What causes "invalid cache_size: %w" in benbjohnson/litestream?

Provide a plain integer in bytes, e.g. cache_size=67108864

invalid cache_size: %w

Error message

invalid cache_size: %w

What it means

Validation in the VFS URI config Set method: the cache_size parameter is not a valid integer. Fires when parsing a vfs:// URI whose cache_size query value cannot be parsed by strconv.Atoi (e.g. 'cache_size=big').

Source

Thrown at vfs_config.go:88

		}
		cfg.SyncInterval = &d
	case "buffer_path":
		cfg.BufferPath = value
	case "hydration_enabled":
		b := strings.ToLower(value) == "true" || value == "1"
		cfg.HydrationEnabled = &b
	case "hydration_path":
		cfg.HydrationPath = value
	case "poll_interval":
		d, err := time.ParseDuration(value)
		if err != nil {
			return fmt.Errorf("invalid poll_interval: %w", err)
		}
		cfg.PollInterval = &d
	case "cache_size":
		n, err := strconv.Atoi(value)
		if err != nil {
			return fmt.Errorf("invalid cache_size: %w", err)
		}
		cfg.CacheSize = &n
	default:
		return fmt.Errorf("unknown config key: %s", key)
	}
	return nil
}

func ParseVFSURIConfig(uriParameters map[string]string) (*VFSConfig, error) {
	if len(uriParameters) == 0 {
		return nil, nil
	}

	cfg := &VFSConfig{}
	var found bool
	for _, key := range vfsURIConfigKeys {
		value, ok := uriParameters[key]
		if !ok {

View on GitHub (pinned to 4ed7a308f6)

Solutions

Provide a plain integer in bytes, e.g. cache_size=67108864
Strip units/separators from the configured value and convert to bytes yourself
Validate numeric params before building the VFS URI

Example fix

// before
litestream://file:///db?cache_size=64MB
// after
litestream://file:///db?cache_size=67108864

Defensive patterns

Strategy: validation

Validate before calling

n, err := strconv.Atoi(v)
if err != nil { return fmt.Errorf("cache_size must be a plain integer (bytes): %w", err) }
_ = n

Try / catch

if err := cfg.Set("cache_size", v); err != nil {
    if strings.Contains(err.Error(), "invalid cache_size") {
        // convert human sizes (e.g. 64MB) to bytes before retry
    }
}

Prevention

Express cache sizes as raw byte integers in URI parameters
Convert human-readable sizes to bytes in your own config layer
Trim whitespace from templated config values

When it happens

Trigger: Calling Set("cache_size", <value>) — directly or via ParseVFSURIConfig — where strconv.Atoi fails, e.g. "64MB", "1_000", "" or "0x100".

Common situations: Writing cache_size=64MB in a URI (units not accepted); thousands separators; whitespace; templated config leaving the parameter blank.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of benbjohnson/litestream@4ed7a308f6 (2026-09-06). Data as JSON: /api/errors/d71d6a2ec827fc87. Report an issue: GitHub.