On Mon, Nov 14, 2011 at 5:11 PM, Thomas Steinmaurer
<t...@iblogmanager.com>wrote:
>
> Ok, but is there a way then to tell how many pages have been fetched
> from the cache as the number above for fetched is more likely
> "referenced" and not real number of pages fetched from memory?
>
Pages aren't fetched from cache. Once a page is in cache, data is fetched
from it. Sometimes the data is a record, to be expanded into a record
buffer, sometimes it's an index node, sometimes it's a page number from an
offset on a pointer page, or the state of a transaction from a TIP, or ...
>
> I guess the same applies to MON$IO_STATS.MON$PAGE_FETCHES? If so, isn't
> comparing MON$PAGE_READS with MON$PAGE_FETCHES a bit misleading if one
> wants to check to possibly increase the database page buffers?
It's more misinterpreted than misleading. You would never increase the
number of pages in the cache to reduce the number of fetches. In an ideal
world, the number of fetches would be enormous and the number of reads
would be *infinitesimal, meaning that all most every request was resolved
from cache and therefor the cache is big enough. The only ways (I can
think of at the moment) to reduce the number of fetches are to do less
work, or work more efficiently (e.g. don't do a count (*) on a big table).*
>
Cheers,
Ann
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