Re: Direct IO

"Dave Haas" <davidh_at_no.spam.hotmail.com> wrote in message news:UGKZ6.79549$Jg4.8380487_at_news1.telusplanet.net...
> Hi Howard :)
>
> How does one enable this direct i/o thing on NT then? I've not seen any
> Oracle parameters to do it and i'm not sure how to enable it at the OS
> level. Is it on by default?

Yup, I think so -but I think that you have to be using NTFS for that to be so (not that you'd want to be running Oracle on top of a FAT32 file system anyway!).

>
> In terms of SORT_DIRECT_WRITES i'm reasonably sure that it's no longer a
> user settable thing. The direct writing of sort blocks to disk is now
> handled automagically.
>

Well, the parameter is still discussed in the 8i Performance Tuning course, so it is still configurable. If sort_area_size is LESS than 640K, it is needed to enable sort direct writes. I guess if you were certifiably insane, if your sort_area_size was larger than 640K, you could use it to disable sort direct writes. But yes -given that a sensible size for sort_area_size on the whole is around 1Mb, it is all automated to be on by default.

Regards
HJR
> Cheers,
>
> Dave
>
>
> "Howard J. Rogers" <howardjr_at_www.com> wrote in message
> news:3b372546$1_at_news.iprimus.com.au...
> > ;-)
> >
> > The little I know about it, and in the context in which our earlier
> > 'discussion' would have raised the issue, this has nothing to do with
> > by-passing Oracle's buffer cache, but to do with by-passing the file
 system
> > buffer.
> >
> > NT and Raw devices don't use a file system buffer. Unix does
 (generally),
> > and its buffer is usually 8K big (hence the need for Oracle to match
 that
> > buffer, and thus need 8K blocks on Unix).
> >
> > SORT_DIRECT_WRITES is a different beast entirely. That tells Oracle
 that
> > when the PGA for a User has filled up doing a sort, and needs to swap to
> > temporary tablespace, could you please not flood my buffer cache with
 the
> > relevant data, but have the Server Process write it directly to the
 relevant
> > datafile. Provided your sort_area_size is at least 640K in 8i,
> > sort_direct_writes is automatically true (as far as I can tell).
> >
> > But although the buffer cache is thereby avoided, you'd still actually
 be
> > passing the write to the file system buffer if your temporary tablespace
 was
> > on a cooked device.
> >
> > Regards
> > HJR
> >
> > "Dave Haas" <davidh_at_no.spam.hotmail.com> wrote in message
> > news:SERY6.338$84.100633_at_news0.telusplanet.net...
> > > Hi.
> > >
> > > I have a question with regard to terminology. In several posts (and
 an
> > > argument I had with Howard a while ago :) people have used the term
 'Direct
> > > IO'. To be perfectly honest I'm not exactly sure what that means.
 AFAIK
> > > the IO options are 1) file-system buffered and 2) Raw IO. I heard (or
 more
> > > to the point, read) a post that said something to the effect of '...
 direct
> > > I/O means that the buffer cache is not involved in the operation ...'.
 Does
> > > that have something to do with the sort-direct-write operation and the
 old
> > > SORT_WRITE_BUFFERS and SORT_WRITE_BUFFER_SIZE? I'm a little confused
 (as
> > > usual) ...
> > >
> > > Dave
> > >
> > >
> >
> >
>
>
Received on Mon Jun 25 2001 - 15:24:41 CDT