K
Keith Sudbury
Guest
How much this matters varies greatly by application and table size. If you are lucky enough to be able to cache your entire working set in one of the buffer pools and you don't shut down the DB nightly... you aren't likely to notice the difference. The benefits come from a potential reduction in the number of blocks needed to buffer the "active" records, how many buffer blocks must be read to satisfy a query and by maximizing the benefit of the read ahead logic on most SAN/Volume managers when the blocks must be read from disk. Back in the 32 bit days this was much more of an issue for me personally with one specific app and a few specific tables. I could see a 40% improvement in report processing when the core table was loaded in the same order that the application used it. This was a 2TB database with several key tables that were in excess of 20GB in size that had close to a billion reads per day... certainly not your average OE install. Type II areas and 64 bit buffer pools have certainly reduced the impact but I still see issues from time to time, only on very large and very active tables. I am not quite ready to declare D&Ls dead and buried, but they certainly aren't needed for most tables on a regular basis.
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