iam doing some sort of transactions based on tpc-c test with hsqldb in-memory mode (no indices, default settings). When i start benchmark transaction speed is about 30000 TPCC transactions/minute but after few minutes the speed was slowed about 4-10x original rate here are rough results:
1:00 - 28000
2:00 - 58000
3:00 - 88000
4:00 - 115000
5:00 - 145000
6:00 - 154000
7:00 - 163000
8:00 - 168000
9:00 - 173000
10:00 - 176000
I think this has something to do with lack of memory but i dont know much about databases and memory management. When in-memory mode only i would expect the same speed all the time and then possibly out of memory error which will also happen after approx 270k transaction. Iam running this on 4GB RAM computer, 64bit OS Linux (Lubuntu).
So my question is if its possible that this is normal behaviour and what should i do when i want to run this test (with in-memory mode) for about two hours to get more accurate results?