Can't set page size for PagedList - Android jetpack

I have just added paged library into my project. This is my implementation.

PagedList.Config pagedListConfig = new PagedList.Config.Builder().setEnablePlaceholders(false).setPageSize(10).build();
        videos = new LivePagedListBuilder<>(
                videosDAO.getPagedVideos(tontonHomePageItem.getId()), pagedListConfig)
                .setBoundaryCallback(boundaryCallBack).build();

    private class VideosBoundaryCallBack extends PagedList.BoundaryCallback<Video> {

    public VideosBoundaryCallBack() {
    }

    @Override
    public void onItemAtEndLoaded(@NonNull Video itemAtEnd) {
        KLog.d(TAG, "onItemAtEndLoaded + next page token = " + mNextPageToken);
        if (loadVideoState != Defines.LOADING_STATE.BUFFERING) {
            KLog.d(TAG, "onItemAtEndLoaded LOAD");
            loadVideoState = Defines.LOADING_STATE.BUFFERING;
            //load more data from web service
        }
    }

}

@DAO

@Query("SELECT * from video_table WHERE channelId=:channelId ORDER BY year DESC")
DataSource.Factory<Integer, Video> getPagedVideos(String channelId);

@Entity

public class Video{
    @NonNull
    @PrimaryKey()
    @ColumnInfo(name = "id")
    public String id;
...

I added these log into activity

model.data.observe(this,(list)->{
        Log.d(Defines.TAG,"list page size =  " + list.size());
    });

There are 13 records in database. After checking above log I got

" list page size = 13"

all 13 items of the list are not null.

I have two questions:

1. Why I set page size = 10 but I got the paged list size = 13.
2. When list view appear then I scroll down to bottom of listview onItemAtEndLoaded didn't trigger.

Finally, I found the solution for this problem. To solve this, I have to custom
VideoDataSource extends ItemKeyedDataSource<Long, Video>

VideoDataSourceFactory extends DataSource.Factory<Long, Video>

VideoDataSourceFactory videoDataSourceFactory = new VideoDataSourceFactory(this, pageSize);
            videos = new LivePagedListBuilder<>(
                    videoDataSourceFactory,
                    pagedListConfig).build();

I hope someone have the same problem can solve this problem quickly.