*: add flag to let etcd use the new boltdb freelistType feature

embed/config.go

@@ -37,6 +37,7 @@ import (
 	"go.etcd.io/etcd/pkg/types"
 
 	"github.com/ghodss/yaml"
+	bolt "go.etcd.io/bbolt"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 	"golang.org/x/crypto/bcrypt"
@@ -75,6 +76,8 @@ const (
 	// maxElectionMs specifies the maximum value of election timeout.
 	// More details are listed in ../Documentation/tuning.md#time-parameters.
 	maxElectionMs = 50000
+	// backend freelist map type
+	freelistMapType = "map"
 )
 
 var (
@@ -273,6 +276,8 @@ type Config struct {
 	ExperimentalInitialCorruptCheck bool          `json:"experimental-initial-corrupt-check"`
 	ExperimentalCorruptCheckTime    time.Duration `json:"experimental-corrupt-check-time"`
 	ExperimentalEnableV2V3          string        `json:"experimental-enable-v2v3"`
+	// ExperimentalBackendFreelistType specifies the type of freelist that boltdb backend uses (array and map are supported types).
+	ExperimentalBackendFreelistType string `json:"experimental-backend-bbolt-freelist-type"`
 
 	// ForceNewCluster starts a new cluster even if previously started; unsafe.
 	ForceNewCluster bool `json:"force-new-cluster"`
@@ -896,3 +901,11 @@ func (cfg *Config) getMetricsURLs() (ss []string) {
 	}
 	return ss
 }
+
+func parseBackendFreelistType(freelistType string) bolt.FreelistType {
+	if freelistType == freelistMapType {
+		return bolt.FreelistMapType
+	}
+
+	return bolt.FreelistArrayType
+}

embed/etcd.go

@@ -159,6 +159,8 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 		return e, err
 	}
 
+	backendFreelistType := parseBackendFreelistType(cfg.ExperimentalBackendFreelistType)
+
 	srvcfg := etcdserver.ServerConfig{
 		Name:                       cfg.Name,
 		ClientURLs:                 cfg.ACUrls,
@@ -182,6 +184,7 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 		AutoCompactionMode:         cfg.AutoCompactionMode,
 		QuotaBackendBytes:          cfg.QuotaBackendBytes,
 		BackendBatchLimit:          cfg.BackendBatchLimit,
+		BackendFreelistType:        backendFreelistType,
 		BackendBatchInterval:       cfg.BackendBatchInterval,
 		MaxTxnOps:                  cfg.MaxTxnOps,
 		MaxRequestBytes:            cfg.MaxRequestBytes,