| Subject | RE: [firebird-support] Re: DB Stats - Header Page |
|---|---|
| Author | Leyne, Sean |
| Post date | 2010-04-15T19:24:09Z |
Kevin,
(How long has the processes been running which generated the 14 million faults?)
A "page fault" represents an disk read operation where the read can't be satisfied by the OS cache (if you are reading from the OS, then the read is not in the FB cache).
"Page Buffers = 0" simply means that you are using the OS cache, which is a slower access than the FB cache. It also leads to stats for a FB query where "Reads from disk" value is very high, compared to "fetches from cache".
So, "Page Buffers = 0" does not lead directly to "Page Faults".
If you don't have a large OS cache memory, then page faults will increase.
If you have a really large database (larger than OS cache), then page faults are a "reality of life".
Further, depending on your disk controller type and setup, "Page Faults" can have a negligible impact due to disk controller cache.
Sean
P.S. We have found that Windows 2008 x64 is actually more likely to use all free RAM for disk cache, which can cause page file accesses to increase (along with page faults), if you are using applications which launch processes (i.e. Classic Server or DCOM application server) or request more memory.
> Would the lack of Page Buffers cause a high number of "Page Faults"It depends. ;-)
> shown in the Task Manager? Right now it's showing over 14 million.
(How long has the processes been running which generated the 14 million faults?)
A "page fault" represents an disk read operation where the read can't be satisfied by the OS cache (if you are reading from the OS, then the read is not in the FB cache).
"Page Buffers = 0" simply means that you are using the OS cache, which is a slower access than the FB cache. It also leads to stats for a FB query where "Reads from disk" value is very high, compared to "fetches from cache".
So, "Page Buffers = 0" does not lead directly to "Page Faults".
If you don't have a large OS cache memory, then page faults will increase.
If you have a really large database (larger than OS cache), then page faults are a "reality of life".
Further, depending on your disk controller type and setup, "Page Faults" can have a negligible impact due to disk controller cache.
Sean
P.S. We have found that Windows 2008 x64 is actually more likely to use all free RAM for disk cache, which can cause page file accesses to increase (along with page faults), if you are using applications which launch processes (i.e. Classic Server or DCOM application server) or request more memory.