vitessio/vitess · error

len(p.Patch)%3

Error message

len(p.Patch)%3

What it means

Layout_uca900.allocPage validates that each Patch's Patch slice length is a multiple of 3 (primary, secondary, tertiary weights per collation element). A non-multiple-of-3 patch means the patch data is malformed. This is a startup/initialization-time panic protecting the generated collation tables.

Source

Thrown at go/mysql/collations/internal/uca/layout.go:137

		return nil
	}

	ceCount := int((*page)[offset])
	for ce := range ceCount {
		result = append(result,
			(*page)[256+(ce*3+0)*256+offset],
			(*page)[256+(ce*3+1)*256+offset],
			(*page)[256+(ce*3+2)*256+offset],
		)
	}
	return
}

func (Layout_uca900) allocPage(original *[]uint16, patches []Patch) []uint16 {
	var maxWeights int
	for _, p := range patches {
		if len(p.Patch)%3 != 0 {
			panic("len(p.Patch)%3")
		}
		if len(p.Patch) > maxWeights {
			maxWeights = len(p.Patch)
		}
	}

	minLenForPage := maxWeights*CodepointsPerPage + CodepointsPerPage
	if original == nil {
		return make([]uint16, minLenForPage)
	}
	if len(*original) > minLenForPage {
		minLenForPage = len(*original)
	}
	newPage := make([]uint16, minLenForPage)
	copy(newPage, *original)
	return newPage
}

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Fix the patch data so each entry has exactly 3 uint16s per collation element (primary, secondary, tertiary)
2. Regenerate collation tables via the codegen pipeline instead of editing generated files
3. Restore the original generated colldata files from a clean checkout

for _, p := range patches {
	if len(p.Patch)%3 != 0 {
		return fmt.Errorf("patch %q has invalid weight length %d", p.Prefix, len(p.Patch))
	}
}

When it happens

Trigger: Building or regenerating UCA 900 collation pages with patch data whose []uint16 length is not divisible by 3 — i.e. a malformed entry in the collation patch tables (colldata generated files).

Common situations: Editing go/mysql/collations generated data by hand; custom collation development where patch definitions were typed incorrectly.

Related errors

• WeightStringLen called with non-MOD4 length
• unreachable
• bad literal argument
• '%n' directive requires a slice
• slow path for `n` directive for slice of type other than Exp

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/1384211c527963c2. Report an issue: GitHub.