Re: Sequential Scan Read-Ahead

On Wed, 24 Apr 2002, Bruce Momjian wrote:

> We expect the file system to do re-aheads during a sequential scan.
> This will not happen if someone else is also reading buffers from that
> table in another place.

Right. The essential difficulties are, as I see it:

    1. Not all systems do readahead.

    2. Even systems that do do it cannot always reliably detect that
    they need to.

    3. Even when the read-ahead does occur, you're still doing more
    syscalls, and thus more expensive kernel/userland transitions, than
    you have to.

Has anybody considered writing a storage manager that uses raw
partitions and deals with its own buffer caching? This has the potential
to be a lot more efficient, since the database server knows much more
about its workload than the operating system can guess.

cjs
-- 
Curt Sampson  <cjs@cynic.net>   +81 90 7737 2974   http://www.netbsd.org
    Don't you know, in this new Dark Age, we're all light.  --XTC