Re: [HACKERS] Sequential scan speed, mmap, disk i/o

>
> Someone was complaining about sequential scan speed, so I decided to run
> a test.

> wc 41 sec
> wc -l 31 sec
> dd if=/u/pg/data/base/test/testv of=/dev/null bs=512 32 sec
> dd if=/u/pg/data/base/test/testv of=/dev/null bs=8k 31 sec
> dd if=/u/pg/data/base/test/testv of=/dev/null bs=256k 31 sec
> dd if=/u/pg/data/base/test/testv of=/dev/null bs=1m 30 sec
> mmap() of file in 8k chunks 99 sec
> mmap() of file in 8mb chunks 40 sec
> mmap() of file in 32mb chunks 56 sec
>
> PostgreSQL sequential scan 37 sec

Let me add, these times are on a PP200, with SCSI Ultra Barracuda
drives, BSD/OS 3.1, 64MB RAM.

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