> Is the only change the absence of a call to "fsync()" when turning > synchronous off? If so, I can conclusively say that fsync() is very slow > on this storage device.
Yes, the only action of synchronous = off is to turn off calls to fsync() which is called at least twice during each commit. Pavel On Wed, Sep 23, 2009 at 11:40 AM, Mark <godef...@gmail.com> wrote: > > On a RAID-5 array of 4x SAS disks, turning the sync off made it about 2x > faster, give or take. > > On the "SSD", it was about 150x faster. > > Is the only change the absence of a call to "fsync()" when turning > synchronous off? If so, I can conclusively say that fsync() is very slow > on this storage device. > > Thanks for the suggestion. > > Mark > > > Pavel Ivanov wrote: >> If you execute >> >> pragma synchronous = off; >> >> you'll be able to compare performance with syncs and without them. So >> if you make this comparison on standard spinning disk and on SSD >> you'll see if syncs on SSD indeed extra-ordinary slow. >> >> Pavel >> >> On Wed, Sep 23, 2009 at 10:09 AM, Mark <godef...@gmail.com> wrote: >>> It's very possible, but I don't know how to tell. Is there an easy way >>> to know if the sync() calls are taking inordinately long? >>> >>> Mark >>> >>> >>> Thomas Briggs wrote: >>>> Is the sync necessary to commit a transaction slow? Performance of >>>> that sync depends on the OS, file system, hardwar, etc. IIRC, so IOs >>>> may be fast but it's possible that the syncs are killing you. >>>> >>>> -T >>>> >>>> On Tue, Sep 22, 2009 at 5:14 PM, Mark <godef...@gmail.com> wrote: >>>>> Lothar Scholz wrote: >>>>>> Hello Mark, >>>>>> >>>>>> Tuesday, September 22, 2009, 3:53:48 AM, you wrote: >>>>>> >>>>>> M> I've currently got a loaner high-performance flash-based "SSD" (let's >>>>>> M> just say it doesn't connect to any disk controllers) that I'm testing >>>>>> M> for performance. I've run my application against it, and I believe >>>>>> that >>>>>> M> I should see numbers MUCH higher than I do. When I run my test app on >>>>>> a >>>>>> M> normal SATA 7200 RPM disk, I get a certain performance, and on the >>>>>> "SSD" >>>>>> M> I get about 1/10th that speed. On an array of SAS disks I get numbers >>>>>> M> that are about 5x faster than my SATA disk, so my software itself >>>>>> isn't >>>>>> M> (I believe) the bottleneck. >>>>>> >>>>>> M> I'm wondering if anyone has any tips for "optimizing" for this sort of >>>>>> M> storage solution. >>>>>> >>>>>> Throw it into the trash bin and buy a new one which has a 3rd >>>>>> generation controller and at least 64MB fast cache. The old JMicron >>>>>> controller that many low cost SSD still use was developed for Flash >>>>>> USB sticks. >>>>>> >>>>>> With modern SSD like the latest Samsung should give you at least the >>>>>> same performance as the SATA. If it gets better depends on file size >>>>>> and cache. Are you sure that the SAS RAID Controller is not keeping >>>>>> everything in the controller cache? >>>>> This isn't an "SSD". It's connected directly to the PCI Express bus, and >>>>> "low cost" it certainly is NOT. It's much more valuable than the server >>>>> it's plugged into. >>>>> >>>>> I've run benchmark tests (iometer), and the benchmarks show it's as fast >>>>> as the mfgr says it should be (~700MB/sec read and write bandwidth, >>>>> >115,000 IOPS) but it performs quite poorly when I run my app on it. I >>>>> can't figure out why. >>>>> >>>>> Mark > > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
