Redis-py读LOWEST_LATENCY或最近

Question

Redis-py版本：4.2.0

如何使redis-py能够从LOWEST_LATENCY节点读取？我们正在使用AWS全局数据存储，所以我们想让redis-py从地理分布的最近节点读取最近的节点吗？

Answer 1

我觉得你做不到。

根据这篇亚马逊文章的说法，Python最初是在这个项目中实现的集成集群支持，因此用户不需要第三方库来支持集群。但是，在写入时，不支持最低延迟模式。支持的模式有PRIMARIES、REPLICAS、ALL_NODES和RANDOM。请注意，其中一些内容在Java库中进行了介绍，如REPLICAS，我认为这是生菜中的ANY_REPLICA。

LOWEST_LATENCY模式是在Java中实现的，它似乎不是AWS支持或提供的参数，据我所见，它不存在于Python中。

/**
 * Setting to read from the node with the lowest latency during topology discovery. Note that latency measurements are
 * momentary snapshots that can change in rapid succession. Requires dynamic refresh sources to obtain topologies and
 * latencies from all nodes in the cluster.
 * @since 6.1.7
 */
public static final ReadFrom LOWEST_LATENCY = new ReadFromImpl.ReadFromLowestCommandLatency();

这显然被称为最近，这可能意味着它最初是与地球空间的接近(但这只是一个猜测)：

/**
 * Setting to read from the node with the lowest latency during topology discovery. Note that latency measurements are
 * momentary snapshots that can change in rapid succession. Requires dynamic refresh sources to obtain topologies and
 * latencies from all nodes in the cluster.
 * @deprecated since 6.1.7 as we're renaming this setting to {@link #LOWEST_LATENCY} for more clarity what this setting
 *             actually represents.
 */
@Deprecated
public static final ReadFrom NEAREST = LOWEST_LATENCY;

看看ReadFromLowestCommandLatency()，这是一个定义。注释有关于延迟模型的重要信息：

/**
 * Read from the node with the lowest latency during topology discovery. Note that latency measurements are momentary
 * snapshots that can change in rapid succession. Requires dynamic refresh sources to obtain topologies and latencies from
 * all nodes in the cluster.
 */
static final class ReadFromLowestCommandLatency

所有这些Readxxx方法都以某种方式使用getNodes()，它返回按延迟排序的节点。但是这种排序发生在库中。库似乎实现了延迟排序，这在Python实现中没有实现。

// Returns the list of nodes that are applicable for the read operation. The list is ordered by latency.
List<RedisNodeDescription> getNodes();

我没有执行完整的代码分析，但例如，TopologyComparators.java中的这个方法似乎证实了这一点：

/**
 * Sort partitions by latency.
 * @param clusterNodes
 * @return List containing {@link RedisClusterNode}s ordered by latency
 */
public static List<RedisClusterNode> sortByLatency(Iterable<RedisClusterNode> clusterNodes) {
    List<RedisClusterNode> ordered = LettuceLists.newList(clusterNodes);
    ordered.sort(LatencyComparator.INSTANCE);
    return ordered;
}

对不起，如果你已经知道一些这一点，但当我看了一下，我想我会把它作为一个答复。