Ian Boyd wrote:
> Customer is running a load test against a websphere application that
uses
> DB2. While the load test is running the memory usage of DB2 climbs from
x
> up to y. When the load test ends, the memory usage of DB2 returns to x.
>
> However, sometimes after running the load test the memory usage does not
> drop down to x right away; sometimes it takes a few hours. This
"problem"
> exists with their current live version of the software, and the version
we
> want to install. Customer will not install update until this "problem"
is
> resolved.
>
> Customer is a government organization, in which the DB2 admin, the DB2
> server admin, the server memory usage admin have collectivly as much
> knowledge as a sack of door knobs.
>
> Besides, "Go f*ck yourself.", what can we tell the customer?
(I hope for your sake your customer doesn't use google...)
Seriously, a PMR with IBM is about the best way you're going to get an
answer that the customer might accept. That said, I'm going to guess that
it doesn't go down right away for performance reasons. That is, the
server
keeps everything loaded in cache because, just recently, it was asked for,
giving a reasonable conclusion that it may just be needed again, and soon.
Only once the cache starts expiring does the memory usage go back down.
As for how long the cache takes to expire, well, that will depend on many
things, including for how long the items in the cache were valid for
(i.e.,
were they being constantly required for the last 24 hours? If so, a
longer
hold on them might be warranted), how busy the server is otherwise (other
connections and queries which may push the cached data out in order to
make
room for new data, or other applications using memory on the server so DB2
may cede some memory up for those applications, not sure), and/or any
number of dbm and/or db configuration variables. Tweaking everything to
configure a database system (regardless of vendor) for optimal performance
is generally not for the faint of heart. And I'm pretty sure IBM would
tell this customer of yours that what they want is in direct contradiction
to getting optimal performance.
|
