vitessio/vitess · error

fillStringTemplate failed: %v

Error message

fillStringTemplate failed: %v

What it means

applySQLShard fills the {{.DatabaseName}} placeholder in the generated SQL template (e.g. CREATE TABLE {{.DatabaseName}}.`...`) using fillStringTemplate before applying it to the destination primary. This error means the template substitution failed - almost always malformed Go template syntax in the schema-change SQL, not an environment issue.

Source

Thrown at go/vt/wrangler/schema.go:293

	if resp != nil {
		for _, e := range resp.Events {
			logutil.LogEvent(wr.Logger(), e)
		}
	}
	return err
}

// applySQLShard applies a given SQL change on a given tablet alias. It allows executing arbitrary
// SQL statements, but doesn't return any results, so it's only useful for SQL statements
// that would be run for their effects (e.g., CREATE).
// It works by applying the SQL statement on the shard's primary tablet with replication turned on.
// Thus it should be used only for changes that can be applied on a live instance without causing issues;
// it shouldn't be used for anything that will require a pivot.
// The SQL statement string is expected to have {{.DatabaseName}} in place of the actual db name.
func (wr *Wrangler) applySQLShard(ctx context.Context, tabletInfo *topo.TabletInfo, change string) error {
	filledChange, err := fillStringTemplate(change, map[string]string{"DatabaseName": tabletInfo.DbName()})
	if err != nil {
		return fmt.Errorf("fillStringTemplate failed: %v", err)
	}
	ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
	defer cancel()
	// Need to make sure that replication is enabled since we're only applying the statement on primaries
	_, err = wr.tmc.ApplySchema(ctx, tabletInfo.Tablet, &tmutils.SchemaChange{
		SQL:              filledChange,
		Force:            false,
		AllowReplication: true,
		SQLMode:          vreplication.SQLMode,
	})
	return err
}

// fillStringTemplate returns the string template filled
func fillStringTemplate(tmpl string, vars any) (string, error) {
	myTemplate := template.Must(template.New("").Parse(tmpl))
	var data strings.Builder
	if err := myTemplate.Execute(&data, vars); err != nil {

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Inspect the createSQL being applied for malformed {{ }} sequences.
2. Escape or rename identifiers that contain template delimiters.
3. Check the fillStringTemplate error text for the exact parse failure position.

if strings.Count(change, "{{") != strings.Count(change, "}}") {
    return fmt.Errorf("malformed template in schema SQL: %s", change)
}

err := wr.CopySchemaShard(ctx, src, dst, tables, excl, false)
if err != nil && strings.Contains(err.Error(), "fillStringTemplate failed") {
    // inspect generated SQL for bad {{ }} sequences
}

When it happens

Trigger: The CREATE SQL string produced by tmutils.SchemaDefinitionToSQLStrings contains invalid template syntax (unbalanced {{ }} or bad directives), making text/template parsing fail inside fillStringTemplate.

Common situations: Table or column names containing template-like characters interfering with the {{.DatabaseName}} substitution; edge cases in schema-to-SQL generation for unusual identifiers.

Related errors

• failed to generate vtgate consul datacenter from template: %
• failed to parse vtgate FQDN template %s: %w
• failed to parse vtgate host address template %s: %w
• failed to generate vtctld consul datacenter from template: %
• failed to parse vtctld FQDN template %s: %w

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/7d58ee118d04f7aa. Report an issue: GitHub.