> I run a test on a small database, around 128MB using Firebird 2.5 64 bit > superserver and the test condition is like these : > > 1) Put database completely on RAM, set DefaultDbCachePages = 2048 and > FileSystemCacheThreshold = 0 > 2) Put database completely on disk, set DefaultDbCachePages = 2048 and > FileSystemCacheThreshold = 0 > 3) Put database completely on RAM, set DefaultDbCachePages = 2048 and > FileSystemCacheThreshold = 65536 > 4) Put database completely on disk, set DefaultDbCachePages = 2048 and > FileSystemCacheThreshold = 65536 > > > I do some extensive select sql on this database, time to finished on each > conditions are : > 1) +/- 37 sec > 2) unknown since it seems took a very long time that I must ended with > task manager > 3) +/- 6 sec > 4) +/- 6 sec > > From those result, I don't understand why result from test condition 1 > (which is, database completely on RAM) is slower than condition 3 and 4. > > Isn't test condition 1,3 & 4, all running on RAM?
Yes, but RAM disk is not the same as RAM. Further, some RAM disk drivers are much better than others. Sometime ago, I found an analysis/comparison of various RAM Disk drivers. Although the analysis was a couple of years old, it did find that there are substantial performance differences between drivers. I can see if I can find the link, if you'd like. Separately, did you run all the tests from the same state -- ie. a fresh reboot. If not, test #1 would be paying the cost to load all of the pages into the OS cache, whereas the other tests would not. Either reboot between tests, or create a pre-test pass which would force the database to be loaded and then run the tests. Sean
