What causes "GetSchema(%s): %w" in vitessio/vitess?

Retry the VTEXplain request; transient tablet errors often resolve once the tablet re-registers as healthy.

GetSchema(%s): %w

Error message

GetSchema(%s): %w

What it means

During VTEXplain, VTAdmin concurrently fetches the keyspace schema from the chosen tablet via cluster.GetSchema. If that call fails, the error is recorded into the request's ErrorRecorder, annotated with the tablet alias, and the goroutine returns; the overall vtexplain will subsequently fail or produce a partial result. It indicates the schema could not be read from that tablet.

Source

Thrown at go/vt/vtadmin/api.go:2733

		// Writes to these three variables are, in the strictest sense, unsafe.
		// However, there is one goroutine responsible for writing each of these
		// values (so, no concurrent writes), and reads are blocked on the call to
		// wg.Wait(), so we guarantee that all writes have finished before attempting
		// to read anything.
		srvVSchema string
		schema     string
		shardMap   string
	)

	wg.Add(3)

	// GetSchema
	go func(c *cluster.Cluster) {
		defer wg.Done()

		res, err := c.GetSchema(ctx, req.Keyspace, cluster.GetSchemaOptions{})
		if err != nil {
			er.RecordError(fmt.Errorf("GetSchema(%s): %w", topoproto.TabletAliasString(tablet.Tablet.Alias), err))
			return
		}

		schemas := make([]string, len(res.TableDefinitions))
		for i, td := range res.TableDefinitions {
			schemas[i] = td.Schema
		}

		schema = strings.Join(schemas, ";")
	}(c)

	// GetSrvVSchema
	go func(c *cluster.Cluster) {
		defer wg.Done()

		span, ctx := trace.NewSpan(ctx, "Cluster.GetSrvVSchema")
		defer span.Finish()

View on GitHub (pinned to 01a25a7d17)

Solutions

Retry the VTEXplain request; transient tablet errors often resolve once the tablet re-registers as healthy.
Check the health of the tablet named in the error (`vtctldclient GetTablet <alias>`) and restart/replace it if unhealthy.
Verify network connectivity and RPC timeouts between vtadmin, vtctld, and vttablet.
Check vttablet logs for the underlying GetSchema failure (mysqld errors, permission issues).
If persistent, ensure the keyspace has multiple serving replicas so a healthy one can serve the schema.

Example fix

// before
res, err := c.GetSchema(ctx, req.Keyspace, cluster.GetSchemaOptions{})
if err != nil { er.RecordError(...); return }
// after (mitigation at caller level: retry)
var res *vtadminpb.Schema
for i := 0; i < 3; i++ {
    res, err = c.GetSchema(ctx, req.Keyspace, cluster.GetSchemaOptions{})
    if err == nil { break }
    time.Sleep(time.Second)
}

Defensive patterns

Strategy: retry

Validate before calling

// Check tablet health first
_, err := apiClient.GetTablet(ctx, alias)
if err != nil { return fmt.Errorf("tablet %s unhealthy before vtexplain: %w", alias, err) }

Try / catch

errGroup, ctx := errgroup.WithContext(ctx)
errGroup.Go(func() error {
    res, err := c.GetSchema(ctx, req.Keyspace, cluster.GetSchemaOptions{})
    if err != nil {
        if isTransient(err) { return retryWithBackoff(...) }
        return fmt.Errorf("GetSchema(%s): %w", alias, err)
    }
    return nil
})
if err := errGroup.Wait(); err != nil { return err }

Prevention

Keep at least two serving replicas per keyspace so schema fetch has redundancy.
Set generous but bounded RPC timeouts for vtadmin->tablet calls.
Monitor vttablet health so failing tablets are detected before vtexplain runs.

When it happens

Trigger: The GetSchema goroutine's c.GetSchema(ctx, keyspace, opts) returns an error — underlying vtctld/tablet RPC failure, tablet died mid-request, timeout, or the tablet rejected the schema query.

Common situations: Tablet becomes unhealthy between selection and schema fetch; network partition between vtadmin and vttablet/vtctld; RPC deadline exceeded under load; mysqld issue preventing SHOW CREATE TABLE.

Related errors

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/835c60716e8da4d6. Report an issue: GitHub.