我有一个Cassandra的5节点集群，每个节点上有大约650 GB的数据，复制因子为3.我最近开始在/var/log/cassandra/system.log中看到以下错误。 p>
INFO [ReadStage-5] 2017-10-17 17：06：07,887 NoSpamLogger.java:91 - 达到的最大内存使用量（1.000GiB），不能分配1.000MiB的块
我试图增加file_cache_size_in_mb，但是很快就会遇到同样的错误。我试图为这个参数高达2GB，但无济于事。
当错误发生时，CPU利用率飙升，读取延迟非常不稳定。我看到这个潮流每半小时出现一次。请注意下面列表中的时间。
INFO [ReadStage-5] 2017-10-17 17:06:07,887 NoSpamLogger.java:91 - 达到的最大内存使用量（1.000GiB），不能分配1.000MiB的块 INFO [ReadStage-36] 2017-10-17 17：36：09,807 NoSpamLogger.java:91 - 达到的最大内存使用量（1.000GiB），不能分配1.000MiB的块 INFO [ReadStage-15] 2017-10-17 18：05：56,003 NoSpamLogger.java:91 - 达到的最大内存使用量（2.000GiB），不能分配1.000MiB的块 INFO [ReadStage-28] 2017-10-17 18:36:01,177 NoSpamLogger.java:91 - 达到的最大内存使用量（2.000GiB），不能分配1.000MiB的块
我所拥有的两个表按小时分区，分区很大。防爆。以下是nodetool表统计信息的输出
Read Count: 4693453
Read Latency: 0.36752741680805157 ms.
Write Count: 561026
Write Latency: 0.03742310516803143 ms.
Pending Flushes: 0
Table: raw_data
SSTable count: 55
Space used (live): 594395754275
Space used (total): 594395754275
Space used by snapshots (total): 0
Off heap memory used (total): 360753372
SSTable Compression Ratio: 0.20022598072758296
Number of keys (estimate): 45163
Memtable cell count: 90441
Memtable data size: 685647925
Memtable off heap memory used: 0
Memtable switch count: 1
Local read count: 0
Local read latency: NaN ms
Local write count: 126710
Local write latency: 0.096 ms
Pending flushes: 0
Percent repaired: 52.99
Bloom filter false positives: 167775
Bloom filter false ratio: 0.16152
Bloom filter space used: 264448
Bloom filter off heap memory used: 264008
Index summary off heap memory used: 31060
Compression metadata off heap memory used: 360458304
Compacted partition minimum bytes: 51
**Compacted partition maximum bytes: 3449259151**
Compacted partition mean bytes: 16642499
Average live cells per slice (last five minutes): 1.0005435888450147
Maximum live cells per slice (last five minutes): 42
Average tombstones per slice (last five minutes): 1.0
Maximum tombstones per slice (last five minutes): 1
Dropped Mutations: 0
Read Count: 4712814
Read Latency: 0.3356051004771247 ms.
Write Count: 643718
Write Latency: 0.04168356951335834 ms.
Pending Flushes: 0
Table: customer_profile_history
SSTable count: 20
Space used (live): 9423364484
Space used (total): 9423364484
Space used by snapshots (total): 0
Off heap memory used (total): 6560008
SSTable Compression Ratio: 0.1744084338623116
Number of keys (estimate): 69
Memtable cell count: 35242
Memtable data size: 789595302
Memtable off heap memory used: 0
Memtable switch count: 1
Local read count: 2307
Local read latency: NaN ms
Local write count: 51772
Local write latency: 0.076 ms
Pending flushes: 0
Percent repaired: 0.0
Bloom filter false positives: 0
Bloom filter false ratio: 0.00000
Bloom filter space used: 384
Bloom filter off heap memory used: 224
Index summary off heap memory used: 400
Compression metadata off heap memory used: 6559384
Compacted partition minimum bytes: 20502
**Compacted partition maximum bytes: 4139110981**
Compacted partition mean bytes: 708736810
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
这里是：
cdsdb/raw_data histograms
Percentile SSTables Write Latency Read Latency Partition Size Cell Count
(micros) (micros) (bytes)
50% 0.00 61.21 0.00 1955666 642
75% 1.00 73.46 0.00 17436917 4768
95% 3.00 105.78 0.00 107964792 24601
98% 8.00 219.34 0.00 186563160 42510
99% 12.00 315.85 0.00 268650950 61214
Min 0.00 6.87 0.00 51 0
Max 14.00 1358.10 0.00 3449259151 7007506
cdsdb/customer_profile_history histograms
Percentile SSTables Write Latency Read Latency Partition Size Cell Count
(micros) (micros) (bytes)
50% 0.00 73.46 0.00 223875792 61214
75% 0.00 88.15 0.00 668489532 182785
95% 0.00 152.32 0.00 1996099046 654949
98% 0.00 785.94 0.00 3449259151 1358102
99% 0.00 943.13 0.00 3449259151 1358102
Min 0.00 24.60 0.00 5723 4
Max 0.00 5839.59 0.00 5960319812 1955666
你能否提出一个解决这个问题的方法？
答案 0 :(得分：6)
根据发布的cfhistograms输出，分区是巨大的。
95％的raw_data表分区大小为107MB，最大值为10 3.44GB。 customer_profile_history的95％百分比有分区 大小1.99GB，最大5.96GB。
这显然与你每半小时注意到的问题有关，因为这些巨大的分区被写入sstable。数据模型必须更改并基于更高的分区大小，以使分区间隔为“分钟”而不是“小时”。因此2GB分区将减少到33MB分区。
建议的分区大小是使其最大接近100MB。虽然理论上我们可以存储超过100MB，但性能会受到影响。请记住，该分区的每次读取都通过线路超过100MB的数据。在您的情况下，它超过2GB，因此所有性能影响也随之而来。