Date: Tue, 10 Sep 2002 16:40:02 -0500 From: Dan Nelson <dnelson@allantgroup.com> To: hackers@d.sparks.net Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Dell 2650 SMP perf question Message-ID: <20020910214001.GB84648@dan.emsphone.com> In-Reply-To: <Pine.BSF.4.21.0209101051021.52716-100000@search.sparks.net> References: <Pine.BSF.4.21.0209101051021.52716-100000@search.sparks.net>
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In the last episode (Sep 10), hackers@d.sparks.net said: > I'm stumped at how little improvement using an SMP kernel gives in a > Dell 2650. System is dual 2400 xeon processors, 2 GB ram. It's > intended to be used as a database processor, among other things. A > perl process that read and input file and updates simple records in a > mysql database actually run much more slowly: processing ~2million > records takes 817 seconds with SMP enabled and 262 seconds with it > disabled. > > Simple things like some_program.pl < some_big_file | another_program.pl > > seem to take full advantage of the second processor, but this system > is supposed to run mysql. Mysql is a threaded database, and FreeBSD's pthreads are user-space. This means that mysql will only ever use one CPU, and disk I/O in one thread will block all other threads. You can try: * Rebuilding the mysql port with USE_LINUXTHREADS=yes. This will help lots if your mysql process is CPU-bound, and will help some if you are heavily I/O bound. * Switching to InnoDB tables, which cache much better than MyISAM tables so you are more likely to get your data from RAM instead of a blocking disk read. * Splitting your single perl program into multiple ones that hit the database simultaneously. You might be seeing a synchronization effect where your perl and mysql processes are competing for a SMP lock or something and the wrong one always wins. -- Dan Nelson dnelson@allantgroup.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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