Date: Sat, 4 Aug 2007 23:20:40 +0300 From: "Abdullah Ibn Hamad Al-Marri" <almarrie@gmail.com> To: "Kris Kennaway" <kris@obsecurity.org> Cc: Greg 'groggy' Lehey <grog@freebsd.org>, arch@freebsd.org, performance@freebsd.org Subject: Re: read-write SQL performance Message-ID: <499c70c0708041320r1f51cb3qe6f05376cfb8a470@mail.gmail.com> In-Reply-To: <20070804080535.GA3952@rot26.obsecurity.org> References: <20070804080535.GA3952@rot26.obsecurity.org>
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On 8/4/07, Kris Kennaway <kris@obsecurity.org> wrote: > I did some benchmarking of sysbench in read-write mode (previous tests > have focused on read-only mode). The reason for this is that the disk > hardware in my 8-core test system is slow (single disk) and is too > easily saturated. In fact mysql and pgsql have identical performance > when writing to disk. In other words, I seem to be mostly > benchmarking the disk performance and not database or kernel > performance. > > Faster disk hardware is necessary to explore database performance > differences or kernel bottlenecks. An upper bound on possible > read-write performance comes from using a memory disk instead of > physical disk hardware. I replicated the databases onto a suitably > large (2gb) tmpfs and reran the tests together with some mutex > profiling. > > Results are here: > > http://obsecurity.dyndns.org/sysbench-write.png > > There are a couple of interesting features. > > mysql has better peak performance than pgsql, but then quickly falls > in the toilet. Profiling indicates that at peak there is some > contention on lockmgr locks and the proc lock, but most of the > contention is in userland (i.e. within mysql itself). At higher loads > the bottleneck is overwhelmingly within mysql (and the system is > actually 90-100% idle). This seems to be a serious scaling problem > within mysql. > > Peak pgsql performance is lower than mysql, but there is comparatively > little degradation at higher loads. Profiling shows that the dominant > bottleneck at all workloads is lockmgr. > > Fortunately there is a lockmgr rewrite in progress by Attilio for SoC, > so there is great scope for performance improvements to pgsql. > Significant mysql performance improvements may require fundamental > architectural work by the mysql developers. > > Kris Maybe Greg would be interested in the MySQL issues? -- Regards, -Abdullah Ibn Hamad Al-Marri Arab Portal http://www.WeArab.Net/
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