On Fri, Mar 10, 2006 at 11:57:16PM -0800, David Lang wrote: > On Sat, 11 Mar 2006, Joost Kraaijeveld wrote: > > >On Fri, 2006-03-10 at 13:40 +0000, Richard Huxton wrote: > >>Your ATA disk is lying about disk caching being turned off. Assuming > >>each insert is in a separate transaction, then it's not going to do > >>10,000 / 6 = 1667 transactions/sec - that's faster than it's rotational > >>speed. > >Could you explain the calculation? Why should the number of transactions > >be related to the rotational speed of the disk, without saying anything > >about the number of bytes per rotation? > > each transaction requires a sync to the disk, a sync requires a real > write (which you then wait for), so you can only do one transaction per > rotation. But shouldn't it be possible to batch up WAL writes and syncs? In other words, if you have 5 transactions that all COMMIT at exactly the same time, it should be possible to get all 5 WAL pages (I'll assume each one generated a small enough change so as not to require multiple WAL pages) to the drive before the platter comes around to the right position. The drive should then be able to write all 5 at once. At least, theoretically... -- Jim C. Nasby, Sr. Engineering Consultant jnasby@xxxxxxxxxxxxx Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
