On Mon, 2002-10-07 at 10:38, Antti Haapala wrote: > Browsed web and came across this piece of text regarding a Linux-KAIO > patch by Silicon Graphics... >
Ya, I have read this before. The problem here is that I'm not aware of which AIO implementation on Linux is the forerunner nor do I have any idea how it's implementation or performance details defer from that of other implementations on other platforms. I know there are at least two aio efforts underway for Linux. There could yet be others. Attempting to cite specifics that only pertain to Linux and then, only with a specific implementation which may or may not be in general use is questionable. Because of this I simply left it as saying that I believe my analysis is pessimistic. Anyone have any idea of Red Hat's Advanced Server uses KAIO or what? > > Preliminary experience with KAIO have shown over 35% improvement in > database performance tests. Unit tests (which only perform I/O) using KAIO > and Raw I/O have been successful in achieving 93% saturation with 12 disks > hung off 2 X 40 MB/s Ultra-Wide SCSI channels. We believe that these > encouraging results are a direct result of implementing a significant > part of KAIO in the kernel using split-phase I/O while avoiding or > minimizing the use of any globally contented locks." The problem here is, I have no idea what they are comparing to (worse case read/writes which we know PostgreSQL *mostly* isn't suffering from). If we assume that PostgreSQL's read/write operations are somewhat optimized (as it currently sounds like they are), I'd seriously doubt we'd see that big of a difference. On the other hand, I'm hoping that if an aio postgresql implementation does get done we'll see something like a 5%-10% performance boost. Even still, I have nothing to pin that on other than hope. If we do see a notable performance increase for Linux, I have no idea what it will do for other platforms. Then, there are all of the issues that Tom brought up about bloat/uglification and maintainability. So, while I certainly do keep those remarks in my mind, I think it's best to simply encourage the effort (or something like it) and help determine where we really sit by means of empirical evidence. Greg
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