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(at)cynic(dot)net> +81 90 7737 2974 http://www.netbsd.org
Don't you know, in this new Dark Age, we're all light. --XTC