.TableStatsRequest,
) (*serverpb.TableStatsResponse, error) {
	// Get table span.
	var tableSpan roachpb.Span
	iexecutor := sql.InternalExecutor{LeaseManager: s.server.leaseMgr}
	if err := s.server.db.Txn(ctx, func(txn *client.Txn) error {
		var err error
		tableSpan, err = iexecutor.GetTableSpan(s.getUser(req), txn, req.Database, req.Table)
		return err
	}); err != nil {
		return nil, s.serverError(err)
	}

	startKey, err := keys.Addr(tableSpan.Key)
	if err != nil {
		return nil, s.serverError(err)
	}
	endKey, err := keys.Addr(tableSpan.EndKey)
	if err != nil {
		return nil, s.serverError(err)
	}

	// Get current range descriptors for table. This is done by scanning over
	// meta2 keys for the range.
	rangeDescKVs, err := s.server.db.Scan(ctx, keys.RangeMetaKey(startKey), keys.RangeMetaKey(endKey), 0)
	if err != nil {
		return nil, s.serverError(err)
	}

	// Extract a list of node IDs from the response.
	nodeIDs := make(map[roachpb.NodeID]struct{})
	for _, kv := range rangeDescKVs {
		var rng roachpb.RangeDescriptor
		if err := kv.Value.GetProto(&rng); err != nil {
			return nil, s.serverError(err)
		}
		for _, repl := range rng.Replicas {
			nodeIDs[repl.NodeID] = struct{}{}
		}
	}

	// Construct TableStatsResponse by sending an RPC to every node involved.
	tableStatResponse := serverpb.TableStatsResponse{
		NodeCount:  int64(len(nodeIDs)),
		RangeCount: int64(len(rangeDescKVs)),
	}
	type nodeResponse struct {
		nodeID roachpb.NodeID
		resp   *serverpb.SpanStatsResponse
		err    error
	}

	// Send a SpanStats query to each node. Set a timeout on the context for
	// these queries.
	responses := make(chan nodeResponse)
	nodeCtx, cancel := context.WithTimeout(ctx, base.NetworkTimeout)
	defer cancel()
	for nodeID := range nodeIDs {
		nodeID := nodeID
		if err := s.server.stopper.RunAsyncTask(nodeCtx, func(ctx context.Context) {
			var spanResponse *serverpb.SpanStatsResponse
			client, err := s.server.status.dialNode(nodeID)
			if err == nil {
				req := serverpb.SpanStatsRequest{
					StartKey: startKey,
					EndKey:   endKey,
					NodeID:   nodeID.String(),
				}
				spanResponse, err = client.SpanStats(ctx, &req)
			}

			response := nodeResponse{
				nodeID: nodeID,
				resp:   spanResponse,
				err:    err,
			}
			select {
			case responses <- response:
				// Response processed.
			case <-ctx.Done():
				// Context completed, response no longer needed.
			}
		}); err != nil {
			return nil, err
		}
	}
	for remainingResponses := len(nodeIDs); remainingResponses > 0; remainingResponses-- {
		select {
		case resp := <-responses:
			// For nodes which returned an error, note that the node's data
			// is missing. For successful calls, aggregate statistics.
			if resp.err != nil {
				tableStatResponse.MissingNodes = append(
					tableStatResponse.MissingNodes,
					serverpb.TableStatsResponse_MissingNode{
						NodeID:       resp.nodeID.String(),
						ErrorMessage: resp.err.Error(),
//.........这里部分代码省略.........