Hi Dmitry and Bojan,
I was trying to apply your suggestions to get some idea about the core problem. Suddenly, it started to work fine. The whole process is now being executed in less than 1 second. I don't know how it fixed, but it's good now.
I am now wondering what was the problem and what changed. Is HANA not stable? I am using version 1.00.110.00.1447753075 (fa/newdb100_rel).
Maybe (just came to my mind), is it possible that it is because of full text index operation? To be able to use text mining function (TM_GET_RELATED_DOCUMENTS), I need to create a full text index on table "TABLE_TEST" and then execute MERGE DELTA OF "TABLE_TEST". As far as I observe, indexing require some time to be completed. I wasn't able to use TM_GET_RELATED_DOCUMENTS function right after I created the full text index. I need to wait for some time. Maybe it needed more time to be able to execute all processes in normal time. Maybe, there is a bug there. I really don't know.
Anyway, I will test it couple of days. If the same problem occurs again, I will try to come back with some hints about problem as you suggested.
Note: Btw, I cannot get PlanViz, because it says "[PlanViz] unsupported statement type: (prepare) trace-only execution of update statements are not supported"
Thanks