The first issue I can think of is the Latency table, if I understand you correctly, has an unbounded size for the partition key of DC and will over time just get larger as more measurements are recorded.
Regards, Ryan Svihla > On Aug 8, 2016, at 2:58 AM, Stone Fang <cnstonef...@gmail.com> wrote: > > objective:get cassandra cross-datacenter latency in time > > existing ticket: > > there is a ticket [track cross-datacenter > latency](https://issues.apache.org/jira/browse/CASSANDRA-11569) > but it is a statistics value from node starting,i want to get the > instantaneous value in a certain time. > > thought > > want to write a message into **MESSAGE TABLE** in 1s timer task(the period is > similar to most of cross datacenter latency ) > ,and replicate to other datacenter,there will be a delay.and I capture it,and > write to **LATENCY TABLE**.i can query the latency value from this table with > the condition of certain time. > > schema > > message table for replicating data cross datacenter > > > create keyspace heartbeat with replication= > {'class':'NetworkTopologyStrategy','dc1':1, 'dc2':1...}; > > > > CREATE TABLE HEARTBEAT.MESSAGE{ > CREATED TIMESTAMP, > FROMDC VARCHAR, > PRIMARY KEY(CREATED,FROMDC) > } > > latency Table for querying latency value > > CREATE TABLE SYSTEM.LATENCY{ > FROMDC VARCHAR, > ARRIVED TIMESTAMP, > CREATED TIMESTAMP, > LANTENCY BIGINT > PRIMARY KEY(FROMDC,ARRIVED) > }WITH CLUSTERING ORDER BY(ARRIVED DESC); > > problems > > 1.can this solution work to get the cross-datacenter latency? > > > 2.create heartbeat keyspace in cassandra bootstrap process,i need to load > Heartbeat keyspace in Scheam.java.and save this keyspace into SystemSchema. > also need to check if this keyspace has exist after first node start.so i > think this is not a good solution. > > 3.compared to 1,try another solution.generate heartbeat message in a > standalone jar.but always i need to capture heartbeat message mutation in > cassandra.so i need to check if the mutation is about heartbeat message.and > it seems strange that check the heartbeat keyspace which is not defined in > cassandra,but third-party. > > hope to see your thought on this. > thanks > stone >
