Messages in this thread | | | Date | Sun, 17 Mar 2002 19:06:53 +0000 | From | Anton Altaparmakov <> | Subject | Re: fadvise syscall? |
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At 18:35 17/03/02, Ken Hirsch wrote: >Anton Altaparmakov writes > > Posix or not I still don't see why one would want that. You know what you > > are going to be using a file for at open time and you are not going to be > > changing your mind later. If you can show me a single _real_world_ example > > where one would genuinely want to change from one access pattern to >another > > without closing/reopening a particular file I would agree that fadvise is >a > > good idea but otherwise I think open(2) is the superior approach. > > > >Sure, a database manager can change the access pattern on every query. If >there's an index and not too many records are expected to match, it will use >a random pattern, otherwise it will use sequential access.
Last time I heard serious databases use their own memmory management/caching in combination with O_DIRECT, i.e. they bypass the kernel's buffering system completely. Hence I would deem them irrelevant to the problem at hand...
If a database were not to use O_DIRECT I would think it would be using mmap so it would have madvise already... but I am not a database expert so take this with a pinch of salt...
Best regards,
Anton
-- "I've not lost my mind. It's backed up on tape somewhere." - Unknown -- Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @) Linux NTFS Maintainer / WWW: http://linux-ntfs.sf.net/ ICQ: 8561279 / WWW: http://www-stu.christs.cam.ac.uk/~aia21/
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