[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: DOM vs JDOM
From: Uche Ogbuji <uche.ogbuji@f...> >Cache management is quite a difficult area, but quite established, so I'd >bet most persistent DOMs have such swapping schemes. And, though perhaps this goes without saying, it is important to know_why_ saving memory is important for your application. Sometimes we consider space important but we are really interested in time. In a web application I worked on last year, we found that at quite a few points during the application the middleware could prefetch data, which dropped response times by 75% for those phases; the process that sends the page then prefetches the data and has it ready in the user's session object. In that case, the time to load data was not important because, by prefetching where it was reasonable to do so, we had lots of time available. On a related issue, size may also not be so important for summary data required by users from a database, where many sessions need the summaries and you can sacrifice tmieliness a little bit: caching the results of summary queries on the middleware and aging it after 10 seconds (or whatever) you can reduce db server congestion and decrease average response times for users. If you have even 2 sessions that need that data during the window you have already saved 50% on size, in effect, for that data. (For one place we were able to do that, we found it dropped response times for the page in question from 10 seconds every time to about .5 seconds best case (10 seconds still the worst case, of course. If we had regularly scheduled updates we could have decreased the worst case; for example using the rule that if there are any active sessions that might soon need the summary data then when cache is old wait the statistically optimal period and update the cache: predictive prefetching. ) So DOM size is important, but if responsiveness is the concern then it can be worthwhile to look at the possibilities for prefetching and for shared query-result caching on your middleware too. Cheers Rick Jelliffe
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