I notice a severe degradation in Cassandra write performance with continuous writes over time.
I am inserting time series data with time stamp (T) as the column name in a wide column that stores 24 hours worth of data in a single row. Streaming data is written from data generator (4 instances, each with 256 threads) inserting data into multiple rows in parallel. Additionally, data is also inserted into a column family that has indexes over DateType and UUIDType.
CF1:
Col1 | Col2 | Col3(DateType) | Col(UUIDType4) |
RowKey1
RowKey2
:
:
CF2 (Wide column family):
RowKey1 (T1, V1) (T2, V3) (T4, V4) ......
RowKey2 (T1, V1) (T3, V3) .....
:
:
The no. of data points inserted/sec decreases over time until no further inserts are possible. The initial performance is of the order of 60000 ops/sec for ~6-8 hours and then it gradually tapers down to 0 ops/sec. Restarting the DataStax_Cassandra_Community_Server on all nodes helps restore the original throughput, but the behaviour is observed again after a few hours.
OS: Windows Server 2008 No.of nodes: 5 Cassandra version: DataStax Community 1.2.3 RAM: 8GB HeapSize: 3GB Garbage collector: default settings [ParNewGC]
I also notice a phenomenal increase in the no. of Pending write requests as reported by the OpsCenter (~of magnitude 200,000) when the performance begins to degrade.
I fail to understand what is preventing the write operations to be completed and why do they pile up over time? I do not see anything suspicious in the Cassandra logs.
Has the OS settings got anything to do with this? Any suggestions to probe this issue further?
Bringing your write timeout in line with the new default in 2.0 (of 2s instead of 10s) will help with your write backlog by allowing load shedding to kick in faster: https://issues.apache.org/jira/browse/CASSANDRA-6059