Re: [HACKERS] Sequential scan speed, mmap, disk i/o - Mailing list pgsql-hackers

>
> 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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