Cassandra中列族的行计数 [英] Row count of a column family in Cassandra

问题描述

有没有办法得到Cassandra中单列族的行计数（键计数）？ get_count只能用于获取列数。

例如，如果我有一个包含用户的列族，并且想要获得用户数。我该怎么办呢？

解决方案

如果你正在处理一个大数据集，并且可以很好的近似，我强烈建议使用命令：

  nodetool --host< hostname> cfstats 
  

这将为每个列族转储一个列表，如下所示：

列族：widgets
SSTable计数：11
已用空间：4295810363
已用空间：4295810363
键数（估计）：9709824
Memtable列数：99008
Memtable数据大小：150297312
Memtable开关计数：434
读数：9716802
读取延迟：0.036 ms。
写计数：9716806
写延迟：0.024 ms。
待处理的任务：0
Bloom Filter False Postives：10428
Bloom Filter False比率：1.00000
Bloom过滤器空间使用：18216448
压缩行最小大小：771
压缩行最大大小：263210
压缩行平均大小：1634


的键（估计）行是一个很好的猜测跨群集，性能是比显式计数方法快很多。

Is there a way to get a row count (key count) of a single column family in Cassandra? get_count can only be used to get the column count.

For instance, if I have a column family containing users and wanted to get the number of users. How could I do it? Each user is it's own row.

解决方案

If you are working on a large data set and are okay with a pretty good approximation, I highly recommend using the command:

nodetool --host <hostname> cfstats

This will dump out a list for each column family looking like this:

Column Family: widgets
SSTable count: 11
Space used (live): 4295810363
Space used (total): 4295810363
Number of Keys (estimate): 9709824
Memtable Columns Count: 99008
Memtable Data Size: 150297312
Memtable Switch Count: 434
Read Count: 9716802
Read Latency: 0.036 ms.
Write Count: 9716806
Write Latency: 0.024 ms.
Pending Tasks: 0
Bloom Filter False Postives: 10428
Bloom Filter False Ratio: 1.00000
Bloom Filter Space Used: 18216448
Compacted row minimum size: 771
Compacted row maximum size: 263210
Compacted row mean size: 1634

The "Number of Keys (estimate)" row is a good guess across the cluster and the performance is a lot faster than explicit count approaches.

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