Question

我正在寻找PostgreSQL中的SELECT pg_sleep(t)或t-SQL中的waitfor。 Cassandra cql中是否存在？

Answer 1

没有任何内置函数。使用UDF以及白名单和黑名单很难做到这一点：

列入白名单的模式

"com/datastax/driver/core/",
"com/google/common/reflect/TypeToken",
"java/io/IOException.class",
"java/io/Serializable.class",
"java/lang/",
"java/math/",
"java/net/InetAddress.class",
"java/net/Inet4Address.class",
"java/net/Inet6Address.class",
"java/net/UnknownHostException.class", // req'd by InetAddress
"java/net/NetworkInterface.class", // req'd by InetAddress
"java/net/SocketException.class", // req'd by InetAddress
"java/nio/Buffer.class",
"java/nio/ByteBuffer.class",
"java/text/",
"java/time/",
"java/util/",
"org/apache/cassandra/cql3/functions/JavaUDF.class",
"org/apache/cassandra/cql3/functions/UDFContext.class",
"org/apache/cassandra/exceptions/",
"org/apache/cassandra/transport/ProtocolVersion.class"

列入黑名单的模式

"com/datastax/driver/core/Cluster.class",
"com/datastax/driver/core/Metrics.class",
"com/datastax/driver/core/NettyOptions.class",
"com/datastax/driver/core/Session.class",
"com/datastax/driver/core/Statement.class",
"com/datastax/driver/core/TimestampGenerator.class", // indirectly covers ServerSideTimestampGenerator + ThreadLocalMonotonicTimestampGenerator
"java/lang/Compiler.class",
"java/lang/InheritableThreadLocal.class",
"java/lang/Package.class",
"java/lang/Process.class",
"java/lang/ProcessBuilder.class",
"java/lang/ProcessEnvironment.class",
"java/lang/ProcessImpl.class",
"java/lang/Runnable.class",
"java/lang/Runtime.class",
"java/lang/Shutdown.class",
"java/lang/Thread.class",
"java/lang/ThreadGroup.class",
"java/lang/ThreadLocal.class",
"java/lang/instrument/",
"java/lang/invoke/",
"java/lang/management/",
"java/lang/ref/",
"java/lang/reflect/",
"java/util/ServiceLoader.class",
"java/util/Timer.class",
"java/util/concurrent/",
"java/util/function/",
"java/util/jar/",
"java/util/logging/",
"java/util/prefs/",
"java/util/spi/",
"java/util/stream/",
"java/util/zip/"

如果您真的需要它，并且愿意做一些可怕的事情，例如：

CREATE OR REPLACE FUNCTION sleep (time int)
  CALLED ON NULL INPUT RETURNS int LANGUAGE java AS 
  '
  long start = System.currentTimeMillis();
  while (System.currentTimeMillis() < start + time);
  return time;
  ';

，但由于紧密循环，这是一个非常可怕的想法。可以采取一些措施来引入暂停循环，但是从我的粗略观察来看，黑名单的限制非常严格。

Cassandra是否有sleep cql查询？

1 个答案: