Date: Fri, 3 Aug 2007 08:18:07 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Jeff Roberson <jroberson@chesapeake.net> Cc: arch@freebsd.org, Alfred Perlstein <alfred@freebsd.org>, Kris Kennaway <kris@obsecurity.org> Subject: Re: Fine grain select locking. Message-ID: <20070803081520.B18327@fledge.watson.org> In-Reply-To: <20070802174819.S561@10.0.0.1> References: <20070702230728.E552@10.0.0.1> <20070703181242.T552@10.0.0.1> <20070704105525.GU45894@elvis.mu.org> <20070704114005.X552@10.0.0.1> <20070729180722.GB85196@rot26.obsecurity.org> <20070802174819.S561@10.0.0.1>
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This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --0-101292342-1186125487=:18327 Content-Type: TEXT/PLAIN; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE On Thu, 2 Aug 2007, Jeff Roberson wrote: > I hope we can hash out a good plan to resolve this for 8.0. filedesc and= =20 > lockmgr are the biggest hitters on mysql writes. I suspect this is also = the=20 > case for pgsql and likely other network server type programs. Actually, I'd scope this claim a bit -- it's certainly going to be an issue= =20 for MySQL and any *threaded* network server type programs. As process base= d=20 parallelism doesn't share the file descriptor table, it shouldn't affect=20 non-threaded workloads such as Apache and pgSQL. This is one of the=20 interesting contradictions with threads -- developers are taught that they = are=20 lightweight, and they are in the sense that they cost less to have many of = and=20 support very easy IPC, but they are also more likely to contend kernel lock= s=20 as they involve more shared data structures being referenced. In contrast,= =20 process-driven parallelism allows a much higher level of independence betwe= en=20 executing threads of control, allowing IPC to be explicit rather than=20 continuous. Anything that reduces the overhead of filedesc locking will=20 improve the performance of all apps,=A0but reducing the contention on filed= esc=20 will only help applications sharing the file descriptor array between many= =20 threads/processes. Robert N M Watson Computer Laboratory University of Cambridge --0-101292342-1186125487=:18327--
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