watchKeyspace initial load not complete

[AmoebaProtozoa]

Bug Report

What did you do?

1. Write a script that continuously create keyspaces

#!/bin/bash

# Set the number of keyspaces you want to create
n=800

for ((i=1; i<=n; i++))
do
    curl -X POST http://localhost:2379/pd/api/v2/keyspaces \
         -H 'Content-Type: application/json' \
         -d '{"name":"test-'$i'", "config": {}}'
done

3. Use pdClient.WatchKeyspace

func main() {
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	pdCli, err := pd.NewClient([]string{PDAddress}, pd.SecurityOption{})
	if err != nil {
		log.Fatal("failed to create pd client", zap.Error(err))
	}

	keyspacesChan, err := pdCli.WatchKeyspaces(ctx)
	if err != nil {
		log.Fatal("failed to watch keyspace", zap.Error(err))
	}

	packIndex := 0
	totalKeyspaceCount := 0
	for {
		select {
		case <-ctx.Done():
			return
		case keyspaces := <-keyspacesChan:
			log.Info("keyspaces received",
				zap.Int("pack-index", packIndex),
				zap.Int("keyspace-count", len(keyspaces)),
				zap.Int("total-keyspace-count", totalKeyspaceCount),
			)
			for _, keyspace := range keyspaces {
				log.Info("keyspace meta",
					zap.Uint32("keyspace-id", keyspace.GetId()),
					zap.String("keyspace-name", keyspace.GetName()),
					zap.String("keyspace-state", keyspace.GetState().String()),
				)
			}
			packIndex++
			totalKeyspaceCount += len(keyspaces)
		}
	}
}

What did you expect to see?

1. The first load from channel should contain all current keyspaces.
2. each subsequent load from channel should contain subsequent update to keyspaces.

What did you see instead?

1. The first load from channel only contains the first 400 keyspaces.
2. subsequent load start from the current keyspace (600+), causing keyspace meta in the middle to be lost

What version of PD are you using (pd-server -V)?

nightly (7.2.0)