Cassandra nodetool cfstats-读取计数始终为0 [英] Cassandra nodetool cfstats - Read Count is always 0

问题描述

我在监视Cassandra节点时遇到问题.我跑了

I've got a problem with monitoring my Cassandra node. I ran

nodetool cfstats keyspaceName.tableName

不幸的是，读取计数始终为0，读取延迟为NaN.我正在执行读写操作，但只有写入指标会被更新.

Unfortunately Read Count is always 0 and Read Latency is NaN. I am doing reads and writes but only writes metrics are updated.

这是我得到的输出:

Starting NodeTool
Keyspace: realtimetrader
    Read Count: 0
    Read Latency: NaN ms.
    Write Count: 402
    Write Latency: 0.09648756218905473 ms.
    Pending Flushes: 0
            Table: currencies
            SSTable count: 1
            Space used (live): 5254
            Space used (total): 5254
            Space used by snapshots (total): 0
            Off heap memory used (total): 40
            SSTable Compression Ratio: 0.0
            Number of keys (estimate): 14
            Memtable cell count: 1608
            Memtable data size: 567
            Memtable off heap memory used: 0
            Memtable switch count: 0
            Local read count: 0
            Local read latency: NaN ms
            Local write count: 402
            Local write latency: 0.106 ms
            Pending flushes: 0
            Bloom filter false positives: 0
            Bloom filter false ratio: 0,00000
            Bloom filter space used: 24
            Bloom filter off heap memory used: 16
            Index summary off heap memory used: 16
            Compression metadata off heap memory used: 8
            Compacted partition minimum bytes: 125
            Compacted partition maximum bytes: 149
            Compacted partition mean bytes: 149
            Average live cells per slice (last five minutes): 0.0
            Maximum live cells per slice (last five minutes): 0
            Average tombstones per slice (last five minutes): 0.0
            Maximum tombstones per slice (last five minutes): 0

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感谢您的帮助.

推荐答案

由于每个节点负责不同的数据集，因此您一直在读取的所有数据可能属于其他节点.许多驱动程序都具有令牌感知的负载平衡策略，该策略会将读取结果发送到应该拥有该读取结果的节点.有了CL.ONE默认一致性，这也意味着它将捷径将读取发送到其他节点(除非遇到读取修复机会).

Since each node is responsible for a different set of data, its possible that all the data you have been reading is belongs to other nodes. Many drivers have a token aware load balancing policy that will send the read to a node that should own it. With a CL.ONE default consistency this also means it will short cut sending the read to other nodes (except in the case of hitting the read repair chance).

根据您使用的版本以及您进行的查询而定，也可能不会看到此增量:

Depending on version you are using and what query you make you may not see this increment as well: https://issues.apache.org/jira/browse/CASSANDRA-7338

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