Re: [PATCH] O_STREAMING - flag for optimal streaming I/O

From: Hank Leininger (
Date: Thu Oct 10 2002 - 23:16:45 EST

On 2002-10-10, Mike Fedyk <> wrote:
> On Thu, Oct 10, 2002 at 03:17:35PM +0200, Giuliano Pochini wrote:
> > Thing again about to backup a large database. I don't
> > want to use tar because it kills the caches. I would
> > like a way to read the db so that the cached part of
> > the db (the 20% which gets 80% of accesses) is not
> > expunged.
> Unless you are pausing the database (causing the files on disk to be in
> a useful state) and then reading the file you will have trouble.
> Anything else will have to syncronize with the database itself, and
> thus can't use O_STREAMING.
Pausing the database != putting the database into readonly mode, which is
all that would really be required. If your writer-processes are distinct
from your reader-processes, you could suspend them (and/or batch up writes
to temp tables to shrink your externally-felt maintenance window), tell
the DB to flush pending writes, then dump with O_STREAMING-aware tar (or
db-specific tools that still must pass through all tables/files) while
read performance is only somewhat impacted, and cache isn't completely
Or, consider the case where the database isn't anywhere near all that the
system does. Think static content + DB-driven webserver, where the DB
*can* be completely shut down (and those parts unavailable) during
backups, while static content serving still goes on efficiently.

Hank Leininger <>  
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