Does anyone have any comments/suggestions for me regarding this? Thanks
I am trying to understand some strange behavior of cassandra row cache. We > have a 6-node Cassandra cluster in a single data center on 2 racks, and the > neighboring nodes on the ring are from alternative racks. Each node has > 1GB row cache, with key cache disabled. The cluster uses > PropertyFileSnitch, and the ColumnFamily I fetch from uses > NetworkTopologyStrategy, with replication factor of 2. My client code uses > Hector to fetch a fixed set of rows from cassandra > > What I don't quite understand is even after I ran the client code several > times, there are always some nodes with 0 row cache hits, despite that the > row cache from all nodes are filled and all nodes receive requests. > > Which nodes have 0 hits seem to be strongly related to the following: > > - the set of row keys to fetch > - the order of the set of row keys to fetch > - the list of hosts passed to Hector's CassandraHostConfigurator > - the order of the list of hosts passed to Hector > > Can someone shed some lights on how exactly the row cache works and > hopefully also explain the behavior I have been seeing? I thought if the > fixed set of the rows keys are the only thing I am fetching (each row > should be on the order of 10's of MBs, no more than 100MB), and each node > gets requests, and its row cache is filled, there's gotta be some hits. > Apparent this is not the case. Thanks. > > cluster information: > > Address DC Rack Status State Load > Effective-Ownership Token > > 141784319550391026443072753096570088105 > x.x.x.1 DC1 r1 Up Normal 587.46 GB > 33.33% 0 > x.x.x.2 DC1 r2 Up Normal 591.21 GB > 33.33% 28356863910078205288614550619314017621 > x.x.x.3 DC1 r1 Up Normal 594.97 GB > 33.33% 56713727820156410577229101238628035242 > x.x.x.4 DC1 r2 Up Normal 587.15 GB > 33.33% 85070591730234615865843651857942052863 > x.x.x.5 DC1 r1 Up Normal 590.26 GB > 33.33% 113427455640312821154458202477256070484 > x.x.x.6 DC1 r2 Up Normal 583.21 GB > 33.33% 141784319550391026443072753096570088105 > > > [user@node]$ ./checkinfo.sh > *************** x.x.x.4 > Token : 85070591730234615865843651857942052863 > Gossip active : true > Thrift active : true > Load : 587.15 GB > Generation No : 1354074048 > Uptime (seconds) : 36957 > Heap Memory (MB) : 2027.29 / 3948.00 > Data Center : DC1 > Rack : r2 > Exceptions : 0 > > Key Cache : size 0 (bytes), capacity 0 (bytes), 0 hits, 0 requests, > NaN recent hit rate, 14400 save period in seconds > Row Cache : size 1072651974 (bytes), capacity 1073741824 (bytes), 0 > hits, 2576 requests, NaN recent hit rate, 0 save period in seconds > > *************** x.x.x.6 > Token : 141784319550391026443072753096570088105 > Gossip active : true > Thrift active : true > Load : 583.21 GB > Generation No : 1354074461 > Uptime (seconds) : 36535 > Heap Memory (MB) : 828.71 / 3948.00 > Data Center : DC1 > Rack : r2 > Exceptions : 0 > > Key Cache : size 0 (bytes), capacity 0 (bytes), 0 hits, 0 requests, > NaN recent hit rate, 14400 save period in seconds > Row Cache : size 1072602906 (bytes), capacity 1073741824 (bytes), 0 > hits, 3194 requests, NaN recent hit rate, 0 save period in seconds >
