etcdctl: add --max-txn-ops flag to make-mirror command

--max-txn-ops flag allows users to define the maximum number of operations permitted in
a transaction during syncing updates.if unlimited syncing may fail when number of txn ops
exceeds the maximum number of server side.

Signed-off-by: xakdwch <xakdwch5@gmail.com>

CHANGELOG/CHANGELOG-3.6.md

@@ -29,6 +29,7 @@ See [code changes](https://github.com/etcd-io/etcd/compare/v3.5.0...v3.6.0).
 - When print endpoint status, [show db size in use](https://github.com/etcd-io/etcd/pull/13639)
 - [Always print the raft_term in decimal](https://github.com/etcd-io/etcd/pull/13711) when displaying member list in json.
 - [Add one more field `storageVersion`](https://github.com/etcd-io/etcd/pull/13773) into the response of command `etcdctl endpoint status`.
+- Add [`--max-txn-ops`](https://github.com/etcd-io/etcd/pull/14340) flag to make-mirror command.
 
 ### etcdutl v3
 

etcdctl/README.md

@@ -1466,6 +1466,8 @@ RPC: UserRevokeRole
 
 - dest-insecure-transport -- Disable transport security for client connections
 
+- max-txn-ops -- Maximum number of operations permitted in a transaction during syncing updates
+
 #### Output
 
 The approximate total number of keys transferred to the destination cluster, updated every 30 seconds.

etcdctl/ctlv3/command/make_mirror_command.go

@@ -33,6 +33,10 @@ import (
 	"github.com/spf13/cobra"
 )
 
+const (
+	defaultMaxTxnOps = uint(128)
+)
+
 var (
 	mminsecureTr   bool
 	mmcert         string
@@ -44,6 +48,7 @@ var (
 	mmpassword     string
 	mmnodestprefix bool
 	mmrev          int64
+	mmmaxTxnOps    uint
 )
 
 // NewMakeMirrorCommand returns the cobra command for "makeMirror".
@@ -56,6 +61,7 @@ func NewMakeMirrorCommand() *cobra.Command {
 
 	c.Flags().StringVar(&mmprefix, "prefix", "", "Key-value prefix to mirror")
 	c.Flags().Int64Var(&mmrev, "rev", 0, "Specify the kv revision to start to mirror")
+	c.Flags().UintVar(&mmmaxTxnOps, "max-txn-ops", defaultMaxTxnOps, "Maximum number of operations permitted in a transaction during syncing updates.")
 	c.Flags().StringVar(&mmdestprefix, "dest-prefix", "", "destination prefix to mirror a prefix to a different prefix in the destination cluster")
 	c.Flags().BoolVar(&mmnodestprefix, "no-dest-prefix", false, "mirror key-values to the root of the destination cluster")
 	c.Flags().StringVar(&mmcert, "dest-cert", "", "Identify secure client using this TLS certificate file for the destination cluster")
@@ -197,6 +203,15 @@ func makeMirror(ctx context.Context, c *clientv3.Client, dc *clientv3.Client) er
 				ops = []clientv3.Op{}
 			}
 			lastRev = nextRev
+
+			if len(ops) == int(mmmaxTxnOps) {
+				_, err := dc.Txn(ctx).Then(ops...).Commit()
+				if err != nil {
+					return err
+				}
+				ops = []clientv3.Op{}
+			}
+
 			switch ev.Type {
 			case mvccpb.PUT:
 				ops = append(ops, clientv3.OpPut(modifyPrefix(string(ev.Kv.Key)), string(ev.Kv.Value)))