coherence Q&A

What is coherence used for in a typical project? What kind of financial data is cached?
[BTan] position data, booking, product data, (less important) market data

[BTan] Coherence could in theory be a market data subscriber.

Why those data need to be cached?
[BTan] replication, cluster failover

Do we know the cached data's structure already before caching them? [BTan] (yes) ( for instance, are they predefined JAVA beans ), is POFSerilizer used ([BTan] no) or are they implementing Portableobject ([BTan] yes) and registered with pof-config.xml ([BTan] yes)? Why one is chosen over the other?
[BTan] we have huge business objects. rooted hierarchy

Do the data have a life cycle?
[BTan]  no

How do coherence know if the data expired and remove them?
[BTan]  http://download.oracle.com/otn_hosted_doc/coherence/341/com/tangosol/net/cache/CacheMap.html#put(java.lang.Object, java.lang.Object, long)

Why do people need coherence? For performance or for large data caching purpose?
[BTan]  both

How many coherence nodes are installed on how many servers?
[BTan]  60 nodes on 6 machines 16GB / machine

What is the magnitude we are looking at?
[BTan]  at least 12GB of base data. Each snap takes 12GB+. Up to 5 snaps a day.

Why that many servers are needed?
[BTan]  machine failover

is it constrained by the individual server's memory? How to define a coherence node's size?
[BTan]  1G/node

What is the topology of the coherence architecture? Why is it designed that way?
[BTan]  private group communication

Is it Multicasting or WKA? Why is it designed in that way?
[BTan]  multicast, because internal network

How do you do the trouble-shooting? Do you have to check the log file, where are those log files?
[BTan]  JMX monitor + logs on NAS storage

coherence 3 essential config files

Most of the effort of deploying/using coherence is configuration. There are only 3 important xml config files, according to a colleague.

* client config
* cache config -- server config
* proxy config

proxy = a jvm sitting between client and server. Load balancer. Knows the relative load of each node. Without proxy, a heavy hitting client can overload one of 2 cache nodes.

HBase internals

http://www.slideshare.net/adorepump/hbase-nosql -- reveals the HashMap-based design

http://www.slideshare.net/ghelmling/hbase-at-meetup?src=related_normal&rel=1711070 -- good pointers + good example