From owner-cvs-all Sun Sep 19 12:30:33 1999 Delivered-To: cvs-all@freebsd.org Received: from proxy2.ba.best.com (proxy2.ba.best.com [206.184.139.14]) by hub.freebsd.org (Postfix) with ESMTP id E81F51532C; Sun, 19 Sep 1999 12:30:28 -0700 (PDT) (envelope-from dillon@apollo.backplane.com) Received: from apollo.backplane.com ([209.157.86.2]) by proxy2.ba.best.com (8.9.3/8.9.2/best.out) with ESMTP id MAA25048; Sun, 19 Sep 1999 12:28:42 -0700 (PDT) Received: (from dillon@localhost) by apollo.backplane.com (8.9.3/8.9.1) id MAA74072; Sun, 19 Sep 1999 12:28:41 -0700 (PDT) (envelope-from dillon) Date: Sun, 19 Sep 1999 12:28:41 -0700 (PDT) From: Matthew Dillon Message-Id: <199909191928.MAA74072@apollo.backplane.com> To: sthaug@nethelp.no Cc: phk@critter.freebsd.dk, mjacob@feral.com, dg@root.com, grog@lemis.com, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: User block device access References: <199909191900.MAA73792@apollo.backplane.com> <44387.937768408@verdi.nethelp.no> Sender: owner-cvs-all@FreeBSD.ORG Precedence: bulk :> In fact, a memory-mappable buffered block device with write-through would :> be much, much more useful to a database then a character device, and I :> think it's only a two line patch to make mmap() work, and probably a :> four line patch to implement write-through. It would be virtually :> unbeatable... : :Possibly so. However, the database systems I'm used to would much rather :control caching themselves rather than rely on the OS. This is a very old :discussion - you'll find it in OS and DB papers at least 15 years ago. : :Finding the appropriate mechanisms that the OS can offer to the DBMS is :*not* easy. : :Steinar Haug, Nethelp consulting, sthaug@nethelp.no True enough. You have to implement both. A big time database will want to do its own caching, but that's because they've spent the time and money to build an infrastructure that can take advantage of it (e.g. in order to perform a query synchronously when it is known that all the necessary data is already in-core). A big chunk of the consumer and freeware database market, however, would find a blockdev with mmap() much more useful. I certainly would. A caching web proxy would find the blockdev approach more useful. -Matt Matthew Dillon To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message