小编nuk*_*kie的帖子

番石榴供应商级包含MemoizingSupplier:

static class MemoizingSupplier<T> implements Supplier<T>, Serializable {
    final Supplier<T> delegate;
    transient volatile boolean initialized;
    // "value" does not need to be volatile; visibility piggy-backs
    // on volatile read of "initialized".
    transient T value;

    MemoizingSupplier(Supplier<T> delegate) {
      this.delegate = delegate;
    }

    @Override public T get() {
      // A 2-field variant of Double Checked Locking.
      if (!initialized) {
        synchronized (this) {
          if (!initialized) {
            T t = delegate.get();
            value = t;
            initialized = true;
            return t;
          }
        }
      }
      return value; …

如何获得CQL查询的执行计划(或类似的smth)？我找不到任何关于CQL查询优化/执行的整合文档.

例如,我想知道,执行查询有什么不同,例如:

select some_column from SOME_TABLE where 
pkField='val1' 
and timestampField='date' 
allow filtering;

和

select some_column from SOME_TABLE where 
pkField='val1' 
and timestampField<='date' 
and timestampField>='date' 
allow filtering;

问题就在这里。我有mongos连接到远程的本地实例mongod。远程数据库使用基本密码身份验证。我正在尝试使用简单的 Scala 应用程序为特定集合设置 ChangeStream 观察器。实际的代码如下所示：

  private val mongo = new MongoClient(
    new ServerAddress("localhost", 27017),
    MongoCredential.createCredential("username", "myDB", "password".toCharArray),
    MongoClientOptions.builder().addServerListener(ServerStateListener).build()
  )
  private val collection = mongo
    .getDatabase(DB)
    .getCollection("someObjectsCollection")

  private val ch = collection
    .watch()
    .fullDocument(FullDocument.UPDATE_LOOKUP)
    .iterator()

它断线.fullDocument(FullDocument.UPDATE_LOOKUP)告诉：

Exception in thread "main" com.mongodb.MongoCommandException: Command failed with error 13: 'not authorized on myDB to execute command { aggregate: "someObjectsCollection", pipeline: [ { $changeStream: { fullDocument: "updateLookup" } } ], cursor: {}, $db: "myDB", $clusterTime: { clusterTime: Timestamp(1524064297, 2), …