java - GAE 数据存储 : Entity deleted only after multiple calls to delete()

Question

我正在使用 Eclipse 在本地计算机上处​​理 GAE 数据存储。我创建了两个 servlet - AddMovie 和 DeleteMovie:

添加电影

Entity movie = new Entity("movie",System.currentTimeMillis());
movie.setProperty("name",     "Hakeshset Beanan");
movie.setProperty("director", "Godard");
datastore.put(movie);

删除电影

Query q = new Query("movie");
PreparedQuery pq = datastore.prepare(q);
List<Entity> movies = Lists.newArrayList(pq.asIterable());
response.put("numMoviesFound", String.valueOf(movies.size()));

for (Entity movie : movies) {
    Key key = movie.getKey();
    datastore.delete(key);
}

有趣的是，DeleteMovie servlet 并没有删除所有电影。连续调用返回 {"numMoviesFound":"15"}，然后返回 {"numMoviesFound":"9"}、{"numMoviesFound":"3"} 最后是 {"numMoviesFound":"3"}。

为什么不立即从数据存储中删除所有电影？

更新:问题似乎只发生在本地 Eclipse 上，而不是 GAE 服务器上。

Answer 1

我认为您应该在一次事务中删除所有电影，这样可以确保更好的一致性。

说到一致性，你的问题就在这里:

Google App Engine's High Replication Datastore (HRD) provides high availability for your reads and writes by storing data synchronously in multiple data centers. However, the delay from the time a write is committed until it becomes visible in all data centers means that queries across multiple entity groups (non-ancestor queries) can only guarantee eventually consistent results. Consequently, the results of such queries may sometimes fail to reflect recent changes to the underlying data.

https://developers.google.com/appengine/docs/java/datastore/structuring_for_strong_consistency