Hi Sean,

Thanks for your reply.

You were right, after fresh boot, test # 1 shows about same result with test # 3 & 4.

I think, test # 4, where database placed in harddisk, shows same result as database placed in RAM, because database is small enough to cache in memory.

When I decreased DefaultDbCachePages or FileSystemCacheThreshold, test # 4 shows a bad performance vs test # 1 / test # 3.

Regards,
Sugi

--- In firebird-support@yahoogroups.com, "Leyne, Sean" <Sean@...> wrote:
>
>
>
> > 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
>