VDiff: add --no-samples option to vdiff show

changelog/25.0/25.0.0/summary.md

@@ -19,6 +19,7 @@
 - **[Minor Changes](#minor-changes)**
     - **[VReplication](#minor-changes-vreplication)**
         - [Default data protection for `_reverse` workflow cancel/complete](#vreplication-reverse-workflow-data-protection)
+        - [`vdiff show --only-summary` omits the per-table row-sample report](#vreplication-vdiff-only-summary)
     - **[VTGate](#minor-changes-vtgate)**
         - [Ingress bytes in query LogStats](#vtgate-logstats-ingress-bytes)
         - [New controls for cross-keyspace reads](#vtgate-cross-keyspace-reads)
@@ -170,6 +171,18 @@ The `--keep-data` flag help text has been updated to note this default explicitl
 
 See [#19906](https://github.com/vitessio/vitess/pull/19906) for details.
 
+#### <a id="vreplication-vdiff-only-summary"/>`vdiff show --only-summary` omits the per-table row-sample report</a>
+
+`vtctldclient vdiff ... show` now accepts an `--only-summary` flag. When set, the per-table diff report has its sampled-row arrays (`MismatchedRowsSample`, `ExtraRowsSourceSample`, `ExtraRowsTargetSample`) stripped on the tablet before the response is built, while the scalar counters (processed, matching, mismatched, and extra rows) and all other summary fields are preserved.
+
+The sampled-row arrays carry actual row data, including large `BLOB`/`JSON` columns, and `vdiff show` aggregates them across every target shard. For diffs over tables with large rows this could push the aggregated response past gRPC message limits and make `vdiff show` fail outright, leaving no way to read the summary or mismatch state. `--only-summary` lets callers that only need progress and the mismatch state avoid transferring the samples while keeping the reported counts accurate.
+
+The option is exposed as `only_summary` on the `VDiffShowRequest` (vtctld) and `VDiffReportOptions` (tablet) protobuf messages. It is opt-in and backward compatible: without the flag, the full report is returned as before.
+
+`vdiff create --wait` also uses `only_summary` for its internal progress polls, so the wait loop no longer transfers the sampled-row arrays on every interval and cannot be killed by the gRPC message limit on large diffs. The text output is unchanged; with `--format json`, the per-interval progress output no longer includes the sampled rows (the full samples remain available via `vdiff show --verbose` once the diff completes).
+
+See [#20870](https://github.com/vitessio/vitess/pull/20870) for details.
+
 ### <a id="minor-changes-vtgate"/>VTGate</a>
 
 #### <a id="vtgate-logstats-ingress-bytes"/>Ingress bytes in query LogStats</a>

go/cmd/vtctldclient/command/vreplication/vdiff/vdiff.go

@@ -82,8 +82,9 @@ var (
 	}{}
 
 	showOptions = struct {
-		Arg     string
-		Verbose bool
+		Arg         string
+		Verbose     bool
+		OnlySummary bool
 	}{}
 
 	stopOptions = struct {
@@ -318,10 +319,17 @@ func commandCreate(cmd *cobra.Command, args []string) error {
 			case <-ctx.Done():
 				return vterrors.Errorf(vtrpcpb.Code_CANCELED, "context has expired")
 			case <-tkr.C:
+				// This is a progress poll that only renders a single non-verbose
+				// summary (state, counts, has_mismatch), so request only_summary:
+				// the per-row sample arrays are never shown here and fetching them
+				// on every interval can push the aggregated response past the gRPC
+				// message limit for large diffs, killing the wait. The authoritative
+				// samples remain available via `vdiff show --verbose`.
 				resp, err := vtctldClient.VDiffShow(ctx, &vtctldatapb.VDiffShowRequest{
 					Workflow:       common.BaseOptions.Workflow,
 					TargetKeyspace: common.BaseOptions.TargetKeyspace,
 					Arg:            uuidStr,
+					OnlySummary:    true,
 				})
 				if err != nil {
 					return err
@@ -645,6 +653,7 @@ func commandShow(cmd *cobra.Command, args []string) error {
 		Workflow:       common.BaseOptions.Workflow,
 		TargetKeyspace: common.BaseOptions.TargetKeyspace,
 		Arg:            showOptions.Arg,
+		OnlySummary:    showOptions.OnlySummary,
 	})
 	if err != nil {
 		return err
@@ -709,6 +718,7 @@ func registerCommands(root *cobra.Command) {
 	base.AddCommand(resume)
 
 	show.Flags().BoolVar(&showOptions.Verbose, "verbose", false, "Show verbose output in summaries")
+	show.Flags().BoolVar(&showOptions.OnlySummary, "only-summary", false, "Omit the per-table diff report body and return only the vdiff and per-table summary state. Useful for large diffs where the report can exceed gRPC message limits.")
 	base.AddCommand(show)
 
 	stop.Flags().StringSliceVar(&stopOptions.TargetShards, "target-shards", nil, "The target shards to stop the vdiff on; default is all shards.")

go/vt/vtctl/workflow/vdiff.go

@@ -566,6 +566,11 @@ func (s *Server) VDiffShow(ctx context.Context, req *vtctldatapb.VDiffShowReques
 		Workflow:  req.Workflow,
 		Action:    string(vdiff.ShowAction),
 		ActionArg: req.Arg,
+		Options: &tabletmanagerdatapb.VDiffOptions{
+			ReportOptions: &tabletmanagerdatapb.VDiffReportOptions{
+				OnlySummary: req.GetOnlySummary(),
+			},
+		},
 	}
 
 	ts, err := s.buildTrafficSwitcher(ctx, req.TargetKeyspace, req.Workflow)