max_replication_lag_module_config.go

package throttler

import (
	"fmt"
	"time"

	"github.com/youtube/vitess/go/vt/proto/throttlerdata"
)

// MaxReplicationLagModuleConfig stores all configuration parameters for
// MaxReplicationLagModule. Internally, the parameters are represented by a
// protobuf message. This message is also used to update the parameters.
type MaxReplicationLagModuleConfig struct {
	throttlerdata.Configuration
}

// Most of the values are based on the assumption that vttablet is started
// with the flag --health_check_interval=20s.
const healthCheckInterval = 20

var defaultMaxReplicationLagModuleConfig = MaxReplicationLagModuleConfig{
	throttlerdata.Configuration{
		TargetReplicationLagSec: 2,
		MaxReplicationLagSec:    ReplicationLagModuleDisabled,

		InitialRate: 100,
		// 1 means 100% i.e. double rates by default.
		MaxIncrease:       1,
		EmergencyDecrease: 0.5,

		// Wait for two health broadcast rounds. Otherwise, the "decrease" mode
		// has less than 2 lag records available to calculate the actual slave rate.
		MinDurationBetweenIncreasesSec: 2 * healthCheckInterval,
		// MaxDurationBetweenIncreasesSec defaults to 60+2 seconds because this
		// corresponds to three 3 broadcasts.
		// The 2 extra seconds give us headroom to account for delay in the process.
		MaxDurationBetweenIncreasesSec: 3*healthCheckInterval + 2,
		MinDurationBetweenDecreasesSec: healthCheckInterval,
		SpreadBacklogAcrossSec:         healthCheckInterval,

		AgeBadRateAfterSec: 3 * 60,
		BadRateIncrease:    0.10,
	},
}

// NewMaxReplicationLagModuleConfig returns a default configuration where
// only "maxReplicationLag" is set.
func NewMaxReplicationLagModuleConfig(maxReplicationLag int64) MaxReplicationLagModuleConfig {
	config := defaultMaxReplicationLagModuleConfig
	config.MaxReplicationLagSec = maxReplicationLag
	return config
}

// TODO(mberlin): Add method which updates the config using a (partially) filled
// in protobuf.

// Verify returns an error if the config is invalid.
func (c MaxReplicationLagModuleConfig) Verify() error {
	if c.TargetReplicationLagSec < 1 {
		return fmt.Errorf("target_replication_lag_sec must be >= 1")
	}
	if c.MaxReplicationLagSec < 2 {
		return fmt.Errorf("max_replication_lag_sec must be >= 2")
	}
	if c.TargetReplicationLagSec > c.MaxReplicationLagSec {
		return fmt.Errorf("target_replication_lag_sec must not be higher than max_replication_lag_sec: invalid: %v > %v",
			c.TargetReplicationLagSec, c.MaxReplicationLagSec)
	}
	if c.InitialRate < 1 {
		return fmt.Errorf("initial_rate must be >= 1")
	}
	if c.MaxIncrease <= 0 {
		return fmt.Errorf("max_increase must be > 0")
	}
	if c.EmergencyDecrease <= 0 {
		return fmt.Errorf("emergency_decrease must be > 0")
	}
	if c.MinDurationBetweenIncreasesSec < 1 {
		return fmt.Errorf("min_duration_between_increases_sec must be >= 1")
	}
	if c.MaxDurationBetweenIncreasesSec < 1 {
		return fmt.Errorf("max_duration_between_increases_sec must be >= 1")
	}
	if c.MinDurationBetweenDecreasesSec < 1 {
		return fmt.Errorf("min_duration_between_decreases_sec must be >= 1")
	}
	if c.SpreadBacklogAcrossSec < 1 {
		return fmt.Errorf("spread_backlog_across_sec must be >= 1")
	}
	if c.IgnoreNSlowestReplicas < 0 {
		return fmt.Errorf("ignore_n_slowest_replicas must be >= 0")
	}
	if c.IgnoreNSlowestRdonlys < 0 {
		return fmt.Errorf("ignore_n_slowest_rdonlys must be >= 0")
	}
	if c.AgeBadRateAfterSec < 1 {
		return fmt.Errorf("age_bad_rate_after_sec must be >= 1")
	}
	return nil
}

// MinDurationBetweenIncreases is a helper function which returns the respective
// protobuf field as native Go type.
func (c MaxReplicationLagModuleConfig) MinDurationBetweenIncreases() time.Duration {
	return time.Duration(c.MinDurationBetweenIncreasesSec) * time.Second
}

// MaxDurationBetweenIncreases is a helper function which returns the respective
// protobuf field as native Go type.
func (c MaxReplicationLagModuleConfig) MaxDurationBetweenIncreases() time.Duration {
	return time.Duration(c.MaxDurationBetweenIncreasesSec) * time.Second
}

// MinDurationBetweenDecreases is a helper function which returns the respective
// protobuf field as native Go type.
func (c MaxReplicationLagModuleConfig) MinDurationBetweenDecreases() time.Duration {
	return time.Duration(c.MinDurationBetweenDecreasesSec) * time.Second
}

// SpreadBacklogAcross is a helper function which returns the respective
// protobuf field as native Go type.
func (c MaxReplicationLagModuleConfig) SpreadBacklogAcross() time.Duration {
	return time.Duration(c.SpreadBacklogAcrossSec) * time.Second
}

// AgeBadRateAfter is a helper function which returns the respective
// protobuf field as native Go type.
func (c MaxReplicationLagModuleConfig) AgeBadRateAfter() time.Duration {
	return time.Duration(c.AgeBadRateAfterSec) * time.Second
}