I am new to WCF data services. I have created one sample POC on WCF data service using ADO .NET Entity framework.
When i test Data service by a test project by adding WCF data service as a service reference, a simple select statement for 1000 rows, it took around 25 sec.
Out of 25 sec it took only 5 sec for querying data from DB (Got this info after profiling database).
its weird that WCF data service took around 20 sec for just translation and transport.
Any idea why its taking so much time for translation and transport?
Your data is simply too big.
It is absolutely normal that transport over the network is several times slower than fetching the data from a database, at least when the query consists of more bulk fetching than of complex narrow filtering, and in absence of major performance issues on the database side.
100 MB in 20 seconds = 40 Mbps which would be quite close to hardware limits on 100 Mbps Ethernet given that ~100 MB is just the payload.