High buffer cache hit ration but low page life expectancy

I've noticed that I have a buffer cache hit ratio consistently around
99% but a page life expectancy chronically below the 300 second level.
I'm wondering how this is possible? Presumably the page life
expectancy is low because the buffer pool needs to clear out pages to
make room for new pages but why would it need to do this if the cache
hit ratio is around 100%?
ThanksHow about the read-ahead manager putting asked for data into ram (thus
forcing out 'old' data) before it is actually needed by various SELECT
statements? Also buffer cache hit ratio and page life expectancy could be
calculated on different time schedules internally which could account for
their apparent disparity.
TheSQLGuru
President
Indicium Resources, Inc.
<pshroads@.gmail.com> wrote in message
news:1177626752.644290.325550@.s33g2000prh.googlegroups.com...
> I've noticed that I have a buffer cache hit ratio consistently around
> 99% but a page life expectancy chronically below the 300 second level.
> I'm wondering how this is possible? Presumably the page life
> expectancy is low because the buffer pool needs to clear out pages to
> make room for new pages but why would it need to do this if the cache
> hit ratio is around 100%?
> Thanks
>|||Hi
"pshroads@.gmail.com" wrote:

> I've noticed that I have a buffer cache hit ratio consistently around
> 99% but a page life expectancy chronically below the 300 second level.
> I'm wondering how this is possible? Presumably the page life
> expectancy is low because the buffer pool needs to clear out pages to
> make room for new pages but why would it need to do this if the cache
> hit ratio is around 100%?
> Thanks
>
Check out
http://download.microsoft.com/downl...aits_Queues.doc
A low page life expectancy with a high checkpoint pages/sec and lazy
write/sec values would indicate memory pressure. Also check for missing
indexes.
John