On 21/04/13 08:15, nadav hoze wrote:
Hi,
We had serious performance degradation once we switched our clients to 64
bit machine.
After a thorough investigation I saw that the default file access mode
determined for the 64 bit is memory mapped files.
When I switched to direct access mode it flied out of the roof!!! (350
times faster).
I have here 3 important questions:
1. Why is that ?
In geenral, memory mapped files are as fast as or faster than caching
within the JVM.
2. Is it safe to use the direct access mode instead of the memory mapped
files ?
Yes
(and it's safe to change modes on a DB if you restart the JVM)
3. I Couldn't find a good documentation on this, can you please explain the
functionality of each mode ?
direct mode - there is a block cache managed in the heap. It's fixed size.
mapped mode - the OS does the caching of files into RAM - it's dynamic,
and adjusts to the load on the machine. And it's faster (usually)
Thanks,
Nadav
(and to Alexander Shapiro from a similar message)
Nadav, Alex,
In both your case, there aren't many details of the setup:
* Size of databsse (in triples).
* Version of Jena software
* operating system
* size of machine in RAM
* whether the machine is a VM or real hardware
* Java heap size
and other details like work load (update? read-mostly?)
Andy
