Redis-py 读取 LOWEST_LATENCY 或 NEAREST

Question

Redis-py版本： 4.2.0

我们如何让redis-py从LOWEST_LATENCY节点读取数据？我们正在使用 AWS 全球数据存储，因此我们希望启用 redis-py 以从地理分布的最近节点的最近节点读取？

Answer 1

我认为你不能。

Python 库，根据 this Amazon article, integrated cluster support originally implemented in this project，因此用户不需要第 3 方库来支持集群。但是，在撰写本文时，不支持最低延迟模式。支持的模式有 PRIMARIES、REPLICAS、ALL_NODES 和 RANDOM。请注意，其中一些包含在 Java 库中，例如 REPLICAS，我认为它是 Lettuce 中的 ANY_REPLICA。

LOWEST_LATENCY 模式在 Java 库中实现，它似乎不是 AWS 支持或提供的参数，据我所知，它不存在于 Python 库中.

/**
 * 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 NEAREST，这可能意味着它最初以某种方式与地理空间接近度相关联（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;

查看 ReadFromLowestCommandLatency()，这是定义。评论包含有关延迟测量的重要信息：

/**
 * 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()，其中 returns 个节点按延迟排序。但这种排序发生在图书馆。该库似乎实现了延迟排序，这在 Python 实现中没有完成。

// 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，但是例如 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;
}

抱歉，如果您已经了解了其中的一些内容，但当我看了一下时，我想我会 post 它作为答案。

Redis-py 读取 LOWEST_LATENCY 或 NEAREST

Redis-py Read LOWEST_LATENCY or NEAREST

python

redis

py-redis