cassandra - 如何计算出 Cassandra 表中键的大概数量？

Question

我在运行 nodetool cfstats 时看到了对 'Number of key(estimate) 的引用，但至少在我的系统中(Cassandra 版本 3.11.3)，我没看到:

           Table: XXXXXX
            SSTable count: 4
            Space used (live): 2393755943
            Space used (total): 2393755943
            Space used by snapshots (total): 0
            Off heap memory used (total): 2529880
            SSTable Compression Ratio: 0.11501749368144083
            Number of partitions (estimate): 1146
            Memtable cell count: 296777
            Memtable data size: 147223380
            Memtable off heap memory used: 0
            Memtable switch count: 127
            Local read count: 9
            Local read latency: NaN ms
            Local write count: 44951572
            Local write latency: 0.043 ms
            Pending flushes: 0
            Percent repaired: 0.0
            Bloom filter false positives: 0
            Bloom filter false ratio: 0.00000
            Bloom filter space used: 2144
            Bloom filter off heap memory used: 2112
            Index summary off heap memory used: 240
            Compression metadata off heap memory used: 2527528
            Compacted partition minimum bytes: 447
            Compacted partition maximum bytes: 43388628
            Compacted partition mean bytes: 13547448
            Average live cells per slice (last five minutes): NaN
            Maximum live cells per slice (last five minutes): 0
            Average tombstones per slice (last five minutes): NaN
            Maximum tombstones per slice (last five minutes): 0
            Dropped Mutations: 0

有没有办法用这个版本的 Cassandra 来近似 select count(*) from XXXXXX？

Answer 1

“键数”与“分区数”相同——同样是一个估计值。如果您的分区键是主键(无聚簇列)，那么您将估计该节点上的行数。否则，它只是分区键值数量的估计。

-吉姆