On Thu, Aug 19, 2010 at 10:56:58PM +0100, Simon Slavin scratched on the wall:
> It might be worth noting that fragmentation is normally seen as an issue > only under Windows which is very sensitive to it however. Most systems are sensitive to fragmentation. It just happens that many other system address the problem with more advanced filesystems and/or filesystem drivers. HFS+, for example (the primary filesystem of Darwin and Mac OS X) will automatically defrag smaller files (< 20MB). I'm told HFS+ will also tend to migrate frequently used files to the middle of the disk platters (smaller average seek time), but I haven't found definitive documentation on this. A number of the more advanced filesystems commonly found in the UNIX world have similar features. I know Vista and Win7 introduced some auto-defrag features, but I don't have any significant personal experience with those systems. > Also, many installations of SQLite are on solid state devices where, > of course, fragmentation has no effect at all. Umm... no. SSDs have very different access characteristics compared to spinning platters, but they most definitely do not allow uniform access times to the whole address space. "Seek time" isn't exactly the right word, but they have read delays based off the last block accessed, and a whole slew of other factors, including how the individual storage chips are "stacked", how the chips are cut up into banks, how the controller is designed, and on and on. Also, because of the way the SSD devices work at the chip level, they tend to "stream" data, rather than just access it, so there are some designs that are even more sensitive to fragmentation. In many ways they're much more challenging to write drivers for, as each device has different characteristics that cannot be accounted for by just looking at the device geometry. This is all made even more interesting by the fact that many SSDs utilize file systems that intentionally fragment and move blocks around with every write (including writes to existing space in existing files) to spread out the write cycles. -j -- Jay A. Kreibich < J A Y @ K R E I B I.C H > "Intelligence is like underwear: it is important that you have it, but showing it to the wrong people has the tendency to make them feel uncomfortable." -- Angela Johnson _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
