how many transactions can be completed per day with splunk services or is that some thing configurable ? what size of typical network transactions and their response time latency ?
Splunk isn't an appliance, but software. Because the hardware will vary in every case, (plus, what does a "transaction" look like?), it is not practical to measure Splunk in terms of transactions per day. Instead, the docs provide a reference architecture that should serve to index 500 GB of total daily volume per day. You can find the details here: http://docs.splunk.com/Documentation/Splunk/5.0.2/Installation/Referencehardware