vitessio/vitess · error

--buffer-window must be <= --buffer-max-failover-duration: %

Error message

--buffer-window must be <= --buffer-max-failover-duration: %v vs. %v

What it means

verifyFlags enforces that the buffering window (--buffer-window) is not larger than the maximum failover duration (--buffer-max-failover-duration). Buffering stops after the max failover duration, so a window exceeding it is contradictory configuration and vtgate rejects it at startup.

Source

Thrown at go/vt/vtgate/buffer/flags.go:70

	utils.SetFlagIntVar(fs, &bufferSize, "buffer-size", 1000, "Maximum number of buffered requests in flight (across all ongoing failovers).")
	utils.SetFlagDurationVar(fs, &bufferMaxFailoverDuration, "buffer-max-failover-duration", 20*time.Second, "Stop buffering completely if a failover takes longer than this duration.")
	utils.SetFlagDurationVar(fs, &bufferMinTimeBetweenFailovers, "buffer-min-time-between-failovers", 1*time.Minute, "Minimum time between the end of a failover and the start of the next one (tracked per shard). Faster consecutive failovers will not trigger buffering.")

	utils.SetFlagIntVar(fs, &bufferDrainConcurrency, "buffer-drain-concurrency", 1, "Maximum number of requests retried simultaneously. More concurrency will increase the load on the PRIMARY vttablet when draining the buffer.")
	utils.SetFlagStringVar(fs, &bufferKeyspaceShards, "buffer-keyspace-shards", "", "If not empty, limit buffering to these entries (comma separated). Entry format: keyspace or keyspace/shard. Requires --enable_buffer=true.")
}

func init() {
	servenv.OnParseFor("vtgate", registerFlags)
	servenv.OnParseFor("vtcombo", registerFlags)
}

func verifyFlags() error {
	if bufferWindow < 1*time.Second {
		return fmt.Errorf("--buffer-window must be >= 1s (specified value: %v)", bufferWindow)
	}
	if bufferWindow > bufferMaxFailoverDuration {
		return fmt.Errorf("--buffer-window must be <= --buffer-max-failover-duration: %v vs. %v", bufferWindow, bufferMaxFailoverDuration)
	}
	if bufferSize < 1 {
		return fmt.Errorf("--buffer-size must be >= 1 (specified value: %d)", bufferSize)
	}
	if bufferMinTimeBetweenFailovers < 1*time.Second {
		return fmt.Errorf("--buffer-min-time-between-failovers must be >= 1s (specified value: %v)", bufferMinTimeBetweenFailovers)
	}

	if bufferDrainConcurrency < 1 {
		return fmt.Errorf("--buffer-drain-concurrency must be >= 1 (specified value: %d)", bufferDrainConcurrency)
	}

	if bufferKeyspaceShards != "" && !bufferEnabled {
		return fmt.Errorf("--buffer-keyspace-shards=%v also requires that --enable_buffer is set", bufferKeyspaceShards)
	}
	if bufferEnabled && bufferEnabledDryRun && bufferKeyspaceShards == "" {
		return errors.New("both the dry-run mode and actual buffering is enabled. To avoid ambiguity, keyspaces and shards for actual buffering must be explicitly listed in --buffer-keyspace-shards")
	}

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Lower --buffer-window so it is <= --buffer-max-failover-duration
2. Or raise --buffer-max-failover-duration (note it also caps how long buffering runs)
3. Also check that --buffer-max-failover-duration >= 1s, since it must satisfy its own validation

Example fix

// before
vtgate --buffer-window=60s --buffer-max-failover-duration=30s
// after
vtgate --buffer-window=30s --buffer-max-failover-duration=60s

if bufferWindow > bufferMaxFailoverDuration {
    return fmt.Errorf("--buffer-window (%v) must be <= --buffer-max-failover-duration (%v)", bufferWindow, bufferMaxFailoverDuration)
}

When it happens

Trigger: Starting vtgate with --buffer-window greater than --buffer-max-failover-duration, e.g. --buffer-window=60s --buffer-max-failover-duration=30s.

Common situations: Increasing --buffer-window after an incident without revisiting --buffer-max-failover-duration; copying flag sets from different environments; typo swapping the two values.

Understand the failure class

Background: "unknown output mode", "invalid value for flag", "expects true/false": fixing invalid flag value errors in CLI tools — this error's family across 24 libraries.

Related errors

• --buffer-window must be >= 1s (specified value: %v)
• --buffer-size must be >= 1 (specified value: %d)
• --buffer-min-time-between-failovers must be >= 1s (specified
• --buffer-drain-concurrency must be >= 1 (specified value: %d
• --buffer-keyspace-shards=%v also requires that --enable_buff

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/37e1392de20b1e60. Report an issue: GitHub.