On Sun, Feb 13, 2011 at 5:31 PM, Jim Wilcoxson <pri...@gmail.com> wrote:
> On Sun, Feb 13, 2011 at 1:15 AM, Max Vlasov <max.vla...@gmail.com> wrote: > > So the final results: > > - the db was always ok and contains the correct value (id=10001 for > initial > > 1). > > - the speed was about 227 commits per second so very close to my system > > flush test (253) > > > > So if the drive is 5400 rpm, 227 is much more than 5400/60=90 and even if > > it's 7200 (manufacturers sometimes upgrade drives inside portable hd > > without > > prior notice), it's still twice as much as 7200/60=120. > > > > My hypothesis to explain the behavior you are seeing is that it takes 4ms > (1/253) for your OS to flush its buffers to the hard drive cache, issue the > sync to the drive, and the hard drive to acknowledge the sync. When it is > convenient, the drive will write this data to the disk. The sync command > may make this more urgent than usual, which would explain why I/O slows > down > if sync is used. Or, the drive could simply have a sync timer: the first > sync command starts the timer, and when 4ms have passed, the drive dumps > its > cache to the platters. > Jim, I see your point, maybe really for removable media on Windows sync is still lazy, but much less "lazy" then general cached operations. Another version is that removable hds can report that they wrote some data while actually work as your described postonning it a little. But I thought about how it would be possible to test this explanation . I'm going to do some tests that works like this. The same id updating, but in the middle of 10,000 operation I will unplug the cord, the sqlite will say that it can't commit particular insert and I can see what is the value of this insert. After replugging two variants possible: - I will find the previous value in the base. If for several dozens tests the result is the same, that would mean that the situation is still needed to be explained. - I will find some value less than previous to the one sqlite could not commit at least in some of the tests (maybe -3, -4 to the failed one). In this case the explanation will be confirmed. How about this? Does it sound reasonable? Max Vlasov _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
