Messages in this thread | | | Date | Thu, 24 Apr 2008 11:53:14 -0400 | From | David Collier-Brown <> | Subject | Re: [RFC][PATCH 0/3] Skip I/O merges when disabled |
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Jens Axboe wrote: > On Thu, Apr 24 2008, Andi Kleen wrote: > >>>Not a good idea IMHO, it's much better with an explicit setting. That >>>way you don't introduce indeterministic behavior. >> >>So you would be deterministically slower. > > > Yes, absolutely. Think about the case for a second - the potential gain is in > fractions of a percent basically, the potential loss however is HUGE. > There's absolutely no way on earth I'd ever make this dynamic.
If this is intended for databases, it might be backwards (;-))
The commercial unix "forcedirectio" option that Oracle and other database vendors usually ask for turns out to be a benefit in large sequential data transfers, because it does two things:
1) transfers directly between user address space and disk, avoiding buffering, and 2) allows enthusiastic coalescence of synchronous writes
Is this intended for DBMSs, or for something esle?
--dave -- David Collier-Brown | Always do right. This will gratify Sun Microsystems, Toronto | some people and astonish the rest davecb@sun.com | -- Mark Twain (905) 943-1983, cell: (647) 833-9377, (800) 555-9786 x56583 bridge: (877) 385-4099 code: 506 9191#
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