Stew,
You forgot to include the memory hit ratios that you are seeing
(or those that your research shows). We do not want to just restrict
memory hit ratios per se, we want to see realistic numbers that you are
seeing. Unfortunately, even your fairly detailed message is missing
those numbers so we are left with no positive info thatwe can use.
Please provide us with the measurements you see in practice, and we will
try to adjust the workload accordingly (given that other vendor's
numbers or expectations match yours to a certain extent). If we do not
have any numbers, we have to take educated guesses and be on the safe
side. The latter is not the best approach, of course.
Thanks,
Alex.
On Tue, 30 Nov 1999, Stew Forster wrote:
> Why 4-6% memory hit ratio? Where has this figure come from? How does
> this relate to real world behaviour? Some vendors have spent a lot of time
> explicity studying real world logs and running simulations and tuning algorithms
> to handle real-world situations. These correspond directly to improved
> memory hit ratios.
>
> I understand the need to prevent the entire working set fitting into RAM, but
> lets face it. If vendor X can get 1000TPS say, then at ~13KB/object and a
> 55% hit rate, we're talking about 5.85MB/sec of new object data flowing into
> the system, or 170 seconds per GB. There's no way any working set will
> fit into RAM in those circumstances.
>
> Further, our research shows that for 1 week's worth of traffic access at 200TPS,
> 75% of all cache hits occur within 7 hours of an object being pulled in, and indeed
> 56% within the first hour. Our research also shows that as TPS increases,
> the percentages increase, meaning that each object is more likely to be accessed
> more quickly. This correlates directly to higher achievable RAM hit rates.
>
> By artificially restricting everyone to 4-6% memory hits you're stating that vendor X's
> approach is invalid if vendor X focussed on improved memory performance.
>
> Stew.
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