Question

我正在.Net C＃中实现推荐引擎，我正在使用Cassandra来存储数据。我仍然是使用C *的新手，刚刚开始使用它2个月前。目前，我的群集中只有2个节点（单个DC），部署在Azure DS2 VM中（每个都有7Gb RAM，2个核心）。我为读取和写入设置了RF=2, CL=1。我在yaml配置文件中设置了超时时间

read_request_timeout_in_ms: 60000
write_request_timeout_in_ms: 120000
counter_write_request_timeout_in_ms: 120000
request_timeout_in_ms: 120000

我在客户端设置了较低的读取查询超时（每个30秒）。存储在cassandra中的数据是用户历史记录，项目计数器和推荐项目数据。我为我的推荐引擎创建了一个API（代表equinix DC），它的工作非常简单，每次用户打开网站页面时，只读取C *中recommended_items表中的所有recommended_items Id。这意味着每个用户的查询都非常简单：

select * from recommended_items where username = <username>

当我为多达500个用户/线程加载测试时，它很好并且非常快。但是当在线站点调用API从C *表中读取时，我经常得到读取超时。但是，同时通常只有不到20个用户。我使用DataDog监视cassandra节点活动，我发现只有节点＃2不断超时（种子节点是节点＃1，虽然我理解的是种子并不重要，除非在引导步骤中）。但是，每次超时发生时，我都尝试在两个节点中使用cqlsh进行查询，而节点＃1是返回的

OperationTimeOut Exception。

我一直试图找到这个问题的主要根源。这与协调器节点关闭（I read this article）有什么关系吗？或者是因为我只有2个节点？

当超时发生时（网页没有显示任何内容），然后我尝试刷新调用API的页面，它将在很长时间内加载，然后再显示任何内容（因为超时）。但令人惊讶的是，即使网页已关闭，我也会在几分钟后得到所有这些请求实际成功的日志。即使页面已关闭，它就像读取请求仍在运行。

例外就像这些（它们没有一起发生）：

None of the hosts tried for query are available (tried: 13.73.193.140:9042,13.75.154.140:9042)

OR

Cassandra timeout during read query at consistency LocalOne (0 replica(s) responded over 1 required)

有没有人对我的问题有任何建议？谢谢。

cfstats .recommended_items

的输出

NODE＃1

 Read Count: 683
    Read Latency: 2.970781844802343 ms.
    Write Count: 0
    Write Latency: NaN ms.
    Pending Flushes: 0
            Table: recommendedvideos
            Space used (live): 96034775
            Space used (total): 96034775
            Space used by snapshots (total): 40345163
            Off heap memory used (total): 192269
            SSTable Compression Ratio: 0.4405242717559795
            Number of keys (estimate): 101493
            Memtable cell count: 0
            Memtable data size: 0
            Memtable off heap memory used: 0
            Memtable switch count: 0
            Local read count: 376
            Local read latency: 1.647 ms
            Local write count: 0
            Local write latency: NaN ms
            Pending flushes: 0
            Bloom filter false positives: 0
            Bloom filter false ratio: 0.00000
            Bloom filter space used: 126928
            Bloom filter off heap memory used: 126896
            Index summary off heap memory used: 40085
            Compression metadata off heap memory used: 25288
            Compacted partition minimum bytes: 43
            Compacted partition maximum bytes: 454826
            Compacted partition mean bytes: 2201
            Average live cells per slice (last five minutes): 160.28657799274487
            Maximum live cells per slice (last five minutes): 2759
            Average tombstones per slice (last five minutes): 1.0
            Maximum tombstones per slice (last five minutes): 1
            Dropped Mutations: 0

NODE＃2

Read Count: 733
    Read Latency: 3.0032783083219647 ms.
    Write Count: 0
    Write Latency: NaN ms.
    Pending Flushes: 0
            Table: recommendedvideos
            Space used (live): 99145806
            Space used (total): 99145806
            Space used by snapshots (total): 15101127
            Off heap memory used (total): 196008
            SSTable Compression Ratio: 0.44063804831658704
            Number of keys (estimate): 103863
            Memtable cell count: 0
            Memtable data size: 0
            Memtable off heap memory used: 0
            Memtable switch count: 0
            Local read count: 453
            Local read latency: 1.344 ms
            Local write count: 0
            Local write latency: NaN ms
            Pending flushes: 0
            Bloom filter false positives: 0
            Bloom filter false ratio: 0.00000
            Bloom filter space used: 129056
            Bloom filter off heap memory used: 129040
            Index summary off heap memory used: 40856
            Compression metadata off heap memory used: 26112
            Compacted partition minimum bytes: 43
            Compacted partition maximum bytes: 454826
            Compacted partition mean bytes: 2264
            Average live cells per slice (last five minutes): 170.7715877437326
            Maximum live cells per slice (last five minutes): 2759
            Average tombstones per slice (last five minutes): 1.0
            Maximum tombstones per slice (last five minutes): 1
            Dropped Mutations: 0

带有2个节点的Cassandra集群获得了Read TimeOut / NoHostAvailable Exception

0 个答案: