Yohanes, > Yesterday in #pgsql, I was talking with neilc about determining rpc > value in a more concrete way. So I created a program that compares > exhaustive (all blocks are eventually read) random reads with > sequential reads. The full source is attached.
Thanks for code. > I tested the db files residing on a software RAID-1 composed of 2 IDE > 7200rpm drives on linux 2.6.12. FWIW, most performance-conscious users will be using a SCSI RAID array. > is not precise enough. Which pages? Those that belong to the dbase > file or sequential pages on the media? Well, it's actually calculating the cost ratio of pulling non-sequential random *rows* from the db files against pulling sequential blocks. > On dbases smaller (calculated from du <dbase_dir>)than 500M, I got a > ratio (random over sequential time) of 4.5:1. A 3.0GB dbase has a > ratio of 10:1. On a 3GB contiguous file, the ratio is about 4:1. All of this goes to uphold Tom's general assertion that the default of 4 is more or less correct but the calculation in which we're using that number is not. -- Josh Berkus Aglio Database Solutions San Francisco ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
