Re: IDS 9.40 Documentation (LRUs).

Andrew Thank you. Helped a lot. RDT. andrew.watson@ardenta.com (Andy Watson) wrote in message news:<5708c605.0309090050.66dcb609@posting.google.com>... > The old algorithm gave pages priority based on assumptions about > importance giving data pages low, index leaf pages medium-low, index > branch pages medium-high and root nodes high (in later versions). > > The problem with this is that in practice many indexes were typically > created on heavily hit tables to improve performance but this meant > that there could often be as many pages associated with a table > holding index pages as there were the actual data. There was no limit > on the percentage of the buffers that could be assigned to the various > priorities. Therefore as pages can only be replaced by pages of the > same or higher priority the buffers could then become flooded with > index pages leading to frantic thrashing of the few remaining pages > assigned to data. > > To overcome this problem 9.40 uses only two priorities (high and low) > and dynamically controls the percentage assigned to each through > maintanence of an Access Frequency Threshold. Access Frequency is > simply a count of the number of times a page is accessed by a user or > the system so it is essentially a vote on relative importance being > reset to 0 for each page at checkpoints. The threshold starts at 36 > and is then adjusted in 10% increments at checkpoints to ensure that > an approximate ratio of 3:1 high to low is maintained. The High band > works as a First In First Out so that once the steady state of 3:1 is > reached pages can only be promoted to High by demoting the first page > that entered the high band. > > Hope this helps, > Andy

"rdtbra" <reitota@hotmail.com> wrote in message news:a0f84695.0309101740.781e6ab4@posting.google.com... > Andrew > > Thank you. Helped a lot. > > RDT. > > andrew.watson@ardenta.com (Andy Watson) wrote in message news:<5708c605.0309090050.66dcb609@posting.google.com>... Would you like to buy him? :-)

"Neil Truby" <neil.truby@ardenta.com> wrote in message news:<bjos24$l3pl4$1@ID-162943.news.uni-berlin.de>... > "rdtbra" <reitota@hotmail.com> wrote in message > news:a0f84695.0309101740.781e6ab4@posting.google.com... > > Andrew > > > > Thank you. Helped a lot. > > > > RDT. > > > > andrew.watson@ardenta.com (Andy Watson) wrote in message > news:<5708c605.0309090050.66dcb609@posting.google.com>... > > Would you like to buy him? :-) I'll open the bidding at 50p. (That is to include payment for his humour as well)