I have simple question but i could find any information about it. I also run some tests but didn't get any results that i measurable. Let say i have same structure with same data on my db and second db. I have same query (second query is with db link). Will it be any performance downgrade when i will query different database by db link on same physical server?
regards
The simple answer is, "Yes, it will".
If you compare performance between a query from the local tables and a query from remote tables - the local tables will always win.
The db link will always put additional demands on your computer. Be it a requirement to send data through network, or resources which a second RDBMS engine take to run on your computer. How much loss you will experience - cannot be said without more detailed look at your hardware environment.
So, in general, if you worry about performance over data in secondary RDBMS - it is often beneficial to do an ETL and load data into primary DB. Only if ETL is difficult or too much time consuming - then you can go with db link solution.
